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Author Topic:   piston clearance
charlie_two
Dirt Full Roller

Total posts: 53
posted December 06, 2001 09:26 PM
hey guys i am running a 355 with 13/1 compression, forged pistons, 6 inch rod. about what clearance do i need on the pistons and rings. running alky

thanks

sdhnc29
Dirt Freak

Total posts: 467
posted December 06, 2001 10:35 PM
What brand of piston ?? Would need to know that before I could tell you the proper clearance .

ford5
Dirt Freak

Total posts: 298
posted December 06, 2001 11:33 PM
charlie generally you would want 4-6 thou piston to wall clearance 32 thou top ring gap 16 2nd ring gap should be ballpark

sdhnc29
Dirt Freak

Total posts: 467
posted December 07, 2001 12:48 AM
I don't mean to disagree , but if he's using JE's , then .004"-.006" clearance will beat the skirt's to death on the pistons ! If he's using a JE piston , then he'll need to run .0025" clearance , and no more than .003" . You are correct that most other brands will run .004"-.006" , but we need to know exactly what forged piston he is using to tell him what clearance to use . Also , .032" top ring end gap is more for a Keith Black piston . On a .030" over alky engine , we use .022" on the top ring , and .018" on the second ring . Not meaning to step on any toe's here , but piston to wall clearance is too critical for a ball park answer . Sorry if I offended you in any way .

ford5
Dirt Freak

Total posts: 298
posted December 07, 2001 07:28 AM
the rings dont know what brand of piston they are on?

sdhnc29
Dirt Freak

Total posts: 467
posted December 07, 2001 10:15 AM
Actually they do ! A cast piston transfer's heat to the rings at a much faster rate than a forged piston . Thus , the ring's on a cast piston expands more in the bore than a forged piston . Consequently , you must run more ring end gap on a cast piston , than you would on a forged piston . A forged piston in an engine that run's nitrous , will run at least .032" end gap , due to the instant heat load that it is operating under . But I assume we are talking about circle track engines in this discussion . The .032" end gap that you are talking about will run just fine ! But if you test your blow-bye at full throttle on a dyno , it will be substantially more than a engine with .010" less gap . So you may find a little more power by closing up your ring gap a little . There really is no reason to run more than .022"-.024" top ring end gap in a circle track engine with forged piston's .

mod257
Dirt Newbie

Total posts: 0
posted December 07, 2001 06:07 PM
What about speed pro hypers

sdhnc29
Dirt Freak

Total posts: 467
posted December 07, 2001 07:03 PM
Same with Speed-Pro hyper's ! Both Keith Blacks and Speed-Pro hyper pistons are made by Silvalite . The material is the same ! So your end gap must be larger than a forged piston .

[This message has been edited by sdhnc29 (edited December 07, 2001).]

race8k
Dirt Forum Racer

Total posts: 98
posted December 08, 2001 12:20 PM
I think the reason you need more ring gap on the KB is that the rings are higher on the piston where there is more heat.Have seen KB pistons burnt with the end gap closed up.They have instructions with the pistons.If you follow you will not have a problem.The speed pro hypers seem to work ok with normal ring gaps.

HENDRENS RACING ENGINES
Dirt Roller

Total posts: 5
posted December 08, 2001 01:46 PM
Very true ! The higher the ring pack , the more end gap you must run .

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