The Bungay "High Speed" 600
by Adrian Duncan
In this article we take a look at the Bungay "High Speed" 600, an almost-forgotten early post-WW2 American model racing engine which was among those which unsuccessfully challenged the "classic" racing engine formula established by the Hornet and McCoy 60 models. This highly individualistic design represented a very sincere and carefully-considered effort by its manufacturers to offer a technological alternative to the leading racing engines of the day. Sadly, it failed to convince the modelling public and did not survive long in production.
The Bungay 600 has considerable significance from a historical standpoint in that it was the last of a series of pioneering crankshaft front rotary valve (FRV) racing engines which challenged the rise to prominence of the "classic" big-bore model racing engine with its disc rear rotary valve (RRV) induction. The telling of the Bungay story thus affords an ideal opportunity to summarize a very interesting technical debate which took place in the context of the early development of model racing engines.
As always when discussing an American model engine from the "classic" era, it's necessary right up front to pay tribute to our friend and colleague Tim Dannels, Editor of the Engine Collectors' Journal (ECJ). Tim's indispensable American Model Engine Encyclopaedia is a required off-the-shelf reference for anyone having an interest in the products of the American model engine industry. Much of the background material for this article was extracted from that work as well as from back issues of the equally highly-recommended ECJ Many thanks for all your efforts in making this material available to us, Tim!
Let's begin now by looking at the background to the development of this very original model engine design.
Prior to 1937, the majority of model engines were used to power large free flight model aircraft. Since these models were uncontrolled following launch, attempts to achieve high speeds would have been potentially hazardous, to say nothing of the difficulty of obtaining accurate speed measurements. Contests were therefore based upon flight duration for a given motor run, thus making light weight and operational consistency the primary goals of engine designers. Although tethered hydroplane racing was taking place during this period, its most consistently successful practitioners tended to make their own specialized powerplants. There was thus little stimulation for the commercial development of all-out model racing engines at this stage.
This all changed in early 1937, when a group of Los Angeles model fliers who were looking for new adventures decided to try using their model aero engines to power model race cars which could be run at high speeds on a tether or rail track, thus keeping them under restraint at all times. The leading lights in this movement were the three Dooling brothers, who were to go on to develop some of the most famous model racing cars and engines of them all. They were soon joined by others, including the legendary Dick McCoy as well as Ray Snow of Hornet fame. The rapid nationwide increase in the popularity of this new branch of the hobby soon created market conditions in which the commercial development of suitable racing engines became a viable proposition.
The resulting powerplants differed quite significantly from their aero predecessors. Weight was far less of an issue—instead, all-out performance and durability were now the primary concerns of the various competing racing engine designers. In a separate article on this web-site, we have traced the origin of the "classic" model racing engine back to 1938, when the A. C. Special was manufactured in very small numbers by Charlie Anderson and Walt Cave in Oakland, California. This ground-breaking design and its direct successor, the Hornet 60 from Fresno, California, set the basic pattern for model racing engine design over the following 25 years or so. The design of the iconoclastic McCoy 60 was very much influenced by that of these two pioneering models.
The "formula" established by these front-running early American racing engines was soon to become familiar to performance-oriented modellers worldwide, being widely emulated in many countries outside the USA. When we reflect upon the classic early post-WW2 10cc racing engine, we tend to think of a design featuring spark ignition (the only available option prior to 1948); an automotive-style timer; RRV induction; cross-flow loop scavenging; a ringed aluminium piston having a high domed baffle crown; and a twin ball-race crankshaft. Apart from the general switch to glowplug ignition in the late 1940's, this basic design package was to remain the standard for large racing engines well into the 1960's.
However, even at the outset there were those who felt that the above layout could be improved upon. One notable and very influential designer who sincerely believed that FRV induction offered greater potential than the RRV system for racing engines was California resident Ira J Hassad (1915—1981).
Hassad's conviction that FRV induction offered a viable alternative to the RRV system for racing engines was to sustain a 10-year struggle for supremacy between the two systems. The Bungay High Speed 600 was destined to be the final FRV participant to enter that contest. This being the case, the need to place our main subject in context requires that we spend some time reviewing this very interesting technical debate of over 70 years ago.
Ira Hassad and the FRV 1940's Racing Engine Movement
Ira James Hassad was one of the true pioneers of model engine development, with a decided preference for ploughing his own furrow in design terms. An expert machinist and a keen aeromodeller, he had started making model engines for his own use in the early 1930's while still in his teens. In 1935 the then 20-year old Hassad was hired by former WW1 fighter pilot Major Corliss C Moseley, co-founder of Western Air Express (later to become Western Airlines), to work on the production of the Baby Cyclone motor which represented one of Moseley's sideline activities. Other colleagues of Moseley's in this venture included Bill Atwood and Mel Anderson, co-designers of the Baby Cyclone—quite a team!
The Baby Cyclone engines were manufactured at a facility owned by Moseley which was primarily dedicated to full-scale aircraft maintenance. This facility was located at Grand Central Terminal in Burbank, California, some 12 miles to the north of downtown Los Angeles. Ira was later to recall that his main task was the lapping of the pistons and cylinders to the required fit. Surviving examples of the Baby Cyclone are a testament to his expertise in this area. A number of Ira's fellow employees were student pilots paying for their instruction by working for Moseley. Some 20,000 of these engines were reportedly manufactured in total.
