I'm working on a 350 with approx. .010 taken off the block deck. It has the Trick Flow twisted wedge G2 geads. I've also installed the LT4 HOT cam. From everything I've read so far, the only thing I can gather is that .525 is too much lift. The valves will hit the flat part of the pistons, since they won't line up with the valve reliefs in the pistons, due to the "twisted" design. I need to know the max lift possible with these heads. I'm sure others here have run across this. Thanks in advance!!!

edit: I'm thinking that I should change the rockers to 1.52 instead of 1.6. This will reduce the lift to .499. Or with 1.50 rockers, it will be .492. Even with the decked block, I think this should be Ok. I just need to hear from someone else who has ran into this.

-Jason

 

The max lift point has nothing to do with it. Very deceiving.
When the valve is at max lift the piston is well down the bore and the valve is not close to it at all.

A short duration .525" lift cam may have tons of clearance. A long duration .525" lift cam may crash into the piston near TDC without piston flycutting to increase
valve clearance.
Its the valve overlap period that the valves are close to the piston. (the piston is near the top and the intake valve is opening and the exhaust valve is closing.The only sure way to tell is to check valve to piston clearance with the motor assembled.
The actual point of closest proxciminty between the piston and valves will occur at some point between 30 deg BTDC and 30degrees ATDC.

part of the joys of twisted wedge heads, ya have to check valve to piston clearance.

 

Here are the cam specs.. 218/228 duration .525/.525 w/ 1.6 rockers on a 112LSA.
Has anyone here ran a cam like this with the Trick Flows?

Thanks

 

TTT

 

I've run a bigger cam (more duration, tighter LSA, similar lift) on an engine with .005" taken off the deck using G2 heads and a Fel Pro .039" head gasket. Never an issue.

That's no GUARANTEE you will be OK, but I don't think you'll have a problem.

A relatvely easy way to check is to mock up the assembly on 1 cylinder. That means install the crank, 1 rod with bearings, 1 piston (don't need to install the rings on it for testing), cam, and the rest of the valve train parts YOU ACTUALLY PLAN TO USE. Timing chain, lifters, pushrods, rockers, head gaskets, etc. However, you want to temporarily yank the valve springs off that "checking" cylinder and install very light tension "checking springs" (available from Crane, Comp and others for about $5). Mock it up like it would actually be, with the excpetion of the ultra-light-pressure "checking" valve springs. Set valve lash at zero, no preload on the lifters. Just to take all the "slack" out of the valve train, no more. Set to zero valve lash at TDC on the compression stroke, like you would normally.

Then spin the motor over 360* to TDC BETWEEN THE EXHAUST AND INTAKE STROKES. Not TDC between compression and power strokes, where you set lash. Between exhaust and intake strokes is when both the intake and exhaust valve will be slightly open- and that's when valve-to-piston interference will happen. Now, push the valve down until it contacts the top of the piston and see if you can squeeze a .100" drill bit between the rocker arm and valve tip. Do this every degree of crank rotation from 15* before TDC to 15* after TDC. If you can fit that .100" drill bit in there at every point you're good to go.

Hopefully, if I have described this correctly, you will be able to visualize why and how this works.

For a hydraulic tappet cam you don't want to use modeling clay on the top of the piston- the lifter plunger will compress and give a false reading if there is close-contact. By using lightwieght checking springs you never compress the lifter plunger unless you do it "gorilla style" and have no mechanical touch whatsoever.