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1G Piston to wall clearance !

Posted by SasaniFab, Jul 11, 2020

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  1. SasaniFab

    SasaniFab Freelancer

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    THis topic has been discussed a bunch of times. My friends came over recently and we discussed the specs they planned on running for their new build. The ptw clearance ended up being over .008 with ring gaps in the 30s . I don’t think this is a good idea even when using forged internals. Have any of you heard anyone running this wide of a clearance and been successful?
     

    Street Build 4K  20

    1992 Eagle Talon TSi
    645 whp · 498 lb/ft · 1G DSM
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  2. bastarddsm

    bastarddsm Proven Member

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    Mendota, Illinois
    That's pretty sloppy. My old shortblock is up near 0.007" now, and it seems to not have very good oil control. Still made good power though.
     

    Showcar Build 6K  1

    1991 Eagle Talon N/T
    9.805 @ 144.00 · 1G DSM
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  3. donniekak

    donniekak DSM Wiseman

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    Surprise, Arizona
    It depends on the piston. Not just material, but design.

    A slipper skirt piston will flop around a lot more than a full round. The amount of “barrel” to the shape matters a lot to.
     

    Street Build 4K  0

    1991 Eagle Talon TSi AWD
    manual · 1G DSM
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  4. SasaniFab

    SasaniFab Freelancer

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    They are standard arias pistons , that seems like a lot of clearance , at that spec I can’t imagine you need to file the rings
     

    Street Build 4K  20

    1992 Eagle Talon TSi
    645 whp · 498 lb/ft · 1G DSM
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  5. motomattx

    motomattx Proven Member

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    wampum, Pennsylvania
    You could expect collapsed skirts or cracked skirts and oval cylinder walls with that type of clearance, thats way too much.
     

    Drag Race Build 4K  24

    1995 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  6. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    Just for reference, I built a Small Block Chevy Corvette 327 back in the 80's. Didn't have the $ to bore and get new pistons back then. One cylinder had .011 PTW clearance and others were well beyond normal but that was the largest PTW. It had factory cast 11:1s and the skirts had been knurled to bring them back out a bit for less slop, needless to say it should have been bored and new slugs.
    I ran that motor to 8k in my 1973 V8 Vega, threw a 150 NOS shot on it and it never gave me any problems. Ran great and really never even used oil.
    I agree with others that .008 is to much PTW but wanted to tell the story so you know that they will run but it is a crapshoot on if it will hurt pistons under pressure. Since a SBC piston has more of a skirt then a DSM piston, it held up and didn't rattle around like a DSM piston will.
    Here was the car it was in, circa 1985.
    Pops
    Dads V8 Vega front .jpg Dads V8 Vega back.jpg
     

    Street Build 5K  29

    1992 Eagle Talon TSi AWD
    14.74 @ 117.04 · 1G DSM

    1K  14

    1990 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM

    793  18

    1967 Chevrolet Camaro RS
    rwd · automatic · Misc Vehicles

    Street Build 1K  7

    1998 Eagle Talon TSi
    fwd · manual · 2G DSM

    Street Build 6K  14  25

    1990 Eagle Talon TSi AWD
    13.620 @ 108.460 · 1G DSM
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    buddahboost likes this.
  7. motomattx

    motomattx Proven Member

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    Oh the Vega and the Pinto, what were the companies thinking back then? they did end up being good for engine swaps though I guess, you see them with big hp engines at every track, they should have just made them with V-8's when they were new, then there was what the Vega Cosworth or something? some high performance version?
     

    Drag Race Build 4K  24

    1995 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  8. SasaniFab

    SasaniFab Freelancer

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    And I thought .005 was a lot of clearance, I’m looking forward to seeing what happens when they start the engine. The real problem around here is that if you are looking for machine work done your going to wait 2-3 months. They didn’t wanna wait that long so instead of over-boring they honed with a torque plate.
     

    Street Build 4K  20

    1992 Eagle Talon TSi
    645 whp · 498 lb/ft · 1G DSM
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    1990TSIAWDTALON likes this.
  9. motomattx

    motomattx Proven Member

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    2-3 months is the norm for about any machine shop in the summer, maybe even in the winter around here, that kind of stuff needs to be planned and the block dropped off asap when your planning a build of any type, people are too impatient these days.
     

    Drag Race Build 4K  24

    1995 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  10. SasaniFab

    SasaniFab Freelancer

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    My machinist usually can have stuff back to me in 2/3 weeks
     

    Street Build 4K  20

    1992 Eagle Talon TSi
    645 whp · 498 lb/ft · 1G DSM
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  11. 1990TSIAWDTALON

    1990TSIAWDTALON Moderator

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    We have alot of dirt tracks around here and my machinist is a good month or more on wait time also. Alot of LS stuff in that place and a big old Buick straight 8.....
     

    Street Build 5K  29

    1992 Eagle Talon TSi AWD
    14.74 @ 117.04 · 1G DSM

    1K  14

    1990 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM

    793  18

    1967 Chevrolet Camaro RS
    rwd · automatic · Misc Vehicles

    Street Build 1K  7

    1998 Eagle Talon TSi
    fwd · manual · 2G DSM

    Street Build 6K  14  25

    1990 Eagle Talon TSi AWD
    13.620 @ 108.460 · 1G DSM
    Loading...
  12. Buddy2

    Buddy2 Proven Member

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    I think going by piston manifactor recommendations on clearances is best way to go as there is alot more than diameter of a piston at play. Ring gaps has more room to play depending on boost and compression.
     

    348  9

    1992 Mitsubishi Eclipse GSX
    awd · manual · 1G DSM

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    1992 Mitsubishi Eclipse GSX
    manual · 1G DSM

    633  8

    1995 Mitsubishi Eclipse GST
    fwd · manual · 2G DSM
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  13. jed344

    jed344 Supporting VIP

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    That is a very large PTW. i target .0045 normally with a build that will be seeing some serious duty. I have heard of people running .005ish, but never that large.
     

    1K  38

    1997 Mitsubishi Eclipse GSX
    awd · manual · 2G DSM
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