Supertech Piston Rings: concern about 'up'
#1
Supertech Piston Rings: concern about 'up'
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
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
#5
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.
#9
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.
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.
#10
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
Why mix and match pistons and rings?
Over the years we have tried just about every piston and ring pack available. We are looking for the same thing you are. Long wear, perfect oil control and of course good power. OEM ring tension is about 15lbs. The NPR rings that Supertech supplies are less than half the ring tension of OEM. That's great for power and lower oil temps but leads to greater oil consumption than OEM. We have found the best overall compromise between power, service life, oil consumption, and oil temps in an OTS (off the shelf) piston and ring is to combine these two brands into one kit. Take advantage of our endurance racing experience. The Wiseco rings cost a few bucks more than the NPR's but they are worth it.
Over the years we have tried just about every piston and ring pack available. We are looking for the same thing you are. Long wear, perfect oil control and of course good power. OEM ring tension is about 15lbs. The NPR rings that Supertech supplies are less than half the ring tension of OEM. That's great for power and lower oil temps but leads to greater oil consumption than OEM. We have found the best overall compromise between power, service life, oil consumption, and oil temps in an OTS (off the shelf) piston and ring is to combine these two brands into one kit. Take advantage of our endurance racing experience. The Wiseco rings cost a few bucks more than the NPR's but they are worth it.
#11
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?)
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?)
#12
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?
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?
Data Acquisition Guaranteed | irtelemetrics.com
#14
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?)
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?)
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