The Baab-Fox .604

by Adrian Duncan

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In a companion article on this site, we have traced the history of the pioneering Hornet 60 racing engine from its introduction in 1939 through to its final demise in 1950. We saw in that article that the Hornet proved to be highly influential in design terms, remaining at or near the top of the competition heap for ten years and establishing the pattern for large racing engine design for the better part of the three decades following its initial appearance.

Many of the Hornet's competitors paid it the highest-possible compliment by following its design in almost all respects. For example, although the iconoclastic McCoy 60 of 1946 exhibited a number of architectural differences from the Hornet, that original version of the McCoy was functionally almost identical, to the extent that a number of parts were interchangeable between the two models.

However, there were those who were convinced that the basic Hornet design could be improved upon, particularly in the bypass/transfer department. As we have seen in our separate article on the tuned Hornets, the major factor limiting the performance of that engine was an unduly constricted bypass/transfer combination. In the present article, we take a look at one designer's attempt to redress this deficiency.

The engine with which we are concerned here is the Baab-Fox .604 cubic inch racing engine of 1946. We may as well state right up front that the rarity of this engine is such that there was never any hope of our orchestrating an opportunity to examine an original engine. We are only able to present this information and the accompanying images thanks to our acquisition of one of a limited series of fine replicas produced in the Ukraine for Woody Bartelt of Aero Electric, one of the world's leading suppliers of replica engines and parts. Woody's replicas were copied directly from an original example in Woody's possession, thus being extremely faithful to the originals.

We are also fortunate in that a very informative write-up on the Baab-Fox appeared in 1993 in MECA Bulletin number 91. The source of much of the information in that article was the late John Pond. Through the kindness of well-known collector Karl Carlson, an opportunity was provided during the preparation of that article for an examination of an original example of the Baab-Fox. We latter-day model engine aficionados are greatly indebted to all concerned for the preservation of this information.

Having acknowledged our sources, let's look at the background to the manufacture of this very interesting engine

Background

As recorded elsewhere, the Hornet 60 was a development of the 1938 A.C Special which had been made in very small numbers in Oakland, California by Walt Cave and Charlie Anderson (seemingly no relation to Mel Anderson). In 1939 its manufacture and further development were taken up by Ray Snow of Fresno, California, at which point the name was changed to the Hornet 60.

The primary application which inspired the successive development of these two designs was model car racing. At the time, the use of large racing engines in model aircraft was impracticable since no technique then existed which allowed the safe operation of high-speed model aircraft under full control. This situation only changed following the wartime advent of Jim Walker's U-control system (far better known today as control line).

During the pre-war period, the Hornet reigned supreme in the big-bore racing engine field. It was challenged by a few others, notably the FRV designs of Ira Hassad as well as one-off specials produced by the likes of Dick McCoy, but there was little other meaningful competition.

The onset of WW2 in December 1941 (as far as the USA was concerned) put an end to racing engine development as a mainstream activity, at least for the time being. A few limited-production models such as Jim Brown's 1944 Thermite 60 from Oakland, California, did appear sporadically, but that was about all. At the end of the war, therefore, little further development had occurred, the result being that the Hornet entered the post-war period as still the engine to beat.

However, this didn't last long! Under an agreement signed during the war years between Dick McCoy and the Duromatic Products Co. of Los Angeles, quantity production of the McCoy 60 was soon underway. Since this engine was very closely based upon the Hornet in purely functional terms, it was only to be expected that it would offer stiff competition to Ray Snow and his Hornet design.

Others watched the emerging competition between the Hornet and the McCoy with great interest. Several of them decided that while the basic design of the Hornet was sound enough, there was still room for improvement. This led to ongoing experiments with FRV induction as opposed to the rear rotary disc valve (RRV) induction of the Hornet—the Hassad, Ball, EDCO, and Bungay engines epitomized this approach to trying something different. More relevant in the context of this article, there were also experiments with changes to the porting system. An example of this approach was the 1946 Ball 60 designed and manufactured in Drayton Plains, Michigan by a fellow named Henry Ball, who had established a facility known as the B&D Racing Engine Laboratory.

