Piston to wall clearance?

Guy's at what point is to much and would need pistons replacement? This is a all out N/A drag motor in a Dragster.

Ace

It'd depend somewhat on the skirt design/mfrs. spec. Pistons can be ran pretty loose but the life of the ring seal will be shorter.

Lem
Picking my stuff up tomorrow and the machine shop said there at .0085. There JE's with a small dome. I'll be contacting you in the very near future for the Cam. It the 555 ci we talked about a few weeks back. It has a Lunati cam right out of the book.

Ace

Call JE with the job # and ask them what the clearance spec. is. If it's .007" you aint in bad shape. One could have the skirts coated if need be.

I dont have the job# these came in the motor that came with the car we bought last year. Funny thing is that the deck of the block needed milled .004 to remove the impression from the steel ring in the head gasket. But the heads were fine? figure that one out.

Ace

A few years ago, our spare road race engine, (a 331 small block Chevy), had .014" piston to wall. It had out of the box Arias pistons and ran very well; just ate up rings rather quickly.
Of course, 60 laps with a road race engine is probably more than 100 runs drag racing.

You could always have the pistons knurled. I had a "dim bulb" machinist who honed my 347 (4.031) bore to .008 piston clearance, 'cause it's got forged pistons' . I had the pistons knurled and DID not return to the "high performance" machinist. With the knurl I was able to set my wall clearance at .0045 and it's still good after 2 seasons. It cost 4$ per piston to have it done.

.0085 is fine.

.0085 used to be normal.

Mark O'Neal wrote:.0085 is fine.

.0085 used to be normal.

Agreed, 0.008" used to be typical. You will likely make a little more power at this clearance than you would at 0.004"-0.005". As Randy noted, it will be at the expense of ring life, but this is racing, right?

I know people that have successfully run double-digit clearances in blown alcohol engines...

Thanks Mark. I was trying to figure out when I would need to replace the pistons. This motor came with the car and has some very odd conditions on how it was built and stupid problems in my mind. I guess 4.600 bore and 4.5 stroke will be later with newer heads.
Ace

JE use to stamp the job# on the back side of the piston,turn the piston over and look just above the pin holes.

these pistons were built in 98-99. they started doing this in 2000-20002 from what i was told.

Ace

Paul Kane wrote:

Mark O'Neal wrote:.0085 is fine.

.0085 used to be normal.

Agreed, 0.008" used to be typical. You will likely make a little more power at this clearance than you would at 0.004"-0.005". As Randy noted, it will be at the expense of ring life, but this is racing, right?

I know people that have successfully run double-digit clearances in blown alcohol engines...

Your right about not as much power with .004" clearance.....if a piston that was designed for .007' is installed with .004" the skirt may very stick to the bore.....which will soon = no power

A typical big bore A460 piston from JE or Diamond, these days, will have an installed recommended clearance of .0065"-.007". Then add clearance for power adders.