Base spacer

[davecara]

B12 motor, Gen1 busa pistons AND rods. Any ideas what thickness base spacer i’ll need to get to around 9.5:1?

i believe the busa rods are a touch stronger than the bandit ones? Anyone have any input?

[Duckndive]

You need to do a dry build and the sums to find out what C/R that combo gives you have then adjust to get to what C/R you want 

[davecara]

I was hoping to avoid doing any maths 

i’ll have to break out the dti and the calculator!!

[Arttu]

Better to do measurements and math if you want any reliable result. Always. There are just too many variables that can throw result anywhere.

Slightly related anecdote. A friend of mine had a set of Wössner turbo pistons for his race Busa, 9.5:1 specified compression. He wanted to increase compression to 10-10.5 range so we started to take measurements to see what needs to be done. Turned out that with his slightly machined combustion chambers the compression was about 8.2 instead of expected 9.5. With stock head it would be maybe 8.5. After some measurements and calculations we got to conclusion that no matter what cylinder block height or piston crown machining we would use the result would be maximum 9.5 with those pistons. So he decided to buy new MTC pistons with 10.5 compression. So just throw them in and it's done, right? I urged him to do measurements once again and guess what, 9.5 compression with those new pistons!

So, always measure and trust nothing. Yes, I know, easier said than done...

[Gixer1460]

Maybe an age thing but I thought the use of Busa rods popped the piston out of the block by a mm or so hence when used with std GSXR rods the CR is down around the 8.5 / 9:1 range?