British Anzani A & B Stock & Alky Racing Engines

[John (Taylor) Gabrowski]

I was asked about information on the Vacturi AO-500s and why in the face of development did the Tenney Spec'd Anzanis and many other Anzanis run here in North America used and stuck to the Vacturi carb?

From available data it was found that the Amal round slide monobloc A and B carbs were woefully inadequate when it came to low fuel flow supply and jetting inadequacy you would need to run in Alky and this was well developed in thought by the later 1950s. Vacturi carbs being already plentiful from their racing uses on C racing and C Service Johnson, Evinrude, Elto and other similar engines seemed to be a no brainer choice. The carb was ruggedly built, had a huge volume capacity for fuel storage in the fuel bowl and sported twin topside of barrel/venturi spill out jets controlled by a single adjustable needle valve so large there was no question they could feed the right amount of fuel to a A or B displacement Anzani.

Similarly adapation was easy buy means of 3/4 inch thick adapter plates bolted to the Anzani cast iron block carb port that initially had to take the round opening of the carb to the mixed squarish to rounded cornered original opening installed for the Amal monobloc carb that used gasoline for UK stock racing. This led to many versions of carb adapters that eventually went from a small rounded plate to the point where the entire adapter plate covered and secured the entire 2 transfer ports on the same side as the carb sat. It was during this adapter phase that matching the Vacturi barrel took place to match the intake port on the side of the Anzani block. Carefully a bell flueted liner/insert was machined to fit within the original barrel of the stock Vacturi carb. As the development of the engine went on it was found to be desirable to not only keeping the barrel round but also doing the same to the aluminum adapters and also to the cast iron block itself to increase flow but also decrease unwanted turnbulence of the blocks squarsih round edged carn intake port. Eventually this was maxed out all the way through to the point where the Anzani's block carb block opening became paper thin cast iron at its inner walls making the opening to 1 and 1/4 inches in opening diameter. This could go no further without changes that would require welding ad machining to go any larger but for most the paper thin cast iron walls from what the casting had was its end in intake sizing.

All Vacturis came with a coated cork float from their original spec as a tank over head gravity feed carb. It was found very quickly that the carb fuel bowl inlet needle valve was entirely too sensitive. This was delt with by installing Del Orto remote fuel bowls from as few as one to as many as 3 of them over the carburator to in effect give it the simulated gravity feed other overhead tanks gave in keeping with the carbs requirements and engineering. This system did work quite well except for a perennial problem of the Alky/Nitro?Caster fuel mix eating at the corks varnish coating causing the cork float to become saturated and stop working flooding the engine with fuel preventing it from remaining in tune.

Two solutions came from 2 different places that would resolve the issue from 2 different directions. The west coast solution was to make the Vacuri floatless and use an OMC fuel pump to charge the carb with a spill over to return the excess fuel to the tank. The eastern solution was to keep pressurizing the fuel tank from cranlcase pressure bleed off on the motor to force fuel into a floatless Vacuri carb with a spillover that would also return excess fuel back to the tank the same gravity way the fuel pumped versions did. Both fuel systems were still capable of "run on" but the OMC fuel pump method did not involve a pressurized fuel tank therefore was less susceptable to feeding runaway alcohol racing fuel fires that did some times happen both in the pits or on the race course.

By the end of the Anzani era in the 1970s most of the Anzani fuel systems were pump and flow through return to the fuel tank, tank unpressurized. During that period the Vacturis and Tillotson HLs used on these engines were the only carbs ever seen on them and with the great Vacturi as the primary carb that started it all came the speed records one after the other. To this date I never saw an Anzani with any other carbs but these butterfly carbs and their secondary Tillotsons. Where the rotating barrel (Konig types) or round slide or similar carbs were if installed on Anzani may have been tried as they were on Harrisons have yet to be seen in any of the Anzani's history of racing use. If any were used the story and perhaps a picture would be a great addition.

Following this story shortly will be a pictorial on the Vacturi carbs (loving called the carbs that acted like a post nasal drip!) and how they were adapted, mounted and used by Anzani.

[John (Taylor) Gabrowski]

All Vacturi AO500 carbs left the factory basically as pictured. The casting and workmanship in the production of these carbs was impeccable. These carburettors were so well thought of in terms of use, aftermarket parts like velocity stacks in front of the carb were cast by by some and machined into being by other makers. Similarly if the carbs were subjected to rotary valved engines aftermarket parts makers made various lengths of after the carb base ram tubes of various lenghts for various tunning effects like "short ram" or "long ram" tunning. Where the carb was used next to reed valve induction, simple bolt up to a suitable adapter to the engine was done.

The following pictures are those of the basic Vacturi "prior to" be modified by Bill Tenney for mounting on Anzani class A and B Alkys.

[John (Taylor) Gabrowski]

Vacturi carb pictures from various angles to see details.

