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Discussion Starter #1
Yeah, I sat and thought about this one day also and right or wrong here's what I cam up with.

Start by picturing an example. A cam with .400" lobe lift and 1.7 rockers would theoretically have .680" valve lift with zero lash. You have to picture what the movement will be at both ends of the rocker arm. On the pushrod end you have .400" of movement and on the valve end you have .680" of movement with zero lash. Now as you start opening up the lash (on the valve end) you are directly subtracting lift from the valve. For an extreme example, you could open the lash to .680" and you would have zero lift at the valve. The full lobe lift of .400" would come and go and the valve would not open at all.

So to make it simple, .020" lash subtracts .020" from the advertised or theoretical valve lift. This may not seem overly important, but it is nice to know when you're setting up valve spring and trying to figure up coil bind clearance.
 

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Yes, you subtract the lash from the gross lift, but...

Lash also eats into the duration. The ramp on the cam lobe starts to try and open the valve, but the lash has to be taken up before the valve starts to open. This is the main reason for the difference.

Yes, hydraulics have a bit of a 'cushion' before they start to open as well, but solids still require around 6 extra degrees to have the same rpm range.

Good Luck!
 

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Discussion Starter #4
N20Mike, I gotta agree with you about the Comp Cams "extreme" series cams. I was just looking at the solid lifter flat tappet designs the other night and the duration is nearly as aggressive as the roller designed lobes except the total lift isn't as much. If I were in the market for a flat tappet cam these would be very attractive.

I currently run a custom grind Comp Cam that is based off of the "extreme" street roller lobes. They will custom grind at no extra charge. These lobes run a lash around .014"-.018", so they are very easy on valvesprings.
 

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Mike R:

wow...just looked at your car for the 1st time.
Dont see many people doing that to "rare" muscle cars from the past much any more.
Very cool


mid 11 sec 2 ton monster...incredible
 

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Discussion Starter #6
Thanks qtrhors, I've been told by a few people that I'm crazy for modifying a rare muscle car like this, but I just like having fun with it. I figure racing is what these cars were built for.

<font size=-1>[ This Message was edited by: Mike_R. on 3/8/02 8:32pm ]</font>
 
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