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Topic Review (Newest First)
06-11-2012 09:31 PM
79bird My Firebird with a 305 is at 8.5 right now stock, yours should be in the same relm
06-11-2012 02:29 PM
78novaman According to my Hayne's manual:

8.2:1 for light duty trucks
8.3:1 for heavy duty trucks

All I can think is maybe slightly different pistons???
06-05-2012 06:09 PM
GMCBEAST I agree with above, 8-8.5:1. Those 76cc heads (Most likely what you have) kill compression, throw in a dished piston and you end up on the low end of the C.R. ladder. On the good side you don't need premium gas. If they are dished pistons I think they are 18cc cups, I'm not positive though, 58cc chambers are ok with dished or most 4 valve relief flat tops but you need to pay close attention to your timing with the flat tops. Summit and Wallace Racing have a compression ratio calculator on their site's once you figure out your specs. Hope this helps.
06-05-2012 05:23 PM
75gmck25 If its stock, then not more than 8.5.

If you measure it you may find some engines calculate out as low as 8.1.

Bruce
06-05-2012 10:40 AM
Madmax305 I don't know exactly, but you can figure in the 8.5-9.0 compression ratio.
06-05-2012 10:35 AM
xzero117
Anyone know the stock compression ratio for a 1979 350 chevy ?

it came out of a truck and as far as i've researched it had 175 hp and 250tq back in the day, previous owner said it is completely stock, does anyone know the compression ratio that came in this engine ? or perhaps the cc's of the pistons

I'm trying to get an accurate compression estimate because i just bought a set of 305 cylinder heads 601 casting which have been ported and machined to have 58cc chambers and 2.02 intake and 1.60 exhaust valves

the engine has a slightly more aggressive than stock cam and i'm hoping for a tad bit under 9:5:1 compression so i can run 89 octane

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