Moly vs Gapless top rings
12-04-2013 | 09:35 AM
#1
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From: AZ
Moly vs Gapless top rings
So I've been in the process of building a 496 stroker and need to make a decision regarding piston rings. The pistons are ICON 2618 slugs 1/16 1/16 3/16. This is a N/A motor that should be knocking on 600hp when all is said and done. Block is a GEN V. After speaking with several knowledgable folks, it seems some love the gapless top rings, while others despise them. The variables have left me wondering... I realize the bore finish is absolutely critical. Seems guys like to use a top gapless, Napier 2nd and low or standard tension oil ring. I need this motor to last a couple hundred hours, so my interest lies in what works in an endurance application. All opinions are appreciated!
12-06-2013 | 11:09 AM
#2
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From: Little River SC
http://www.federalmogul.com/en-US/Me...S200976080.pdf
There is quite alot of information on rings out there, it can either be simple or quite; complicated. Radial tension, ring thickness, material of compression ring, cross hatch and angle, finish RA value. All things will be affected from oil re tension and A/F ratio, to much oil left on cylinder wall or washing away of oil and vertically grooving top ring or removing cross-hatch.
A moly ring will be more forgiving under bad conditions, some moly rings can have the plasma moly, blown from the surface under detonation. A Hell Fire, or harder top ring, will either wear the bore out or vertical groove, if fuel is washing cylinders down, also the face of the 2nd ring, will become worn completely across the face.
Using a gapless 2 nd ring, creates a whole other issue. Building pressure between the top and second, creates the rings to flutter and creating blow-by at higher RPMs and even worst under boost. Yes; I know the leak down is 2%, go run the engine and read the blow-by, or just vent the breather at the valve cover and not back to the flame arrestor.These gapless 2 nd will work fine in a stock racing, 2 barrel carb set-up when you need all vac to pull that intake charge in. I myself was a Total Seal or a C&A, Z gap user, this was ended about 11 years ago, when I was informed; of the destruction of the rings and ring lang. The second ring is not intended as a compression ring, it's a oil wiper.
I would probably use a gap-less top ring, in a racing application, being that this is going to be looked at on a regular basis. Using a gap-less top for the long run endurance, raises some concerns. First; the machined face in which the bottom ring sets in better be perfect, ring groove clearance in piston, the bottom ring sets .003-.005" below the surface of the top ring. Once the face of the bottom ring starts to run on the surface of the cylinder what are the consequences, going to be. Being that the top and bottom are different materials, how does heat affect the growth of the bottom ring. Remember that ring is like or about the same thing as, an oil control ring.
I either use a moly top on a NA, and a Hell Fire on a forced induction, my cylinder wall finishes are different for each ring pack. Napier 2, with low tension oil control rings. Open the 2nd ring gap .006-.010 larger than the top and you will have a sealed up combination for the long run. You can use a Hell Fire for the top also one a NA, but it stands; you better have the proper A/F ratio, or you will be contaminating your oil having blow-by.
No; I would not use the gap-less top ring, for a 200-300 hr set-up.
There is quite alot of information on rings out there, it can either be simple or quite; complicated. Radial tension, ring thickness, material of compression ring, cross hatch and angle, finish RA value. All things will be affected from oil re tension and A/F ratio, to much oil left on cylinder wall or washing away of oil and vertically grooving top ring or removing cross-hatch.
A moly ring will be more forgiving under bad conditions, some moly rings can have the plasma moly, blown from the surface under detonation. A Hell Fire, or harder top ring, will either wear the bore out or vertical groove, if fuel is washing cylinders down, also the face of the 2nd ring, will become worn completely across the face.
Using a gapless 2 nd ring, creates a whole other issue. Building pressure between the top and second, creates the rings to flutter and creating blow-by at higher RPMs and even worst under boost. Yes; I know the leak down is 2%, go run the engine and read the blow-by, or just vent the breather at the valve cover and not back to the flame arrestor.These gapless 2 nd will work fine in a stock racing, 2 barrel carb set-up when you need all vac to pull that intake charge in. I myself was a Total Seal or a C&A, Z gap user, this was ended about 11 years ago, when I was informed; of the destruction of the rings and ring lang. The second ring is not intended as a compression ring, it's a oil wiper.
I would probably use a gap-less top ring, in a racing application, being that this is going to be looked at on a regular basis. Using a gap-less top for the long run endurance, raises some concerns. First; the machined face in which the bottom ring sets in better be perfect, ring groove clearance in piston, the bottom ring sets .003-.005" below the surface of the top ring. Once the face of the bottom ring starts to run on the surface of the cylinder what are the consequences, going to be. Being that the top and bottom are different materials, how does heat affect the growth of the bottom ring. Remember that ring is like or about the same thing as, an oil control ring.
I either use a moly top on a NA, and a Hell Fire on a forced induction, my cylinder wall finishes are different for each ring pack. Napier 2, with low tension oil control rings. Open the 2nd ring gap .006-.010 larger than the top and you will have a sealed up combination for the long run. You can use a Hell Fire for the top also one a NA, but it stands; you better have the proper A/F ratio, or you will be contaminating your oil having blow-by.
No; I would not use the gap-less top ring, for a 200-300 hr set-up.
12-06-2013 | 11:46 AM
#3
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From: AZ
Mark,
Excellent info as always. If one were to order either a hellfire or moly ring pack, it seems sealed power makes it difficult to get these with Napier 2nd and low oil tension rings. Is the solution to just order the other necessary rings at a higher cost separately? Thanks again for your opinion and data regarding this topic.
Excellent info as always. If one were to order either a hellfire or moly ring pack, it seems sealed power makes it difficult to get these with Napier 2nd and low oil tension rings. Is the solution to just order the other necessary rings at a higher cost separately? Thanks again for your opinion and data regarding this topic.
12-06-2013 | 12:01 PM
#4
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From: Little River SC
Your bore size of 4.310 C&A for Hell fire top, about $18 each, oil control and napier, reg stock loose for CP. CP Pistons has all the rings in bulk or they get them for me, my ring sets do not come in the standard packaging as you typically see. Napier about $7-8 each, oil control $3-$4 each.
12-08-2013 | 03:20 PM
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From: CONCORD, CALIF
When I built my 502 I was fortunate enough to get the advice and knowledge of Bob Madera on many parts, etc.... When it came to the rings he recommended that I call someone he suggested at Total Seal. I ended up with molly top rings, napier second rings and standard tension oil rings. I believe it was the v.p. of Total Seal that I ended up talking to if memory serves me correctly.
