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clearance

  1. #1
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    Default clearance

    How much clearance do you need between Piston and steel head for safety?

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    Senior Member Futs's Avatar
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    I would be more concerned about piston to valve clearance clairence!!!!

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    .040 if using steel rods.

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    Village Idiot fc-Pilot's Avatar
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    That is a very loaded question. Steel heads vs. Aluminum heads does not make any difference. Do you mean Steel rods? Also the make-up of the pistons makes a big difference. For instance, with cast or hyperutectic pistons you can run slightly tighter clearances due to having less piston rocking. Also, where the engine will run in the RPM range will make a difference also.

    So here is the questions,
    What rods does it have?
    What pistons does it have? Also bore size?
    What crank does it have?
    How many RPM's is it going to spin?

    OK guys, what else did I forget?

    Paul

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    yeah .040 for steel rods and iron block...but way 2 many factors. If your concerned about total safety set it at .060.

    rpm, bore size,piston clearance,,arghhhhh the list goes on and on

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    How much is the piston going to rock?

    Are you chasing optimum quench?
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    Quote Originally Posted by fc-Pilot View Post
    That is a very loaded question. Steel heads vs. Aluminum heads does not make any difference. Do you mean Steel rods? Also the make-up of the pistons makes a big difference. For instance, with cast or hyperutectic pistons you can run slightly tighter clearances due to having less piston rocking. Also, where the engine will run in the RPM range will make a difference also.

    So here is the questions,
    What rods does it have?
    What pistons does it have? Also bore size?
    What crank does it have?
    How many RPM's is it going to spin?

    OK guys, what else did I forget?

    Paul
    Rods are steel. Forged Sealed Power pistons. Bore size 4.310. Forged GM 4.00 stroke. 6500 RPMs.

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    Quote Originally Posted by Infomaniac View Post
    How much is the piston going to rock?

    Are you chasing optimum quench?
    No . Problem is exhaust side of top of piston catches edge of combustion chamber in open chambered head 119 cc. So i need to die grind a little clearance in one spot on each chamber. I think Sealed Powered had these 12.5 to 1 pistons made in China. Piston to wall clearance is .005. My thought was .040 clearance minimium. Thanks for the imput. Pat

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    Village Idiot fc-Pilot's Avatar
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    Quote Originally Posted by Wicked Performance Boats View Post
    No . Problem is exhaust side of top of piston catches edge of combustion chamber in open chambered head 119 cc. So i need to die grind a little clearance in one spot on each chamber. I think Sealed Powered had these 12.5 to 1 pistons made in China. Piston to wall clearance is .005. My thought was .040 clearance minimium. Thanks for the imput. Pat
    .040 could be OK, but I would shoot for .045 for that setup. If you were keeping the RPM's down around 5000-5500 I would say .040 would be fine with that piston clearance, but if you plan on running 6500 than .045 would work well and provide a good squish.

    That is just my opinion though as that is what I have used successfully.

    Paul

  12. #10
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    Quote Originally Posted by Wicked Performance Boats View Post
    No . Problem is exhaust side of top of piston catches edge of combustion chamber in open chambered head 119 cc. So i need to die grind a little clearance in one spot on each chamber. I think Sealed Powered had these 12.5 to 1 pistons made in China. Piston to wall clearance is .005. My thought was .040 clearance minimium. Thanks for the imput. Pat
    Just because you have to do a little grinding on the chamber doesn't mean the pistons were made in China. There dozens of different chambers. And when you trying to push 12.5 to 1, TRW/SpeedPro, Sealed Power, shoved that dome all the way to the edge. Some chambers just aren't "open" as others. You want to clearence issuse. Try that piston in an Edelbrock head!



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    I've had to grind out the chambers for clearance (and a little unschrouding
    of the exaust valve since I was there) on a set of trw 2399 small dome
    pistons! glad I check things like that, cuz you would think a trw would
    be considered a replacement piston, ya know?

  14. #12
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    Quote Originally Posted by Blownjet 468 View Post
    I've had to grind out the chambers for clearance (and a little unschrouding
    of the exaust valve since I was there) on a set of trw 2399 small dome
    pistons! glad I check things like that, cuz you would think a trw would
    be considered a replacement piston, ya know?
    I agree. Mine are 2307. Supposed to be replacements for ls7 12.5 to 1 pistons. Gm didn't grind on them! And i Have 990's heads, largest combustion chambers from factory. This was supposed to be a simple build. guess nothing is easy.

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    Be especially leary of anything that fits out of the box.

  16. #14
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    Only .001" when everyting is at max load, max rpm, max hp, max piston rock, etc.
    Very helpful, huh?
    Wags

    (OK, steel rods, not sloppy bores, .040 min)

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