I did a search on this subject, and I have learned that heat affects the gap on the rings, especially heat created by nitrous, and/or blowers.
In my particular case, I want to re-ring my 383 stroker. It's 11.5:1 compression, and it's all N/A no nitrous here. That's how I want it.
To my question...what's the industry standard for file-gapping a N/A motor. Is there any particular gapping numbers I should be above of or below of?
I was thinking between 0.17-0.22? But I want to know a specific number.
Hope all of this makes sense.
Thx-Goose.

 

Typical ring gap on a late model engine is:
Top ring = bore x .0050"
Second ring = bore x .0053"

Since you have higher compression you should use:
Top ring = bore x .0045"
Second ring = bore x .0050"

NOS should use:
Top ring = bore x .0050"
Second ring = bore x .0055"

 

I find those formulas interesting. Just wondering where they come from. When we design OE piston ring gap ratios, we usually shoot for 1.5-2.0:1 ratios 2nd/top. That makes it take longer to build up enough pressure in the 2nd land to unseat the top ring. Once the top ring shifts to the top of the ring groove, it serves as a pump to put oil into the combustion chamber and your ring sealing is much less effective.

The 1.5-2.0:1 is just a guideline and isn't always optimum, but it's normally a starting point. Your ratios above are almost 1:1.

 

Depends on the piston alloy, how far the ring pack is down from the piston crown, the ring manufacturer..... lots of factors.
Speed Pro recommends ("moderate performance") .004 x the bore diameter on the top ring and .003 x bore diameter on the 2nd ring. I have found that factoring at .0045 and .0035 produces satisfactory results for me so that's typically what I use. To give you an idea... Total Seal recommends .0025 x bore for the top ring. Different ring maker, different recommendation. Also consult with the piston manufacturer to see where they stand.

-Mindgame

 

Hmm, now I'm even more intrigued. You seem to be saying you run a tighter ring end gap on the 2nd ring than you do on the top ring. What's led you to this strategy? I'd have to believe you're almost guaranteed to unseat the top ring with this approach.

Just trying to understand how some of you are building your racing engines differently than I would design an OE application. I don't see why they should be different.

 

What's led me to this strategy is a great deal of confidence in the engineers at Speed Pro (the only rings I use) and their recommendations. I have confidence that they know more about rings than I do so I take their advice.
You'll likely find that just about every manufacturer out there recommends more gap on the top than the second. My guess is... it has to do with thermal expansion. The top ring is closer to the heat so it gets more gap.
I've been racing cars and building engines for quite a number of years now and this strategy has never let me down. I wish I could say that many of the other things I've tried have worked as well.

-Mindgame

 

Hmm, yes, the top ring does see more heat and the gap will close down more, but you never want your 2nd ring to be gapped near 0, for the reason I stated above. Thus, I think you'll find that just about every OE design has the 2nd ring gapped at more than the 2nd ring in a cold state.

I appreciate that it's never let you down, but what I'm asking is how you're convinced it's the best general strategy. All my experience in the OE sector leads me to the exact opposite conclusion you have come to. That includes engine testing measuring blowby and oil consumption and doing ringpack motion simulation using Ricardo's program. BTW, you'll also find that on a stock LT1, the 2nd ring gap is speced at greater than 50% more than the top ring gap (nominal 13 top and 22 2nd).

 

In a perfect world I guess you'd just keep all the cylinder pressure above the compression ring but that aint real life. In that case you'd maintain a "0" gap at running temperatures and no ring butting. No pressure getting to the 2nd ring either. That would be nice.

