FORGED ALUMINUM AUTOMOTIVE PISTONS - CLEARANCE

What are the correct values for different types of pistons, depending on materials, size, and application?

How to measure?

Concrete examples!

Apparently it is a simple subject and producer offers suggestions, but it's good to let speak those who actually know the real situation.

 

use a dial bore gauge to measure the cylinder. And the piston manufacturer will tell you where to mic the pistons.


As far as what clearance I run, usually .0035-.004 on the 4g63. I haven't built any 1000hp builds to see how the tighter clearance lives. It works great at 600whp though. Good luck getting an race builder to come in here and tell you what they run..

 

That appears in the documentation, but the truth is not always so.

 

Really? The manufacturer of the piston doesn't know where to measure their piston? Come on.... This is dejavu of you whining about FP/Xona not having compressor maps.

 

Clearance is given by several factors.
The manufacturer gives a general guide line.
Make a simple experiment. Measures in the correct area, a forged piston at 25 degrees and 250 degrees Celsius.

 

Why would I do that? The "guidelines" given for clearance are meant to be measured at room temp, just like bearing clearance. Measuring at 250*C does me know good.


I don't even know why I keep responding to these silly threads you make..

 

You bring interesting information. You may display and their source?
I think it's not good to speak only in memories.

 

Yes. They're saying don't set your tolerances in a garage that is freezing cold, or extremely hot. And if you do, to keep in mind that you need to account for contraction/expansion. And you would have to make note of that for the block as well. Its best to do engine work in a somewhat temperature controlled environment for best results. If your shop is 80*F vs the 68*F listed by SRP, your talking a difference in size likely in the 1 ten-thousandths range, if that.


They are not telling you to "keep in mind expansion with heat, and leave the gap extra loose so that it comes down to spec at operating temp."

 

Yes, I saw what they say. I read a lot of documentation but ...
It is more correct what you said in previous message. ("Measuring at 250*C")
The cylinder has a specific expansion.
The piston has another expansion, higher.
Between the piston and the wall must be a film of oil.
An engine can not operate fixed odds, should be tolerant correct.
Most people in the field working between 20 to 25 degrees C.

http://www.yellowbullet.com/forum/sh...=479816&page=3

http://ls1tech.com/forums/generation...clearance.html