[John (Taylor) Gabrowski]

With thanks. It has all been followed up. The notice concerning Anzani pistons/parts for sale has been followed up successfully by a member other than myself also involved in Anzani restorations. Such finds are going to help with restorations any time they happen and please keep up the watch for any more that comes available in term of what ever pieces there are.

[John (Taylor) Gabrowski]

If the Anzani had a feature some found unique is it started off it was how it fogged or spit back through the Vacturi carb at lower rpm under 5,000 where it stopped until it got to its normal 9,000+ operating rpm as a A, B, C (twin bloc) or D (twin block) Alky(s). So at the top 4000 to 4500 Rpm (top rpm was about 9,500) powerband it ran at the top it was fog / spitback free. When they tried expansion chambers from open exhaust bells the situation worsened. According to Jim Hallum the nature of the engine fogging was all tied up in its overlapping porting. Ordinary B stock gas Anzani engines with round slide carbs Amal monoblock carbs, the carb and its round slide managed the fogging problem with the engines mild porting. With the use of the Vacturi carb with its throttle butterfly and enlarged porting all around all this all changed. As ports were altered and grew so the narrowness of the powerband at the top got tighter. It was found very early on that cutting back between 1/8 to 1/4 of an inch off the piston skirt at the block carb intake window set increased Anzani power further so it was a raft of porting improvements gave the engine speed and power but a lot of fogging until it got up there.

Many Vacturis were simply intake sleeved and belled at the same time as part of the adapting to the engine block. Some Vacturi sleeves were simply slightly fleuted and a racing velocity stack added on the end to give the engine extra ram length to deal with the lower rpm fogging. The following pictures is that of the simple but nice velocity stack that was also commonly used before Anzanis too on C-Service and C racing engines of old like Johnson P50s, 4-60s, Eltos and Evinrude Speedytwins. Enjoy the pictures.

[John (Taylor) Gabrowski]

I had quite a discussion with Jim Hallum and some history on how the inner throat liners were developed for the Vacturi AO500 and adapted to British Anzani. This would not be a good article without evolutionary and historical pictures of the efforts involved to do all this. That all will be in the up and coming post coming very soon.

[John (Taylor) Gabrowski]

If having open ball combined with bronze bushed top of crank Anzani main bearing systems seems amazing finding bottom of crankshaft main bearings of oilite bronze without a seal is amazing too!

Pictures of these Anzani bottom bearing systems to follow shortly.

[John (Taylor) Gabrowski]

Adapting any carb to British Anzani outboard racing engines let alone a Vacturi AO500 was a daunting task. Anzani at source used the round slide Amal monoblock carb for gas class stock outboard racing in UK. These carbs could never supply the amount of air/fuel required of North American Alky outboard racing. For that reason Bill Tenney had the foresight and experience with using for years the Vacturis as the best for use carb on the Anzani as an Alky.

Not only did they have to sleeve the Vacturi carb barrel / venturi, they had to make the block adapter too that came in 2 configurations from Anzani. One configuration Anzani had as in the later models was round and did not present a great problem. It was the initial type that was molded not only to recognize the 2 piston ports but also the crank rotary valve "S" tunnel. That meant you had the air/fuel going in 3 different divergent directions to accumulate in the crankcase prior to transfer to each cylinder in turn. It was not an easy task. Pictured is a fraction of the 23 adapters made to mount the Vacturi carb to the early irregular Anzani carb block inlet holes. In the end engine preparers and racers like Jim Hallum and Ron Anderson rounded the Anzani carb inlet holes entirely to perfectly round ones to make the match not only round but large in the cast iron block and within the Vacturi carb venturi / throat. That kind of thinking and innovation kicked the British Anzani engines into the 10,000+ RPM ranges where they ran methanol fuels sometimes sporting more than 40% nitromethane as the power boost additive in Alky racing of that era.

Enjoy the pictures.

[John (Taylor) Gabrowski]

Pictured is the typical late model Anzani B Stock Gas racing carb spacer / adapter. In this case this later block was a 348CC for UK B stock racing. The earlier blocks for B Alky as delivered to North America were 322CC and both the early B Alky as well as the smaller early A Alky blocks had these difficult irregular openings on their cast iron blocks.

[John (Taylor) Gabrowski]

Anzani went through some 3 stages in bottom end crankshaft seals. Pictured are examples of bottom end crankshaft seals with the earliest being just singular "Oilite" porous bronze bushings in a machined collar end cap. This type of metalic seal did offer bearing support itself as bronze bushings do. By the start of the 1960s the bronze bushing/seal was replaced with a "rawhide" collar type spring loaded seal. It was deemed the bronze bushing was no longer required as the caged ball bearing race above was adequate bottom of crankshaft support. These rawhide seals proved better suitable but hardened quickly from the heat and the affects of the methanol based racing fuel. Finally in the later 1960s Anzani came to rely upon modern single and double lipped collar coil sprung compression neoprene type synthetic seals.

Enjoy the pictures.