Current build:
LS/VTEC
GSR head - mostly stock except for upgraded valve springs
b18b block bored to 81.5mm - stock sleeves
Redesigned low compression stock cast pistons as seen here. Opted for them to be machined to accept aftermarket rods.
Eagle rods
ACL bearings

What would you guys recommend I set the piston-to-wall tolerance to if I'm shooting for 400whp @ 17 psi? I have read all the recommendations for forged pistons but I need help deciding what it should be for a cast piston since they wont swell as much.

 

My setup

i gapped at .002500

or somthing like that
you know what i mean

But these arent cast....

 

Cast will not expand like a low silicon forged piston. You should run tighter tollerances. I'm not sure exactly what though, I'll let someone else with cast experience chime in

 

I appreciate your help so far. Anyone had first hand experience with these pistons or knows someone I can contact for help?

 

Use oem specs for those pistons. .001-.0015 will be fine.

 

There is your answer. Synapse knows their ****

 

I've used up to .0020" without piston slap. I did a stock bore refurb with a ball hone once and the clearance was as high as .0028" and the pistons slapped a little on cold starts.

 

Thanks for the responses guys! This will help a lot! Judging by whats been said I think 0.0020" would be my best bet.

 

I personally would stick to .0015 or stock specs. IMO if these are anything like OEM design, your going to melt or crack the ringlands on those pistons long before you run into PTW clearance issues.

 

These pistons are based of the stock LS design but also incorporate thicker ringlands to prevent such failures. Several members, such as boostedEF91, are making large amounts of power successfully without any issues. I will take your opinion into consideration.

 

ur not getting what i've said. i'm not saying these pistons are garbage or will break on you...

 

I understand what your getting at now. These pistons will fail structurally before the OEM recommendations for ptw tolerances would be jeopardized.

 

Well im telling you that I would not run that tight with a forged piston and 400 whp. Im running a LS @ 81.50mm and .003200 Ive got a little slap on start up for about 1 1/2 - 2 min. After that it goes dead quiet and all you hear is the injectors ticking away. .0015 is WAY TO TIGHT!! the people that are saying run stock tolerance are dumb! Sure if it was a stock piston sure, but the foged pistons will swell much more that stock due to the fact that its forged. I would at least run .002500, but no less.

 

if you took the time to actually read it thoroughly, he is running cast pistons.

 

i personally wouldnt run less than a .0025" PTW, but thats me.

 

My bad, I just skimmed through and saw 400 hp and 17lbs adnd I assumed foged. But I would still run them a little loose.