Confirm my ring gap math
 

Quick run-down of the build:
IA2 535 forged bottom end
4.5" stroke w/ 6.8" rods
Ross flat tops 4.350 bore
Edelbrock non-wide ports

Due to potential of running mild amount of nitrous, ordered Total Seal "TNT" rings

Per Total Seal instructions, 150-350 hp shot, gap = bore x .0065 for both top and second rings.

4.350 x .0065 = .028 (.028275)

I'm not even 100% sure I will run nitrous, but it's something I've considered. Also considered running boost at some point, and per the total seal instructions, I think that gap would suffice for up to at least 20 psi.

This .028" gap seem sufficient? For both top and second rings?

I did gap mine at .026 top and second, herd guys going up to .032 for boost.

I'm freshening a 598 Chevy right now for a friend and it was gapped over .030 on the top and 2nd. It was going to get a 250ish hit. Since the nitrous is off the car now, I tightened it up a little on a total seal classic race and went .0055 x inch on the top and .006xinch on the 2nd. Just couldn't bring myself to not opening the 2nd slightly.

I would follow what is recommended for what bore size you have at the highest level of nitrous you plan on using. I have a 4.155 bore with forged SRP's . At the time, I built the motor I was never intending to using nitrous so I gapped for N/A . Then later on decided to run a 150 shot of nitrous. I tried a 210 shot a handful of times as well and never had 1 problem with the rings. Went back to the 150 for a year now with the N/A gaps still no problems... ..

You're way better off being a little too loose on gap versus a little too tight...

I have not used the Total Seal TNT top ring, but we do use the Federal Mogul "Hell Fire" top ring which is the same type of material. Heat treated ductile iron. We also run a napier second ring like the ones in the Total Seal Kit. If I was building the engine for a customer who doesn't have a clear picture of future use for the engine, I would open the top and second ring gaps some for general safety. I would feel more comfortable with .032" on the top and .035" on the second ring at that bore size. If you were sure you would be running NA only, then the Total Seal recommendations are fine. As soon as you start talking about 2-300 HP nitrous or up to 20 PSI boost, the end gap goes away quickly as the rings become red hot little boring bars riding on the pistons. When they expand and the end gaps butt, they will tear the cylinder walls up in a few seconds. As mentioned, there is little down side to running some extra end gap.

Fair enough, lean towards the looser side for a safe cushion.

I'm curious as to why many run a slightly looser gap on the second ring? Total seal (with the rings I purchased anyway) recommends the same gap on top and second ring, regardless of n/a, nitrous (any amount), boost (any amount), and even with nitro meth w/boost. (Refer to picture attached to original post). So where does the wider second ring gap thing come from, and why?

It keeps the rings from fluttering is what my understanding of it is...

Charlie is correct, a looser gap on the second ring keeps pressure from building between top and 2nd causing the ring to flutter. Evidence of fluttering is a blotchy surface on the ring and the start of micro welding in the ring groove. Not good, because the ring doesn't seal in the groove. Piston companies started putting a groove in the ring land to help prevent pressure, but that is a band-aid.

Yes, that seems to be the current thinking at least. It is important to make sure have excellent fit ring to groove. I don't like more than .0015" clearance. Ring flutter is another reason I typically don't use Total Seal rings. They make fine piston rings, I just don't believe the zero gap stuff gains anything other than great leakage numbers when the engine is not running. But everyone has their opinion and they have been selling them for 40+ years. So some people must really like them. The ring set you are going to run looks like a nice set.

^^^^^ Thruth^^^^^

You want a little more flow area on the second ring to make sure you're not lifting the top ring due to pressure in the gap.

At what point does ring end gap affect blowby?

If you are doing a "static" test of course you will get more by wider ring gaps. However, on the dyno wider gaps will have no impact on power production whatsoever as the events are happening so quickly there really isn't enough time for the slightly increased leak path past both rings to really make any difference.

I used to really worry about this sort of thing many years ago, but these days I don't give it a second thought. I still remember shooting for .012"-.014" bottom and .016"-.018" (for example) upper ring gaps and buying additional rings if/when we'd take a little too much off one by mistake. This cost me a LOT of time and money before I perfected my ring filing techniques for sure!

Anyhow, these days for most N/A set-ups that will NOT see power adders we use .018" ring gaps for both rings and have had zero issues. I opened up that bottom number about a decade ago due to new information about ring "flutter", but never had any issues before or after.

IF and WHEN the manufacturer or application calls for wider gaps, we follow those recommendations and don't give it a second thought.

The only problems I've witnessed, but never had happen here because we don't use them, is the tops getting "zanked" off of the KB HT pistons even when they were given additional clearance by the engine builder. This happens because they have a very high top ring location and this leaves much less material above the top ring for integrity. If/when you lean out a cylinder or two and temperatures spike quickly, those rings grow enough to butt the ends together with catastrophic results every time.

I also tried the "gapless" variety one on a N/A 455 around 700hp, and they didn't work worth two squirts of duck poop, so we went back to tradition rings. The gapless had EXCELLENT leak down numbers, and did everything very well except on the top end of the track in high gear we kept blowing out oil pan gaskets. When we took steps to keep the pan gaskets in place they would blow out a gasket someplace else. I suppose at really high rpms for some reason they would become un-seated and crankcase pressure would build very quickly.

Hope this helps some......Cliff

At every point. In oil testing it's common practice to open up ring gaps to increase test severity by putting more combustion gases in the oil sump. However... to Cliff's point, with regards to power production a little more gap will likely go unnoticed. What you don't want to be is too tight - potential gains are not worth the potential risk.

Anytime it's more than zero. Folks doing production work target touching at worst tolerance, 3 sigma, etc. You want them as close to zero as possible at max ring temp. If you go too far you will see ring butting which will show up as a ring scuff where the bore is scuffed where the rings butted and put load into the bore due to gaps being too tight. Make sense?