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Thread: Motor blown on dyno tune...??

  1. #76
    Junior Member Grease Monkey The GW's Avatar
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    Default Re: Motor blown on dyno tune...??

    hey guys, resurrecting an old thread here
    went in with the blown head gasket i took from my motor (as pictured above) to the mechanic to show him, now keep in mind im not trying to flog a dead horse i just want to find out what happened to my motor and i am also learning.

    we put the engine back together, didnt touch tune on haltech, base timing the same and distributor was marked and put back to the same. took it for a drive...still detonated on boost. retarding distributor a bit eased it, so its clearly ignition making it detonate.

    i told him this, as expected he said things had changed with the motor since id had it apart etc. questioned him over the gasket itself and said i believed it looked like detonation and he said that he thinks itd be impossible for ignition to cause the evident damage as only the outside ring of the gasket is exposed....he said if ignition causes a gasket to go it usually splits or blows the gasket out, and mine didnt look at all like this?? asked what may have been problem he said he thinks head may have lifted.

    it has been dyno tuned before, no problem, motor was professionally rebuilt with new head studs etc 6000 ks ago, torqued and retorqued correctly...when i dropped it there had not one symptom and no leakage. by the photos, do you guys think ign still couldve caused the blow out?

    regards,
    grant
    1984 SA63 Celica - RIP , 1979 Ford XD - The Lunar Lander
    1972 TA22 Celica - Project Car ,1986 ST162 Celica SX - Gone
    1985 RA65 Celica - Me & ryleys rally car
    1974 TA22 Celica - Current project, 1972 TA22 - Wetish

  2. #77
    Sucks to be a Domestic Engineer YelloRolla's Avatar
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    Default Re: Motor blown on dyno tune...??

    I have had problems with the head bolts stretching and allowing combustion gas past the fire ring as per your pics. In my experience this has always required at least some detonation to cause it to happen.
    This is why I went and had custom head studs made, combined with o rings to improve teh margin for failure.
    YelloRolla's KE20 1/4mi = 11.32 @ 119mph @ 22psi on slicks
    12.44 @ 113 mph on 165 wide street tyres
    210rwkw - not bad for a smelly 3TGTE running pump fuel.

  3. #78
    Not in the diner Alf! Conversion King RyleyMA61's Avatar
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    Default Re: Motor blown on dyno tune...??

    these were aftermarket bolts that were around 6000/7000kms old... could they still have stretched? unfortunately we didn't measure them when it was apart... do aftermarket items have a higher tensile strength than standard ones?

  4. #79
    Junior Member Grease Monkey
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    Default Re: Motor blown on dyno tune...??

    Quote Originally Posted by Ryley
    these were aftermarket bolts that were around 6000/7000kms old... could they still have stretched? unfortunately we didn't measure them when it was apart... do aftermarket items have a higher tensile strength than standard ones?
    With the amount of junk metric fasteners around you are asking for trouble. If they are not ARP or genuine, don't use them !

  5. #80
    ......... Carport Converter jeffro ra28's Avatar
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    Default Re: Motor blown on dyno tune...??

    Just to throw another spanner in the works.

    iv had first hand experience with my old boss's twin plug 430 C.I.D. blown alcy engine.

    From engine dyno testing (2090hp.1600ft/lbs), firing both plugs at 28 degrees btdc and firing only one plug at the same timing did NOT make any difference to power, nor torque. However, experimentation with wasted spark and firing the exhaust(closest to exhaust valve) after the intake plug saw improvements of up to 200hp(10%).


    But from first hand experience with a dyno it does not make measureable difference (large scale, cause of high horsepower) having two plugs(fire at same time) rather then one.

    End rant

  6. #81
    is the bestest Conversion King LeeRoy's Avatar
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    Default Re: Motor blown on dyno tune...??

    Correct me if im wrong but i thought the consensus was that the twin spark was to help deliver a more complete burn and for better emissions due to the combustion chamber/piston shape.
    Daily Driver: Red Ae93 Project: My TA22 - now with 3s-gte
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  7. #82
    Junior Member Grease Monkey off-road's Avatar
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    Default Re: Motor blown on dyno tune...??

    Piston engine aircraft engines use twin plug. It obviously mainly for added reliability but also increases power.You are able to select each plug and both as part of pre-flight checks and selecting 1 only results in about 100 rpm drop from 1800rpm.
    These motors were built before anyone new what emissions were.

  8. #83
    Junior Member Carport Converter Billzilla's Avatar
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    Default Re: Motor blown on dyno tune...??

    Quote Originally Posted by off-road
    Piston engine aircraft engines use twin plug. It obviously mainly for added reliability but also increases power.You are able to select each plug and both as part of pre-flight checks and selecting 1 only results in about 100 rpm drop from 1800rpm.
    These motors were built before anyone new what emissions were.
    .... because they have shitty combustion chambers and those chambers are something like 130mm+ in diameter - That makes for a flame front that takes to completely fill the chamber, so twin plugs having two ignition sources helps things along a lot.
    FWIW if you go back to one magneto in flight there's not a huge rev drop, say, 50rpm - 100rpm.
    www.billzilla.org
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  9. #84
    Sucks to be a Domestic Engineer YelloRolla's Avatar
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    Default Re: Motor blown on dyno tune...??

    Quote Originally Posted by Ryley
    these were aftermarket bolts that were around 6000/7000kms old... could they still have stretched? unfortunately we didn't measure them when it was apart... do aftermarket items have a higher tensile strength than standard ones?
    A head stud is not a head bolt. I had them made as there was no listing from ARP - OR as pointed out by rms, you would be mad to use anything but. The head studs that I had made were made by the same company that makes them for Sainty Engineering, they have been made from 4140 and have been heat treated to 38Rc. They utilize rolled threads and have 1/2 x 20 UNF top threads, M12 x 1.25 bottom and correspondingly larger shafts (and therefore torque values). Head studs offer higher clamping force for a given torque value, and while I cannot comment on the material that the standard bolts are made from, I can state for certain that the ones that I use have worked as intended. I am almost out of them and I am considering getting another run of them made - these will be made from a superior material to the 4140.

    Head studs do not cure the massive cylinder pressures caused by detonation though, they only increase the tolerance for error.
    YelloRolla's KE20 1/4mi = 11.32 @ 119mph @ 22psi on slicks
    12.44 @ 113 mph on 165 wide street tyres
    210rwkw - not bad for a smelly 3TGTE running pump fuel.

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