Piston ring gaps - what do you guys run?

[SHEPPO3930]

Hi all,

Building my 4agte, running forged Ross pistons (81.5mm / 3.21" bore) and they were supplied with Total Seal rings. I'm at the stage of setting ring gaps, and have found conflicting info regarding this, more specifically, if the top ring's gap should be bigger or smaller than the second ring's gap.

The info supplied with my rings say the gap should be bigger on the top ring than the second ring. This opposite to what I have read. Everything I have read suggests a bigger gap on the second ring will help avoid ring flutter, etc.

So... What do you guys do? Does anyone have any rules of thumb, secret squirrel info, etc to share?

I have seen a rule pop up frequently that says:
Top ring gap = (bore diameter x 0.0050") + 0.001" for race applications
Second ring gap = (bore diameter x 0.0055") + 0.001" for race applications

Does his sound about right?

I have emailed Total Seal but yet to receive a reply. Here's there tech page: http://www.totalseal.com/TechPage.aspx . I am using "conventional" rings, not their gapless type.

FWIW- motor will be turbo, ran on 98 octane PULP, up to 20psi, etc.

Thanks for any help,
Dave.

[fixeruperer]

.003" per inch of bore.

i run the 2nd ring with a slightly larger end gap.

i run hastings rings in pretty much every thing except bikes.

[SHEPPO3930]

.003" per inch of bore.

i run the 2nd ring with a slightly larger end gap.

For NA or turbo applications?

[fixeruperer]

im running turbo.
.003" per inch of bore is rule of thumb (some rings say .004" per inch), if youre going to track it or get up it all the time you might wanna go slightly larger.

.004"-.005" per inch of bore would be safe.

[Ken_T]

"It only takes a couple of thou to little gap to kill a ring, the ring gap is there to take up the expansion of the ring when it heats up, the hotter the ring gets the more gap it needs (ie - turbocharged), even a mild NA engine will need more gap than stock.
A .0005" variation in bore size will cause a .0015" change in ring gap.
I check the gaps on every ring in every engine I build, even the stock ones, you'd be suprised how much variation you get - even with all the bores exactly the same size.
It's very rare for a set of rings to have enough gap for a performance application, they are generally made with stock engines in mind.
A good rule of thumb is .004" gap per inch of bore, ie a 4" bore will require at least .016" gap, higher performance NA engines need more, .020" on a 4" bore it fairly normal, turbo engines need more again - how much more depends on the amount of boost & the ring type - up to .006" per inch of bore is quite normal.
As a side note, in theory the second ring dosen't need as much gap as the first due to cooler running, but in practice the gap should be the same or slightly larger to avoid pressure buildup between the rings which can cause 'ring flutter' at high rpm - this occurs when the pressure buildup between the rings gets high enough to lift the top ring off it's land allowing combustion gas under the ring & screwing up the ring seal completely.
A CA18 has a bore of 3.27", so a suitable ring gap for a turbo version with decent boost would be around .017-.018" for the top ring & .018 for the second.
On a stock ring set you may have .012-.013"...

Cheers
TK"

[4th surf]

I've always run 10 thou ring gaps as a rule of thumb no matter if it's been a worked V8 or turbo diesel. Never done me wrong but I tend to stay away form Hastings piston rings as the top ring for reasons unknown doesn't like ACL pistons. I have always used "Sealed power" ring sets and assemble the rings into dry bores. Also in the instance of engine building "Cleaniness is next to godliness" and I'm not religieous in any sense of the word, but white "T" shirt material and either acetone or metho and keep wiping the bores out with a new rag each time until the rag comes out the same colour that it went in and you can't go wrong

[SHEPPO3930]

Thanks for the quick replies.

Motor is a 4agte with a 20v head, Ross pistons, spool rods, ACL race bearings, etc. 14psi to start with, then closer to 20psi later. Engine will be going in a track car for hill climbs and sprints, etc. So it won't have an easy life.

[SHEPPO3930]

Total seal got back to me, 0.018" top ring and the same or up to 0.020" 2nd ring gaps.

This is on a 81.5mm (3.21") bore.