compression ratio - Team Camaro Tech
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post #1 of 10 (permalink) Old Mar 21st, 08, 04:15 PM Thread Starter
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RJ
 
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compression ratio

Hi guys,
Is it possible to estimate compression ratio from cranking compression. If my cranking compression id 185-190 on all cylinders, is there a reasonable guess on c/r or is that not possible.
RJ
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post #2 of 10 (permalink) Old Mar 21st, 08, 05:10 PM
 
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Smile Re: compression ratio

The very much EXPERIENCED guys can tell by your cam timing and the spun compression test!

But I can't!

I use this for SCR!!

http://www.campbellenterprises.com/R...alculators.htm

And this for DCR..

http://www.rbracing-rsr.com/comprAdvHD.htm

And I use 7.75 to right at 8 DCR for cast-iron head street engines MYSELF ONLY b/c of fuel octane quality is all.

DCR can be fudged by using a quench between .035" and .045", cam timing that hold's the intake valve open longer and by running aluminum heads since they bleed combustion heat out faster than cast-iron heads, imho...

This stuff's a hoot by me..

pdq67




Last edited by pdq67; Mar 21st, 08 at 05:31 PM.
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post #3 of 10 (permalink) Old Mar 21st, 08, 05:22 PM
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Re: compression ratio

My car is '68, with 460ci. My calculated compression ratio is 10:1, using SRP pistons and Edelbrock Performer RPM heads. My cam specs are below. My cranking compression is about 185-190 psi, pretty much exactly same as yours................



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post #4 of 10 (permalink) Old Mar 21st, 08, 05:31 PM
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Re: compression ratio

My truck is 9.5:1 with 175-180psi. My camaro is 10.5:1 with 195-200psi.

69RS/SS,383,10:1cr,4.10,60ft1.6sec,1/[email protected],1/[email protected],Vicjr,RPMheads,750dp, Proform main body, cam,246*-250*@.050,.510,522,1.6rr,700r4,3200stall
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post #5 of 10 (permalink) Old Mar 21st, 08, 06:20 PM Thread Starter
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Re: compression ratio

appreciate the info guys
rj
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post #6 of 10 (permalink) Old Mar 25th, 08, 09:08 AM
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Trevor
 
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Re: compression ratio

my cylinder pressure on my 356cid is 195 and I have 11.12:1 compression ratio.
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post #7 of 10 (permalink) Old Mar 25th, 08, 09:19 AM Thread Starter
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Re: compression ratio

Thanks again for the info, guys. The calculators I have used pretty much seen to come out at 9.6/1 to 10/1 at most.
Just seems to run pretty well for a slightly modified 350. Has run 8.10/88mph in the 1/8, and 12.65 in the quarter, and so far it really hasn't launched well off the line at all. I went from the Vic Jr to the Performer RPM with a lot of improvement on the lower end, but haven't run it at the track yet with the intake change. It is a 4-speed car too, with 2.2 1st gear. Could have used more gear than the 4.10, but didn't want to get nutso for the street.
Anyway, thought maybe it had a bit more compression than 9.6/1.
Would love to drop the compression a bit more and then go with Procharger, but my wife would have a nervous breakdown if i spent that money. probably have $40K into the car now, and I hear about that most every day. Oh well, If she gets too bad, I'll probably miss her when she's gone!! Aww just kidding.
rj
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post #8 of 10 (permalink) Old Mar 25th, 08, 05:07 PM
 
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Re: compression ratio

I bet it has flat-tops and 64 to 66 cc heads so will be right at 10 or so. Jmho..

pdq67



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post #9 of 10 (permalink) Old Mar 25th, 08, 05:31 PM Thread Starter
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Re: compression ratio

Mine has flat tops with the 4 valve reliefs, and 65 cc aluminum heads, .041 gasket on a .o60 overbore
rj
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post #10 of 10 (permalink) Old Mar 26th, 08, 05:21 PM
 
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Re: compression ratio

Please run the numbers here.

http://www.campbellenterprises.com/R...alculators.htm

Use -5cc's for the valve notches will put you close imho and right at .025" DITH piston IF it hasn't been decked?

If it's been decked, then you have to measure your deck height.

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