I agree with the "No 0 at the 2nd ring" remark. That's the whole problem behind the whole gapless 2nd ring theory. The 2nd ring gets double duty... it gets to scrape and retain cylinder pressure. I think we're putting a little too much emphasis on the "gap" thing though. I can see where a smaller gap is recommended for the 2nd ring.... it sees less heat and still has to perform a similiar duty while allowing enough bypass to not unseat the top ring. On that subject, and all theory aside, I have not seen any evidence of this in any of my engine dyno results. Ring unseat and flutter are usually pretty easy to spot on a dyno graph. Same goes for unseat due to detonation. I think ring weight plays a big part in that too... at least that's what I've read over the years. I think that more important than any of this is the radial seal (bore and ring) the concentricity of the ring groove and the proper clearance in the ring grooves. My engine builder of choice (and some engines I build myself)... well he pays real close attention to this as do I. The bore machining goes a long ways to ensuring a good seal and I trust my machinists work there as he is competent in building engines with output 2-3x that of my own and does so on a regular basis. So, I think there's a bit more to the subject and too much weight is being given to the whole gap thing. I've actually found excessive ring gap in some of my engines and they seemed to perform just fine. Either way, a smaller 2nd gap works for me and I see no need to change it until I see other guys doing the same. All the top guys I know of are doing it the same way so who knows.

How many race engines have you built putting this theory to test. I'd be interested in seeing any results.

-Mindgame

 

You're talking strictly thermal issues here. I'm talking about gas dynamics issues, dealing with pressure balances in the ring lands. They're really separate issues.



I'm interested to hear how you would notice top ring unseating with a dyno. I'm not talking about flutter, just unseat. You might notice it in a power loss if excessive blowby results, or you might notice it with crankcase pressure rise if you monitor that, but it's very likely you wouldn't notice it without a blowby meter or oil consumption monitoring in place. What other ways do you use?



Ring motion due to inertia would occur in a different portion of the crank cycle than if it's due to pressure balancing in the lands. The ring inertia is greatest when approaching TDC. That's also when you're building up tremendous pressure in the combustion chamber. That combustion pressure will outweigh the inertia force if you do it right. However, it can be much harder to avoid ring unseating due to pressure balancing in the lands. Here, ring mass has very little to do with it in comparison to pressure balancing. Towards BDC, when your combustion pressure is getting less, and a lot of your combustion pressure has bled to the 2nd land, you'll hit a point where the 2nd land pressure can be greater than the top land pressure. It's at this point where the top ring will begin to migrate to the top of its groove. When that happens it loses its seal, and "blowback" occurs. This can have a very bad impact on oil consumption, which maybe racing engine builders aren't concerned with, but we are. However, that blowback will only occur for a split second, and then it will also affect your blowby. Again, I'm not sure you'd see this on a dyno without some very good instrumentation or at the very least, a blowby meter. It will also occur more easily under lightly loaded engine conditions, which again, racing engine builders may not care about. We have to care though. That's what I was trying to get at in my original post. I'm trying to figure out why racing engine builders are doing this differently than we do. I'll do some more research at work on some of the WOT testing we do vs. part throttle testing and try to judge the effects.




That's kind of my point. With the level of instrumentation you have on most aftermarket dynos you'd probably never notice if the gaps aren't optimum. Winning is all in the details though isn't it?

Well, my experience with studying ring motion and piston/ring design is with the OEs (meaning original equipment manufacturers - Nissan, GM, Chrysler). We don't have the same design criteria as racing engine builders since we have to take emissions, ring life, oil consumption, and cost into consideration. However, I have a strong feeling the aftermarket may be a bit behind here in how they're doing things. I can't share most of the data I have with you because I work for Ricardo, an engineering consulting company in Detroit. We sign confidentiality agreements with the OEs when we start on contracts. I'll see if I can find some information I can post though, maybe if some of the details are omitted . . .

 

I guess I'm a bit perplexed here, cuz Speed Pro has/does recommend the larger 2nd ring gaps for reason 94Bird stated. I don't how many years Speed Pro has held this position. As 94Bird also stated, oem service manuals for LT1 engines, have in the specs, a larger 2nd ring gap as well. So we are going back 10 years (at least) for oem. Not to take anything from companies such as the one 94Bird is employed at, but I would consider it doubtful they would be, cutting edge wise, ahead of ring mfrs. such as Speed Pro. From a performance standpoint, I would think an outfit like Speed Pro, would actually be taking the lead.

