Low dynamic compression under load, pushrods to blame?

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Jul 24, 2006 | 05:59 AM

#11

Bowtie70SS

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I would think you'd have lost some bottom end from the cam. The lifter itself has preload distance built into the bore. Are you experiencing backfire thru the intake? If the valves aren't closing then I'd think it would pop thru the intake some. I'm running a .640 lift cam with stock length pushrods.

Dave

Jul 24, 2006 | 10:16 AM

#12

RoninsDenali

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Yea i was getting some "noise" through the intake that wasnt normal. Kind of a mild popping noise.

Anyway, i just spoke to Lunati and i should be running either a 7.400" or a 7.410" pushrod. So i really screwed up the math there lol.

So, should i just stick to the stock lenght of go with an extra 10 hundreths. (i'm thinking of just going stock lenght) But i'll let others chime in on this

Jul 24, 2006 | 03:16 PM

#13

Zick

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FYI, I think your title is a little off. Because Dynamic compression does not change at any time during the operation of the engine.

http://cochise.uia.net/pkelley2/DynamicCR.html

Jul 24, 2006 | 03:32 PM

#14

RoninsDenali

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Quote:

Originally Posted by Zick

FYI, I think your title is a little off. Because Dynamic compression does not change at any time during the operation of the engine.

http://cochise.uia.net/pkelley2/DynamicCR.html

Good read there Zick. Ok so i should have said, my engine must not be building ANY compression lol.

Anyways, tell me what i should order 7.400" or 7.410" pushrods. If no one responds in the next hour i'll just order 7.400" and say to hell with guessing

Jul 24, 2006 | 03:36 PM

#15

RoninsDenali

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Quote:

It is necessary to determine the position of the piston at intake valve closing to calculate the DCR. This can be calculated or measured (using a dial indicator and degree wheel). Since compression cannot start until the intake valve is closed, it is necessary to use seat times when calculating the DCR. Using .050" timing will give an incorrect answer since the cylinder is not sealed. At .050" tappet lift, using 1.5 rockers, the valve is still off the seat .075" and .085" with 1.7 rockers. While the flow is nearing zero at this point, compression cannot start until the cylinder is sealed.

Heh according to this paragraph of Zick's link. I should state that my engine is producing technically zero compression. Heh, i hate math lol.