high compression psi numbers

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Jan 31, 2007 | 03:42 PM

robertbourque

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high compression psi numbers

whats the stock compression a 79 302 should make with d70e heads cause i trying to figure out if ive got higher compression .heres what i got 180 psi .

Jan 31, 2007 | 03:55 PM

CARV

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I run 289 crank and rods, 302 block bored 30 over, 351 heads cut 20 thou and 13.5 to 1 speedpro pistons.

My cranking compression with all plugs removed and closed throttle is around 190.

Kind of heard to tell by your compression readings what heads or pistons are installed.

Jan 31, 2007 | 04:24 PM

robertbourque

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ive got ****ty d7oe heads with 69cc chambers but un sure of the pistons thats why i asked 180 seems high for 69cc chambers .but i compression checked it cold tho shoul i warm it up first ? thanks bro

Jan 31, 2007 | 04:40 PM

HemiEater

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your cranking compression will give you a good idea of the engine condition by checking every cylinder and then compareing them, it's had to say what your compression ratio is. Plus the cam will make a huge difference in your results, a cam with a long duration will have lower compression readings then say a stock cam.

so 180psi you could have 13to1 pistons with a huge cam
or you could have 8.0to1 with a stock cam

thats why you don't want to run a big cam with stock compression ratio, it will take for ever for the cam to come on.....but if you get your compression ratio up where the cam needs it, it will work much better.

Hard to explain........

Jan 31, 2007 | 04:43 PM

CARV

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Compression should be checked while hot or warm at least. By the book throttle should be open and engine spun with a good battery untill no more increase on compression gage. But even doing all of the above, figuring what pistons you have is almost impossible. A bone stock 1970ish motor should be about 175psi. The one I discribed above is very far from stock and must run on racing fuel and only showes 190 on a good day. Good Luck!

Jan 31, 2007 | 05:13 PM

robertbourque

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the cam in this motor is deff not stock not sure how big just not stock .the guy i bought this motor from had two motors one was an 80 high output and the other was the one i got a 79 302 1000 miles since rebuld i asked whitch one had better power he pointed to the 79 302 he said it was unbelivbly powerfull and was even more powerfull than his high output 302 in his stang he said he took it out to test the ho and he would put the 79 302 back if he could. he sold it to me for 300 bucks i ust dont get it how can a 79 302 be faster than a 80s 302 high output ? he had no reason to lie i could have easly bought the late 80s high output but i got the one that was rebuilt ande that he said was most powerfull .

Last edited by robertbourque; Jan 31, 2007 at 05:19 PM.