How much do the valves hang open during the overlap period on the average
street/strip cam?

I realize you'd need the lobe profile, but I'm curious about the amount of lift
present during scavenging with the piston near TDC.

Would it be about 25% of maximum valve lift, 50%....more?

Using my combo below, is there a method of approximation?

Hydraulic flat tappet lifter: 0.021" pre-load
Rockers: 1.6 ratio
Camshaft: Comp Cams 292H-10

http://www.compcams.com/Technical/Se...umber=31-330-3

Lobe lift: 0.334"

Valve Timing At 0.006
IVO: 40
IVC: 72

EVO: 80
EVC: 32


I've already clearanced the motor using clay and turning the motor over by
hand. The valves didn't make an impression in the clay which seemed to be
about 0.040" thick.

Wiseco pistons, 'flat' with valve relieft (4 eyebrow, (~9:70:1 compression)
Piston in hole: 0.022"
Gasket compressed thickness: 0.017"
Sportsman II 72 c.c. heads: decked 0.010"
Gen 1 SB, stock crank and rods.

 

There is a spec in lobe catalogs that shows you how far open a particular lobe would be at TDC on a certain lobe centerline. Your average 224 @ .050 duration hyd roller lobe is open around .050" when it's on a 110 ICL.

It's pretty hard to run a street cam into problems with P to V when you have forged flat top pistons.

Just put more clay in there!

Your cam will have the valve open .100 at TDC with the 106 ICL on the intake, which is what specs you just gave us. The exhaust valve shouldn't be an issue since the ECL is 114 and you have a smaller diameter valve.

Bret

 

Awesome, thanks for the reply.

I was surprised that I didn't get any closer to the piston with
my setup.

If the valve is hanging about 0.100" at TDC, with no sign of hitting
the clay, my engine must have quite a bit of quench height to play with.

With a street motor, you'd say at least 0.040" clearance minimum for PTV?

 

.100 PTV on exhaust
.080 PTV on intake