Im using wiseco 81.5mm K541M815 pistons in a gsr block. What kind of piston to wall clearance should I tell the machine shop Im looking for?

 

There should be a spec sheet that comes with the Wiseco's, and it will have their recommended piston-to-wall clearance on there. If you're looking for big (600+ WHP) power, your machine shop might decide to run slightly looser than spec to give you a bit more room when they heat up.

If you don't have the sheet with the pistons, you can call up Wiseco and they'll either fax you the sheet or give you the specs over the phone.

 

The P2W clearance on the spec sheet of my Wisecos was .0025 and that is what I ran. It ended up being way too tight for me. I realize they have the coating on them and once it wears off it will create more clearance but its still too tight. I went with CP since I was going with 83mm bore. This time around I went with .004 to give me some more wiggle room.

 

When you say .004.

is it .004 on each side of the piston? or .002 on each side?

eg --|_|--

 

idk but i called wiseco and they told me .003 and to measure it apx 1/300 below oil skirt ring

 

I hear so many people say .0025" is too tight, or they had problems with it. Why would Wiseco suggest this on a piston that is clearly designed for a forced induction engine? I'm sure they are fully aware of how much the particular alloy they use expands.

 

On most of our turbo cars we run .0035. this is the limit given by Arias as well

 

I am sure that is fine but it does not give much room for error especially for higher horsepower engines.

 

no, it's .004 total.

example, if your piston was 83mm (3.267"), they will bore the cylinder to 3.271"

 

.003 is recomended by all high sylicon forged pistons and stop saying on each side when they say three thousands its total but any where from .0025 to .0045 is fine you would have to go over .008 for leaks in compression.. you dont want it to tight or loose but .003 is recommended

 

Mine are set at a loose .0025" and tight .003" (so, between .0025" and .003").

 

My Manleys are at 5 thousands.

"Build it loose only you will know, build it tight, everyone will know. "

 

haha nice quote.

I bet people know when you start your cold motor though. clack clack clack clack

 

We had a big discussion on this a little while ago, that ended up with me talking to a good guy at Wiseco. He said for a ~400-450hp motor, .0045" was good. A little more would be good for a motor making more power than that.

 

my wisco pistons are @ .0025" too no problems so far. 350whp

 

For 400 whp and below, I use 0.0035" above that I think you should start looking at 0.004 or larger.

 

exactly! Dont say you only want 350whp so you will do .0025. Boost is addicting so give yourself that extra room to play with just like you would with injectors. A 350whp goal will turn into 450whp sooner than you think.