NEHA

WOW! I really missed that one. How does going from 2 valves to 4 valves = 10% per cyl?

Should have included before clicking send.
I just don't see how +10% per cyl adds up to = the power advantage. I always thought it was +10% wether you had 4 cyl or 8 cyl. Must have been the rules meeting I missed.

The number of valves is when looking at one cylinder. Normal would be 2 valves. If you have 4, then it is +20% (2 extra valves at 10% each), if 5 then +30% (3 extra valves at 10% each) [edit: accidentally put 25% instead of 30% as John M. pointed out]. I don't think we have any 6 or more valves per cylinder engines out there.

Walter has this correct:

That would be 20% 4 (valves) - 2 (free) = 2 X 10% = 20%

I was hoping that someone would put an end to this. "3 extra valves 25%" Then I lost it again. not 30%??
John

Yes, you are correct. 30%, not 25%. I'll fix my post.

Ok. That's a little better. I was thinking it was # of valves + # cyl. So it's actually # of valves per one cyl. I still think 10% per valve is a little high (for non-forced induction, w/ boost it may be apropriate). But I haven't run U or SP in a while. So...just something that cought my eye when reading through.
Brian

An example of 2 vs 4 valves in the same basic motor (same bore, stroke and CR):

'85-'89 VW 8V RD motor (the "big" valve performance model) - stock CHP - 102

'86.5-'90 VW 16V PL motor - stock CHP - 123

It is nearly impossible to come up with comparative HP limits on these 2 engines when they are built to race (normally aspirated, no NOS, race fuel) as the results depend a lot on money and goals. However getting to 200 CHP with the 16V appears easier than with the 8V based on my reading and personal experience (I ran a built up RD in 2007 and part of 2008, dropped in a stock but cammed 9A (2.0 version of the PL) mid 2008 and am running the 9A with a P&P job and cams now.

Based on my experience the 10% award per valve seems well founded.

"I see said the blind man to his deaf son on the telephone"
Thanks for the info and example. Brian