Combustion Chamber Volume??

[FXDX-103]

Mike,
First; I'm new to this forum and absolutely thrilled to have stumbled on it! Thank you for a willingness to help & share your extensive knowledge, keep up the great work!!

I ride an FXDX 2002, while planning my next upgrade (4 3/8 stroke) I wanted to make sure that (mechanical) compression ratio and choice of cam (TW50) is a good match. When googling I found statements that TC88 has a combustion chamber volume of 85 cc I got somewhat concerned and decided to check my heads which I got off eBay. They measured 97 cc. Out off curiosity I checked the stock heads and they also measured 97 cc. Now I'm confused, what *is* the volume of a standard head, pls? I'm assuming there's only one definition of combustion chamber volume; I put a thin sheet of clear plastic on the upside-down head and measured the amount of liquid I was able to pour into the chamber thru a tiny hole.


Thanks,
Bertil

[Mike]

Apologies for late reply. The stock Twin Cam heads that we've CC'd over the years have ranged from 83-86cc. Advertized volume is 85cc. Your method seems correct but I do not have an answer for the numbers you're getting.
The SE performance head cc's at 77 (decked .060), the HTCC's at 86 and the 103+ at 96 actual measurements. the TW50's will want 10.2-10.5 static compression.
Thanks, Mike

[FXDX-103]

Thanks for your input. Any thoughts on what CR the stock starter is capable of handling?

Thanks,
Bertil

[Mike]

Just depends on cam match to compression. The number to look at is the corrected compression. Corrected numbers (accounting for intake closing) above 9.8 make for hard starting with stock starter motors. We start our 14:1 Buell with the stock starter but our cam closes so late it does not build a lot of cranking pressure.