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Piston to Valve clearance versus New Cam....
I currently run a Hydraulic Engle 517/292 (may actually have 288 degrees of duration) and I have lost mid range performance over the last 5 years. The performance loss and some slight lifter noise has finally convinced me to start looking at the cam, lifters and springs. The motor is a 12.5:1 .040 over 318 with Aries pistons and it uses stock stamped non adjustable rocker gear.
The previous cam showed at least an 1/8 inch of clearance (or .125) after doing the clay test with the old cam (without head gaskets installed). Based upon this I would assume that I could run a cam up to .600 lift, on the safe side a .550. But, I also have a set of 273 rocker gear that will be going on with the new cam and lifters. I'm afraid the extra preload will result in a slighter more than the advertised lift of the cam, as well as a longer duration may result in a lower piston to valve clearance. The two cams I am debating on are: Racer Brown Hydrualic .510/292 Jim at Racer Brown was the one who stated that Engle never made an advertised 292 duration cam. He also stated the longer duration could create piston to valve clearance problems if the cam had more lift. CompCams Hydraulic .525/304 Most of the local hardcore Mopar small block racers are 100% behind the CompCams products (even if they are Chevy grinds). I know a guy who has this cam in a Duster that pulls high 11's, and the stockers and super stockers rave about thier grinds. I will be doing a cranking compression test for Jim at Racer Brown to try to more accurately determine actual compression, rather than rely on what the previous owner of my motor said what the pistons were. The pistons have some serious domes, but not much more that my Dad's 11.5:1 TRW's. Am I relying too much on the "bigger is better" philosophy by even considering the .525? Will the .525 send the valve too close to piston since it has a larger lift and longer duration than my existing Engle 517/288? All I know is that I don't want to eat a cam that is too large for my application. I don't think Racer Brown or Comp Cams really wants these cams back for a refund or exchange. Dartman PS - This motor has run a 12.87 in a 3200 pound car, and I think it should run about 12.40's by the time all is said and done. |
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Listen to Jim.........
I do, works for me .....everytime. |
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My compression test yielded right about 175 in every hole, with the exception of #8 which had 170. Which also coincides with an oil leak between the block and head right there too.
The plugs were removed, but this motor was cold and the throttle was not at WOT. I imagine a motor at operating temp and the carb at WOT will only improve the cranking compression numbers. Taking this into consideration, are these numbers within the normal range for a motor with *apparently* this much compression? I saw a calcualtion somewhere for this, but I can't find it now. Dartman |
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