Four ring pistons

All of the four ring style pistons I've dealt with are cam ground. These are all NOS or NORS.
The fourth ring does nothing to stabilize the piston skirt, the ring is free to float in the ring land.
I'd still leave it out. With a nice honed bore and your cast rings, you'll not have any need for the fourth ring.
Martin.
 
Just to keep the record straight here I had the chance to check after I posted about the OEM pistons being "cam-ground" and they are definitely done on a cam profile. I wasn't able to check during the day!

Thanks, Gary in N.Y.

P.S. Having established that fact I would stand by my post and use the 4th ring. It isn't something we've tested and if we did choose to leave it out we would most likely remove that section of the piston. I would say this issue would most likely be a customer choice.
 
Russ/40 said:
First, this is just my opinion, but let's think logically for a moment. I believe talk of reduced friction as the result of eliminating the fourth ring, or as encouragement to delete the fourth ring, is total nonsense. The difference in perceptible friction as the engine is turned by hand has no bearing on the amount of friction occurring in a running condition. Rings, like everything else in a running engine, float on a film of oil. If they didn't, they wouldn't last two days. You can delete the fourth ring, but why if you have it on hand? JMHO
Click to expand...

And I repeat, it's making a mountain out of a mole hill. I'd bet a dyno pull would not show any measurable difference.
 
Harry and Russ, Just curious, have either one of you built and engine without the fourth ring? My concern here is not so much reduced friction, but that the top rings may be compromised by "too good" oil control caused by modern rings and bore finishes as reported by others here.
 
Yes I have run three ring Pistons, but not in an stock engine. Ran them in a pop up configuration. They were the Grant set in Ross Pistons.
 
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