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footbraker
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Discussion Starter #1
My motor is a 350 w/ stock flattop pistons(4 valve reliefs). It has fresh 882 heads w/ 1.94/1.50 valves and gasket matched intake ports. I'm using an edelbrock performer intake and 1406 carb (jetted 12% richer than stock). The cam is a Crower 267 HDP (210/216 dur. and .444 lift). My cyl pressure with this cam is 150 psi. I was wondering if a larger cam (221 dur. and .465 lift) would improve my ET's even though I'll lose 15psi of cyl pressure?
 

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Isnt the stock 350 cam about .420 lift? The cam you have know is the same lift as a stock Ford 302 H.O. motor. (not that it matters). The bigger duration will allow the vavles to stay open longer, and the more lift the further the valves will open...So I guess the answer would be yes, it will make more power. Will you be able to tell it in the drivers seat, probably not. Although I could be wrong, someone correct me if I am.


Bit
 

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footbraker
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Discussion Starter #3
I had a 224 dur and 465 lift cam in before and the bottom end was nonexistent. Cyl pressure also dropped to 120psi. I guess I'm more concerned about the relation between cyl pressure and performance.
 

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With the heads and piston combo your running I'd figure you've got around 8/8.5 to 1 compression.Longer duration will kill the bottom end like you said it did.

Try calling comp cams their Extreme series has openings and closings that are supposed to help cylinder pressure.

I had the same problem years ago w/a comp magnum 292 cam,in a stock bottom end 350.Sounds like your following the same path I went down.

BTW,when I changed from a mld roller to a much bigger one I went from,220 cranking pressure to 190,and picked up over 1/2 a second.
 

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footbraker
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Discussion Starter #5
RANDY406 said:
With the heads and piston combo your running I'd figure you've got around 8/8.5 to 1 compression.Longer duration will kill the bottom end like you said it did.

Try calling comp cams their Extreme series has openings and closings that are supposed to help cylinder pressure.

I had the same problem years ago w/a comp magnum 292 cam,in a stock bottom end 350.Sounds like your following the same path I went down.

BTW,when I changed from a mld roller to a much bigger one I went from,220 cranking pressure to 190,and picked up over 1/2 a second.
was the motor NA or NOS?
 

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footbraker
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Discussion Starter #6
Also told that 140 psi=8:1
160 psi=9:1
180 psi=10:1 etc.
That would be effective compression, not what the piston/head combo is rated at.
 

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It picked up both NA and sprayed.

Dynamic compression,includes valve overlap,and duration.The number is usually in the 9 to 1 range(high compression race motor) or less,if I remember correctly.I had read some articles on this awhile back.

Static compression involves the piston at BDC vs.TDC.(what you see advertised)

The compression guage your using gives you a reading based on dynamic compression.You can't really tell the static compression with it.Too many variables cam,engine temp, air temp,starter cranking speed and the fact that rarely do 2 gauges read alike.

They make great tools for finding potential problems,ie drastic drop in all cylinders or more then 10% between them.

I try to check and log mine every couple of months to see if I've got something going south.
 

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Discussion Starter #8
can you predict cyl pressure if you know the head/piston combo and the cam overlap? That's some of the info i'm trying to collect.
 

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Probably,but beyond me.Some dyno programs may do it.Just call the cam company of your choice and get their opinion,or call a few and see if they all come close to the same specs.Usually their very helpful.
 
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