Okay! Ya got me curious, so I had to go look some stuff up...
The factory competition dept. was dyno-testing 120+ hp out of the 1147cc Spit motor, 130 hp out of the 1296cc and 150 from the 1500cc. The first two motors proved to be near bulletproof and won a lot of races. The 1500 had some problems early on that needed sorting out.
Of course, those HP figures are from an engine dyno (i.e., are not "rear wheel" HP) and were being produced by radically cammed race motors revving up and over 8000 rpm, probably with very high compression and 100 octane fuel. Those engines would have to have been carefully balanced to be able to achieve those rpms with stock crank and sometimes even stock conrods, as required by production class rules (later changed to allow upgraded conrods, thankfully). In all the Spit motors they built, Kastner said he only ever used two rings per piston: one oil control and one compression. But because the cars were run in production class, they had to stick with SU carbs, standard cyl. bores, stock valve sizes, standard rockers, etc. I seem to recall something about using a larger diameter cam follower, too.
Even with the 1147cc motor, they ran into somewhat of an "aerodynamic barrier" on the track at around 120 mph, before they ran out of engine! Significant lowering, front spoilers and some other tricks all eventually helped get the car closer to its full potential.
120, 130 or 150 hp in that small/light car sound like enough? Of course, with a streetable car "Your mileage may vary" a little!
Problems with the newly introduced 1500 engine were primarily in main bearing lubrication. This showed up when the first engines were put out on the race track and quickly broke (long before street cars experienced much trouble).
Testing showed that in stock form all was okay at low to mid rpms, but the front main was only seeing 10 psi oil pressure by about 4500 rpm. A little bit over 5000 rpm, the front main dropped to 0 psi. At the same time while, the rear main and the readings on the cockpit gauge were fine: 60 to 75+ psi.
Good grief! No wonder the crankshaft didn't last long when the engine was revved a little!
Initially the problem on the track was helped a lot by installing an external oil feed coming from the oil cooler directly to the mains. That helped insure an adequate oil supply and equal pressure to the all the bearings. It worked, but sounds like sort of a bandaid on the actual problem.
Later it became obvious that the original crankshafts had the main bearing oil supply holes drilled in the wrong location in the journals. Centrifugal force was pushing the oil out of the bearing before it could reach into the higher stress areas of the journal, and the problem became progressively worse as rpm increased.
The rear main got enough oil to compensate. But the front main was the last to receive oil, so there was no pressure left for it by the time the other mains had taken more than their share and "spun it off".
The poor crankshaft could only stand this for so long, before it gave up completely.
Replacement crankshafts were improved with a somewhat relocated oiling hole, but there are still a few more tuner tricks that can improve the situation even more.
Some day I'm gonna have to play around with a Spit with these engines for myself. Or, maybe a GT6 with the 2 liter (and some similar oil pressure problems!).
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