Hassad remained with Moseley until 1939, when he left to strike out on his own. Initially he joined former colleague Bill Atwood, who had also left Moseley and was getting production going on the Phantom series at this time. However, Ira had now become interested in model car racing and was tempted by the challenge of developing his own all-conquering race car engine. In September 1939, using a $300 loan from close friend and Lockheed employee Louis Schock, Ira bought a lathe which he set up in the garage of his home in Maywood, California, a little to the south-east of Los Angeles. Here he commenced the manufacture of the H/S .604 race car engine, with part-time assistance from Schock.
This engine featured the unusual combination (for a racing engine) of a front exhaust with twin stacks, a plain bronze-bushed main bearing, a lapped piston, a five-bolt backplate and FRV induction. It also sported an early rendition of the remote needle valve system later to be employed by Cox, among others. Some 200 examples of this model were reportedly made and sold, a figure which encouraged Ira to continue on his own after Louis Schock found it necessary to return full-time to his regular job at Lockheed. A basically identical model was still in production in 1941, albeit by that time under Hassad's own name.
The twin-stack front exhaust was to remain a Hassad trade-mark for most of the following decade. There is much to commend the layout when the engine is used in aircraft service, since it places the hottest side of the cylinder at the front where it receives maximum cooling airflow, thus contributing to more uniform cylinder temperatures. However, any advantage which this layout may possess in terms of operating temperatures is often negated when the engine is used in car service, since in a typical bevel-geared car featuring rear wheel drive (like that illustrated here) the exhaust would then face the rear of the vehicle. The same would apply to the engine's use in hydroplane service.
The Hassad engines were very successful in competition, a fact which did not go unnoticed by other California-based model engine designers. In 1941, Los Angeles resident Johnny Lockridge produced a very few examples of the Black Panther .607 car engine. While the Black Panther certainly incorporating a good deal of Lockridge's own thinking, it displayed a very definite Hassad influence, featuring FRV induction to go along with a twin-stack front exhaust system. The flywheel and timer of this ultra-rare model were neatly enclosed in a forward extension of the main crankcase. Production of this engine was apparently suspended rather abruptly after a well-heeled friend of Ira Hassad's called on Lockridge and threatened him with legal action over what he saw as an unauthorized Hassad "rip-off"!
Another small-scale effort which applied a bit of a twist to the basic Hassad formula was the .604 cuin. Batzloff Triumph of mid 1941. This very intriguing engine was developed by model car racer (and noted pioneer free-diver) Bill Batzloff (1912-1966) of San Diego, California under the Batzloff Racing Engines label. The very clear Hassad influence arose from the fact that Bill Batzloff and Ira Hassad were close friends and racing buddies who together pioneered the sport of I/C car racing in the San Diego area. Batzloff actually used one of Hassad's engines at the 1941 US National model car race championships in Chicago, a meeting at which Ira himself finished second, competing against the best in the country.
The Triumph was made by Batzloff in very small numbers, production being quickly curtailed by the onset of WW2 (as far as the USA was concerned) in December 1941. Seemingly no more than a dozen complete engines were supplied to custom order, although others were reportedly sold to fellow enthusiasts as casting kits for home construction. The illustrated example was constructed from castings by the noted model car reproducer Don Sohn.
The Triumph clearly embodied Batzloff's views regarding how the basic Hassad design could be improved upon. The engine reversed the usual Hassad arrangement by using a rear drum valve instead of FRV induction. The operating principle was of course identical, the difference being that the drum valve did not have to do double duty by transmitting the engine's torque in addition to controlling the induction cycle.
This arrangement allowed the designer to take far greater liberties in terms of induction port size and associated timing without introducing any undue structural weakness. It was presumably this advantage which led Batzloff to adopt the design approach that he did. The engine retained the twin exhaust stacks of the contemporary Hassad models, but these were placed at the rear of the cylinder instead of at the front, thus keeping them in the same orientation relative to the induction system as in the Hassad designs. In effect, the Batzloff Triumph was a "back-to-front" Hassad model—a twin-stack FRV Hassad design with the power take-off at the rear!
During the period just described, Hassad engines dominated the rail-guided model car racing category at meets in Southern California. This was evidently due to their superior torque in the 12,000-13,000 rpm range, which helped them to accelerate out of the turns. However, in tethered cable car racing where the runs were not interrupted by changes in track radius, the higher peak horsepower of the RRV Hornet 60 gave it a commanding edge.
The onset of WW2 put an end to Ira Hassad's experiments with FRV racing engines, since his engineering talents were required for the war effort. He spent the war years working at the University of California in San Diego. However, once the conflict was over he was quick to resume his model engine development activities, continuing to pursue the concept of FRV induction applied to model racing engines.
By 1946, Ira had established himself in San Diego, California under the company name of Hassad Experimental Machinists. Here he produced around 125 or so examples of the individually hand-crafted Hassad Custom .61, a true masterpiece once again featuring FRV induction and a twin-stack front exhaust. However, the "standard" formula was beginning to make inroads into Hassad's thinking—the new model featured a ringed aluminium alloy piston as well as a twin ball-race shaft. Even so, the continued use of FRV induction and the front exhaust set the design well apart from other leading racing engines of the period.
Jim Walker's wartime development of the control line system for model aircraft had now made all-out speed contests for model aircraft a practical proposition, since high-speed models could be flown safely under complete control at all times. Accordingly, Ira's engines were now appearing in aircraft service in addition to the car and hydroplane racing applications in which they had hitherto been employed. The illustrated example of the Hassad Custom .61 is clearly set up for aircraft use. From this point onwards, the model aircraft market became increasingly important to the designers and manufacturers of model racing engines, to the point where it eventually became dominant.
