chas0218

I have:
4.060 bore
3.750 stroke
5.7" rods
-5 cc valve relief
.040" head gasket
62 cc combustion chamber

i cant find for the life of me the piston to deck clearance in order to calculate the compression ratio. i know it has to be right around 11:1 but not entirely sure. I also am not sure if 93 will run in this w/o pinging. any help would be greatly appreciated.

Thanks, Chas

Damon

Assuming the pistons were made for a 383 stroker application it should be around .025" in the hole at TDC. If you had the block decked it will be less.

Yes, you'll be right around 11:1 with that combo of parts, even with an undecked block.

Will it ping? Depends on a lot of things, but that's certainly pushing the limits with pump gas in most cases.

GTA Sammy

iTrader: (1)

4.06" x 4.06" x 3.75" x .7854= 48.548 Cylinder Swept volume in cubic inches
62cc x.061= 3.78 cid of Combustion chamber
4.06" x 4.06" x .040" x .7854= .517 cid of head Gasket
4.06" x 4.06" x.025" x .7854=.323 cid for deck height
4.06" x 4.06" x .100" x .7854= 1.294 cid Valve reliefs

(Swept Vol + Chamber Vol + Gasket Vol +Deck Vol + Piston Vol)
-------------------------------------------------------------------------- = Comp Ratio
(Chamber Vol + Gasket Vol +Deck Vol +Piston Vol)

48.548 +3.78 +.517 +.323 +1.294= 54.462
--------------------------------------------------
3.78 + .517 +.323 + 1.294= 5.914

54.462 divided by 5.914= 9.208 compression ratio

Calculations right out of John Lingenfelters book.... if my math is right (correct me if I'm wrong- My feelings won't be hurt) you shouldn't have anything to worry about.... You never said if you were using aluminum heads (cause you could use a higher compression ratio without detonation) and what the duration of your cam was.....

Checked a few different online calculators and get different results.... see for yourself....
http://www.rbracing-rsr.com/compstaticcalc.html
http://www.csgnetwork.com/compcalc.html
http://www.bgsoflex.com/cr.html

chas0218

those 2 both gave me 12.2
but i know it isnt that high seeing how the manufacturer of the rotating assembly said that it will be right around 11:1

my duration at .050" is 240*/246*
and my heads are irons

o well i guess ill find out otherwise i might be buying octane booster by the barrel

and suggestion on the brand?

GTA Sammy

iTrader: (1)

The big duration might blow off some of that compression ratio.....

chas0218

just re-did the math and i was using -4 when i was supposed to be using 4. The new total is 10.97:1 so im a lot happier and less worried (not completely gone.)

KlutchKiller

I know this is an ancient thread but I'm building a 383 right now with the identical specs.
How did it turn out?
What head gasket thickness did you run (if you remember)?
Any pinging?
Did you have to run 93 octane?
Thank you!