I'm about to take my block to the machine shop and I just wanted to make sure my p2w is good.

B18c5
81.5 supertech pistons(high silicone,4032 alloy)
Pump gas

It will be a dd and I plan on between 400-500 hp

Will .0035" p2w clearance be to tight or should I go to .004"?

TIA

 

Need help please

 

0.0045" is what you should go with.

 

Cal supertech and se what they recommend.

 

You sure that's not to loose for a dd?

The spec sheet from them recommends .0025" I'm not going that tight

 

Anybody else?

 

.0035" will be fine for your HP goals and the fact its a daily driver. Keep that in mind however once you get used to 400-500hp, because you WILL want to turn up the boost.

Im sure Extralargnog will chime in though. as many have said its better to go loose than tight. If Supertech recommends .0025 then .0035 should be good. It also wouldnt hurt to actually call up Supertech and tell them exactly what you plan to do with your car they may give you some better insight.

Also do some research, as I've been told .0035" will be fine especially as long as you break in your motor very slowly & not on the dyno or extremely fast.

 

.0035 is plenty for that hp goal with high silicon content pistons as the expansion rate is. Ju h less than low silicon content pistons. .0045 is overkill. I'm running .0035 with srp pistons at 450hp been going strong for years

 

So would .004 be better then .0035? This motor will be broken in pretty hard. I just don't want it to end up being to tight

 

you guys gotta remember these are not 2618 so they don't need as much room to grow

 

.0035 is plenty with that alloy, you can run it very hot without scuffing. mahle had an expansion chart somewhere with that metal and what it does. long story short at .0035 you would be melting valves along with the pistons to reach that expansion. if i remember right the supertech sheet said .0025 to .003 so .0035 is on the loose end for that piston. that alloy actually expands slightly less than even 4032

personally i would call supertech and talk to them about what your boost goal and hp goal are, get their take. you sure as **** don't want .0045, the piston would never stop rattling, that's a 2618 number

 

Thanks for the info guys

 

Not to turn this into a pissing contest, I see alot of people rattling off the same number. How many have you built a motor with those pistons? Or a different piston with the same alloy.

OP, I'm telling you from personal experience. Also, my current motor using CP pistons with 4032 alloy is running 0.0045".

 

Yep same here. I used to be at 84mm with. 0035 and it made ptw contact on the dyno. Its a little chattery/ noisy until warm but id rather have that than piston scoring

 

So would .004 be best? Or you guys think .0045 would be best but that kind of scares me I don't want a lot of piston slap on start up, but I also don't want it to be to tight

 

Sorry guys I'm just getting a lot of different answers and I need to know in the next hr. More then likely ill be going with a .004" any opinions?

 

sure, split the difference then. all im saying that that you'd much rather have it slap on startup than be too tight

 

i ran the mahle's at .0035 before and they expand slightly more than the supertech alloy. they rattle cold but are quiet warmed up. more than anything it depends on cylinder temps. if you have a sleeved block and a ton of boost...that will require more clearance.

you are always better too loose than too tight but the drawbacks of too loose are blowby, rattling and shorter ring life

 

Thanks guys. It has stock sleeves and it will have some boost but not a ton, as said I'm shooting for just over 400. I know as said its better for it to be loose then tight but I don't want it being to loose. Looks like I'm going to go with .004" thanks again everyone

 

Props for making up your own mind.

 

Thanks man. And thanks for your help and input on your personal build

 

Laskey just finished my short block assembly and went with .0035 for ptw....cp pistons 10:1 comp shooting for 500whp with room to grow...

Not sure off hand what alloy cp's are compared to other piston options but i trust them with the assembly.

 

I believe the CPs are 4032 alloy also. Im going with .004"

 

I run the supertechs in my setup... 84mm gsr and I run 0.0035 clearance, it rattles a little on cold start but once it warms up it gets quiet.. I run 15psi daily, and a max of 32psi @ the track...

 

0.0035" on Mahle 81.25's here. Rattles cold but quiet warm.