Piston Ring End Gap [Archive] - Chevy Nova Forum

: Piston Ring End Gap


SeventyNova
9th-June-2007, 10:33 PM
I just file fit my Total Seal rings according to the instructions that came with the rings. For my 4.030 bore with 150 hp Nitrous they were:

Top - Bore X 0.0060" = 0.025"
2nd - Bore X 0.0045" = 0.018"

I then opened up the instructions for my SRP pistons and they had a section on ring gap. They say that "the second ring end gap should always be larger than the top ring end gap" They say for street nitrous which I am guessing would be similar to up to a 150 shot that I should set the gap at:

Top - Bore X 0.0050 = 0.020"
2nd - Bore X 0.0055 = 0.022"

Which is right?

I have allready filed them to Total Seals reccomendation so the top one is going to stay at 0.025" or higher but should I take the 2nd one up or what?

Tubbed63
9th-June-2007, 11:50 PM
In my oppinion I would call srp on monday and speak with them directly. If it were me I would go by what the piston manufacturer says. They are the ones that know how there pistons expand and react to differing situations.

I would leave the top ring gap alone where you have it now. But I would open the 2nd ring up to .022 like srp says to do. Lets face it here being off .005 on the top gap isnt going to make any difference at all. ;)

veno
10th-June-2007, 01:27 AM
I have PC rings and Probe SRS pistons I am running .022 top and .024 bottom. according to PC after some dyno testing that have found measurable HP with the larger second gap. so any time I can gain a measurable HP with so little effort why not take full advantage. and NO sauces ( N20)

Real McCoy
10th-June-2007, 09:20 AM
In the old days I use to go with a larger top gap when on the bottle. When I did the new 565 Duggins told me if I was going to spray it heavy to open the bottom gap bigger than the top. He's pretty smart about what works in todays world and NOS and he said the top ring gland will lift from no place for the pressure to escape if the bottom ring is not a bigger gap. I gapped my .043 wide ring set at .022 top and .024 bottom with no bottle. He said to go .032 top and .036 bottom if I was going to spray it. That's the info I got. RM

stock z/28
10th-June-2007, 09:27 AM
Hello,

My limited concept of the top ring gap is that you want it about as tight as you can get it with out it butting. That's the tricky part. Obviously when the load is highest the cyl temps are the greatest and the ring expansion the most, so you have to compensate for that on the gap. In my opinion the "exact" gap may vary a bit (even from cyl to cyl) with each application.

The piston manufacturer is best source of general guide lines for basic gaps. It may make a significant difference if the piston is coated or not as well.


On the second ring gap, for about the last 8 years or so the trend seems to be a wider second gap to "vent" top ring leakage quicker. It seems differential pressure between the top and second ring (high pressure above the top ring) "blows" or forces the the top ring out against the

cyl wall. If the top ring leakage is allowed to equalize between it and the second ring, you effectively have no "pressure forced" seal of the top ring.

That is why more and more pistons are machined with a small accumulator grove between the top rings to add volume, and increase the amount of leakage that it would take to equalize pressure.

I wouldn't recommend it but I leave the second ring ring out on a lot of drag race engines. This adds volume and cuts drag. its not for someone who doesnt like taking engines out and apart though.:)

The increased second ring gap is one of the reasons I personally hardly ever use the gapless style second rings. It seems to increase high load blow by and generally slow most cars down.

In general I try to use about the lightest tension top ring (in racing applications) I can get, and try to get the maximum pressure seal of the ring.

That's also the main reason for gas ports in pistons.


Remember these are just the ramblings of distraught individual, please regard accordingly.


Jeff

69NovaSS
10th-June-2007, 09:32 AM
that is good info Jeff, thanx;) :)

Paul Wright
10th-June-2007, 12:03 PM
The SRP specs are for conventional rings. Use the Total seal specs when using their rings.

stock z/28
10th-June-2007, 12:19 PM
Hello,

You know Paul, the only concern I have with exclusively following the ring manufactures specs is that sometimes they dont differentiate gap variations based on piston material. The KB and Silvolites are a good example of this.

I would think that normally an SRP would use more conventional gap settings, but Im not sure.

Whats the material used for the total seal rings in this case?

I have spent a lot of time on the phone with piston and ring companies on this issue, and In my opinion you kind need info from both especially if you are adding NOs-etc.

But I tend to complicate about anything.

Jeff

SeventyNova
10th-June-2007, 01:06 PM
This is the info on the rings from total seal:

Part Number : CR3690 35
(CR) Classic Race sets feature ductile iron plasma moly top rings conventional 2nd rings & 3 piece standard tension oil rings.

I emailed their tech to see what they think I should do.

How does the piston material effect ring expansion and end gap? It seems to me that the rings are independent of the piston and that the expansion of the ring and resulting end gap should have little to do with the piston, it would be more a function of ring material and temperature. The only way I can see it mattering is if the varying piston materials dissipate the heat differently resulting in different ring temps. What am I missing?

stock z/28
10th-June-2007, 02:18 PM
Hello,

Pleas bear in mind these are only views and are certainly no facts of any kind.

When the KB pistons (I know yours are SRP) hit the market the piston material supposedly "reflected" heat in to the chamber apparently raising cyl termps and causing massive differences in what was allowable for top ring gaps before they would butt. Im just using this as an example of how various piston alloys and/or coatings can effect cyl temp by reflection (I guess) and varying abilty to transfer heat to the cyl walls and/or the rings themselves.


Some of the engines I build I use larger gaps on certain cyls just because experience has showed me that the cyl temps (under very high load) typically will be higher with the this specific engine/fuel combination.

I know very little, or possibly nothing about piston design or aluminum alloys etc., so I usually depend on what the guys who make them recommend. In my opinion even the skirt design can effect the piston temp.. Some of the pistons I use are ground to have very minimal contact with the cyl wall to try and reduce loaded drag.

I guess Im rambling here, its been a tough couple of days sorry. Any way thats how I think piston design/alloy may have an effect on ring gap.

SeventyNova
10th-June-2007, 05:25 PM
stovk z28 - You might have a point about the reflecting and the various coatings, I don't know anything about piston design and was just thinking that after a period of time running two different chunks of aluminum would heat up to the same temperature.

SeventyNova
11th-June-2007, 10:24 PM
Total seal came back with:

"I would go .022-.024"" on the top ring and about the same on the 2nd rings. this should work great."

So I guess thats what I am going to do.