Compression ratio on 383

dubs chops · Feb 28, 2017

OK guys I have tried using a CR calculator bu I keep coming up with a CR less than some of the factory numbers I have seen.

can someone help me.

.383 stock bore and stroke
.039 Head gasket
Flat top pistons with no valve releif
84cc edelbrock heads milled .010
piston to deck height stock???? .025-.05

the calculator I used kept saying 8.6-1

I may have been entering something wrong. anyways stock is listed as 9.5-1 for a 69 or 10.0-1 for a 68

65-440 · Feb 28, 2017

This is what I use ....

dryheat · Feb 28, 2017

I calculated 8.9 given those numbers ... changed the head gasket to .020 and got 9.6

Darter6 · Feb 28, 2017

Yep, factory steel shim head gaskets were .020 ^^ like what dryheat posted above.Then put in the factory + or - of .5 and that gets you close to the 9.5 to 10.0 range.

Meep-Meep · Feb 28, 2017

383's are hard to get big compression out of with flat top pistons because of the short stroke. My 383 with -.005" deck flat top pistons and 915's with comp gaskets yielded 9.5:1. If this is a street car 9.5:1 is plenty.

moper · Mar 2, 2017

You're math is right. The factory blocks are taller than blueprint too. So it is substantially lower than what the books said and without cutom pistons there's not much you can do about it aside from milling the heads to reduce the chambers when running aluminum heads. The E street heads come with a smaller chamber than the RPMs IIRC.

dubs chops · Mar 3, 2017

these were the 84cc RPM heads/

lewtot184 · Mar 3, 2017

dubs chops said:
these were the 84cc RPM heads/

from my experience those 84cc heads will probably check between 81-82cc's. KB does make a piston with a dome that may get you to 10:1.

Compression ratio on 383

dubs chops

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65-440

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dryheat

FBBO Gold Member

Darter6

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Meep-Meep

дворянин

moper

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dubs chops

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lewtot184

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