Flyer

iTrader: (1)

Building a 408, trying to decide on ring gap.

Following the card advice, what would be the result of keeping it on the tight side.

I'm aiming for around 12:1 compression in a daily driven truck, might see some nitrous use. 200-250 absolute MAX!

Keith

http://www.jepistons.com/pdf/2005-proseal.pdf

Check out page 12. What transmission are you going to run behind the 408?

Flyer

iTrader: (1)

4L80e

Flyer

iTrader: (1)

Taht info's kinda contradicting the sheet in the rings.

Mahle says up to 150 shot go with .006/.007
JE says moderate nitrous apps go with .005/.0055

Mahle over 150 shot go with .008/.009
JE RACE only nitrous use .007/.0073

Keith

So I take it you are running the Mahle rings then. Why not split the difference between the two. Maybe something like the .008 per inch of bore. Thats on the low side of Mahle's suggestion and on the high side of JE's suggestion.

I'll bring it back to the top for you. Maybe you can get some more suggestions.

Flyer

iTrader: (1)

What do you mean by per inch of bore?

What would happen if they were to tight for my application?

Keith

The little table on JE's site gives you a number to multiply the bore size by. For example, JE recommends a minimum gap of .0050" per inch of bore for street turbo/moderate nitrous use.

So, your 408 has a bore of 4.060" If I remember my numbers correctly.

Multiply your 4.060" bore by .0050" gap per inch and you get: .0203" ring end gap for the top ring, if my math is correct.


If you were to use too tight of a ring end gap, under high loads, like when using the nitrous, the heat in the cylinder would cause the rings to grow and butt together. That would score the cylinders. Thats no good.