The Ball 60 featured FRV induction, a twin ball-race shaft and a ringed aluminium piston. More to the point, it also 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. A considerable improvement on the three transfer ports used by the Hornet and McCoy models at the time! Both exhaust stacks discharged to the left of the engine, imparting a highly unusual appearance to the unit.

As of 1946, the use of large racing engines in model aircraft was just beginning its rise to prominence as a result of the post-war emergence of control-line flying. However, at this time the majority of such engines continued to be used for model car racing. The model car racing fraternity was very close-knit, the result being that developments in various parts of the country quickly became known to those elsewhere.

One of the individuals who soon began to put his mind towards the improvement of the basic Hornet design was hobby shop owner and keen race car competitor Cliff Fox (as far as I can tell, no relation to Duke!) of Oakland, California. Fox was a regular competitor in the Proto and Streamliner classes of model car racing. His Fox Specialities hobby shop at 2915 61st Avenue in Oakland was exclusively devoted to the model car racing hobby, an interesting reflection of the popularity of that branch of modelling at the time.

Fox was obviously well aware of the Hornet 60, since it was still the leading model car racing engine as of 1946. He had undoubtedly also taken note of the Hornet-influenced Talisman 60 and Atomic 60 models produced in very small numbers in the San Francisco Bay area by William P. "Bill" Cubitt, a marine operating engineer by profession and a model car racer by inclination. Finally, there's little doubt that he would very quickly have become aware of the twin-transfer approach taken by Henry Ball when designing his Ball 60 model mentioned earlier.

This is not to say that the Ball influenced the design of what was to become our subject engine, the Baab-Fox .604. At this distance in time, there's no way of knowing which of these two designs had priority, nor does it matter very much. It's entirely possible that both designers reached similar conclusions independently—we'll never know for sure.

Be that as it may, both Cliff Fox and Henry Ball (independently or otherwise) clearly recognised the limitation on performance represented by the Hornet's rather constricted bypass/transfer system. Both designers evidently reasoned that twinning the bypass/transfer system would improve top end performance by increasing the engine's pumping efficiency. However, Fox appears to have considered the balance of the RRV Hornet design to be perfectly satisfactory, while Ball elected to add FRV induction to the mix when finalizing his own design.

In accordance with his own ideas, Fox drew up a design for an engine which was basically a Hornet bottom end grafted onto a cylinder unit having twin bypass passages together with twin exhausts. In addition to retaining the RRV induction of the Hornet design, Fox placed his exhausts to the sides of the engine with the transfer ports fore and aft, in contrast to Henry Ball's placement of the exhausts at front and rear with the bypass passages to the sides. Otherwise, the porting of the Ball and Fox designs was basically similar.

Having described the background to the development of the Baab-Fox .604, let's take a look at the main design features of this very individualistic engine.

Description

It seems best to begin with a few vital statistics. The Baab-Fox .604 featured the "racing standard" bore and stroke measurements established by the Hornet 60 of 0.937 inch (23.80 mm) and 0.875 inch (22.22 mm) respectively for a displacement of 0.604 cubic inches (9.89 cc). It was of course designed strictly for spark ignition—the emergence of the commercial miniature glow-plug still lay several years in the future at the time when it was produced. The volumetrically-measured compression ratio of my own replica Baab-Fox is a fairly healthy 10 to 1.

I have no way of knowing what the original examples weighed—all that I can report is that the Bartelt replica in my possession weighs all of 18.0 ounces (510 gm) complete with plug and timer but minus any ignition support equipment. This is some 1.75 ounces heavier than the Hornet 60, and is in fact only exceeded among 10 cc racing engines of my acquaintance by the 1948 Rowell 60 from Scotland, which weighs in at a megalithic 19.25 ounces. Since all three of these designs were intended primarily for model car use, the issue of weight was presumably seen as less important than all-out performance and structural durability.

There can be no question that the Baab-Fox .604 owed much to the design of the Hornet 60. In fact, the two designs were very similar indeed below the exhaust stacks. There were some detail differences, but it would have been useless for Cliff Fox to deny the influence of the Hornet upon his new model. I'd almost bet that the prototype Baab-Fox was a Hornet with Cliff Fox's upper cylinder assembly attached!

