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Old 03-13-2006, 11:38 AM
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matching up parts to CR

hi everyone, i was recently reading another post on here and it was mentioned that this member did not have enough compression for the cam that they were using. this got me thinking about my own combo and how recently i've figured out my cr to possibly be less than 9:1. i say possibly because i cannot find an exact number of cc's for the 4 relief valves in my pistons. using the calculators in the knowledge base i figure to be in the 8.75: - 9.1:1 range. i've been told anywhere from 8 cc's to 15 cc's.

my question is... can someone please tell me how you determine if the cr is appropriate for the cam. or if my cam is a good match for my combo. i have been playing around with the idea of stroking the engine and also reducing my quench area to about .050 from .090(rebuilder pistons .020 in hole)

my combo ... 355 sbc with ported vortec heads, air gap intake, holley 750,
228 @ .050 with 525 lift hyd roller cam, cr 8.75-9.1:1. th350 w/ 3000 stall, 4.10 gears and the car weighs about 3700 lbs without me in it. a note about the cam, because of a high int-ex ratio on the heads(85%) i went with a cam that has same specs for both intake and exhaust.

anyways, just wondering if my cr is too low and what kind of gains could i see by upping it. last fall the car made 305 rwhp but i had some problems with my fuel pump, distributor and running hot. engine temp was about 215. i've since bought parts to hopefully solve all those problems.
thanks for your time.
keith

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Last edited by classic keith; 03-13-2006 at 01:16 PM. Reason: vague
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Old 03-13-2006, 12:48 PM
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sounds like a killer combo as is cause with the low compression you probably can burn hotter fuel (87 octane) with more base and quicker and more centrifugal timing in the distributor (18b/20c in at 2600??)without detonation problems, winding up that much quicker

no question higher C/R is more HP top end at the track...but less C/R can be alot more fun/quicker to drive on the street....and gas ain't gona get cheaper...use NOS at the track and drive home on 87 octane??

do a compression test for "real" world C/R of how all the parts are working together
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Old 03-13-2006, 01:16 PM
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thanks for the response red. i just bought a digital timing light with all the goodies, so i plan trying to set the curve this year and hopefully see a little improvement that way. i will try setting to your suggestion and see how that goes. i know there will be lots of tinkering to dial her in.
keith
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Old 03-13-2006, 03:45 PM
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classic,

the 18b/20c/2600 is strictly a best guess for max due to the 3000 stall....get up on the torque curve alot faster....complains on 87 octane...try 89

just a couple of degrees more or less in the total (34-38) or the base (14-18 does make a big difference depending on the car, suspension and motor...it is "tune and test" or "back to the dyno"
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