5efe pistons on 4e block

Discussion in 'ENGINE' started by elton, Dec 15, 2009.

  1. elton

    elton Registered User +


    As far as i can remember during my last rebuild, i purchased a set of pistons which were domed on top. I skimmed em flat already, probably from a 5efe. Jut aftermarket 74.5mm ones.

    Queestion is, after shaving em flat, whats the compression now? Will the pistons be reliable for .9bar?

    I was thinking that if the pistons were domed shape, will the top material be thinner than the top of a stock 4e piston after skimming? Or was the dome made just 'thicker' and not 'higher' than a stock 4e dished piston?
  2. weeJohn

    weeJohn Paid Member

    Did you not work out how much to skim off to get the compression you wanted or did you just hit them in a mill?

    There are calculators out there but you will need to know the distance your piston crown stops at tdc in relation to the block deck, and the size of your combustion chamber in cc`s.
  3. elton

    elton Registered User +

    I guess not mate... engineering shops and workshops do not work like how they do in your country. No offense, but we do very much less calculations.

    I totally shaved it off till its flat, until the lowest part of the top of the piston.

    Will it last?
  4. finx

    finx Paid Member

    sounds like 5efhe or 5efe pistons.
    if they were correctly machined they should handle .9bar no worries as long and the rest of the set up and the tune is up to scratch. its impossible to give you an exact compression ratio because we dont know how much you took off the pistons.

    do a cylinder compression test and that will give you an idea vs stock comp ratio as to if its higher or lower
  5. elton

    elton Registered User +

    alright. will do a comp test when i am free..

    Well, i can confirm its a 5efe piston, just shaved till the the whole dome is gone. Not as low as the valve pockets, but just till the lowest part of the crown.

    here's a pic:

  6. elton

    elton Registered User +

    is the thickness of the metal on top of the crown still as thick as the top of a 4efte's piston crown? Or is it much thinner already?
  7. billybob

    billybob Untrusted Seller

    you mybe should shave them more ,you get a compression of 200 psi if useing a standerd gasket mybe,it will be higher than a standerd 4e compression,looks like there was .8 just took off them
  8. elton

    elton Registered User +

    well, no plans of high boosting. indeed i understand that it may be harder to tune a piggyback with high comp turbo.

    Well, im using a 4efe gasket, which makes the compression much higher. 4efte head gaskets are .2mm thinner than the 4efte as far as i can remember.
    The head was skimmed off 0.25 as well if im not mistaken.

    These pistons are 74.5mm.
  9. finx

    finx Paid Member

    thats an odd set up indeed. there is no chance in hell anyone could guess what the comp ratio is without having a compression test done and then working it out.

    billybob no offence but you are just speculating as to how much has been shaved off those pistons.
    its impossible to tell by just looking at them they would have to be measured and know exactly what engine they were from to begin with for any kind of accurate measurement to be taken so we can tell how much they have been shaved. if they were fhe pistons for example there would have been allot more than .8mm taken off them to get to where they are now.

  10. elton

    elton Registered User +

    ok guys, screw the compression. Will it be reliable then? Like i asked again, the thickness the top crown compared to a stock 4efte piston
  11. weeJohn

    weeJohn Paid Member

    Boost it and find out, no one knows with the info you provided.
  12. elton

    elton Registered User +

  13. finx

    finx Paid Member

    there should be no problems with stregnth of the piston in relation to the thickness of the crown and its chances breaking.
    what will cause it to be more prone to damage is the fact that it sounds like a very high compression set up. so you must be cairfull about a few things.

    ignition timing
    i would be backing it off a bit to be safe. last thing you need on a high compression boosted engine is pre ignition as it will stuff things doubble quick due to the heat and pressures in the cylinder.

    spark plugs
    put some deicent cold plugs in it (not irridium) standard type heat range 7 at least and a low gap to help reduce detonation (pre ignition)

    run as higher octain as is available to you. this is a main player in weather the thing implodes or lives to see many a day.

    and finnay boost level
    make sure you are running a reliable boost controler. electronic preferably so inceasements in boost levels are accurate. and to reduce chance of spike or creep as these will bring an end to your top end i very quickly.
  14. elton

    elton Registered User +

    thank you for your advice.
    Will keep those im mind. I plan to go .9 bar. Guess have to change the plugs.
    Well, I'll be wiring the Haltech Platinum Interceptor next week.
  15. Odain

    Odain Fresh Recruit

    4efe pistons in a stock 4efte.. Head gasket keeps blowing
  16. gorganl2000

    gorganl2000 Registered User +

    did you check the head and block for flatness?
    is your car tuned (ignition and fuel)?
  17. Skalabala

    Skalabala Registered User +

    Your compression ratio will be close to 0.4 points above stock.
    Yes those pistons will work no problem. However you need good fuel and timing.
    Also only try to use Hastings piston rings.
  18. Skalabala

    Skalabala Registered User +

    The ignition timing will be to high for the new CR, its safer to use 5EFE pistons.
  19. suzieboy

    suzieboy Fresh Recruit

    yup I experienced this using the high comp pistons. The high compression is gr8 for daily and spools turbo fast. It would work but you cant trash it if its not tuned correctly.
    1 out of 2 tings happens or both. Broken ringlands and/or blown head gasket.

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