This being the case, let's begin by dealing with a few of the major similarities between the Baab-Fox and the Hornet. Both models were based upon a set of four major castings having parallel functions—the main crankcase/main bearing unit, the backplate, the cylinder barrel with exhaust stacks and bypass passage(s) and the cylinder head. In both cases, the main crankcase casting incorporated the main bearing housing cast in unit rather than being bolted on as in the cases of engines such as the McCoy and Atomic models. Both designs also featured crankcase castings which were truncated just above crankdisc level, with a sturdy rectangular flange being incorporated at that point to serve as the seat for the upper cylinder barrel casting. In both cases, the latter unit terminated at its lower end in a matching rectangular-section flange, being attached to the lower casting by four screws placed at the corners of the flange.

At the front of the engine, the heavily-counterbalanced one-piece steel crankshafts of both the Hornet and Baab-Fox were carried in two ball bearings. The timers of the two engines were also extremely similar in design terms. In fact, the only real difference to be found here was the method of securing the flywheel or prop driver to the shaft. In the Hornet, the race car version used a plain shaft which relied either upon friction or a split collar to secure the flywheel, while the aero version with its steel prop driver used the standard square-on-shaft keying system to lock the driver. By contrast, the Baab-Fox followed the McCoy pattern by using a Woodruff key at this point, regardless of the type of fitting to be mounted. The length of the Baab-Fox shaft was adequate to permit the use of a McCoy style bobbin prop driver with sleeve nut for aircraft service—the illustrated replica example has been so equipped, mainly to facilitate testing but also because I'm an aero guy at heart! However, Woody's replicas are supplied with a flywheel.

The backplates too were basically very similar, being attached to the main crankcase with four machine screws. The main difference was that the Baab-Fox's backplate did not incorporate part of the cylinder location flange as in the Hornet. Consequently, it was possible to remove the backplate of the Baab-Fox without disturbing the two rear cylinder attachment screws, something which was not possible with the Hornet. However, that was the main architectural difference—both models used a cast alloy rotary disc valve controlling induction through a screw-in venturi of basically similar design in both cases. The rotary disc valve in both engines was mounted on a steel spindle and driven in the usual manner from the end of the crankpin.

The one substantial design change in this assembly was the Baab-Fox's use of a single ball bearing to support the disc valve spindle—a rather deluxe feature which we encountered in our examination of the tuned Hornet engines discussed elsewhere. Apart from this, the disc valve followed the Hornet pattern in being retained in its bearing by a soldered-on washer at the rear of the rotary valve spindle. The needle valves too were more or less identical, both being of the standard surface jet type with gland nut for needle tension.

So far, we could almost be talking about minor variants of the same engine! However, when we look above the split between the lower and upper castings, we find that things are very different indeed! As mentioned earlier, Cliff Fox's chief goal in designing the Baab-Fox .604 seems to have been to increase the engine's pumping efficiency by freeing up the bypass system. To do this, Fox elected to use two pairs of transfer openings in place of the Hornet's single group of three openings, placing these paired openings at the front and rear of the cylinder. The two groups of three exhaust openings each were placed at the sides between the two sets of transfer ports, each group discharging through a stubby exhaust stack.

The manner in which the fore-and-aft transfer ports were supplied with mixture from the crankcase was both interesting and ingenious. The presence of the disc valve at the rear and the crankweb and rear main ball race at the front precluded the creation of straight bypass passages which were fed from directly beneath the transfer ports. Instead, the upper cylinder casting incorporated what amounted to a set of annular passages running around the cylinder liner from the lower gas entry point to connect to the transfer ports through suitably-positioned risers. Careful routing of these passages was required to prevent any overlap with the exhausts.

The bypass passages were fed from the lower crankcase by a pair of relatively small openings, one on each side directly beneath the exhaust ports. Since these entry points were radially located at 90 degrees from the transfer ports, incoming mixture had to spiral up from the lower bypass entry ports to the transfers, following a somewhat tortuous path in doing so.

