AES Racing

iTrader: (6)

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

orangeapeel

iTrader: (18)

It's about time someone put a picture up!

Duffster

iTrader: (103)

http://soriano.co.uk/hdew.html

orangeapeel

iTrader: (18)

Took me a minute to realize that banging noise was coming from that site. haha

Duffster

iTrader: (103)

Not the sound, but that animation was the reason I shared it Didn't have sound on computer at work when I posted this

Sales2@Texas-speed

iTrader: (5)

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).

barkingspud

iTrader: (3)

Fraser, what software did you use for that illustration?

Nevermind....Duh...

98LSGun

iTrader: (2)

So how are low lift numbers determinted and will having a quicker duration eliminate those issues

Sales2@Texas-speed

iTrader: (5)

Most cam cars and lobe series have their low lift durations which are labeled @.006" of lift (advertised duration) as well as the duration @.200" of lift.

What do you mean by a quicker duration? Do you mean a more aggressive ramp rate?

ShevrolayZ28

iTrader: (4)

I musta had too much coffee because the sound of that combustion made me jump! Nice link though.