I am building a pair of supercharged 509's and i am looking for a recommendation on piston ring end gap. I am using flat top forged JE pistons and Total Seal gapless rings. The engines will be running cool with no t-stats. I will be running between 6-8 lbs of intercooled boost.

Who knows the right end gap???

I went with .028" on my 4.600" bore NA 598. That should be pretty close for a 4.5" bore blower motor. I went .026 on the second. It never hurts to err on the wide side when it comes to this! I got my recommendation from JE's marine technical guy. The paperwork that comes with the rings relates everything to the street, which makes it hard for us weekend warriors with our boats!

I just gapped mine last week,540 w/no stat,10lbs boost,total seal top,went .030-.031 top,.021-.022 2nd,that was using the guidelines for supercharged w/4.500 bore. I gapped it same exact way 2 yrs ago,no broken rings when i tore it down. Motor had excellent leakdown at 90hrs but terrible leakdown at 138hrs,Smitty
Are you using ring seating compound,i did and motor had NO blowby on dyno last time.

Power has been found by opening up the 2nd ring. Whatever the top ring is, open the 2nd up 30 to 50% more. Ring flutter with the piston velocities that some of these engine with big strokes see are terrible. Once PV reaches above 3500 ring flutter is HP robbing effect. This is caused due to pressure area between the top and 2nd ring. By opening up the 2nd ring you equalize the pressure by allowing it to equalize and freeing up HP.

Chris

9 times out of 10 when you see a ring land broke (not melted) it is caused from ring butt.
Don't skimp on this. The wider the better within reason.
I have run as much as .038 on 4.600 bore with no problems.
The determining factor seems to be how much heat and how high up the top ring is on the piston.
As far as the second ring goes, It does not see the amount of heat the top does, so It's my belief it doesn't have to be as wide.

Bump