Need piston ring end gap specs

[Stephen@NCAutoUSA]

What's everyone running? I've run into another delay and decision that I'm not sure what to do...

My engine is being assembled now and the specs are a little off than what we'd hoped for.

Can people post up if they have laying around their "top ring end gap, and 2nd ring end gaps". Or PM me please? Our target was a .016 top ring which we achieved but the 2nd ring is .002 larger than expected...

I probably won't drive the car much even when I do get it back, but I'd like to rest assure that my built motor will have a long healthy life if I don't abuse it. I don't feel like getting my car back, putting 10k miles on it, and having to pull the motor for a rebuild in 2 years.

Stephen

 

[E-Nough Logic]

What's everyone running? I've run into another delay and decision that I'm not sure what to do...

My engine is being assembled now and the specs are a little off than what we'd hoped for.

Can people post up if they have laying around their "top ring end gap, and 2nd ring end gaps". Or PM me please? Our target was a .016 top ring which we achieved but the 2nd ring is .002 larger than expected...

I probably won't drive the car much even when I do get it back, but I'd like to rest assure that my built motor will have a long healthy life if I don't abuse it. I don't feel like getting my car back, putting 10k miles on it, and having to pull the motor for a rebuild in 2 years.

Stephen

since this is in the forced induction section im going to assume you are using some set of off the shelf forged piston for a forced induction build. im not sure what size pistons you have but using CP specs even with the smallest bore available for the nsx 90mm your top end ring gap would be larger than .016", you would want something along the lines of .019 or .020 for pistons as large as 93mm.

more information would help what exact pistons are you using? what forced induction setup are you running and what are your power goals?

 

[yamahaSHO]

A forged piston should come with specs for ring end gaps for different applications. If not, check their site... Here is what Wiseco provides:

http://www.wiseco.com/PDFs/Manuals/RingEndGap.pdf

 

[Stephen@NCAutoUSA]

I know what they recommend and I'm saying that my specs are a little off and I'm wondering if anyone else has run into this and went with it anyways...

My specific specs are
Bore size: 3.565
Top ring end gap: .016
2nd ring end gap: .025

Pistons are SOS 90.5mm pistons. They are 3.563 when new. Mine are at 3.560

It's an air to air, no meth, grav fed. Goal is around 500-550whp.

Stephen

 

[E-Nough Logic]

I'm not sure what brand piston SOS uses but your second ring gap should be fine and I would want to open up the top ring gap more if anything. .016 would be more appropriate for an all motor build.

 

[Stephen@NCAutoUSA]

SOS uses wiseco. The motor has arp rod bolts and arp head studs.

Stephen

 

[angus]

You could go .020 but even the .016 would most likely be just fine.

 

[E-Nough Logic]

You could go .020 but even the .016 would most likely be just fine.

if its already together sure i wouldnt worry about it, if its still apart i would open up the top rings to .018-.019 and the second ring gap at .025 are fine i wouldnt worry.

 

[gsrboy]

I think I did like .016/.017 and I had like .018-.020 for the bottom on my NA build. I didnt even need to grind the bottom ring. Theres an equation to figure out the ring gap on the CP site.

http://cp-carrillo.com/LinkClick.aspx?fileticket=LjC4jLmI4Ls=&tabid=74

 

[Stephen@NCAutoUSA]

I think I did like .016/.017 and I had like .018-.020 for the bottom on my NA build. I didnt even need to grind the bottom ring. Theres an equation to figure out the ring gap on the CP site.

http://cp-carrillo.com/LinkClick.aspx?fileticket=LjC4jLmI4Ls=&tabid=74

According to that table if I take my bore size of 3.565 and use the formula for the nit/turbo application then I can run a Top ring end gap of .019 And also according to them my .025 2nd ring end gap would fit into the range for both of them.

Can I just leave my 2nd ring end gap at .025 and file my top ring end gap .018 or .019?

Stephen

 

[gsrboy]

yeah sounds about right. The bottom ring for all the motors that I built never needed to be filed. It always fell into spec. CP requires ring 2 to have a larger gap than ring one. .019 for the first and .025 for the second sounds fine for turbo/nitrous.

 

[Stephen@NCAutoUSA]

You could go .020 but even the .016 would most likely be just fine.

I assume you're talking about what the top end ring gap is. That's leaving the 2nd end ring gap at .025? Have you ever run those on a motor and with what pistons?

A forged piston should come with specs for ring end gaps for different applications. If not, check their site... Here is what Wiseco provides:

http://www.wiseco.com/PDFs/Manuals/RingEndGap.pdf

That's the chart we're following since they're wiseco. CP has a different formula. Wiseco has both the top and 2nd ring end gaps within .002 of each other basically where CP says you can run the 2nd between .004-.008.

Again I'm not sure if wiseco makes their own rings or out sources them. I'm not sure if CP makes their own rings or has a company make them as well?

