Bore and piston wear boosted aplication

[Gtv-racer]

The standard piston to head clearance on these engines is 1.6mm on the most outer edge of the piston. The head does not have a flat part on the outer edge like the piston. It starts right away hemespherical. So no squish area.

[Gtv-racer]

What do you guys think of the ring end gaps. It is a 93mm piston. Is it oke for a supercharged aplication on 10psi?

[Boosted LS1]

Ring manufacturers issue their own SAE guidelines on end gaps. Do yours show any signs of butting?

[stevieturbo]

As long as they are not too tight, I wouldnt worry.

If there are no signs of rings butting....that has proven they were fine.

Although if 0.7m is correct, ie 27-28thou......there's definitely little chance of that being too tight.It sounds large for a 93mm piston.

But totally safe.

[227bhp]

Generally top ring gap for boosted engines is bore diameter x 0.0055
Second ring is 0.0065 x bore diameter.

[Gtv-racer]

Thanks for the answers! It helps a lot.
Only why does the second ring need a lager gap. It runs cooler then the top ring.

Edited by Gtv-racer on Wednesday 23 January 16:46

[stevieturbo]

Whether it needs a larger gap or not depends on the design of each ring installed, and how much pressure you want behind each ring etc.

[Boosted LS1]

227bhp said:

Generally top ring gap for boosted engines is bore diameter x 0.0055
Second ring is 0.0065 x bore diameter.

I think there's a school of thought to make the second ring tighter these days iirc. It can be the same as the top ring or tighter.

When the second ring gap is larger this is to allow some blow bye thus preventing pressure pushing against the underside of the upper ring and maybe unseating it.

Edited by Boosted LS1 on Wednesday 23 January 17:55

[Mignon]

The biggest scratches in the bores are from the corners of the piston rings. I always chamfer new rings with a fine oilstone but very few engine builders know to bother doing this.

[Boosted LS1]

Mignon said:

The biggest scratches in the bores are from the corners of the piston rings. I always chamfer new rings with a fine oilstone but very few engine builders know to bother doing this.

I champher all my rings because they're usually file to fit :-)

[Inline__engine]

Boosted LS1 said:

I think there's a school of thought to make the second ring tighter these days iirc. It can be the same as the top ring or tighter.

When the second ring gap is larger this is to allow some blow bye thus preventing pressure pushing against the underside of the upper ring and maybe unseating it.

Edited by Boosted LS1 on Wednesday 23 January 17:55

pretty sure that's backwards, having the 2nd too tight upsets the top ring seal as anything that gets past the 1st causes the pressure builds up thats why gapless 2nd are a POS