For those who run 10.5 compression and turbo what did you use as a PTW clearance? *coughbulletcough

My new setup will consist of JE pistons (2618) 10.5, ceramic coated and anti friction skirt coating.

Currently using a HRC 16g, 3" exhaust, stock head (may port the exhaust side a bit), water/meth will be used. Car is used as a DD during the summer season, so a lot of the mileage it sees will be highway. Engine temp is 180-185.

I'm thinking .0035 will be enough since a lot of the added heat will be reflected from the coating and reduced from the W/M injection, but would like some first hand experience in case it is too tight.

Even if you don't have the coating or W/M, I would still like to hear your opinion.

Thanks in advance

get the 160* thermostat as well

0.004", which is actually what JE recommends, will work just fine. .0035" will be fine if you are taking the measurement on the coated skirt. I've run those JE pistons as tight as 0.0025" with no issues upon dis-assembly inspection after about 30,000 miles.

It's not a bad idea to build the engine with respect to possible future mods, within reason. I wouldn't try to build it super tight unless there's a good reason to. It would be nice to have the extra clearance if you decide to go hog wild on the boost or nitrous in the future. Just food for thought. Good luck with your build!

I've done all my JE's at .004. My 420a turbo was at .004 as well. I could see .0035 with coated being safe with JE's, but you are asking about experience and I never ran my JE's that tight.

Thanks for the replies.

I got the engine back from the machine shop a little over a month ago, with .0035 ptw clearance, measured with the coating.

Haven't had a chance to build it, because I've had a few spots claim they could get a gasket set but just ended you wasting my time.

Finally picked up my gaskets today, so I will hopefully have it built in the next few days. If I get it built/installed within the next week I will post some results after a bit of driving. If I don't have time this week I will not be able to install it until next year.

Just for future reference, did you experience much piston slap on start up with .004?

Originally posted by Islandertalon
Just for future reference, did you experience much piston slap on start up with .004?

JE's are notoriously noisy. But hardy, very hardy

I've heard from some guys, and also read on numerous online message forums, about claims of excessive piston slap with JE pistons. I use about 15-20 sets of JE pistons per year and I have NEVER experienced piston slap under normal start-up temperatures (over 20 deg. f) with up to .006" piston clearance. However, very slight piston slap is expected for a short duration during start-up in freezing temperatures with "race spec" clearances.

I have had the opportunity to inspect a couple rebuilt engines with piston slap, built by other shops, and both of those engines had double the claimed piston clearance.

I think the reason that this "JE piston slap" rumor had started was due to amateurs, and some so-called professionals, improperly measuring and machining the piston cylinder wall clearance.

The proper way to measure piston cylinder wall clearance is:
Clearance = Bore_ID - Piston_OD

In constrast, the proper way to measure crankshaft bearing oil clearance, with the bearings installed, is:
Clearance = (Bore_ID - Crankshaft_OD) / 2

I think this is the reason for the reported piston slap issues. I bet a lot of these guys have 0.008-0.010" piston clearance, and that much clearance will most definitely be audible.