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calculating gross cam lift


Guest chevsun

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Guest chevsun

while I have the motor out of the Z I am considering shaving the heads .025 from stock (running flat tops)and going to add roller rockers. How can I calculate the added lift if the cam I'm running has a gross .465 lift now and I add 1.60 rockers. Also how much will the shaving change the compression. Any input appreciated. thanks

 

Steve

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quote:

Originally posted by chevsun:

while I have the motor out of the Z I am considering shaving the heads .025 from stock (running flat tops)and going to add roller rockers. How can I calculate the added lift if the cam I'm running has a gross .465 lift now and I add 1.60 rockers. Also how much will the shaving change the compression. Any input appreciated. thanks

Steve

 

Steve,

 

I'm guessing your current valvetrain is stock; stock meaning your rockers are 1.5; divide the 1.5 into your .465 & this will yeild .310 "Cam Lift". Take your .310 "Cam Lift" & multiply that by the newly installed 1.6 rockers & that will yeild .496 lift. The actual lift depends on how you achieved your initial .465 lift.

 

About the Compression question; Its a rule of thumb that for every .004-inch removed that the cyl.head chamber volume is approximately reduced likewise by 1cc.

 

To make it simple; if you wanted to reduce your Chamber Volume CC's down by 6cc you'ld ask your machinist to mill your heads .024-inch (.004 x 6.0 = .024).

 

Becarefull about cutting too much from the heads. If you're not sure about the previous history of your heads you may cut too much as they could have possible already been cut by a previous owner. Also you can remove metal from the Deck of the Block as well. I know you said you'ld be using flat top pistons...but dont forget Piston/Valve Clearances; discuss this w/your machinist.

 

I'm not sure how to put this formula into this forum but here goes. If you want to know how much metal to remove from your cyl.heads:

 

Amount to Mill = New Disp.Ratio - old Disp.Ratio; once you have that figure you will need to divide it by New Disp.Ratio x Old Disp.Ratio. After you have divided the second number into the first number you will need to multiply that answer by the "Stroke" of the crank you're using. The final answer will be the amount you need to mill.

 

Unfortunately; the only true way to know your comp.ratio or the Cyl.Head's CC's is to have the Cyl.Heads CC'd. Anything else is just a guess.

 

Hope that helps & wasnt to confusing.

 

Kevin

 

 

 

[This message has been edited by Kevin Shasteen (edited February 27, 2001).]

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