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Old 01-21-2008, 12:48 AM
63CustomCab's Avatar
Like two monkeys...
 

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Performance is a new one for me

I have rebuilt several engines at the ripe old age of 22 (lots of sarcasm there, I've done 2; 283 sbc and ls1). On both though, I simply bought the stock replacement parts for the motors, my dad guided me through doing it and I learned how each peice and part worked in the engines, but didn't really get into the mod/performance side of the whole thing. It was simply a lesson in basic mechanics. Now I am planning on building my first performance engine. I could have bought the crate with the output ratings that I want, but as any hotrod enthusist, I am a hands on guy and want to do it my self and learn it.

My biggest question, and perhaps I am missing a part of the bigger picture, is how does the Max valve lift, the rocker ratio, the rod length, and cam lift all come in to lay?? I understand the interation between the mechanical pieces, but say for example, I have a set of Trick Flow heads with a max lift of .600", a set of 1.7 ratio Crane roller rockers, a std length rod and a Comp Hydraulic Roller cam with a lift of .531/.517. Will this work?? What makes it work and what doesn't?? Basic math would tell me that my lift would be .903/.879. Is this correct?? Am I way off?? Need some help here guys. I am starting the learning process young here, perhaps I can one day be in your guys' shoes...

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Old 01-21-2008, 01:07 AM
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Small Block Chevys typically come with 1.5:1 ratio rocker arms so most camshafts you see advertised will list the gross valve lift using a 1.5 ratio rocker. Usually the cam card will show you gross valve lift and lobe lift. If you want to know what a 1.7 rocker will do to your lift you have to figure out what the actual lobe lift is. For a cam advertised at .531/.517 lift with a 1.5 rocker you have to divide valve lift by the rocker ratio. In this case you would get .354/.345. Now you can take those numbers and multiply them by the new rocker ratio, 1.7:1. You'd end up with .602/.586
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Old 01-21-2008, 01:09 AM
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So then these heads would not work with this cam??
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Old 01-21-2008, 03:37 AM
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I'd check to see what the info is on the springs on the trick flows but comp recommends #26918-16 good to 625 lift or #26986-16 good to 650 lift .
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Old 01-21-2008, 08:16 AM
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Piston to valve clearance may be an issue. Do you know how to check that?
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Old 01-21-2008, 08:20 AM
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tips...imo

the crank throw is the handle on the wrech . lever principle. longer is more advantage to spin.

rod lenth is the lever principle again but this time a recipricating lever(rod and piston on crank) going up and down make a eslipse . the longer the rod the tighter the oval the increase in piston speed adavantage


believe it or not a 375hp only need s a 650cfm to kick butt. dont overcarberate. its the combo that really makes the power. always use peices designed to work in a package together.

higher ratio rockers are a no no on flat tappet, increases pressure at the lifter lobe area. hi spring pressures and high ratios account for alot of cam failures.

always use a enclosed type airbox with an attempt to vent fresh air toward the intake. cool air is real power.
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Old 01-21-2008, 05:52 PM
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Quote:
Originally Posted by XNTRCI-T
Piston to valve clearance may be an issue. Do you know how to check that?
Isn't this the clearance between the piston at TDC and the valce seating and the clearance between the piston and the valve at BDC??
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Old 01-22-2008, 08:20 AM
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Piston to valve clearance is measured at the point the open valve comes closest to the piston at or near TDC. Depending on cam timing, the intake valve may actually come closer to the piston slightly after TDC and the exhaust valve may be closest slightly before TDC.

Here is a good article on how to check clearance.
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