compression ratio figure


Old 05-25-02, 09:01 AM
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Question compression ratio figure

Can anyone who knows the formula to tell me what my compression ratio is on my truck. Since I dont know here is what I got. Its a chev 350, bored 40 over with flat top pistons and valve reliefs. The cylinder head volume is 67cc. I would like to know what my compression is to help me to determine my pinging problem and if high compression is the problem then I know I need to run higher octane fuel other than the reg. unleaded. Thanxs.
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Old 05-25-02, 10:39 AM
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Smile Just a story.

Since I don't know the specs on your engine, I will just teel you a story. Last summer a friend brought his 1970 Chevy C/10 over because of very bad missing problem. I quickly found a blown head gasket between 2 cylinders.

Knowing he had the orignal engine that had not been apart before and he had 9 to1 comp ratio. I told the machine shop to just true the heads as not to increase his pinging problem. It was so bad he unhooked his Vac-advance & ran 93 octane just to get by.

Of course I found the thin steel permatex head gaskets on the engine from 1970. Now for the good part. I finished up and gave him a call to come and get it. It was running great after the 3 angle valve job & I forgot & even hooked his vac Advance back up.

He lives about 250 miles away & that evening he called me up to tell me how great it ran & to ask me what I did to get rid of the ping, and hook up the vac-advance. He was so happy he sent me a new CD-RW he works for, oh well never mind

The only way I can explain how it happened was the much thicker Fel-Pro head gaskets I used must have dropped his Comp ratio just enough X 8 that he now can run 93 octane with good mileage and no flat spot (vac-advance unhooked) the pinging in his case was under power with bad gas mileage.

I did not measure thickness of factory steel and Fel-Pro gaskets but I could see there was quite a difference.

You are not the only one having problems with todays gas and older engines. In fact you can get pure copper head gaskets and others in a thicker build to reduce your commpression ratio just to let you run the gas of today.

Unhook and plug your vac advance to see if it makes a difference in the pinging. It will have a small flat spot.

When he ran any fuel less than 93 it would sound like he had a head full of marbles & no power at all. All I did was to put thicker head gaskets on and now it runs great.

You may have to get even thicker gaskets if your heads have been cut more than once. Call or e-mail there Techs are all ages and some of the older ones like me remember getting pump gas that would run 10 to 1, oh the good ol days.
Good luck, Marturo
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