The Hassad Custom .61 proved to be a formidable competitor, a fact which did not go un-noticed by others. A certain Mr. Frank Howarth, owner of a company called Engineering Development Co Inc (EDCO), decided that a mass-produced version of this engine would enjoy good sales prospects and invited Ira Hassad to come to work for him on the engine side. The company was established in premises located at Del Mar Airport in the oceanside community of Del Mar, a little to the north of San Diego, California, where Hassad had been living since the beginning of WW2. Both engines and model race cars were manufactured.
Hassad's involvement with this company during 1947 resulted in perhaps his most recognizable design of them all, the EDCO Sky Devil 1500. This was in effect a slightly simplified mass-produced version of the Hassad Custom .61. It was another FRV twin-stack front exhaust unit with a twin ball-race shaft and ringed aluminium alloy piston. The engine was offered in both a .649 cuin. aircraft version (the regulations then in force for model aircraft allowed engines of up to .650 cuin.) and a .607 cuin. race car variant which was used in EDCO's own race car offerings.
A sideport induction .45 cuin. fixed compression diesel was also planned by EDCO, but it never got past the prototype stage. Ira Hassad later stated that he had nothing to do with the diesel design, although he did recall having test-run one of the prototypes at Del Mar.
Original examples of the EDCO engines are pretty rare these days. The illustrated example of the EDCO Sky Devil is one of some 250 fine .649 cuin. replicas produced in 1983 by Randy Linsalto of RJL (now combined with MECOA). These were made under contract for the late Terry Toupes. Internally, they are not exact replicas, utilizing some readily-available parts from other engines to keep costs under control. However, in many ways their quality equals or even exceeds that of the originals, from which they may be readily distinguished by having the inner surfaces of their exhaust stacks anodized as opposed to the plain milled finish of the originals. They also carry serial numbers having a TDCxxx pattern. These engines run very well indeed and are now fine collectibles in their own right.
Randy began work on a second series which was to be closer to the originals, but this project never reached completion. Randy might complete it someday if a demand becomes apparent. My sincere thanks to Randy for personally sharing this information with me. Check out Randy's website—he continues to do fine work!
The EDCO Sky Devil never achieved the performance levels of the earlier Hassad Custom model, in large part because it was not individually fitted and assembled as was its progenitor. For an extra charge of $15, Ira Hassad would undertake to rework a Sky Devil to realize its full potential, and a number of smart purchasers took advantage of this. However, the big-bore racing engine market was becoming dominated by the McCoy 60, with the Hornet 60 also still very much in evidence. The arrival of the Dooling 61 later in 1947 did nothing to help. Consequently, the Sky Devil did not meet sales expectations, with only some 1000—1500 examples being produced in total before financial difficulties forced the EDCO company into liquidation.
As a result of the liquidation process, the bulk of the remaining Sky Devil parts and tooling ended up as the property of EDCO's major creditors, the Tyce brothers, who owned a company called International Tool Corporation of Chula Vista, California, just to the south of San Diego. The established business of this company was the provision of full-sized aircraft engineering services, but they decided to see if anything could be salvaged from the remains of the EDCO venture. To that end, they hired Ira Hassad to come up with a model engine design in which the former EDCO parts and tooling could be used. The design brief this time was specifically for an aero engine for free flight and control-line applications—cars were no longer seen as the major market that they had once been.
The result was Ira Hassad's last model engine design—the Bluestreak 65, still featuring FRV induction and using many EDCO Sky Devil parts. However, the "classic" formula had made further inroads, since the new design used a revised crankcase casting which featured a conventional side-stack exhaust in place of the twin-stack front exhaust layout used on all previous Hassad designs. Since the engine possessed all of the other classic racing features such as twin ball-race shaft and ringed alloy piston, it followed the now-established racing engine pattern in all respects apart from its continued adherence to FRV induction.
Reflecting its time and place, the Bluestreak was offered in both spark ignition and glow-plug versions. It was reportedly a fine engine for free flight and non-racing control line applications. However, in a racing context it could not hold its own with the then-current crop of big-bore racing engines from other manufacturers. Even so, all 2000 or so examples of this engine which were manufactured did eventually find buyers, although it took a while. Long before that happened, Ira Hassad had moved on into other engineering ventures, leaving model engines behind together with his own legend.
Although he was the most prominent and persistent advocate of FRV racing engines during the period just covered, Ira Hassad was not the only such individual. Over in the small community of Drayton Plains, Michigan, a fellow named Henry Ball had established a facility known as the B&D Racing Engine Laboratory. Here he developed and manufactured another FRV racing engine, the Ball 60 car unit. The initial model of this engine appeared in 1946, with limited production continuing into 1948.
The Ball 60 was even more individualistic than the contemporary Hassad designs. Like the Hassad, it featured FRV induction, a twin ball-race shaft and a ringed aluminium piston. However, there the similarities ended. The Ball featured dual exhausts with dual bypasses between them—shades of Cox in years to come! The exhausts exited at both front and rear, with bypass passages on both sides of the case. This allowed the use of six transfer ports (three to a side) along with the six exhaust openings, which were of course split between the two exhaust stacks. Both exhaust stacks discharged to the left of the engine, imparting a highly unusual appearance to the unit.
The advent of the Ball 60 seems to have influenced the thinking of another Michigan model engine designer, Wilfred Gibbs Orr of Lansing, Michigan. Earlier in 1946 Orr had introduced the Orr Tornado, a basically conventional .647 cuin. RRV racing engine showing a certain Hornet influence along with some original thinking. Later in 1946, Orr made a few prototypes of a .604 cuin. FRV version of the Tornado. These were advertised but seemingly never actually reached the market. The Orr engines do not appear to have enjoyed widespread market success, although they were still listed as being available in compendiums of current model engines published in early 1948. Originals are extremely rare today.
