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Thread: Piston / Build question

  1. #1
    Mitsu booster Turbo Mopar Contributor
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    Piston / Build question

    So I rebuilt my 88 TII Shelby Z from the bottom up. Stock forged crank cut 10/10, Clevite Bearings, TII rods, MP perf head gasket, 804 injectors, block bored 20 over... I plan to run a stage 3 SMEC with a max boost of 15 psi. I will add a 2 stage controller that is switchable between a G valve set at 15 psi and line pressure which should open the wastegate around 6 or 7 psi...

    Here's where I think I royally screwed up... I used a set of Sealed Power/Federal Mogul pistons. I am not seeing anything good about these. They are not the H code pistons, but I still have now read enough to make me scared of them. Please weigh in... Thanks, Jim

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    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Piston / Build question

    I have some of the older cast Sealed Power pistons and they have done well. Just tune with prudence and they should hold up fairly well.

  3. #3
    turbo addict
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    Re: Piston / Build question

    Well, with a good tune they dont hold much over 20psi. I just pulled my engine apart, and all the top rings were broke in pieces, and one pistons had a broken ring land.

    I think you will be fine with 15 psi, but if I spent all the money like you I would spend the extra 400 and throw in some forged slugs for insurance.

  4. #4
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    Re: Piston / Build question

    Brian Slowe has a smokin deal on some JE's that IMOHO would be perfect for the build you described. No copy/paste on my phone with the link but I'll bump it so you can find it in "new threads"

    Rosie

  5. #5
    turbo addict
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    Re: Piston / Build question

    Yea I had those in a fresh rebuild with a stock mitsu running 12PSI.. Wasn't even beating on the car and lost the pistons.. I'd get rid of them :/

  6. #6
    Mitsu booster Turbo Mopar Contributor
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    Re: Piston / Build question

    Just found the post on the JE's and replied to him. Thanks for the input. I am pulling it back out to change the clutch and turbo anyway....so what's a few more bolts to turn?!?

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    Mitsu booster Turbo Mopar Contributor
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    Re: Piston / Build question

    One more question... my machine shop simply took stock bore and added 20 thousanths to it when they bored it. Will a set of 20 over pistons be fine or will I need to go back through the whole process again?!? Again, 15 psi max here...

  8. #8
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: Piston / Build question

    Quote Originally Posted by James Neidig View Post
    One more question... my machine shop simply took stock bore and added 20 thousanths to it when they bored it. Will a set of 20 over pistons be fine or will I need to go back through the whole process again?!? Again, 15 psi max here...
    Since you are now going forged you will most likely need another trip to the machine shop. You will need to check the clearances as the forged pistons require a greater clearance than cast.

  9. #9
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    Re: Piston / Build question

    never just toss them in...always check your piston to bore clearances.

    JEs are made "smaller" on purpose so the stock rings can be file fitted.

    Also, just adding .020 to the bore of what they measured was not a good thing to do at all....

    JE's are kick-azz.... but if you cannot use those in the FS section I reccomend
    TU's forged Wiseco's with pins, clips and RINGS for $450.
    Quote Originally Posted by 22mopar
    have a look at my feedback on the forum. all positive.

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  10. #10
    Mitsu booster Turbo Mopar Contributor
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    Re: Piston / Build question

    Quote Originally Posted by Directconnection View Post
    never just toss them in...always check your piston to bore clearances.

    JEs are made "smaller" on purpose so the stock rings can be file fitted.

    Also, just adding .020 to the bore of what they measured was not a good thing to do at all....

    JE's are kick-azz.... but if you cannot use those in the FS section I reccomend
    TU's forged Wiseco's with pins, clips and RINGS for $450.
    I may be a bit off on that, as the machine shop did wait to bore it until they had the pistons on hand, so they may have bored it off of the piston dims. I guess now I need to know what clearance I should have. I would prefer to not remachine it if at all possible. Can I measure the bore and order the pistons and rings off of it? I think I recall Forward Motion telling me he can order them in any size... Is this accurate?

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    Re: Piston / Build question

    Quote Originally Posted by James Neidig View Post
    I may be a bit off on that, as the machine shop did wait to bore it until they had the pistons on hand, so they may have bored it off of the piston dims. I guess now I need to know what clearance I should have. I would prefer to not remachine it if at all possible. Can I measure the bore and order the pistons and rings off of it? I think I recall Forward Motion telling me he can order them in any size... Is this accurate?
    No, not accurate.... sorry.

    You get the piston(s) measure them, and fit them to the bore. The pistons are all made with the clearances in them. meaning: a standard bore 3.445" "bore" will have a piston measure smaller than 3.445". It may be 3.4420 for a wiseco, and 3.4435 for a stock mahle cast.
    Quote Originally Posted by 22mopar
    have a look at my feedback on the forum. all positive.

