apollard

Yes, the narrow bright area. no carbon/ crud on it and slightly polished. That was the only one I found like it, so either that cylinder detonated when the others weren't or the gap slightly was tighter. Or something else nobody I talked to thought about yet.

Icon (KB) forged pistons and Total Seal rings. I called both and discussed the application, fairly mild power but run for long times at 2500 while under moderate load and longer times at WOT. Both said that required increased ring gap. I went to 0.034 on the top ring. It is the gapless design, so no loss of compression to worry about.

Rage

What was the cylinder bore diameter that these ring gaps were assigned to?

Total Seal gapless rings sounds like a goo option.

I looked up KB pistons. All I could find available from KB were 4032 alloy for other than motor cycles or ATV's which the latter could be had in 2618. Is 4032 what you used?

donzi matt

From the research I have done it looks to be rather difficult to find a 2618 alloy off the shelf piston for a 8.1 liter. Just about all of the pistons I have found are of the 4032 variety as they are a drop in replacement. Mark Rinda had CP custom make him a set of 2618 dish pistons for a Whipple motor he did.

Keith Atlanta

What are the Diamond Piston alloy?

Rage

2618 is available from JE and Diamond supposedly. I have been talking to JE for about three days for a set of custom pistons for my stroker but so far I am not getting a guarantee that pistons will be made from 2618. I do not know what is going on with them.

donzi matt

The Diamond drop in is listed as a 4032 in their catalog. I'm sure just about any piston manufacturer will custom make you a 2618.

Back to your original worry of detonation during your initial tuning run, when I would street tune my 4 cyl turbo initially after making changes to the setup, I would mix 50/50 with 100 octane low lead from the local airport to give me a safety margin against knock until I got a relatively clean tune in it I liked. Maybe it is an option for you.

compedgemarine

I have always been paranoid about ring gap so I did a lot of reading on it. the general thought from those that had done a lot of dyno work with different gaps was that being too big did not hurt the power noticeably but being too tight could cause butting and break something. after that I always run them bigger than recommended and just take the slight loss rather than risk damage.

SB

Here is JE's 4032 ring gap spec's:
Note: How high/low the ring are placed on the piston obviouly effect things - I did not take the time to compare heights between JE and Mahle

[Edit in: oh schit, wrong table. I'll be back. LOL.

SB

I can't copy and paste their info.

Here is JE's 4032 piston and ring recommendations:

Click on: http://www.jepistons.com/PDFs/TechCo...instrc4032.pdf

Here is Mahle's, however they don't note which aluminum alloy for some reason:
http://www.us.mahle.com/media/motors...tion-sheet.pdf

Keith Atlanta

Shouldnt standard pistons be more than adaquate for this build? Isnt the root cause your AFR? You have a bad azz engine but it isnt off the charts bad azz (in a respectful way)

I think we need to re-direct the topic here... Are you sure this isnt a combustion chamber or possibly a quench issue?