Didn't have sound on computer at work when I posted this 
PTV clearance in pictures
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FormerVendor
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From: Elk Grove Village IL
PTV clearance in pictures I'm asked questions often, will this cam fit, it only has .600". I try to
explain what the piston and valve are doing on a stroke cycle, on the intake stroke the valve is chasing the piston. Heres some pictures to explain PTV.
Here is whats going on at TDC intake stroke, on a large cam, the intake valve is cracked open before top dead center, depending on how early the intake valve opens, valve drop on the heads, radius of the valve, is going to affect PTV. Heres a pic.
piston continues down on the intake stroke
Here is max lift (basically), piston is down in the cylinder, max lift means almost nothing for PTV
explain what the piston and valve are doing on a stroke cycle, on the intake stroke the valve is chasing the piston. Heres some pictures to explain PTV.
Here is whats going on at TDC intake stroke, on a large cam, the intake valve is cracked open before top dead center, depending on how early the intake valve opens, valve drop on the heads, radius of the valve, is going to affect PTV. Heres a pic.
piston continues down on the intake stroke
Here is max lift (basically), piston is down in the cylinder, max lift means almost nothing for PTV
Last edited by AES Racing; Jul 26, 2010 at 01:17 AM.
Here's another that shows a generic camshaft from Comp and its valve events/lift versus the piston's position relative to TDC and BDC. You can see when the camshaft is at max valve lift, the piston is about half way down the cylinder. So even a .650" lift cam on a 3.622" stroke LS1 engine the valve is still over an inch away from the piston when it hits max lift.
Those low lift numbers are the problem, and the faster the cam has the valve coming off the seat the closer your clearance is (in general, of course the duration plays into this as well).
Those low lift numbers are the problem, and the faster the cam has the valve coming off the seat the closer your clearance is (in general, of course the duration plays into this as well).
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Verdad Gallardo What do you mean by a quicker duration? Do you mean a more aggressive ramp rate?
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Largest Stocking Distributor of LS-x Engines / CHECK OUT OUR NEW WEBSITE!
COMP - FAST - PACESETTER - DIAMOND RACING - EAGLE SPECIALTY PRODUCTS - CALLIES - COMETIC GASKETS
RAM CLUTCHES - MOSER ENGINEERING - KOOK'S HEADERS - ARP - GM BOLTS AND GASKETS - MSD - NGK
POWERBOND - ASP - AND MORE!
Largest Stocking Distributor of LS-x Engines / CHECK OUT OUR NEW WEBSITE!
COMP - FAST - PACESETTER - DIAMOND RACING - EAGLE SPECIALTY PRODUCTS - CALLIES - COMETIC GASKETS
RAM CLUTCHES - MOSER ENGINEERING - KOOK'S HEADERS - ARP - GM BOLTS AND GASKETS - MSD - NGK
POWERBOND - ASP - AND MORE!