The upshot of the above experiments with FRV induction was that as of 1948, only the Bluestreak and Ball 10cc FRV racing engines remained available to competition modellers who wished to try something different. However, the 1947 introduction of the RRV Dooling 61 had raised the performance ante significantly, to the point where even such leading RRV models as the McCoy 60 and the Hornet 60 suddenly found themselves badly outclassed. This event prompted Dick McCoy to develop his famous Series 20 version of the McCoy 60 which was to outlast the Dooling and remain the world standard for 10cc racing engines well into the 1960's. Despite the speedy development of a bulge bypass performance enhancement kit, the once-dominant Hornet quickly fell by the wayside, and it remained to be seen whether or not the surviving FRV models noted above could carry on in the face of the overwhelming strength of the ever-improving RRV opposition.
Under these circumstances, it may appear in some ways a little surprising that yet another FRV racing engine should appear in 1948. However, it was in that year that the Bungay "High Speed" 600 model (remember that?!?) which is our main subject made its all-too-brief appearance.
The manufacturers of the Bungay 600 traded as Bungay Brothers of 323 E. 38th Street in New York City, New York. I've been able to find out absolutely nothing about this company beyond the simple fact of its involvement with the Bungay model engine venture. However, the design and manufacturing complexity of this engine is such as to imply that they must have had prior experience in the precision engineering field. This was no entry-level model, either in design or manufacturing terms. It's not unlikely that the firm was involved in precision engineering in a broader sense and that the model engines were very much a sideline undertaken as a labour of love. There are many precedents for this.
The Bungay 600 is today one of the rarest model racing engines of them all. I've never so much as seen an original in the metal. I am only able to undertake this review at all because of my acquisition of one of a series of 100 fine reproductions of this engine which were produced to a very high standard in the Ukraine for Woody Bartelt of Woody's Engines/Aero Electric fame. The engine which appears in the attached images is number B17 of this series. Woody's offering is an almost exact replica of an original example, so I'm satisfied that it may legitimately be used as an object for study of this otherwise "invisible" engine. My sincere thanks to Woody for making this possible.
The Bungay High Speed 600 Described.
In many respects, the Bungay was a typical large racing engine of its time. It featured spark ignition controlled by an automotive-style timer; cross-flow loop scavenging; a sidestack exhaust; a ringed aluminium piston with a high domed baffle crown; and a twin ball-race crankshaft. In fundamental design terms, its only real departure from the established formula was its use of FRV induction.
The Bungay featured then-standard bore and stroke measurements of 0.940" and 0.875" respectively, exactly as used in the McCoy and Hornet 60 models among others. This gave the engine a displacement of 0.607 cuin. (9.95cc). Claimed all-up weight minus coil and other ignition equipment was 16.25 ounces, although the Bartelt replica in my possession weighs in at 485 gm (17.10 oz.) bare with plug.
In keeping with normal racing engine practise at the time, the engine featured a cast aluminium alloy piston with a high domed crown incorporating a baffle. The cylinder head casting was formed so as to create a conforming combustion chamber. Compression ratio was 9.8 to 1. The plug was slightly offset towards the transfer side to promote more rapid involvement of the pocket of mixture behind the baffle in the combustion process.
An unusual attribute of the Bungay 600 was the use of steel piston rings as opposed to the more usual cast iron items. The Bartelt replica maintains this material specification. The con-rod in the original engines was a drop forging in 14S-T aluminium alloy. Woody Bartelt specified a fully machined rod in his limited-edition replicas, but this does not affect the engine's functionality in any way. The cylinder liner was of heat-treated steel with six square exhaust port apertures separated by the usual narrow pillars to prevent ring snag. There were three similar openings to serve as the transfer ports.
As with the Hornet 60, the cylinder liner was carried in a separate casting which in this case was attached to the main crankcase casting by four studs with hex nuts at the corners of the square location flange. The main crankcase casting also followed the Hornet pattern by incorporating the main bearing housing in a single unit. The upper casting incorporated both the exhaust stack and the machined cooling fins. The cylinder head was very securely attached to this casting by no fewer than 8 machine screws, a feature also seen in the contemporary Dooling 61 as well as the Rowell 60 from Dundee, Scotland.
The bypass passage was necessarily formed in part in both the upper and lower castings, again exactly as in the Hornet. The passage used in the Bungay was relatively narrow in a fore and aft sense, but was laterally made far deeper than those used in the Hornet and the 1946-48 blackcase McCoy 60 models. Hence it offered a relatively free passage for mixture to reach the transfer ports despite its comparatively narrow width. The passage was flared significantly at the top to provide unimpeded gas access to all three transfer openings.
Although the bypass passage was open at its base in the usual way, a single extra port having an ovoid shape was cut in the cylinder wall below the transfer ports. This corresponded at and near BDC with a similar port in the piston skirt. The result was improved gas access to the bypass passage as well as enhanced piston cooling due to the flow of cool incoming mixture through the piston interior.
The Bungay designer was clearly concerned with reducing crankcase volume to the extent possible. To this end, the bore for the cylinder liner was not carried through the combined upper and lower castings to intersect the axial bore for the crankweb and rod. Instead, it was only carried sufficiently deep to accommodate the liner and the piston at bottom dead centre. This left a pair of wedge-shaped metal intrusions which reduced the working volume of the case. The con-rod operated through slots milled in these intrusions. The slot on the transfer side was widened considerably to facilitate gas access to the bypass passage. A parallel arrangement featured in both the Hornet 60 and the contemporary Rowell 60 from Dundee, Scotland.
