piston to valve clearance with 243's.
 

hey guys just had a few questions. its a 2001 ls1 with 241 heads right now. will be getting an ms3 cam and a set of ported 243 heads. has any one had any p to v issues? someone at texas speed said the ms3 cam wouldn't work with ported 243 heads. but it would work with untouched 243's. how does that make since? also i have some low milage ls6 lifters ill be using. an some low milage rocker arms that i plan on doing the trunion upgrade too. also opinions on which oil pump and timing chain to go with. i dont want to convert to double chain (shimming oil pump sounds like a PITA). hoping to see 425rwhp. :secret2:

I think texas speed probably was talking about if the heads were milled to raise compression, and decreasing chamber volume CCs.

The ported heads have larger valves. That cuts into PtV clearance.

Btw, the freedrop on the LS6 is .155" - so you can rough estimate how much ptv clearance you have by factoring in the piston out of the hole .006", gasket thickness, valve diameter increase over the 2.00"/1.55" stock valves, and then look at the cam lobe catalog from Comp. They give you tappet lift numbers at 106 and 110 ICL. Once you have those, you multiple by your rocker ratio 1.7 to get valve lift @ tdc.

Then the formula is this (assuming stock valves):

Freedrop - piston depth - .080 (recommended clearance) + gasket thickness = total Lift clearance @ tdc.

If your valve lift at TDC if more than the calculated clearance then you have to flycut.

An example would be the Torquer 2 at 232/234 110+0.

.155" - (-.006") - .080" + .051" (gm stock) = .120"

232 XE-R lobe at 110 ICL = .069" * 1.7 = .1173"

So you'd have approx .083" clearance with that cam on an otherwise stock short-block. Of course, you measure, but this helps if you're ordering prior to measurement.

Jake. why did you decide to go with ls3 valves? did you have to shim the synergy oil pump to use the double roller timing set?

FYI, minimum PTV isn't when the piston is at TDC.

It's about 15 degrees past or before IIRC. But, for the purpose of a swag, you can use the above calculation, assuming your cam is ground close to the specs.

Synergy pump is clearanced for double-rollers. Just bolt and go.

LS3 valves are lighter. Always go lighter on the valve side of the rocker. It helps with control and stability.