Ring gap... in a non-drag application?

[Turbo6inKY]

Anybody know what the ring gaps were on the mid 1980s Buick Indy Car engines?

I ask because I'm getting close to beginning reassembly on my engine. I'm running Optima USCA events, which includes a lot of road racing. Instead of going 1420' WOT after a dead stop, I'll run 2200' WOT after entering the straight at 80mph.

That puts a whole lot of heat into the system that the drag guys don't normally see. And instead of going to the pits and cooling off, I go around and do it again, for twenty minutes.

So, ring gaps? Add a couple thousandths? Add nothing? Add a lot?

Looking for input from people that have broken things badly and learned from the experience.

 

[Turbo6inKY]

And just to fuel the fire (and try to make it look like I'm not a complete moron), Mahle has a recommendation:

http://www.engineprofessional.com/TB/TB011117-2.pdf

This works out to .027" for the top two rings (my engine is a 3.830 bore).

Is there any good reason to deviate from this guidance?

 

[earlbrown]

That sounds wide for the the top ring. (keep in mind I don't know how thick your rings are and lots of other stuff).

That being said I start with roughly .005" per inch of bore on the top ring and .006" per inch on the second ring.....

,...then go from there.


Here's the cool thing about being 'loose and sloppy' (giggidy) with ring gaps.... It's not like bearing clearances. You through an extra thou or two on rods and/or mains, and you have a sloppy piece of shit that needs gear dope in the pan to run.

You though an extra 10 thou on ring gaps and you lose 1/2 a HP and gain an extra 1% leak down MAYBE.

..On the inverse if you're .0001" tight on the gaps, you gain a piston crown that came loose from the piston and the entire engine is trashed!


Ring gap is the only time I drink profusely and remove a little more metal than usual.

 

[Turbo6inKY]

Thank Earl!

That sounds wide for the the top ring. (keep in mind I don't know how thick your rings are and lots of other stuff).

I actually don't know that, either. I'll need to check the thickness on the ones I'm buying. Highly likely to be 1/16", though.

That being said I start with roughly .005" per inch of bore on the top ring and .006" per inch on the second ring.....

,...then go from there.

So that'll put me at .019 top and .023 middle... as a starting point. I'll probably follow your lead, drink heavily, and split the difference between the Mahle recommendation and yours. Everything else I'm finding for a boosted race application is between 0.05" * bore and 0.07" * bore for the top ring, with the bottom being anywhere from .055" * bore to "add .004 - .008 to the top ring."

 

[No disintegrations]

happily I never had such a blow up. I think a large part of it has to do with coolant temp since the rings are so close to the water jacket and are shedding heat out that way. Also the bottom of the piston is splashed by fairly cool crankcase oil.
For really long wot throttle runs you want a richer mixture by quite a bit, which goes without saying.

 

[Turbo6inKY]

happily I never had such a blow up. I think a large part of it has to do with coolant temp since the rings are so close to the water jacket and are shedding heat out that way. Also the bottom of the piston is splashed by fairly cool crankcase oil.
For really long wot throttle runs you want a richer mixture by quite a bit, which goes without saying.

The fueling is a good thing to bring up. I'm planning on doing the MS3Pro PnP (assuming it launches this month, they're running out of month), but it has this neat capability:

High Power Time enrichment. Literally adds fuel to cool the cylinder on long runs, and it'll keep adding the fuel (up to the limit, 1.8 in this chart, so if the AFR Target is 11.2:1, it'll add fuel until its running at 9.4:1 after 25 seconds at WOT) until you get your foot out of it, then it ramps back down by running the curve backwards.

This chart isn't what I'll be using, it's just the default in the software. I'll have to play with this, obviously.

 

[No disintegrations]

that's awesome because it will run better in a short straight with a more "normal" mixture and then go to a safer mode if the straight is longer as needed.

 

[Turbo6inKY]

that's awesome because it will run better in a short straight with a more "normal" mixture and then go to a safer mode if the straight is longer as needed.

Yup, you can set something like 11.2 in the AFR target table and it'll dig out of the hole like a banshee, then it'll walk it down to 10.2 or whatever as needed.

The trick will be not to add too much and make damn sure the exhaust doesn't leak anywhere. If too much unburnt fuel meets O2 from a leak and ignites in the header, it'll spin the turbo up and overboost it.