The Bungay 600 used a one-piece steel crankshaft having a counterbalanced disc-style crankweb with integral crankpin. The main journal diameter was 0.500 in., again exactly as in the McCoy and Hornet models. So far in fact, apart from the use of steel rings and the method of assembly, we could be talking about almost any racing engine of the early post-WW2 period.
But here the similarities end! A central gas passage having a measured diameter (on the replica) of 0.334" was drilled down the centre of the shaft from the rear to provide communication with the FRV induction system. A rectangular induction port of considerable area was cut into the wall of this shaft to register with an opening of similar shape which was machined into the main bearing housing.
The next design anomaly with the engine was the fact that the intake was located beneath the main bearing housing rather than in the more usual position on top. This was actually an extremely inconvenient location from a mounting standpoint since the needle had to pass through the right hand bearer directly beneath the mounting lug. Mounting in a conventional test stand was thus quite impossible. The location also impeded access to the intake for priming or choking when the engine was mounted.
It would have been a perfectly straightforward matter to design the engine so as to place the intake in the conventional upper location, implying that the chosen arrangement was the result of a conscious design decision. This of course begs the question of why this arrangement was adopted.
My own view is that it was probably motivated by a desire to improve crankshaft integrity at the very high speeds for which this engine was designed. The milling of a rectangular induction port in the shaft undoubtedly created a potential stress-raiser in the middle of the main journal. In particular, the cyclic placement of this feature under high tension loadings would not have been an ideal condition in terms of stresses at this location. The Bartelt replica's induction port has nicely radiused corners and it seems likely that the originals did as well, but even so the feature must retain some tendency towards creating stress concentrations, particularly at the corners of the opening.
In a twin ball-race engine, downward pressure on the crankpin imposes a bending force on the crankshaft which places the upper sector of the main journal in tension—not a good situation when a stress-raising aperture is present. By placing the intake below the main bearing, the designer ensured that at the moment of maximum bending stress (Top Dead Centre following ignition), the portion of the journal that was placed in tension was free from any discontinuity—the induction port would still be on the compression side of the journal at this moment and thus less subject to possible fatigue failure at stress concentration points.
An additional factor which may have had an influence was the issue of fuel feed. With the venturi bore and needle valve design adopted, suction draw would likely be minimal. The location of the intake beneath the engine pretty much guaranteed that the unit would be supplied by gravity from any tank mounted in a rational location, at least with the engine mounted in an upright position as it would normally be in a typical speed model aircraft, race car or hydroplane. Moreover, as the manufacturers pointed out, the engine was virtually immune from flooding with this arrangement—any excess fuel would simply drip out of the intake under gravity.
The designer solved the problem of creating a rectangular induction port opening in the main bearing in a neat and effective manner. The actual register was milled into the underside of the main bearing housing, taking the form of a rectangular opening with a flat rectangular surface around the edges. The dimensions of the register opening were 0.400" wide by 0.562" long. The axial length of the crankshaft induction port was cut to match the latter dimension. Apart from providing an unusually generous register area, this arrangement also promoted extremely rapid opening and closing of the induction system along with an increased fully-open dwell period. For an FRV design, the induction timing was quite aggressive. The Bartelt replica features a full 180 degree induction period extending from 50 degrees ABDC to 50 degrees ATDC.
The tubular venturi was carried in a separate casting which was attached to the register opening using two machine screws with a gasket to seal. The venturi itself was of brass, with a generous internal diameter of 0.375" A surface jet needle valve assembly was employed, the installation of which served to retain the venturi within the casting. The externally threaded needle was very effectively tensioned by a spring clip of bronze sheet which bore against an externally serrated thimble.
Somewhat uniquely, the braced mounting lugs extended on both sides for almost the full length of the engine. While this permitted an unusually secure mounting, it was more than a little awkward for mounting in a model aircraft or a test stand. The full 2.55" lateral width of the lugs was carried through to the front of the engine, only some 0.875" behind the front face of the prop driver. The use of this engine in a speed model aircraft pan (the unit's obvious model aircraft application in view of its performance characteristics) would have required both the trimming of the lugs at the front and the use of some kind of bobbin-type prop driver extension with a sleeve nut for prop attachment.
Even then, the location of the intake beneath the engine would have given rise to further problems. It would have been necessary to create an opening in the underside of the pan for the intake as well as cross-drill a passage for the needle valve. In fact, from a mounting standpoint the engine was undoubtedly best suited to model car or hydroplane applications.
The timer design was quite original. The components were mounted on a stamped steel frame which was a close fit over the outside diameter of the front ball race housing. This housing incorporated an expanded section at the rear which formed a flange against which the timer frame abutted. The unit was secured against this flange by two screws with washers. These screws passed through slots in the frame which permitted it to be rotated through 90 degrees using the integrally-formed timer arm. The ability to vary the tension on the screws allowed easy adjustment of the unit's resistance to rotation. Overall, the arrangement provided very secure fixing of the engine's timing while permitting easy adjustment if necessary during operation.
The fixed point was attached to a lug which was brazed onto the timer frame at the front. A conventional automotive-style moving point was employed. The cam was machined at the rear of the steel prop driver, which was secured to the shaft using a Woodruff key. Interestingly enough, the prop driver had no serrations of any kind on its driving face to resist prop slippage. It did however feature a hole drilled through it at one point, presumably to accommodate a plug key inserted into the prop or flywheel hub. With an engine of this torque potential, such a provision would have been very necessary. A conventional prop nut and washer were used to secure the airscrew.
