My spec sheet for them came with .0025" clearance listed, but that just seems really tight unless you were going to break the motor in REALLY slowly and for a long time. That doesn't sound great to me. . .

I'd rather not have an excessive amount of piston slap on winter mornings (daily driver sometimes, and more so during the winter), but at the same time, I'd like to not have to worry about sticking a piston like I used to in my kart motors! LOL.

So, I see Evans Tuning recommends .0045 but maybe at a higher power level than this. If the experienced builders of forced induction 4-bangers on here can provide any insights/suggestions, I'd really appreciate it.

Thanks in advance! ! !

 

add another .001

 

400hp is my goal too, i called wiseco to see what they recomended and i got a person in tech who seemed to know what they were talking about, she(yes i said she) asked me my power goals, turbo and boost levels and she recommended .0035 so thats what i did. My advise call the manufacture.

 

I am not sure if you take to take into consideration the coating that comes on the skirt of the piston, I think Wiseco calls for that tight clearance because the coating eventually wears off. I am not sure what the thickness of it is, I would imagine somewhere in the region of .0005". But even at a P2W of .0030" you are still on the tight side.

 

Thanks guys. I was thinking I'd feel a little more comfortable if I started out with at least .0035, but I generally like to go by what the manufacturer says, and I talked to a guy at Wiseco who I could swear also told me .0025". . . . It was a while ago, so maybe I've got it twisted. I'll probably have to call them back as you suggest.

I think Jeff Evans (if that's who that was assembling the engine) was saying .0045" on that video for a motor in the 500-600 HP range IIRC, so I guess a thou less than that would be reasonable for the 400 range.

Thanks for the input so far!

 

Go with at LEAST .0035". I also followed Wiseco's recommendation of .0025" and when my engine overheated 2 of them cracked from the expansion and the tight clearance. I had swapped the head before this and noticed quite a bit of wear on the cylinder walls but I did not do anything about it. This time around I went with CP just because they have 83mm off the shelf and went with .004" clearance. I have a bit of piston slap but nothing bad at all. I've been at 425whp for almost a year and its been daily driven. So far so good!

 

Thanks champLSinteg, that is some great information. This makes me really glad I asked. It would have sucked to get the whole think put together with the specified .0025", and then found out I had problems.

If you have a little bit of piston slap with .004" on your CPs, then maybe I really don't want to go with more than .0035" figuring that some of that diameter is the skirt coating mentioned previously.

Thanks again!

 

good thing i put mine together at .0025" before seeing this......lol o well atleast its not running yet. ill pull it apart n put it at .0035 after seeing this.

 

Ive got manufacturer specs on my wisecos around 500whp.. no problems!

 

I build motor every day my clerance is .0045 never had a problem

 

By manufacturer specs, do you mean .0025", or some other spec they gave you for your specific power level? Can you please be more specific?

JO TECH, when you build them at .0045", do you get a fair amount of piston slap on a cold start? I understand a cold start is a little different for you in Florida than it is up here in ther frigid north! LOL. . .

Thanks guys!

 

The recommended clearance that came on the spec sheet.

 

So that would probably be .0025", or you're not sure? Do you have a build sheet that came with your engine?

 

Not trying to thread jack but i have some Ross pistons and the spec sheet says to go with a .006 P.T.W. clearence. Does that seem a bit large?

 

I do, but id have to do some digging to find it

 

might sound like a dumb question but if the piston to wall clearance is too tight would you have to send the block to get remachined? and if its too loose would you have to get new pistons?

 

For a wiseco piston, PTW is about .00101 in/in of piston diameter. For a 81 mm bore, this is about 0.0035".

 

is that a wiseco spec?

cuz my 81.5mm pistons came with a recommended clearance of .0025"

 

Mine are 87.5mm, so I guess that is another factor indicating that I should be on the larger end of the range we're discussing so far? . . . . I'm calling Wiseco this afternoon if I get a chance!

 

yes your ptw will be much larger than that of say a 81.5mm wiseco piston

i'll call wiseco in a minute or so.

 

Yes, that is a wiseco spec. I got the number from 2 different professional engine builders.


0.0025" is too tight. The skirts will get scuffed 1st then the motor will start smoking and eventually fail.

 

You should be at about 0.00378" PTW.

 

sweet, pulling mine apart this weekend to have it honed out to .0035", thanks for the info buddy.

when that coating wears off how much do you think the ptw will increase?

 

I just talked to a real nice guy at Wiseco, and he said he'd use .004" if I was going to break the motor in slowly, but if I was going to break it in hard and fast, then he'd recommend .0045".

Also, for ring gaps for that application he'd use .006"/inch of bore diameter for the 1st ring, and .0063"/inch of bore diameter for the 2nd ring.

I think that helps! Agreed? Matches Evans Tuning which is nice.