Black18Ice

iTrader: (2)

So I've searched a ton and I've read mixed opinions on PTV clearances. Everyone states there should be .080 on intake and .100 on exhaust however a lot of the cams offered by the big name brands don't meet these requirements. I know people are running them without fly cutting but I'm looking at best practice I guess.

Here's my scenario...I have a used ls3 that I'm putting in a custom cam that's pretty close to BTR's stage 3. It's a 231/244 112+4 at .600 lift and is within one degree as installed. The issue I have is my PTV on the intake is only .030 and exhaust is .080. As far as I know the heads were only surfaced .007 just to be cleaned up but who knows for sure being used. I'm using stock gaskets and used feeler gauges set up at .050 for this check. So I'm planning on fly cutting the pistons for the intake but wondering about the exhaust. The confusion comes from the measurement methods. I used solid lifters, checker springs, and a gauge. I've read that using the clay method will give you higher/better numbers due to deflection but counter to that I've read those parts also expand causing the verse affect. Should I be concerned with my exhaust clearance? I'm guessing I'd have .100 using the clay method. It's just no one has stated you should have .080 using a gauge and .100 using clay for example. They just state those numbers as a guideline. I know people run tighter so no need to state that, really should you go by the gauge or clay measurements? If I had the money I'd go with tfs255s or prc255s to help out, but it went towards a dry sump.

Btw I'm planning to do some HPDE events so I will be running high rpm for extended periods and have the chances for missed down shifts if that plays into your decisions.

Mercier

iTrader: (15)

I went through the same agony and ended up trusting the clay after flycutting. FWIW, LS2 bottom end with LS9 heads shaved to 64cc(requested .025" off from machine shop and by measuring I hit the mark). Using Fel-Pro .041 head gaskets. I redneck-decked my block and deck clearance looks to be about .0065. I am betting on keeping the revs low until the (aluminum) block warms up and expands and gives me a little more clearance(quench and PTV). Cold and tight I ended up about .80-.100(first time fly-cutting) on exhaust and .060 intake by the clay. I've got to pull the valves out to send to Del West for a polish and will probably check again just for sanity before I run it. Cam I'm running is somewhere around 238/250 110+4 and .63x lift but it's a LLSR so the .010 hot lash will help also.

I'd clay it. And make sure you wipe the piston with WD40 first or the clay will stick and possibly hurt your measurements. Hopefully with this bump one of the experts will come along and tell me everything I am wrong about.