I need some help figuring my compression of my new engine and it just doesn't seem to be right to me, I have com up with 10.79 or 11.20.

400 sb .040 over
flat top pistons with 4 valve releifs(sorry cant spell)
pistons are .032 in the hole,
Heads are 64 cc
Standard head gaskets (felpro) Assuming .03 thickness????
Top ring gap .0022 (I think thats right)

Please help
John

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82 Firebird,355,Cam 224/234, .466/.488,TH350 Tranny,650 HolleyDP,Hooker Headers(I.E. POS) Manual steering
Best 8th et 8.62@80mph.
NEW for 01
A 408,dart iron eagle heads,street dominator intake, 750 SD,cam 229/239, .497/.520, Also a big hole in the hood.
Shooting for low 12's.
Check out my birds new home. It isn't much to look at but give me a couple years.
Http://www.geocities.com/spuds82firebird

 

Go to www.Northernlight.com and do a search on "compression ratio"(be sure to use the quotation marks for a better search). This is where I have found a lot of calculation tables.
Later,
Ozman

 

We'd have to make some assumptions here since you didn't list the specs.

I assumed 6 ccs for the piston valve reliefs and a 3.75 for the stroke. The head gasket thickness would be either .039 or .041 depending on which Fel Pro you used. I took the average, .040. I used a gasket bore diameter of 4.200, which is the size of the performance Fel Pro head gasket bore diameter.

Using Engine Analyzer Pro's compression calculator feature, I came up with 10.71

Of course, if your stroke is 3.48 (350 crank) and/or the valve relief ccs are different, the CR will change accordingly.

I can send you the 'Texas Instruments' way of doing it if you'd like.

Jake

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1986 Corvette Coupe, 415 CID, Edelbrock 6073s, ZZ9

 

Thanks
Atleast I was in the ball park, With 10.79.
I can live with just being that close.
Thanks
JOhn

------------------
82 Firebird,355,Cam 224/234, .466/.488,TH350 Tranny,650 HolleyDP,Hooker Headers(I.E. POS) Manual steering
Best 8th et 8.62@80mph.
NEW for 01
A 408,dart iron eagle heads,street dominator intake, 750 SD,cam 229/239, .497/.520, Also a big hole in the hood.
Shooting for low 12's.
Check out my birds new home. It isn't much to look at but give me a couple years.
Http://www.geocities.com/spuds82firebird

 

4 valve relief pistons are -12 cc. -6 is for 2 valve reliefs.

With -12cc flat tops, my spreadsheet formula came up with 10.122 with a .039 head gasket and 10.078 with a .041 head gasket. Assuming for some reason they are -6cc then the 10.7 range is more accurate.

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Follow my racing progress on Stephen's racing page
and check out the race car

87 IROC-Z Pro ET Bracket Race Car
383 stroker (carbed) with double hump cast iron heads and pump gas
461 Big Block installed and ready for the 2001 racing season

Best results before the 383 blew up
Best ET on a time slip: 11.857 altitude corrected to 11.163
Best MPH on a time slip: 117.87 altitude corrected to 126.10
Altitude corrected rear wheel HP based on power to weight ratio: 476.5
Best 60 foot: 1.662

Racing at 3500 feet elevation but most race days it's over 5000 feet density altitude!
Member of the Calgary Drag Racing Association

87 IROC bracket car, 91 454SS daily driver, 95 Homebuilt Harley