The resulting bypass system was undeniably rather convoluted, also increasing crankcase volume somewhat. I would guess that the rather small bypass entry openings (which were unassisted by any piston porting), the increased crankcase volume and the more convoluted gas pathway would together have more than offset any potential advantage gained with the extra transfer opening. Objectively speaking, it has to be said that it's difficult to see any real advantage for this arrangement over the standard Hornet setup with its piston ports and more direct gas pathway. However, Cliff Fox clearly felt otherwise.

An interesting observation is the presence of a single round hole in the cylinder wall immediately above each of the two entry points to the bypass system. Each of these holes communicates with its respective bypass passage. At first glance, these holes look very like part of a piston port system intended to ease gas entry into the bypass passages, but there are no corresponding piston ports, nor indeed could these be provided without destroying the engine's crankcase compression seal since they would be open to the exhaust ports for much of the stroke. It seems likely that the function of these holes was simply to improve piston lubrication and cooling. There is also a shallow cutaway in the cylinder wall at each of the entry points, which has the effect of marginally increasing the entry area.

It will be appreciated that the system of porting employed rendered the use of a Hornet-style domed piston with a single baffle no longer practicable. Both engines employed a cast alloy piston having two rings. However, the Baab-Fox used what was in effect an X-baffled piston having a basically rectangular crown. The intent of this design was clearly to keep the exhaust and transfer gas flows as separate as possible—always an appropriate goal when designing a two-stroke engine which does not feature a resonant exhaust system. The attached illustration of the situation at bottom dead centre will hopefully show the very high degree of directional channelling of gas flows into and out of the cylinder which this arrangement promoted.

The resulting piston was unusually high-domed, requiring that the underside of the cylinder head be contoured to match. If the engine had followed the usual pattern of having the piston crown remain below the top of the liner at top dead centre, the overall height of the engine would have become somewhat unwieldy. Indeed, one of the designer's goals was clearly to keep the engine as compact as possible.

To get around this issue, the engine was designed so that at top dead centre more or less the entire piston crown protruded above the top of the liner. The domed combustion chamber was thus entirely contained within the cylinder head rather than in the cylinder barrel. Bill Cubitt had used a similar design approach in his Talisman 60, a model with which Cliff Fox was doubtless familiar. The combustion chamber was of course contoured to match the X-shaped piston baffling system.

The length of the piston skirt in the Baab-Fox was such as to create an approximately 30 degree period of sub-piston induction around top dead centre. It's difficult to see much benefit arising from this feature, although it must be said that the Baab-Fox was not alone among racing engines in using a small amount of sub-piston induction.

The final feature which distinguished the Baab-Fox from its better-known Hornet competitor was the use of a plug which was steeply angled towards the rear of the unit. The adoption of this angle allowed the creation of the required material thickness to accommodate the plug thread without the need to increase the vertical material thickness of the combustion chamber's upper surface. Both the reduced vertical material thickness requirement and the angled plug contributed to the evident goal of keeping the engine's overall profile as low as possible. The location of the plug was such that the actual ignition point remained quite close to the centre of the combustion chamber despite the rearward orientation, thus avoiding the creation of an overly long flame propagation path.

In summary, the Baab-Fox .604 was basically a Hornet 60 with extensively-revised cylinder porting, a modified piston/combustion chamber combination and a ball-bearing disc valve spindle. Clearly Cliff Fox believed that these modifications would give his design a competitive edge. It's actually sad to have to reflect upon how wrong events quickly proved him to be. Let's now turn to the engine's production history.

Production History

As with our companion article on the equally-rare Bungay High-Speed 600 from New York, this section won't take long! Having developed a design which he clearly felt would offer a performance advantage over the Hornet and McCoy opposition of the day, the next problem facing Fox was arranging for the engine's manufacture. This challenge was greatly simplified by the fact that Fox was already collaborating on the manufacturing side with W. Lloyd Baab, a very well-known figure in the model car racing world who was then serving as the Managing Editor of "Rail & Cable News" magazine located at 8215 Outlook Avenue in Oakland.

