Determining compression ratio with several know values
Forum: C3 Engines, Driveline and Handling
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Greetings,
Happy holidays to all.... I have an opportunity to buy a set of aluminum SBC heads that are 202/164 with a 64cc chamber volume. I have a 1975 L48 with 8.5:1 compression with the standard 333882 heads with I believe a 76cc chamber volume. I am looking to figure out what the end compression ratio increase would be if I went to the Aluminum heads.
A Little background. I have a bad exhaust valve guide on the number 6 cylinder and have the choice to just replace the 333882's with a refreshed set with 202/164 valves but same chamber volume or go with the aluminum set with 64cc chamber volume. My main concern is the additional compression and its effect on the short block.. rings, bearings etc...
Any advice is appreciated.
Thanks,
Pat
Daytona Yellow '75 350 Muncie 4 spd

'73 454 on the engine stand.

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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/
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The small difference in chamber volume between the two heads is not enough to make a noticeable increase in compression. Definitely will not create any issues with the rings or bottom end. Won't hurt to use them at all, and you'll loose some weight at the same time.

Joel Adams
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I read on a pro touring forum that roughly 1cc equals 1/10 of a ratio, if you make the chamber 10
cc smaller you will end up with an extra whole number of compression ratio
which would put me about 9.5 plus. Not sure but it seems about right. I
am definitely thinking about it. I took a comp reading on all 8 and
they are all at 150 +/- 3 so it could be worth the extra money.
Thanks for the response,
Pat
|UPDATED|12/10/2015 9:15:10 PM (AZT)|/UPDATED|
Daytona Yellow '75 350 Muncie 4 spd

'73 454 on the engine stand.

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if you go to jegs or summit ,look at heads and they have a guide to compression and head vol.
|UPDATED|12/10/2015 11:49:26 PM (AZT)|/UPDATED|
what are the ali heads you can get??
ok I took a look for you,and that will take you to about 9.5/1
which is a good compression for most cams.
for the record this is not joanne,but her hubby.
|UPDATED|12/10/2015 11:49:26 PM (AZT)|/UPDATED|
1979 Corvette
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I have 64cc vortecs that I installed when I rebuilt and I think I calculated my ratio at 9.4 ish.
1976 Silver/Firethorn. L48, 4spd. Original 2 bolt, vortec heads, 9.4:1 CR, Speed Pro Cam: 224/224@0.050, 112 LSA, Eagle Steel Crank.
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The last small block I had in my vette had 64cc Vortec heads. The CR was about 9.5:1. The CR will vary slightly between castings and whatever thickness of a head gasket you go with. I would go with the aluminum 64cc heads if it was mine. Makes no sense not to take advantage of the benefits of bumping the compression up, losing a few pounds of weight and quicker heat dissipation.
GEN III 5.7L "LS6" Engine swap
TKO500 5 spd.
3.54 Dana 44
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Thanks for all the replies. I am heading out to pick the Aluminum 64cc's up in a few. Hope to get them in and running tomorrow.
Daytona Yellow '75 350 Muncie 4 spd

'73 454 on the engine stand.

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in Forum: C3 Engines, Driveline and Handling
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