comp. ratio

scs65 · Post by **scs65** » Sun Jan 26, 2003 8:09 pm

needing some info. planning to buy a pair of 044 heads to fit on a 90.5 x 78.4 (2017). The dealer says the combustion chambers are approx. 55cc. I'm wanting a compression ratio of about 10.5:1. My math says i need a combustion chamber of about 41cc. How much needs to be flycut from the heads to reduce the chamber by 14 or 15 ccs.??

Searoy · Post by **Searoy** » Sun Jan 26, 2003 9:24 pm

What deck height?

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*** Teach a Man to Fish ***
Darth Searoy

"I tend to lean toward a tighter gap and a
looser skirt....a little slap never hurt." --
Joe Locicero a.k.a. Joe of the West

scs65 · Post by **scs65** » Sun Jan 26, 2003 9:36 pm

I'm assuming a deck of .070. Just going from memory of what the last piston/cylinder had. goigt to install same size and brand of jugs as previous. its been a year since I looked at this so memory might be a little fuzzy.

Post by **Marc** » Mon Jan 27, 2003 8:30 am

If it's an option you'd be better off reducing the deck to .050" and only cutting the heads down by 10cc.
The "rule of thumb" is that you'll need to cut .010" for every cc. It varies with the chamber shape of course, but that'll get you quite close on most heads.

scs65 · Post by **scs65** » Mon Jan 27, 2003 9:00 am

I'd like to reduce the deck height but don't know any way to do it other than machining the case. dont want to get into that. theres no barrell spacers used. I'm trying to verify the deck height today. hoping thats its less than .070. .140 seems like a lot to flycut, but the 044s are supposed to have a much thicker combustion chamber casting. Anyone know about this?

bedlamite · Post by **bedlamite** » Mon Jan 27, 2003 5:28 pm

What length rods are you using? If you're not willing to cut the cylinders, it may be better to bump the rod length to get the combustion out of the cylinder, especially with that high compression ratio.

Assuming you are using stock length rods and the deck height of .070 is correct, I would change to 5.5" rods, add .060" spacers, and cut the heads to 50cc. That should get your CR up to about 10.3

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If you can make black marks from the apex of one turn to the braking point of the next, you may have enough horsepower.

scs65 · Post by **scs65** » Mon Jan 27, 2003 8:50 pm

well, actually, it looks like my deck height was .110. I assume the new setup will be about the same. The rods are stock length. Is cutting the cylinders to a shorter length a routine job? If so, thats a simple solution. I'd prefer a much smaller deck clearance and be able to leave the combuston chamber alone. I'm new to VWs and this board. It seems that compression ratios in the 8 to 1 range is common for the VWs. I'm racing on a dirt oval, is a 10 to 1 ratio going to hold up?

James2 · Post by **James2** » Mon Jan 27, 2003 8:59 pm

Any machine shop can cut the cylinders. Chances are you may have have both the cylinder and head cut.

You can run the deck as close as .050 with no worries. Other, including me are running much tigher decks.

[This message has been edited by James2 (edited 01-27-2003).]

scs65 · Post by **scs65** » Mon Jan 27, 2003 9:16 pm

yes, with my math, it looks like I'd have to get the combustion chamber down to 45 CCs even if I had .050 deck clearance to get the 10 1/2 to 1 ratio. Seems strange to increase displacement by 25% and still have to do machine work to get compression.