 

Speed Pro has been recommending larger 2nd ring gaps for about three years now. Many old timers and very successful engine builders are still using the old standards with success... many aren't even aware of the new recommendation and an even bigger portion don't seem to care. Tis the way with those who are set in their ways.
Either way you look at it, this is an area of some controversy among engine builders. The theory is sound but many (non-engineering) builders like to go on what has worked for them in the past and if they've had a great deal of success no one can really blame them. However sound the theory is, you will be hard pressed to find actual performance increases in every case. I've been involved in quite a few tests of this nature and I can only say that it will not hurt to run a larger 2nd ring end gap. I would recommend a minimum of .020 for mild performance engines. Cold nominal gap ratios of 1.55:1 will do no harm and may be helpful but for non-competition street engines there are more important issues. Not to understate this topic but the gains I have seen in low to moderate performance engines (80hp per L) could be best classified as miniscule.
However, many builders are playing the happy medium in running the same gap on both rings and have had success in doing so.

Interesting thread though.

Take care

 

I raise my hand.
I fit right into that category Chuck and I was not even aware of the new information. Haven't indulged myself in a Speed Pro Performance catalog in probably 6 years. Shame on me.

Exactly my point. Here are a few links I've found that show where quite a few engine builders are placing their ring end gaps. I'd venture in saying that the vast majority are still doing it with the smaller second gap:

http://www.moparmusclemagazine.com/t...345/index.html

Merkel makes mention of the new gap recommendation in this article but still lists the old standard
http://www.merkelengines.com/documents/Buick38.html

http://www.fordmuscle.com/archives/2...e/index2.shtml
http://www.edelbrock.com/automotive/7176pp.html


Merkel using same gap 1st and second:
http://www.gmhightechperformance.com...07gmhtp_buick/

I don't know of too many race/performance engine builders who are overly concerned with hydrocarbon emissions and the like but who knows. I agree, this has been an interesting thread and I've learned a bit from it. 94bird, if you have any information..... something that you could pass along, I'd be more than ready to read it. That'd be great, and thanks.

-Mindgame

 

Well, if Speed Pro has been using/recommending this thinking for just 3 years, so much for believing THEY are on the 'cutting edge' when compared to companies that support the oem.

 

I can't think of any aftermarket companies that are on the cutting edge compared to the OEs. The OEs just have so much more resources. OTOH, I know many aftermarket companies that tap into OE resources to help them come up to speed. For instance, Speed Pro is owned by Federal-Mogul. F-M makes piston rings for the OEs, and I guarantee you that most of what Speed Pro knows about rings came from F-M or AE Goetze, who F-M bought out. Before I started for Ricardo, I worked for F-M as a piston/ring/rod application engineer. Generally technology transfer is from the OEs to the aftermarket. That's one reason I'm up here in miserable Detroit now. This is where all the fun jobs are. I worked at Comp Cams in college and had a good time, and worked at Holley in KY for 2 years after college, but the knowledge base in Detroit is just so much ahead of the aftermarket in general that if you want to really pick up knowledge quick, this is the place to be. Maybe eventually I'll go back to the aftermarket, possibly with my own business. Who knows. I know I'd much rather be in Florida or California right now.


I'd agree that you might not see a benefit for a racing engine in going with a larger 2nd gap, but I'd be tempted to say in most engines the benefit is there, it's just not large enough for you to see it (depending on how you test), and therefore may be inconsequential for your intended purpose. We generally start looking at ring motion in the groove using a simulation program. The inputs required to make this simulation program accurately predict engine performance are more than what most aftermarket companies can measure. Our base design starts there, and then we back it up with engine testing, and we always vary the gap ratio in the engine to doublecheck our simulation runs. Every engine is a little differernt than another, and you can't just have a rule of thumb of 1.5:1 2nd/top gap ratios, but it's a good starting point for analysis and testing.

I'm still amazed at how something as "simple" as an engine where the concept has been around for over 100 years, is still so hard to design. That's what makes it so interesting though.

 

I'm using the SRP flat tops, and I gapped mine at their nitrous recommendation of .026 top, and .022 second...