TRW piston clearance?
 

will be putting together a new short block for a bracket racer. he has a set of older TRW forged SBC pistons [12 to 1] the previous block had .007" clearance. i believe that is too much for a drag engine. however with the AZ heat, i also believe .0055" is too tight.
you're experience and or your thoughts please.
thanks rod in AZ

Re: TRW piston clearance?
 

I've run the old TRWs in smallblocks with up to .010 wall clearence. It'll go faster than stink but will wear the rings in a hurry and be noisy. Also, don't run your piston to head clearence too tight.

Re: TRW piston clearance?
 

What Billy said is right, I have ran them at .003. Usaully as example say it was a 350+ .030 skirt measured 4.026 then it was made to be @.004 min.
If pistons have been ran be sure to check skirts were bad to be collasped on those pistons
Mike Taylor 3601

Re: TRW piston clearance?
 

Exactly what Billy and Mike said as tight as .003 and as loose as .010 and even looser at .012-.013 when customer had no money for block or pistons.The barometer for piston condition is skirt collapse and Rockwell B scale test,Current 2618 material starts out at 75-83 Rockwell B scale ,We test all pistons at rebuild ,When they go below Rockwell 50 they are junk.Bill C.

Re: TRW piston clearance?
 

They seem to "like" about 0.004" to 0.006" on a 4.0" to 4.125" bore size.

The most important thing to know about those is the pin is not great, and the pin fit is too tight. Replace the pin if possible, and open the pin clearance up by about 0.0002 to 0.0005" from where it starts. Way too many of those things have seized a pin, with ugly results.

Re: TRW piston clearance?
 

I mike piston middle or a little lower on skirt and 90 deg from pin....
is that how you guys do it?

Thanks