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  #1  
Old 10-28-2003, 12:54 AM
FARGO318 FARGO318 is offline
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Default Need to change ring gap for nitrous?

Hello everyone,

I built my 360 with KB107 hypereutectic pistons, and of course, opened the ring gap up to the nessesary gap, I think it was 17 thou but I cant remember exactly what it was, the normal naturally aspirated gap. I want to drag my truck next summer, and to get the truck REALLY movin down the 1/4, I wanna use a 150hp shot of nitrous. My question is, do I have to open up my ring gap to the nessesary gap that KB recomends, or can I leave it.

I put quite a bit of money in this motor, and Im in school, so I dont have a whole lot of time to tear the motor down and re-gap new rings/hone the block, but I also dont wanna pull a piston top off and blow my motor.

Whats the deal eh?
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  #2  
Old 10-28-2003, 01:21 AM
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Much too tight, you'll break the lands.
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Old 10-28-2003, 01:36 AM
FARGO318 FARGO318 is offline
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Yeah, thats what I think I set the ring gap too, dont have the guide anymore and the web sites currently being updated. If anyone knows what normal ring gap is for KB pistons please let me know, I think I remember doing 17 thou which sucks though cause now I got a lot more work to do before summer rolls around. Aww well, its a good pastime.
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Old 10-28-2003, 09:59 PM
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mdeane mdeane is offline
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For the KB 107's to get the exact top ring gap you need to know the bore size. For a standard bore the end gap for a normally aspirated street engine should be .026 and for a nitrous application it should be .032. The formula is bore diameter x end gap factor with the end gap factor being .0065 for normally aspirated and .0080 for nitrous.
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Old 10-29-2003, 03:17 AM
FARGO318 FARGO318 is offline
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Thanks mdeane
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Old 10-29-2003, 04:02 PM
b-1ken b-1ken is offline
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David Reher wrote an article about ring gap in the National Dragster last year. He said he runs his Pro Stock engines at about .025". He said if the engine made any more power by running them tighter he'd certainly do it. On the other hand I spoke to an engine builder some time ago, who built some pretty fast 440's and he said that my ring gap of .014" was too loose! I use .015" with my 800+ HP B-1 engines which have a bore size of 4.375". I don't run nitrous but they do have a compression ratio of 13 - 14:1. I would definitely err on the loose side if I were you though. I would think that .025" would be plenty.
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Old 10-29-2003, 06:58 PM
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mdeane mdeane is offline
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The reason for the larger than normal end gap on the KB pistons is because of 2 things the top ring has been moved up on the piston to accomodate the accumulator groove between rings one and two and the hypereutectic material transfers heat differently then a forged piston. If you do not use the end gap recommended by KB you run the risk of the top ring butting up against itself during expansion and causing the ring land to break. I have been working with KB pistons for about 10 years now and the only real failures I have seen were created by not giving enough ring end gap.
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Old 10-29-2003, 08:00 PM
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In the list of failures of KB hypereutectic pistons, the following covers complaints #1-100:
"No, I didn't read the instructions."
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Old 10-29-2003, 09:18 PM
b-1ken b-1ken is offline
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Quote:
Originally posted by mdeane
The reason for the larger than normal end gap on the KB pistons is because of 2 things the top ring has been moved up on the piston to accomodate the accumulator groove between rings one and two and the hypereutectic material transfers heat differently then a forged piston. If you do not use the end gap recommended by KB you run the risk of the top ring butting up against itself during expansion and causing the ring land to break. I have been working with KB pistons for about 10 years now and the only real failures I have seen were created by not giving enough ring end gap.
How much gap do they recommend for a 4.350" bore?
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Old 10-29-2003, 09:52 PM
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"The formula is bore diameter x end gap factor with the end gap factor being .0065 for normally aspirated and .0080 for nitrous."

Normally aspirated = 4.350 x .0065 or .028 gap

Nitrous = 4.350 x .0080 or .035 gap
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Old 10-29-2003, 11:54 PM
FARGO318 FARGO318 is offline
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Yeah mdeane, I was aware of the KB's heat transferring properties, but thought maybe enough people ran it that there was not a problem. It wasnt 17 thou that I opened the gap too, but 27 thou. I know KB states 2 different gaps for nitrous and natural, but I thought that I could sneak away with a few shots down the 1/4 a few times a year.

I'm not looking for the easy way out, just wondering

Thanks a lot for all the replys, much appreciated.
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