According to the company's literature, the flywheel-equipped race car version of the Bungay 600 possessed a feature called automatic timer advance. This was presumably some kind of spring-actuated delayed-action system which advanced the timing automatically from the retarded starting setting to the best running setting over a short period of time after starting. This would have been a great advantage for push-starting a model race car. Since we don't currently have an example of this fitting to examine, we can provide no details of the mechanism.
The engine was completed by the use of a cast and machined backplate which was secured by four screws with a gasket to seal. Even here, there was evidence of original thinking. The absence of the usual rotary disc meant that the con-rod was unrestrained from moving to the rear and partially slipping off the crankpin while at the same time scraping metal particles off both itself and the alloy backplate to spoil the engine's working finishes. The Bungay designer solved this problem very neatly by installing a steel disc on the front face of the backplate. This both minimized rearward movement of the rod and presented a steel restraining surface, thus creating an alloy-on-steel working combination which was far longer-wearing and less likely to create metallic particulates. The plate had a central spigot which passed through a hole in the centre of the backplate and was secured by swaging from the outside once installed.
Overall, one gets the impression that some well-focused design thinking went into this engine. The castings too are unusually complex, indicating either that the manufacturers were experienced producers of high-quality castings or that they had ready access to such expertise.
Although the commercial glow-plug had well and truly arrived by mid-1948 when the Bungay first appeared, the engine was specifically designed for spark ignition operation. In fact, the manufacturer's instruction sheet stated that the use of glow-plug ignition would reduce power output by some 30%. Given the rapid rate at which the glow-plug displaced spark ignition from this time onwards, we might doubt this statement for an engine that was properly set up—other contemporary engines suffered little if at all from the change in ignition systems once the criteria for successful glow-plug operation were fully appreciated. It may simply be that the somewhat black art of getting the best out of glow-plug ignition was not completely understood by the Bungay designers at this pioneering stage, since there seems to be no reason whatsoever why the Bungay should not give a very good account of itself on glow-plug ignition.
Recommended fuel was a straight mixture of methanol and AA castor oil. The original typed instructions specified an 80/20 mix of these two components, but the copy reproduced here has had these figures altered by hand to 75/25—whether by the manufacturers or by an owner is unclear. Perhaps experience showed that the higher oil content was an aid to longer life and greater reliability at the very high speeds at which this engine was intended to operate. The instruction sheet specifically warned against the use of gasoline in this unit.
The instructions also claimed that each engine was fully run-in at the factory and was therefore ready to run fast as supplied. If this was indeed the case, the Bungay Brothers must have enjoyed a certain notoriety among their New York neighbours when it came to ongoing noise levels emanating from their operation!
The Bungay 600 High Speed Design Considerations
When speaking of an engine of this vintage and rarity, we are generally left with little source material against which to test our present-day evaluation. In most such cases, we would now have said all that there was to be said regarding our subject. Thankfully, in this case we do have a credible contemporary source through which we are accorded a direct glimpse of the design thinking behind this very interesting engine.
This comes about because the early post-war model engine commentator for Model Airplane News, Mr Edward G Ingram, took a close interest in the Bungay 600, going so far as to spend some time in New York with the manufacturers discussing the design and observing actual tests on the engine. Ingram's detailed comments were published in the September 1948 issue of the magazine, along with similar comments on the Ball .604 unit which remained available at the time.
Ingram was clearly very impressed with the observed performance of the Bungay, which prompted him to delve quite deeply into the details of the design. Fortunately for us, he asked a number of the very questions that we would ask the designers today given the opportunity.
The first question was of course the reason for the manufacturer's choice of FRV induction at a time when the RRV Dooling 61 and its ever-improving McCoy opposition were sweeping all before them. Ingram obtained a very direct answer from the designers to this question. He recorded their belief that "the shaft-type rotary valve is less subject to mechanical failure and leakage than the disk type, provides better bearing lubrication, and when designed for maximum port area is the best means of admitting fuel mixture to the crankcase". A valid additional point that was not made was the fact that the use of FRV induction eliminated the friction and viscous drag of the rear rotary disc which were inescapable elements of the classic RRV layout.
The manufacturers put their money where their mouth was on the lubrication issue, machining the shaft to very close dimensions to leave a specified clearance of only 0.003" between the rear edge of the outer rear ball race and the front face of the crankweb. The stated idea here was to effectively eliminate the volume of the bearing forward of the crankweb from the working volume of the crankcase, thus promoting better operating crankcase compression and improved transfer. Reliance was placed upon oil supplied from the induction system to lubricate the ball races. The front race was shielded at its forward end by a thin bronze disc which rotated with the prop driver, a system which was apparently patented by the designers.
Ingram reported that the Bungay designers were very much aware of the desirability of reducing reciprocating weight to a minimum. To this end, the Bungay employed an unusually thin-walled piston and a rod which was forged to minimal dimensions consistent with reliability. The rod featured an unbushed big end bearing with an oil hole for lubrication. Ingram observed weight measurements taken on the Bungay piston/rod assembly against a similar measurement for another unidentified "typical" racing engine of the same displacement. Using the same scale, the Bungay assembly reportedly weighed 205 grains (13.28 gm) against the 290 grains (18.79 gm) of the other unit—a difference of some 29% in favour of the Bungay.
To put this in perspective, the piston/rod assembly from a McCoy 60 weighs a checked 18.4 gm complete with rings and gudgeon pin. It's thus likely that this (or perhaps the very similar Hornet assembly) was the standard against which the Bungay was checked in Ingram's presence. The unusually low weight of the Bungay assembly would certainly have improved both performance and mechanical reliability. A commendable and worthwhile achievement by the Bungay designers!
