Egt range

Discussion in 'PSI Superchargers Tech Questions' started by Flyboy68, Oct 1, 2010.

  1. Flyboy68

    Flyboy68 Member

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    What do you guys shoot for as far as EGT spread at the end of a run? Our EGT's are within 50* of each other, but have 2 egt's that are about 50* above the others. But all together they're within 100* spread. Is this good? Or should we work to get them all even closer?

    Josh
     
    #1
    Last edited: Oct 1, 2010
    Flyboy68, Oct 1, 2010
  2. shawn davis

    shawn davis Member

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    I'd forget about the 50 degrees and read the plugs
     
    #2
    shawn davis, Oct 1, 2010
  3. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    x2

    Like Shawn said, read the plugs first. You probably won't get them perfect off nozzling alone. One cylinder may need a short rod or decked piston to get everything perfect.
     
    #3
    Will Hanna, Oct 1, 2010
  4. Flyboy68

    Flyboy68 Member

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    Roger that.
     
    #4
    Flyboy68, Oct 1, 2010
  5. wagspe208

    wagspe208 Member

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    Huh, no kidding?
    So in his case the 2 cyls with +50 degrees would need slightly less compression?
    Thanks
    Wags
     
    #5
    wagspe208, Oct 1, 2010
  6. Mike Canter

    Mike Canter Top Dragster
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    Well not so fast. One only changes rod lengths in the specific cylinders for a specific reason. Don't just start randomly changing rod lengths to balance the plug readings or the EGTs.

    Josh, read the plugs and see if they match what the EGTs are telling. If so then change those port nozzle jets one size at a time and see if you can get them closer. If you are using non-flowed jets then it may take a little more time and maybe try some different jets that are the same stamped size on them.
     
    #6
    Mike Canter, Oct 1, 2010
  7. T.A.D. 776

    T.A.D. 776 New Member

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    I agree with Mike and second that just because the jet says the same size it may flow a surprising % different.
    I also want to add some other food for thought.

    Valve event timing has an effect on EGT

    A 50 degrees lower temp could be an exhaust valve opening later in the power-stroke. Looser lash
    A 50 degrees higher temp could be an exhaust valve opening sooner in the power-stroke. Tighter lash
    Variations in rocker arm ratio.
    Variations in combustion chamber size.
    You can increase chamber size by using a Tulip head valve instead of a flat head. Easier than changing rod lengths that create strange harmonics along with changing flame fronts around the piston.
     
    #7
    T.A.D. 776, Oct 1, 2010
  8. wagspe208

    wagspe208 Member

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    Wow, never thought of all that.
    My PE boat was 75 deg high to low first time out. Plugs look close. I'll get it a little closer... to busy racing last weekend to be screwing with nozzles. I also don't have flowed nozzles.
    I am just a 8.0 boat guys, so we are not thrashing our stuff to do that.
    Was just curious.
    Thanks
    Steve
     
    #8
    wagspe208, Oct 2, 2010
  9. Dale Finch

    Dale Finch Member

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    Wow Will, lets not tip everyone over! I agree with Mike and we need to find out what we are working on here. If we aren't trying to run 5.50's here then we can get everyone off track. A competitive tuner will have the rod bearings pulled and measured every run. EGT's have really no bearing on the tune up if the bearing is not squished over a certain amount and no detonation is happening...... if you are just trying to keep everything equal then slow experimentation in very small increments is the way to go if you don't have flowed nozzles and jets. I have seen nozzles out by .003 from their original sized marking. Really depends on what you are trying to accomplish by being within 50 degrees.
     
    #9
    Dale Finch, Oct 2, 2010
  10. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    clarification

    Let me explain a little further from my experience.

    First off, I think it's wrong to go to the EGT's first. While important, plugs and bearings will tell a more accurate tale of what's happening, it's up to the tuner to properly interpret what they are saying. There's only one sure fire way of finding out what the upper EGT limit is, and that's usually burning a piston. Not everyone wants to run like that...

    If you have two cylinders within 50 degrees of each other, as I said, you may not get there with a nozzle change. Depending on the nozzle size, type of nozzles, etc, up or down one nozzle may put you back to a 50 degree difference on the other side, or create other cylinders to change their 'balance' and now you have another set of cylinders 'different'. Not saying you can't. Personally I think 50 deg is a decently tight shot group for EGTs.

    You make one change and it effects the rest of the motor because other cylinders will work harder/less as a result.

    Sometimes you may have a cylinder that lags behind the rest on EGT, then when you pinch it it goes from cold to burning the ground strap off.

    As mentioned on here, flowed nozzles are a must if you're really trying to balance an engine. Non flowed nozzles could be off a few thou in either direction, so when you think you're leaning it, you may be richening it, or vice versa.
     
    #10
    Will Hanna, Oct 3, 2010
  11. wagspe208

    wagspe208 Member

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    Roger, Thanks.
    I am only making 800 to 1000 hp to run the number. Hell, we don't squish the bearings. This is not my world. I was just wondering for information. I am a one small step guy anyway and we have been running this combo for years. It is pretty close. I just wondered how good was "good".
    Thanks
    Steve
     
    #11
    wagspe208, Oct 3, 2010
  12. Greg Kelley

    Greg Kelley Member

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    egt's

    I'm with the "within 50 is great" crowd
     
    #12
    Greg Kelley, Oct 6, 2010

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