I was thinking the other day (yes i actually thought) about what would make an A series engine more boost friendly, when it hit me...

An A15 block, pistons, rods etc etc. all swinging on an A12 crank.

How do people think that would go? coz you have the larger bore& longer rods of the A15, but then the short stroke of the A12 and also a larger combustion chamber due to the shorter stroke...

What's peoples opinions? do the A12 and A15 even share the same big end diameter?

anyway, it was just a quick idea i had. most likely never going to happen...

I'm picking you'll end up with comp ratio of about 5:1 with that combo. A14 crank in an A15 might work?

For one thing, the piston will stop rising 6mm before it reaches the top of the block. This isn't much good for compression or squish.

All bearing journals on all A series cranks share the same dimensions with all other A series cranks & are therefore interchangeable with the exception of the A10 crank due to it's 3 main bearing configuration.

All A series engines will handle boost. Just how well depends on the amount of boost, the materials used in the components & the way the engine is built & used.

dont go chasing big cubes with overbores
you will make more power with thick, stiff cylinder walls
dazza

i always remeberand quote a theory by martin donan from zoom magazine many years ago, get more power from short storke motors with more boost than long stroke motors that are limited by boost as then bend conrods due to pressure.

I think this can be proven by wrx drag racers that had ej20 then made hybrid ej22 then went back to high boost ej20's again.

by this theory, a12 would be ideal candidate, over bore or not, and 1200rc's set up made good power on an a12 but still mightly imressive on the a15's.

Quote:If that is the main factor, then the A10 engine certainly is the "best". It has the shortest stroke. And same bore as the A12.

What about our 4 speeds? will it take the extra boost? and the clutch? wont it slip?