Apart from his journalistic activities, Baab operated a manufacturing facility under the name Baab Model Products at 1749 Pleasant Valley Avenue in Oakland. One of his more popular products was the Fox Proto model car design which was marketed by Cliff Fox through his Fox Specialities hobby shop on 61st Avenue in Oakland. We'll never know the terms of the arrangement, but Fox was successful in obtaining Baab's agreement to add what was to become known as the Baab-Fox .604 racing engine to his existing manufacturing program.

The first (and seemingly the only) national advertisement for the Baab-Fox .604 appeared in the June 1946 issue of "Model Craftsman" magazine. It's probable that the engine was marketed regionally, most likely through local promotion and over-the-counter sales at Cliff Fox's hobby shop, but we have no evidence for this. The single known advertisement stated that "small quantities" would be available as of May 30th, 1946 (i.e., just in time for the appearance of the national advertisement). The advertised selling price was a rather hefty $38 complete with plug, some 10% higher than the $35 then being charged for the competing Hornet and McCoy models.

An interesting observation relating to this advertisement was the fact that the illustration of the engine showed the name "FOX" cast in relief onto the rear of the upper cylinder casting. All of the surviving examples which have been reported have carried this name at the front of the casting, with the name "BAAB MODEL PROD" appearing in relief on the rear surface of the casting. Woody Bartelt's replicas follow the pattern displayed by the actual engines rather than that implied in the advertisement. Having said this, there's actually no impediment to the mounting of the upper cylinder block in either orientation.

The Baab-Fox was promoted as "the first four-port motor in the Class C speed field". This characterization of the engine clearly implies either that Baab and Fox were unaware of the similarly-ported Ball 60 or that their design did indeed appear first. Although the engine was clearly aimed directly at the model race car market, it's noteworthy that the shaft was dimensioned to accept a conventional bobbin-type prop driver of the kind typically used in the Class C control-line speed category which was then rapidly gaining popularity. The promoters of the engine were evidently keeping their marketing options open...

Despite this, the engine appears to have made very little impression upon the market, even in the hotbed of model car racing activity that flourished at the time in Southern California. It was likely a combination of high price and a failure to match the performance of the Hornet and McCoy opposition that led to the engine being withdrawn very soon following the placement of that one national advertisement. It actually seems likely that the "small quantity" advertised as being available by May 30th, 1946 was the only batch manufactured.

There's no way of estimating production figures, but the number actually completed must have been extremely small. When researching his indispensable American Model Engine Encyclopedia (AMEE), Tim Dannels uncovered only three surviving original examples (of which Woody Bartelt's example was one), although there may well be a few more hiding out there. Interestingly enough, all of these examples reportedly displayed machining differences of one sort or another, implying that the engines were individually constructed rather than being cranked out on a production line. Woody's replicas are of course based upon his own example—others may have exhibited minor variations.

The Replica Baab-Fox .604 on Test

Given our comments on the rarity of this engine, it will come as no surprise to learn that I don't have an original example to test—in fact, I have never seen an original Baab-Fox .604 in the metal. However, the fact that I'm fortunate enough to have one of Woody Bartelt's fine replicas on hand places me in a position to at least report on the performance of the replica. The fact that Woody's replica was copied directly from an original example in Woody's possession (the actual example illustrated on page 21 of AMEE, in fact) should result in performance figures which at least approximate those of the original.

In the interest of simplicity, I elected to test the engine on glow-plug ignition. I used my usual test fuel containing 10% nitromethane along with a good helping of castor oil. Experience with other 10 cc racing engines of similar vintage gave me a pretty good idea of the range of airscrews that might yield useful information.

As far as I'm aware, no performance claims were ever published for the Baab-Fox .604. However, beating the Hornet 60 was clearly the engine's performance target. Accordingly, we might look to see peak power developed in the vicinity of 15,000 rpm or so—a little higher than the official post-war Hornet claim of 0.85 BHP @ 14,000 rpm. This expectation influenced my decision to set 15,000 rpm as the upper speed limit to which I was prepared to push the engine.

