Mudflap

I've got a set of Supertech rings (GNH8400) and the "N" marking, which I am certain defines which way faces towards the top of the piston, is on the side opposite the inner chamfer. In other words, when installed per their instructions, the inner chamfer is facing the bottom of the piston.

Nearly every reference I've found about top rings say that the chamfer is supposed to be facing the TOP of the piston. Does anyone have experience with this?




Thanks

cal_len1

Any pictures? I've never seen a negative twist top ring (chamfer on the bottom), and I design them for a living. My guess is the chamfer is on the top side (positive twist).

Mudflap

I figured someone would ask for pics. Those rings are probably too tiny for my crappy camera. I'll try.

Mudflap

UPDATE: I got on a microscope to look very closely. Turns out the chamfer is tiny and it is on both sides. With my simple magnifying glasses I only could see the one consistently.

So that's a different question: shouldn't this have an appreciable chamfer on the top side?

Thanks Cal

cal_len1

If the chamfer is the same on both sides, it could just be that they are not trying to put a twist on the rings, this is fairly common in gasoline engines. Not all rings have twist, and we could discuss why the chamfers are there if you would like. I would say install them the way the instructions say, and don't worry about it.

Girz0r

iTrader: (1)

For what it's worth, those rings possibly will cause issues down the road due to the lower tension vs oem.

IMO, I'd use the wiseco xx rings.

Mudflap

I'd like more info on both issues. The twist is something I don't understand (why design it to even do that) and what is the chamfer for?

Other issue: Supertech piston rings. Why are wiseco superior? Tension? What do you mean?

ryansmoneypit

iTrader: (6)

Tention.. all about the tention. XXX around these parts.

cal_len1

For example, let's look at this gasoline engine top ring:



Notice how the chamfer is on the top side of the ring. When you cut out the material on the top side of the ring, it takes away stiffness from that side of the ring, and causes it to twist up. IOW, when you see a chamfer on the inside of the ring, it will twist to the side of that chamfer. More directly, this means that if the chamfer is on the top side, it will be positive twist, and if on the bottom side, will be negative twist.

Now, let's assume that cylinder pressure is 2000 psi, as that's probably typical of a new engine today. The top ring will see all of that pressure as it is exposed to the combustion gas. When the pressure starts to build, the back edge of the ring contacts the groove, creating a sealing of the combustion gas. At this point, the ring is flatted to the bottom of the groove, because 2000 psi (picture B). As the cylinder pressure dissipates, the ring will twist back up to it's normal state (picture B).

Reminder, blow-by is really just combustion gases that have leaked by. If the top ring has a good seal on the bottom side, the blow-by comes from flow through the end gap.



The reason a ring manufacturer would use positive twist on a top ring, is because at times when the cylinder pressure is not as high, the ring seals blow-by a lot better.


Consider a top ring with negative twist (chamfer on the bottom side). You can see that there is a gap a the back of the ring for which cylinder pressure can build up under, and possibly lift the ring. This would mean the ring would seal very poorly, and blow-by would be significantly higher. High blow-by will be noticed as a power loss, as you are effectively losing compression.



I hope this helps. Middle rings also have rings with twist, but that's a whole other subject.

Girz0r

iTrader: (1)

The supertech rings are known to have a lower tension (than oem) against the wall causing blowby and oil leaks into the cylinder.

I went with 949 Racing's recommendation presented on their page. I have had zero issues with my pistons so far. No oil leaks and no burn off from my motor build. Oil level stays the same after each change.

Link: https://supermiata.com/supertech-pistons-miata.aspx

Mudflap

Cal:

Thanks so much for the very clear description. Question: How are these evaluated and designed? How would they even know how these are behaving in those locations? Are they some how measuring or monitoring the ring positions? Or do you guys use some kind of simulations?

Girz:
I'm doing a full "no expense spared" build - I've got the supertech rings installed and ready to go. Would you throw those out and replace with Wiseco right away??

Anyone else out there believe that I should spend the $120 (total cost) to replace the rings or should I just stick with the Supertechs?

(I just tossed the stupid Supertech valve seals.. Now I'm going to toss the rings? What's next the pistons?)

cal_len1

They are designed using software mostly. Something like AVL EXCITE Piston and rings, or Ricardo also has a software too. However, I have done actual measurements of pressures in between the rings, and their axial position in the groove. These guys provide that equipment, along with tons of other crazy stuff.
Data Acquisition Guaranteed | irtelemetrics.com

Mudflap

Sweet measurement techniques for sure. Burying the tiny measurement equipment and sending the data out via RF. Very cool stuff.

andyfloyd

Definitely do the wiseco rings instead. Do it now while the motor is apart.