I'm looking for some advise on maximum and minimum ring end gap. I've installed the top compression ring in each cylinder about 1 inch and I'm measuring .024 and a maximum of .026 on another cylinder. The motor is a freshly bored and honed mildly modified (no NOS) 396 .60 over with TRW 2240 non forged pistons. Using the calculation with bore size and .0045 as a multiplier I come up with .019 as the target end gap. My question is how much can I get by with on maximum end gap before performance and reliability suffers? Thanks in advance for any advise.

You mentioned that the TRW pistons were non-forged. Are the pistons the hyperutectic variety? Because if they are the gap shold be set a little wider as the heat will be higher when using them. You do NOT want the rings to expand to the point where they touch.

The gap that you measured isn't too much out of line for a cast piston and definitely not if the piston is the hyperutectic variety.

John

Kid,
The only way to get the exact gap you want is to use file fit rings. .024" is probably what you will generally get with a stock type set of rings and will not cause a problem. The only Hyperutectic pistons that require a big top ring gap are the Keith Black ones because of thier construction. I do know the Federal Mogul hypereutectic's use a normal ring gap. I dont have my catalog here at home but I thought the L2240 pistons were forged. You may want to check the part number, I will try to remember to check in the morning. Even if they are forged the ring gap should be the same. Hope this helps, e-mail me if you have any questions.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Kid,
The TRW L2240 pistons are definitely forged piston, just thought I would let you know.

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Bill Koustenis
Advanced Automotive Machine
Waldorf Md

Bill,
Thanks for your help. This is my first engine build and I'm basically trying to follow along with books I've purchased. I aquired the motor disassembled and I assumed the pistons were non forged by the number of 2240NF on the top. Although I failed to include the "NF" on the first email which is my fault. I ordered a new set of rings because after further inspection I found one package had (2) 2nd groove rings and no top compression ring??
I went ahead and ordered the fileable rings from Jegs. Should I file those to the .019 gap or should I go wider? Just to give you a little more info my engine is a 396 .60 over with Lunanti 221/230 @50 500/510 lift cam. Stealth intake, 750 BG Sports Claw, 1970 vintage 290 heads with 219/188 valves, pocket porting and headers.
Thanks again for all your help.

Ring gap is determined more on usage than anything else. The tighter the gap, the better the seal, the better the seal, the more power you make... To a point. Close em up too much and you'll "Black death" (seize) the piston. Typically .004 per inch of bore diameter is widely accepted by most builders and manufacturers. You can get a lot of differing opinions on this, but your combo is straight forward. .018 to .022 is just fine for what you're doing. (I'm assuming 90% street, 10% race). If you use nitrous, you'll need to open em up more because nitrous increases cylinder pressure. If you call any ring manufacturer, they almost always will ask you what your intended use is (Boat, car, race, daily driven, etc.). When all else fails and you get too many differing opinions, call the manufacturer and go with what they tell you. You can't go wrong with .019 though. By the way, your combination is excellent!

[This message has been edited by Glenn Kent (edited 01-11-99).]