Compression Ratio

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Jul 18, 2001 | 03:47 PM

dmoc1

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Joined: Jul 2001

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Compression Ratio

[font size="1" color="#FF0000"]LAST EDITED ON 18-Jul-01 AT 04:49 PM (EST)[/font][p]Hi,

I have a 429 with I believe Dove c heads from a 71 T Bird. My question is when I did 030 over bore how much did that change the compression ratio. Lower it? I know right now I have to advance the dist so much to get the power and then I run into pingin problems.
Mallory promaster coil, mallory unilite dist. MSD 6a box.
Any recommendations ?

thanks

Dennis

Jul 18, 2001 | 05:09 PM

85351ho

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Joined: Feb 2000

Posts: 2,759

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From: Auburn,Al

Compression Ratio

i used to have that exact motor in my old f-250, it has 10,5:1 compression, anyway the only way i could get it to run on pump gas (93)without pinging was 4 degress of timing , any more and the motor pings like crazy, something fun to do is find some 100 octane av gas or sumthing and bump the timing up to around 12 degrees and run it, you sure as hell can feel a seat of the pants difference

1985 F-150/351Ho/c6/4wd
1979 F-150extcab4x4/460/c6/6inchlift w/60rear44frnt
on a quiet night your can hear a chevy (lol,you can watch a dodge) rusting away

Jul 18, 2001 | 09:25 PM

cobrajet

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Joined: Feb 2000

Posts: 309

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From: michigan

Compression Ratio

if your using the style of piston it will lower the compression.it is not going to be much but it will lower the ratio, because you actually increase the volume by making the cylinder bigger.if you were using a 19cc. or 22cc. dished piston it would probally be in the range of 9.5:1 to 10.0:1 compression.

Jul 18, 2001 | 10:08 PM

bigsnag

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Joined: Apr 2000

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From: Pryor

Compression Ratio

If you are using the same type of piston and you bore the engine, you actually increase CR. As can be inferred, it is a ratio (hence "compression ratio") of swept volume, i.e. CID, plus the volume above the piston at TDC to the volume above the piston at TDC, ergo, if you increase swept volume, by boring the engine, then the ratio must increase. Generally speaking, with a 460, boring an engine by 0.030 should increase the CR, but not by a significant amount.