DragStuff

How much piston to head clearance should there be? I have .035 and not sure if that enough. Steel rod motor.

Supernova;

I've always gone for a 0 deck with steel rods. Engines have been anywhere from 12.5:1 up 14:1 with no problem. Never used NOS or a turbo or blower as they might be different.

Some guy I know back in Ca had an engine builder put his stuff together and he told him he wanted to see the deck before the heads were put on. Anyway he came over there to his place and the heads were on---duh!! He said its okay-its a zero deck like you wanted. Well after hearing some noises when he was running it-he took the heads off and the piston number was imposed into the top of the aluminum head. The pistons were .005" above the deck. When will they ever learn?

Ron

My motor is decked at .005 and I have .030 mls gaskets. I just wonder if thats enough

Ive done a few 0 deck but always had .039 -.041 gasket but none high rpm nos engines just basic street strip stuff, never any issues.

supernova wrote:How much piston to head clearance should there be? I have .035 and not sure if that enough. Steel rod motor.

Mine has .080, on the intake and .115 on the exhaust, but that is piston to valve. Not sure about how close I am the the actual head surface. And my pistons are .005 down in the hole. My head gaskets are .041 thick.

.035" is pretty tight for a motor with heavy nitrous pistons. I've run that tight with very light winston cup pistons in a 383, but my heavier nitrous pistons in my 434 all but kiss the heads with .040" clearance. I can read the part number from the piston in the carbon on the bottom of the head. It wipes off, so its not actually touch. Perfect if you ask me.

I have to check my pv clearances this weekend also crossing my fingers. I have heard that .045 is a minimum safe distance and Im not sure if nitrous hasa bearing on that number. If it were me I wouldnt take the chance, especialy with all your pretty new parts.

I've been told a minimum of .100 on the exhaust, and a little closer on the intake. But I don't remember exactly how much.

Might want to bump that up, sounds too tight to me for a nitrous motor.

High rpm steel rod nos motor..... Just kissed at 40 didnt hurt anything and ran all year ... no problems at 45

I assume by your first post that you are asking about piston to head and not piston to valve. I noticed you have some replys covering piston to valve and I want to make sure I am not missing something.

Alot will depend on what the piston to bore clearance is and the skirt design on the piston. If you have a nice new modern piston and the minimum piston to bore clearance recommended by the manufacturer., you should be ok. Don't bounce it of the limiter tho.... If there are older pistons or there is excessive Piston to bore clearance you are probably going to have issues.


Keith

Thanks for the reply's everyone... I'm putting a .040 gasket in it so it will have .045 clearance now. No worrys!!!!! What compression it's losing is better then hitting the head.

And it is piston to head not piston to valve.....

I have a nitrous bbc and my piston was made to set .010" below deck height. I think my head gaskets are .040". I've seen alot of nitrous guys use .060" gaskets.

Apples to oranges maybe, but I ran an aluminum 7.000 long rod motor at .050 with no problems, at .045 it just touched.

.035 sounds a little too close...especially if your cylinders a worn any. If you get any pistons rock at TDC it could cause a problem.
I'd open it up a little. JMO.

TS1955