The V8 Owners Forum -

Hi all, ive read somewhere on here about opening the gap on the top ring to make the 2nd ring do more work,?. do i measure them when compressed in the piston, and what gap should they be opened to,??. would rater ask before i do anything, is 45 thou opened to and file only going inwards to stop burrs,??. only running with about a 150 shot of gas rich

install the ring squarely in the bore, approx 1" down, and measure the gap there ( off the piston obviously )

You'd need to refer to the manufacturers specs for gaps though for different applications.

Thanks for the reply, does anyone have a rough idea on a gap size please, or is it a case of measure them first and then decide, rich

Rich,

Talk to Perry as he has done a lot of experimentation in this area.

Your going in the right direction as its the top ring that can expand the most with the heat of combustion when nitrous is used, and you may need 20-25thou.

Also the ring gaps on 1 + 2 should be opposite each other on the piston.

Kevin.

have measured the gap and its only 0.44mm or 0.017",. Been reading up in a nitros book, and Federal-Mogul advice this, A little larger gap in the 2nd ring than the top ring. They say they find a better seal with this gap configurationin in hot conditions, What happens in this case the top ring closes more than the 2nd even if you do them both to 25" the top will close more than the 2nd ring. It is important for the gaps to be this way because you want pressure between the top ring and 2nd ring to go out faster and easier than it gets passed the top ring gap, what gap sizes then in 1st and 2nd ring?? rich

Make sure you fit and gap each ring to each bore individually Rich.
As Stevie say's, put the ring in the bore and use a piston to push it down square to about 30mm into the bore. Measure the gap you have and adjust with a needle file etc. I use a mini dremmel thing to tweak mine. Once you have the gap set, you should then use a needle file to put a slight chamfer on the edge of the ring ends.

There is a rule of thumb regarding nitrous use, but I have my own sums done now, which you already know via PM if you are going to be using 150hp shot or bigger.

I normally gap the second ring to factory setting + 5 thou or thereabouts.

There can be two issues with nitrous use. One is the ring gap closing completely and causing a friction line on the bore which can generate a hot spot which can lead to detonation.
The other issue is the ring closing up but not touching. This can lead to the ring ends glowing red due to the friction of the gas passing through the small gap. This again can lead to detonation. So I use the ring gaps I told you about.

Ok, thanks all for the help and advice, will get them done at the weekend, rich

ive done the top ring at 25 thou and bottom ring 20 thou, rich