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Egts climb fast help

Discussion in 'GM Diesel & DuraMax' started by RAYSRANDP, Oct 5, 2010.


    RAYSRANDP New Member

    I have an 86 box truck with a 6.2 in i ported the intake and exhaust the
    i also fabed a set of headers 3 in off the header straight pipe went a eigth
    turn on fuel all glow plugs are good no black smoke its fast now no prob going up hills barely on the pedal i asked about porting on here and no one could give me a straight answer. So i just went for it wow what a difference do i need to do something with the timing no odd noises it has 410 gears maybe they need to be changed or maybe just need more air in?
  2. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    With Diesels if you increase fuel you need to increase incoming air or you'll get increased EGT's.
    You could try a water injection set-up to bring EGT's down or an LPG injection will help the burn and bring EGT's down if you tune it right.
  3. Crawdaddy

    Crawdaddy Epic Member Staff Member 5+ Years 1000 Posts Platinum Contributor

    I can't say I'm terribly familiar with how diesels work, would increasing the boost that the turbo puts out add more air to the mixture allowing it to drop the egt some?
  4. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Increasing Turbo boost could help reduce EGT's by introducing air to the mix, it would lean out the mixture with the added air from the boost. Depending on how efficient the intercooler is you can lean out the mix by adding an intercooler.
    Cooling the incoming air (with out an intercooler) would also reduce EGT's due to the size of the air molecules (larger charge of incoming air theory). Problem is I believe you'd need to cool the incoming air by about 20-30 deg. to get the desired effect.

    Truthfully though the best method might be to back off the fuel to a mix that works well as a compromise.
    With the porting he's done I'm not sure if the EGT increase can be fully blamed on turning up the fuel.
    While increasing the exhaust flow he might have changed the head structure enough to start building heat due to less metal to suck the heat off the exhaust and by speeding up the exhaust flow (kinda like when you speed up the flow of a radiator it doesnt cool as efficiently).
    While it isnt all bad it's probably gonna take some time and testing to find a happy medium to work correctly.
  5. stephan

    stephan Rockstar 3 Years 5000 Posts

    Glad everything worked out with your porting and you are happy with the results. You never did reply to my que. about the % ratio valves to ports on your other thread. Did you measure before you put it back together? I'd be interested to know the ratios...

    Why are diesels so much different than gas engines as far as c.c.t.'s cooling. When my gas engines EGT's start climbing I have to richen my mixture to bring them back down. (I have to add more fuel, usually waaaaay more fuel)
    My diesel knowledge is almost 0% ha ha, so can you explain in terms I'll understand. Ray has increased his air flow a lot by porting so why doesn't he need to richen his mixture to match it in order to bring his EGT's back down?

    RAYSRANDP New Member

    I opend the exhaust port to 28 mm by 31 mm i only went back 26 mm and the transitioned the
    port a lil more so it wasnt so sharp i only ported the intake manifold not the head it runs great. This is a na motor am afraid to add turbo now maybe to much power for the motor as for percentage got me just grabed die grinder went to town got the dimensions off a site that deals with hummers just did what they said srry they say 250 hp bout all this motor can take but with these few mods power seems to be where it needs to be i am a hands on guy i have another motor out back that i been useing for mock up i hope i didnt do something wrong thanks
  7. stephan

    stephan Rockstar 3 Years 5000 Posts

    Ok, from the other thread you started I thought you were porting the head too....
    Anytime you can FEEL the difference in power this is a monumental gain and a welcome result for all your hard work. Congrats :)
  8. tbplus10

    tbplus10 Epic Member Staff Member 5+ Years 5000 Posts Platinum Contributor

    Diesels can burn everybit of fuel and air you can force into them, in proportionate amounts, if the mix isnt kept balanced and gets to lean or rich it will heat up the EGT's.
    Most of this has to do with the fact that a Diesel engine creates it's own fire for the stroke, this means the fuel air mix needs to be very volatile to burn evenly, but Diesel fuel isnt very volatile so the mix has to be almost perfect to create a powerful and complete burn.

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