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Old 04-27-2005, 03:59 AM
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Compression Ratio with 64 cc heads & Federal Mogul Sterling 345np

Hi everyone!

Until now, I was almost sure that I'm having a 10:1 compression ratio for my new engine, but saw this thread which made me confused!!!

This guy had mentioned that with 64cc Vortec Heads and flat top pistons WITH NO valve relives he is making 10:1 compression.

But in Federal Mogul's catalogue, it says that 345np flat tops with four valve relives will produce 10.2:1 compression ratio when used with 64cc heads???

I'm exactly using Federal Mogul Sterling 345 np's with four valve relives + Edelbrock 64 cc heads and 0 deck.
What is finaly my compression ratio? Is it 10.2:1 as Federal Mogul declares?

Thanks for helping me out of this confusion.

Houman

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Old 04-27-2005, 05:50 AM
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Here`s where the fun part begins. The 345NP piston, is ".020 destroked" meaning, it has .020 off the top of the piston, where a normal 350 piston would have a 1.560 compression height, these have 1.540. so even with a zero deck height, it would still be .020 down in the hole. They really seem to go out of there way to hide this too, they don`t mention it anywhere on the box, and many sites on ebay list them as 1.560 compression height, but being they have .020 off the tops, this is why there so cheap. with a zero deck with these pistons and a 64cc head compression will likely come in around high 9:1 ratio, depending on what the head gasket thickness is.
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Old 04-27-2005, 06:34 AM
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compression

I do not have exact figures for this piston but i figured it out at..

Pistons.......4 cc with valve pockets
pistons down in the hole .020 = an additional 5cc's, assuming it is zero decked
head gasket 9.1 cc's
and 64 cc head. the edelbrocks that i have checked have been close to advertised volume.

So all that comes out to a static compression of 9.86:1

Keith
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Old 04-27-2005, 08:10 AM
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I think k star is really close. I had a 355 with vortec heads, and flat top pistons with four valve releifs. It also had .050 quench. The shop that built it said that it had 9.89:1 static compression.

Adam
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Old 04-27-2005, 09:01 AM
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9:1 or 9.8:1 Which is the correct Compression ratio?

Doublevision,

What do you say?
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Old 04-29-2005, 12:59 AM
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Federal-Mogul's website is claiming that the 345's now have 1.56" compression height. Wonder if anybody's measured?
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Old 04-29-2005, 09:50 AM
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It's a boo-boo. I have a brand new set here and from the center of the pin bore to the crown it measures 1.541"

Larry
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Old 04-29-2005, 09:50 AM
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Quote:
Originally Posted by jimfulco
Federal-Mogul's website is claiming that the 345's now have 1.56" compression height. Wonder if anybody's measured?
The regular cast versions are 1.54". The hypereutectic versions are 1.56"

tom
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Old 05-01-2005, 11:12 AM
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Tom,

I think it's the other way round, because if you look in Jeg's, h345 np which is the Hypereutectic is said to produce 9.5 with 64cc heads and 345npstd is said to produce 10.2.

This is what it says, do you think that now cast is 1.54 and hypereutectic is 1.56?

Kindly clarify and let me know how it should be.

Thanks,
Houman
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Old 05-01-2005, 11:42 AM
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The piston I measured at 1.541 is the regular cast version.

Larry
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