etperformance

I have an LS1 that I am building the bottom end on for the bottle(250 Wet).
I am using Diamond Racing 11502, 2cc Valve relief pistons. Diamond told me to gap the top ring at .24, and the second ring at .18, with stock oil ring gap. After taking it to the machine shop, the shop told me that they recieved info that gapping the second ring tighter than the top ring, causes the pressure between the first and second ring, to be equal to the pressure at the top of the piston. They say that this can cause the top ring to blow off the piston????? I don't understand. Can anyone help? The machine shop says this is new information that they recently recieved.

BoostJunkie

iTrader: (11)

Gaping the 2nd ring tighter than the top ring is standard procedure for NOS or Boost. The top ring is going to get hotter and expand more than the 2nd ring, therfore the need for a larger gap on top. Follow the manufacturers directions for gapping the rings, they should have different specs for N/A vs. NOS or Boost applications in their instructions. If not give them a call and them tell your engine builder to install them as the MFR instructs.

fast98

iTrader: (16)

rule of thumb is .006 for every inch of bore on a bottle motor, only on the top ring. the second ring should be tighter as stated above

etperformance

So, what do you think that the machine shop was saying?

LOnSLO

iTrader: (15)

Either - "We have no idea how to gap rings on a race engine",
or, you just misunderstood them.

BoostJunkie

iTrader: (11)

What do you think the machine shop was smoking?

Why can't they just read and follow the mfr's instructions?

I seriously doubt they know more about the metalurgy of the ring set than the mfr does.

etperformance

I agree. My thougts exactly. I just wanted to verify he may be on a pipe or something.
Thanks

427

iTrader: (3)

Current technology ring sets call for a larger ring end gap on second than top. The second ring is a oil control ring. If you set the gap tighter than top ring, pressure will build and cause the top ring to flutter when the piston changes direction.
If you check a drop in LS1 ring set you will find it is this way from the factory.
Kurt

fast98

iTrader: (16)

that goes against everything i have ever heard or been taught. i could be wrong but it is my understanding that the top 2 rings are compression rings and the 3rd is oil control. have anything to back this up? article i could read or sumthin, i'm very interested

10secondZ

iTrader: (24)

There is alot of truth to what he is saying. The .006" per inch of bore is a standard for ductile iron rings and with newer style rings they are gapped slightly larger on the bottom. For N20 still follow the .006" but the 2nd ring should see .0065" per inch. But talk to diamond and see what gaps they would reccomend for that particular ring material and purpose. Factory rings are gapped larger on the bottom...But sometimes I like to tighten them up with ductile rings.

Jason99T/A

iTrader: (21)

The 2nd ring is used primarily to scrape excess oil from the cylinder walls, not to seal combustion gasses. If you wanted to use the 2nd ring to aid in sealing combustion gasses, you would need to close the end gap on this ring to nearly 0" (i.e. Total Seal gapless 2nd rings). The problem with this, as Kurt mentioned above, is the combustion gasses get "trapped" between the top and 2nd ring, causing the top ring to loose it seal on the cylinder wall, leading to ring flutter.

You ideally want to keep all of the combustion gasses above the top ring. However, this is not a perfect world, and there will be some leakage past the top ring. These gasses need to go somewhere and getting trapped between the 1st and 2nd rings is not the answer.

Jason

etperformance

So are you saying that the gaps that Diamond gave me are wrong???
Now I am confused again....

427

iTrader: (3)

Not trying to confuse you!! The trend towards opening up the second gap started about ten years ago. There are different schools of thought on this topic from different company's. We came up with the gaps we use based on piston and ring tests we ran on gen 3 road race engines. We ran testing for HP and durability. Bottom line the factory gaps are larger on second ring and that showed the best results.
Kurt

etperformance

Even on nitrous applications?

S_J_H

I'm just a hobby guy myself. Have built maybe 10 engines over the years of different types. I used to use the old smaller 2nd ring gap method as that was what everybody did. I tried the extreme version of this method with a gapless 2nd ring design once. And let me tell you that design had the worst oil control I have even seen.
2nd ring is mainly an oil scraper.
I now use the larger 2nd gap method which is the current theory on ring gapping. The engine seems to run very clean with excellent oil control. It seems to allow a tighter top ring seal and the escaping gasses seem to help clear out the oil ring for better control.

I run .025" top and .028" 2nd on my supercharged 348.
Steve

Taspeed

iTrader: (1)

No.. on nitrous apps you really want to keep the bottom ring about .004 larger than the top ring. I usually open up the gaps a little when spraying. My high compression motor is gapped at .022 top, .026 2nd. I am also planning to spray a little shot later, so I set it up that way now. Totally N/A I wanted to be right at 18-20 top, and 22-24 2nd.

etperformance

I also run a high compression motor. This theory is the same that Diamond told me. I feel really dumb, but sometimes we rely to much on old technology. I guess that is the reason that I asked. So what about the 18 on top , and 24 on bottom?

Taspeed

iTrader: (1)

i'd go 18 and 22.

Cstraub

iTrader: (1)

Opening up the second ring will make more power at mid to upper rpm in a NA engine. . . proven fact. Even more power in a blown or NOS application. For years we have gapped the second smaller. With R&D by the professionals ring flutter was found to be a "robber of HP" in mid to upper rpm. Flutter is caused by the unequal atmosphere pressure between the top and second ring. Flutter is significant at upper rpm. ..say above 5K and on. Experimenting with 2nd ring gap, power was found by opening the second up. Amount to open 2nd ring is based on intended rpm range. Some run as much as 50% more on the second then the top.

New info on this is being published by the piston mfgs since about last year. The practice has been going on for years now.

Note, this makes power for upper rpm. For a street engine, I would go by what the ring mfg. recommends.

Chris

etperformance

This is definetly a race only application. I do appreciate the input. That is what makes LS1Tech so great.

Anyone else have suggestions on gap numbers, for nitrous applications?
Thanks to all