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Author Topic:   Piston, compression
eaton89
Dirt Freak

Total posts: 268
posted January 29, 2005 07:34 PM  
Can anyone tell me what the compression would be on a flat top 4v relief cast TRW piston with a 64 cc head. I run this in a 350 motor last year and woundering what it would be so when I upgrade I could get something close only in a hyper. This was in a stock 30 over bottom end motor I got from a freind that was built for a regular daily driven truck.

sledgehammer
Dirt Forum Racer

Total posts: 94
posted January 29, 2005 08:56 PM  
Roughly 10.6 to 1

supwitchew
Dirt Maniac

Total posts: 122
posted January 29, 2005 08:59 PM  
I have it at a little over 9 to 1. That's if the heads haven't been milled, the block hasn't been decked, and you're using the standard head gasket thickness. How did you get 10.6 to 1? Did I do something wrong?

[This message has been edited by supwitchew (edited January 29, 2005).]

eaton89
Dirt Freak

Total posts: 268
posted January 30, 2005 05:50 PM  
I am using standard thickness gaskets. I was thinking it was less than 10 but I am only guessing.

supwitchew
Dirt Maniac

Total posts: 122
posted January 30, 2005 08:42 PM  
I got 10.6 to 1 when using no valve relief flat tops and bored 60 over. Like I said, maybe I'm doing something wrong. There are way more qualified people that will answer this than me.

eaton89
Dirt Freak

Total posts: 268
posted February 01, 2005 08:58 PM  
Thats alot of difference. Anyone else want to add or verify one of these. How do you figure it out. I think it was a cast TRW piston, four valve flat top,30 over, standard head gasket and deck height ,64 cc head.

racin78p
Dirt Freak

Total posts: 333
posted February 06, 2005 04:10 AM  
Need a more acurate cylinder head combustion size (relief cut pistons add volume), and the height of the flat tops to deck surface measurement, but I guessed and with a .041 head gasket came up with 10.25 (high #) and 9.7 (low #).

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racin78p
if it ain't fun, then don't run

Speedracer92
Dirt Full Roller

Total posts: 70
posted February 06, 2005 06:31 AM  
I would agree with the roughly 10.6 to 1 if the deck is stock.

supwitchew
Dirt Maniac

Total posts: 122
posted February 06, 2005 10:42 AM  
OK. So I did it again and I ended up with 10 to 1 plus or minus a couple of tenths. Whatever I did the first time, it was wrong. I agree with the numbers that racin78p came up with. It does depend on the relief cuts. I added 8 cc's to the volume to make up for the 4 valve reliefs. The 8cc's should be pretty close for a stock flat top.

sledgehammer
Dirt Forum Racer

Total posts: 94
posted February 06, 2005 02:46 PM  
The 10 to 1 figure is correct not 10.6 to 1.
The 10.6 to 1 was based upon -3 cc's added for the valve relief. The four valve relief is more like -8 to -9 cc's. Below is an address to a good compression calculator.
http://www.angelfire.com/fl/procrastination/motor.html


eaton89
Dirt Freak

Total posts: 268
posted February 06, 2005 07:28 PM  
I did some calling and found the same from 9.8 to 10.13. That got me close enough and ordered a kit. So I am on my way. Thanks for all the help.

racin78p
Dirt Freak

Total posts: 333
posted February 07, 2005 11:50 PM  
I also added the 8cc's to the volume. Rough estimate as I posted. Nice to know old age served me well this time!

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racin78p
if it ain't fun, then don't run

hobby10k
Dirt Freak

Total posts: 226
posted February 08, 2005 05:57 AM  
what about 100th domes on a 400 SB with 64 cc heads?

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LIVE RACING, WHAT ELSE IT THERE?

racin78p
Dirt Freak

Total posts: 333
posted February 08, 2005 09:09 AM  
Ahhhh, Maaaannnnn,.....

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racin78p
if it ain't fun, then don't run

eaton89
Dirt Freak

Total posts: 268
posted February 08, 2005 07:27 PM  
I think its like 10.9 to 1.

sledgehammer
Dirt Forum Racer

Total posts: 94
posted February 09, 2005 03:24 PM  
Ok here goes.

Two assumptions below bore and piston cc

Bore 4.155
stroke 3.75
added volume for piston 3cc for .100 dome(probably close)
head gasket volume .041

That computes out to be 12.9 to 1

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