I know different materials expand differently so if you're running a set of CP pistons vs wiseco they'll react differently under stress since they're not made the same. However the rings not to sure. Has anyone heard of rings being made by 1 common company or do they all make them in house?

if its already together sure i wouldnt worry about it, if its still apart i would open up the top rings to .018-.019 and the second ring gap at .025 are fine i wouldnt worry.

Can I ask what other motors you've run ring gaps on and if they're still alive? Is there a problem if I keep my rings as they are that far apart? With 2 different formulas to follow, one being at .002 or so between the top and bottom and the other being a range of .004-.008 I wonder what if anything that matters.

I'm trying to understand things like if my rings were at .009 apart like they are, does that mean the oil from the bottom ring since the gap is a tad bit larger than the top get stuck inbetween rings and cause something "bad" to happen since it can't exit the top?

yeah sounds about right. The bottom ring for all the motors that I built never needed to be filed. It always fell into spec. CP requires ring 2 to have a larger gap than ring one. .019 for the first and .025 for the second sounds fine for turbo/nitrous.

Have you ever run those specs? What pistons did you use? According to CP it should be fine. According to wiseco both are too loose for what my application is. For wiseco it puts me in the "blown race only" in their chart...

Stephen

 

[yamahaSHO]

That's the chart we're following since they're wiseco. CP has a different formula. Wiseco has both the top and 2nd ring end gaps within .002 of each other basically where CP says you can run the 2nd between .004-.008.

Again I'm not sure if wiseco makes their own rings or out sources them. I'm not sure if CP makes their own rings or has a company make them as well?

I know different materials expand differently so if you're running a set of CP pistons vs wiseco they'll react differently under stress since they're not made the same. However the rings not to sure. Has anyone heard of rings being made by 1 common company or do they all make them in house?

As I'm sure you know, rings are not created equal (different thickness, composition, cut, etc) and that is why it is ALWAYS recommended to follow the manufacturers specs when sizing rings. On both my Wiseco SHO builds, I used the PDF I posted earlier and 5 years later, one motor is running very strong (3.2L, 600ish hp on 91 octane), the other is still on a stand in unused condition.

I will be building another motor for my STi this winter and will be going with Mahle pistons. With that said, I'll likely look at what ever recommended specifications are supplied.

I'm trying to understand things like if my rings were at .009 apart like they are, does that mean the oil from the bottom ring since the gap is a tad bit larger than the top get stuck in between rings and cause something "bad" to happen since it can't exit the top?

Oil should be controlled by the oil control rings, so you shouldn't be seeing a lot of oil up past that point. Ideally, the top ring should be doing most of the work. Because of this, builders like to run slightly larger ring gap on the bottom compression ring to help prevent ring flutter which will load up the top ring and breakup the seal.

With a little more research (probably google), you can probably gather enough information to make your own choice for ring gaps. On the current motor I've got in my SHO, I actually deviated a little from what Wiseco recommended and went with a little larger bore all around as I've known this motor to run very hot. You may be just fine with what you have, however, what you're ultimately trying to attain, in addtion to the multitude of theories out there for building motors, you may not get an exact answer you're looking for.

Have you tried all the bottom rings in all cylinders to measure the gaps?

 

[gsrboy]

if your using weisco use their gap specs. I use CP specs cause I only use CP pistons.

 

[Stephen@NCAutoUSA]

if your using weisco use their gap specs. I use CP specs cause I only use CP pistons.

Yeah, I kind of figured that. That's my problem now though. We've talked to wiseco and they said that the pistons I have there's only 1 ring size that they carry and whatever next size up is to large to file and fit or couldn't be done.

To use the wiseco specs which would be .016 top ring end gap and I think a .020 ring gap I would need to find another ring that fits around my pistons, that's made out of the same material I would guess as the top ring or what wiseco uses, and file and fit that to make it the correct size.... That's my problem now.

Stephen

 

[E-Nough Logic]

Yeah, I kind of figured that. That's my problem now though. We've talked to wiseco and they said that the pistons I have there's only 1 ring size that they carry and whatever next size up is to large to file and fit or couldn't be done.

To use the wiseco specs which would be .016 top ring end gap and I think a .020 ring gap I would need to find another ring that fits around my pistons, that's made out of the same material I would guess as the top ring or what wiseco uses, and file and fit that to make it the correct size.... That's my problem now.

Stephen

Wiseco's specs for a street-moderate turbo build are not .016 it is .0178. Like i said earlier if you can open up the gap on the top rings and keep the .025 gap on the second ring then you should be all set. yamahaSHO already commented on why they run a larger gap on the second ring than the first.

I'm not a professional engine builder but as far as engines ive built, a couple b series setups last one making 500+whp with a 35r on pump gas, i put about 10k miles on it myself and sold it, since then last i heard it was making 700+whp on a 6262. i used cp pistons, like the others have said always use the ring manufacturers specs. ill be building my first NSX engine next winter, i just began fabrication for the turbo kit on my 1992 a couple weeks ago.