Ingram questioned the rationale for the use of steel piston rings. In response, the makers claimed that "steel rings have more elasticity than the usual cast iron rings and therefore provide a better seal".
Ingram also commented upon the castings used in the engine, stating that they were produced by a special process developed by the manufacturers. This was claimed to practically eliminate blow-holes and yield a superior finish when machined. No further details were provided, although this sounds like a form of pressure die-casting.
The manufacturers mentioned a specific problem which they had had to overcome during the design of the unit. This was the fact that at the very high speeds for which this engine was designed (in accordance with its name!), timer operation was so rapid that there was insufficient time for the primary current in the ignition circuit to build up to satisfactory levels unless the applied battery voltage was increased to 4-1/2 volts or more. The solution adopted was to design the cam so as to increase the proportion of time during which the points were closed prior to the initiation of the actual spark through the opening of the points. A further concession to high speeds was the recommended use of a point gap of only 0.004" to minimize point float. Using this set-up, the engine could be operated on a 3 volt supply.
Ingram was also able to report on a number of experiments which had been undertaken by the designers during the course of the Bungay's development. A range of compression ratios all the way up to 18 to 1 (!@#?! Diesel fuel, anyone?!?) had been tried, with the final ratio of 9.8 to 1 being selected only after the completion of these experiments. There had also been experiments with piston design, including one in which the piston interior above the gudgeon pin was completely solid, the idea being to further reduce crankcase volume at the expense of increased reciprocating mass. A con-rod with a ball-race big-end bearing was also tried, presumably influenced by the Dooling 61's successful use of a needle roller big-end bearing. The results achieved did not justify the application of these ideas to the production version of the engine, although Ingram was shown the experimental parts used in these tests.
As far as performance went, the manufacturers claimed in their introductory advertisements that the engine developed 0.96 BHP @ 18,000 rpm. Although generated at unusually high speed, this output was very comparable with reported figures for the blackcase McCoy 60 and the Hornet 60 which were still in production when the Bungay was introduced. However it was well below the claimed 1.5 BHP output of the new king of the big-bore racing engines, the Dooling 61, and was shortly to be greatly surpassed also by the soon-to-be-released McCoy 60 Series 20.
Ingram reported seeing a Bungay 600 turning an 8x6 airscrew at 19,400 rpm on the bench using straight methanol/castor oil fuel. If that prop had been a present-day APC, it would have taken an output of around 1.1 BHP to achieve that figure based on established power absorption coefficients. Not having details of the prop involved, all that we can say is that the performance observed by Ingram seems entirely consistent with the manufacturer's performance claims. Ingram reported that no mechanical failures were observed during the course of the tests which he witnessed.
A parameter which was widely reported by model engine manufacturers at the time, particularly those involved in the production of car racing engines, was the engine's free speed capability when running without load. Although this is completely irrelevant in terms of the engine's performance under load, it was frequently quoted by manufacturers, presumably in an effort to impress the customers. The Bungay advertising claimed a free speed of 27,000 rpm, although the claim made to Ingram during his visit to the factory and repeated in the instruction sheet was increased to 28,000 rpm. Apart from leaving us impressed that the engine could withstand such abuse, the fact that this was 10,000 rpm beyond the unit's claimed peak renders the figure of little practical value. One supposes that it might have had "insurance" value to car and hydroplane users given the fact that engines used in those disciplines had to withstand very high speeds when the unit was unloaded either during the start-up procedure or as a result of airborne "excursions" during operation!
Overall, Ingram was clearly very impressed with the Bungay, summarizing it as the result of "extensive research directed towards development of a racing engine of unusually high output" and characterizing the results achieved as "outstanding". Quite a testimonial!
The Replica Bungay 600 On Test
Having gone so far in researching the Bungay, plain curiosity drove me to give the replica engine a few runs on the bench. In order to do this, I had to put in quite a lot of preparatory work—you can't just mount one of these things in a conventional test stand and fire it up! In fact, I very much doubt that many of these fine replicas ever get run, simply because of the hassle involved in getting them set up to do so.
To begin with, I made up a simple mounting cradle out of 3/8" aluminium alloy plate. There are some commercial firewall mounting units with adjustable bearer spacing available for engines in this displacement category, and I have no doubt that one of them could also be made to work, especially if mounting in a model aircraft was on the agenda.
I was also unwilling to consider trying the engine without some kind of positive measures to prevent prop slippage given the plain un-knurled driver. To deal with this issue, I made a bobbin prop driver extension having an offset blind recess at the rear which matched the location of the existing hole in the standard steel prop driver. A steel mushroom stud was made to fit in this recess and engage with the hole in the standard prop driver. I have little doubt that anyone planning to use this engine in a speed model aircraft would have made similar arrangements. I used a "shim" of gasket material between the steel driver and the rear of the bobbin to minimize any marking-up of the steel prop driver face.
To simplify initial testing and make the establishment of a running setting somewhat easier, I elected to try the engine on glow-plug ignition. I usually begin tests on vintage 10cc engines using an 11x6 prop. Given the Bungay's intended operating speed, in this instance I elected to start with a 10-1/2x6 APC prop instead. I ran the engine on suction fuel feed, although in fact the location of the intake meant that in real terms I actually had some help from gravity.