As things turned out, I need not have worried at all about limiting the speeds! The Baab-Fox replica never got anywhere near 15,000 rpm on any of the props tested. It proved to be a very easy starter as long as a good prime was administered. The challenge here was keeping the prime in the cylinder. The very steep sides of the piston crown encourage the prime to run straight back out of the exhausts or down through the bypass passages into the case. The best approach was to prime through an open exhaust and then immediately close the exhaust with the piston. Then connect the plug, hit the prop and away you go.

The engine was completely happy running on suction feed. Response to the needle was excellent, making the establishment of settings very straightforward. Running was very smooth at all times, with no tendency towards misfiring or sagging.

I put on 25 minutes in slightly rich 5 minute runs to give the rings a chance to bed in and then took some brief leaned-out spot readings. I have to say that the results were somewhat less than I had expected. The following table tells the story:

Obviously there's insufficient data here to allow the development of a truly representative power curve. However, the above figures seem to imply that the engine is more or less done by around 11,100 rpm, at which speed it probably develops around 0.61 BHP. I was frankly hoping for a little more than this! It's probable that more running would yield some improvement, but not to any major extent. It's also quite likely that a slightly higher output could be achieved using spark ignition.

Having said that, it must be recognized that we are dealing with a design which dates from early 1946 which was specifically intended for spark ignition operation on straight fuel. This was the time before glow-plugs or nitromethane, remember! When we reflect that the manufacturer's claimed performance for the original pre-war Hornet 60 was only 0.55 BHP @ 15,500 rpm (less power, and obviously far less torque), it's clear that the Baab-Fox was at least in the general ball-park if we go by that standard (as Cliff Fox may have done). Perhaps more significantly in a tether car context where torque is important, the Baab-Fox peaked at a relatively low speed, seemingly as a result of developing considerably greater low-end torque than the pre-war Hornet.

However, the performance of the Hornet was quickly improved once production re-commenced in the post-war period. By mid 1946 the factory claim for the post-war Hornet (which remained the performance standard at the time) had risen to 0.82 BHP at 13,800 rpm. Present-day testing amply supports this claim. This of course left the contemporary Baab-Fox in its wake if the above test is anything to go by.

Even allowing for the probability that the original engines may have performed somewhat better than the replica, there seems to be little doubt on the basis of this test that the Baab-Fox failed to match the performance standard which had been established by the 1946 Hornet and was even then being challenged by Dick McCoy with his popular 60 model. It's probable that this performance shortfall became immediately obvious to the modelling fraternity, which would completely explain the engine's extremely short market tenure.

The Baab-Fox .604 Today

We trust that our earlier remarks have made it quite clear that original examples of the Baab-Fox .604 are rare to the point that the engine has achieved near-mythical status. Examples do exist—Tim Dannels located three of them when researching AMEE—but your chance of finding one is probably a little less than your chance of finding that someone has stolen the Rock of Gibraltar and stashed it in your garage!

Even if by some miracle an original example did cross your path, you'd better have your line of credit well cleared before commencing negotiations! Woody Bartelt tells me that the original example which was used in the creation of his replicas was later sold for no less than $5,000!

This being the case, a far more cost-effective option is to get in touch with Woody and arrange for the purchase of one of said replicas while they remain available. As of the time of writing (December 2013) Woody still had a few of these engines in stock at a price of $499, but they won't last forever and Woody has no plans to arrange for the production of any more. These replicas are highly desirable collector's items in their own right which will only appreciate in value as the supply dries up. Contact Woody for availability.

In summary, the Baab-Fox .604 was a very interesting example of one designer's attempt to take an existing and highly successful model racing engine (the Hornet 60) and rework the design to deal with a few aspects of that model which appeared amenable to improvement. A very worthy effort by Messrs. Baab and Fox—too bad that it was not rewarded by greater marketplace success.

Still, thanks to Woody Bartelt's initiative in making his fine replicas available, we can still enjoy contemplating this very creditable effort to create an improved model racing engine. It's a story well worth preserving—we hope that you've enjoyed our attempt to prevent yet another "ship that passed in the night" from disappearing completely from the consciousness of model engine enthusiasts worldwide!