    Steve

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  12. #12

    Re: Piston / Build question

    Well Im sure custom pistons take a bunch more time to get. If you already bored .020 for cast then .020 forged piston will need more clearance so you wont need boring just hone BUT if there is at least .003 and you run synthetic oil exclusively that would be okay....Venolias and Weisco will run at .003, JE should also, check though. Is you use Weisco you can order them with stock wrist piston off the shelf from TU instead of dealing with getting rods reworked.

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    Re: Piston / Build question

    Unless Venolia's have changed, they need at least .006" clearance as some were running .007" back in the day.

    JE's are .003... yet I had mine a tad more per Fm's suggestion at .0035.

    For the most part... clearances are built INTO the piston, not the bore. You open up the bore if you wish to exceed the manufacturer's reccomendation.
    Quote Originally Posted by 22mopar
    have a look at my feedback on the forum. all positive.

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  14. #14

    Re: Piston / Build question

    ^^ Yeah Venolias recommend the .006, or whatever the math says BUT I was informed that .003 with synthetic is okay, they told me this AFTER I set mine at .005, which Im sure is what most vendors advise to cover themselves. I agree for the most parts, .005-.006 will be noisy but no seize or scuffing, but kinda noisy, Im sure a search will give him plenty of reading confusion on clearance opinions...

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    Re: Piston / Build question

    I have NEVER heard of the "synthetic" thing requiring less clearances.

    I would believe if you set Venolias to only .003" you'd have seized them up for sure. Has very little to do with the oil, but moreso with the piston material and density giving it it's thermal expansion characteristics. Venolias I believe have low silicon and therefore... a more dense piston. Not as light, but possibly a strong piston is my opinion.
    Quote Originally Posted by 22mopar
    have a look at my feedback on the forum. all positive.

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    Re: Piston / Build question

    Wrong Stevo, you can set Venolia's at the low end, mine were set at .0035",

    If your tune is right, you can run cast to 30 psi, just ask the 11 sec Minivan, "gasketmaster"

    Many of us have run cast at high psi, but if you make a tuning mistake, they are ashtrays.

    15psi, just run what you have.
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    Re: Piston / Build question

    Wouldnt you put the cylinders at 3.465 if its a .020 over cast or forged? I just thought they made the forged smaller for the clearence issues.

  18. #18
    Supporting Member Turbo Mopar Contributor turbo84voyager's Avatar
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    Re: Piston / Build question

    I have been running 18 psi in my 84 mini and 91 shadow on Sealed power cast pistons and I have not had any problems. Both motors were built 5-6 years ago so I am not sure if they changed their pistons since. The shadow has been over 20 psi with a 46 trim hybrid when the wastegate froze and knock on wood its fine. If going forged take a look at wiseco's. I like mine. In my opinion it all comes down to tune. I am very cautious about tune and since I am not looking for every last bit of HP I would rather run them a little on the rich side and save the motor.

    Looking at your goals, I personally would be to not worry as much about the pistons but to make sure you use a good cal. I don't even run a custom cal in my 84 mini. I have 40+ injectors with lowered fuel pressure. I have had bad experiences with some of the custom cal's available for these cars. Also make sure you have a good working knock sensor.
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    Re: Piston / Build question

    Quote Originally Posted by Mopar318 View Post
    Wouldnt you put the cylinders at 3.465 if its a .020 over cast or forged? I just thought they made the forged smaller for the clearence issues.
    Yes! It just took you many less words to say what I was trying to

    Simo: all the oldschoolers running the Venolias in the late 90's were running them at .006-.007 One guy just posted that is in their range, so I'm not totally wrongo.
    Quote Originally Posted by 22mopar
    have a look at my feedback on the forum. all positive.

    Steve

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  20. #20

    Re: Piston / Build question

    Weisco and Venolias are made of the SAME material, and they require .0035, nothing more. FYI synthetic oils do a much better job than dinosaur guts, better lubrication means closer tolerances. If you made pistons and understood the general populace isnt going to wait for the vehicle to warm up you wouldn't tell them .0035.
    Fact-
    Fwd told me .0035 is fine for Venolias with synthetic
    Weisco has.0035 printed and included with piston kit again with synthetic
    Forged pistons are twice as strong..period

    Once the pistons and engine are hot both pistons are at the same outer dia, its during startup that is the issue because cast pistons have a steel strut cast into them to control expansion. Yes you can run 20+ psi with good gas but good luck with that, how well is octane monitored at gas pumps? You can run cheaper fuel with forged pistons and keep boost low when you want to save a few bucks commuting to work!
    Go forged and you cant go wrong.

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