Choking or intake-priming the unit was of course impossible—all that I could do was open the needle valve all the way, ensure that the fuel line was full and then administer a healthy port prime. However, this did the trick nicely—so nicely in fact that the engine started on the very first flick! A good beginning ...and it didn't stop there. Once running, the needle could be closed down a bit to give a nice even break-in rich-lean setting. The engine proved to be a superb runner, needling very well and running extremely smoothly with no signs of distress at any time. Noise levels were pretty spectacular, and the level in the fuel tank dropped like a bath-tub with the plug pulled on the slightly rich setting that I used in deference to the engine's new and unused state.
I put on 20 minutes in 5-minute runs on a rich needle with this prop, leaning out briefly just before the end of each run and allowing complete cooling between runs to ensure complete heat cycles. At the end of this, spot tests showed that even on a slightly rich needle the engine could easily get the 10-1/2 x 6 prop up to 12,800 rpm on the 10% nitro fuel that I was using. The implied output at this speed is around 0.91 BHP. There's little doubt that it would get past 13,000 rpm if leaned out all the way. This is of course well below the engine's claimed peak, but the implication is that there's plenty of performance on tap by 1948 standards. More importantly, it confirms that the manufacturer's performance claims were by no means exaggerated—possibly the reverse, in fact, especially with a little nitro thrown in.
At this point in its operating life, the engine felt truly superb—compression seal was up to diesel standards and there were no signs of any developing play in the rod or shaft assemblies. Since I didn't plan to actually use this engine in a model, I saw little point in completing the break-in procedure at this time. Suffice it to say that the replica Bungay proved to be a delight to handle and undoubtedly has the performance to give a very good account of itself against the majority of the 1948 opposition.
Sadly, this section of the article won't take long! The Bungay was announced in June 1948 through the placement of advertisements in the major modelling magazines. These ads stated that the engine was then available direct from Bungay Brothers from a "limited stock" which was then on hand. The performance claims noted above were prominent in the adverts, as was the fact that the engines carried a 90-day guarantee.
The price of the engine was $37.50 post-paid within the USA. This was relatively steep by then-current standards—the Hornet and McCoy 60's both sold for $35.00 at the time, while the McCoy 60 Series 20 which appeared later in 1948 carried a reduced dealer price of only $27.50.
It seems not unlikely that the manufacturers had decided to hedge their bets by making a relatively small initial production run of the engines and testing the market by offering them direct to customers. Both aero and car versions are known to have been offered, but neither model appears to have attracted much market attention. This was likely due to a combination of price and the Bungay's failure to match the performance of the new breed of RRV racing engines which had been introduced by the Dooling 61 and was continued with the McCoy 60 Series 20. The awkwardness of the design from a mounting standpoint as well as its marginal adaptability to aircraft use may also have played a part in this outcome.
Whatever the reason, the Bungay seems to have been withdrawn relatively early on, most likely during the first half of 1949. The number actually completed and sold was clearly very small. It's actually quite possible or even probable that the "limited stock" to which the initial advertisements referred was the only batch ever manufactured.
The final mention of the Bungay 600 that I've been able to find appeared in another article by Edward G Ingram which was published in the June 1949 issue of Model Airplane News under the title "Present Day Motors". The Bungay engine was covered in a single paragraph in this article. It seems that the manufacturers had continued their development program, since Ingram reported that they had found an extra 1000 rpm on a given load through an increase in the transfer port area of some 50%. If this is applicable to the engine's performance in the 18,000 rpm range, it implies an increase in power output of some 17%—a very worthwhile gain, albeit insufficient to bring the engine up to Dooling and McCoy performance levels.
This modification must surely have been achieved through the addition of at least one extra transfer opening in the cylinder wall, perhaps in combination with an increase in area of the individual openings. It's possible that a revised upper casting was also involved, although Ingram made no mention of this.
The balance of the paragraph was devoted to an operational description of the auto-advance timer to which reference was made earlier. The implication was that this timer was a later development which followed the initial release of the engine. It seems that the engine was started with the timer in the fully retarded position, after which it automatically advanced itself to a pre-set running position. The operational advantages of this are obvious. Unfortunately, Ingram did not provide any details of the mechanical design of the timer, leaving us still in the dark on that point.
This was the Bungay’s final appearance in the modelling media until it made an appearance in the January/February 1965 issue of ECJ, some 16 years after it had disappeared from the scene. Thereafter, no more was heard of the engine until the appearance of the present article in September 2012.
The consequence of the engine's failure to excite the contemporary marketplace is that the Bungay 600 is one of the rarest racing engines of them all today. Originals do exist, but in very small numbers—finding one nowadays is rather akin to finding Long John Silver's original wooden leg, and you'd better have your credit card well warmed up! A nice example of a custom-built tether car powered by an original Bungay 600 was recently offered on eBay for no less than $8,000!
There's undoubtedly a far better chance of acquiring one of Woody Bartelt's fine reproductions than an original—all it takes is money and a note to Woody! These beautifully-made replicas are quality collectibles in their own right as well as being excellent units for actual use if that's what's desired. As of August 2012 Woody still had a number of these models left in stock at a price of $459.50, but these won't last forever and Woody has no plans to arrange for the production of any more. Those interested in acquiring one while they remain available should contact Woody through his website.
Overall, an intriguing and refreshingly individualistic design which proved to constitute the final rearguard action for the proponents of FRV induction in large racing engines as opposed to the all-conquering RRV models, at least at the time in question. History shows that the RRV designs swept the FRV units aside and remained dominant until the early 1960's, when new developments in scavenging technology brought about a resurgence of the FRV racing engine, initially in the smaller displacements. What goes around, comes around...
Regardless, we hope you've enjoyed this look at an interesting piece of model engine history. Hats off to the Bungay Brothers for a very sincere effort to carry the FRV torch by putting their very original ideas on model engine design into actual practise!