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Thread: EGT thread

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    West Texas RXP skoepp's Avatar
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    EGT thread

    I wanted to start a thread on EGT (exhuast gas temperature) for our skis to help some of us understand them better. So this thread is for anyone that has any experience or input on EGT readings on our skis.
    AND for us that want to learn.

    Thanks for the input.


  2. #2
    West Texas RXP skoepp's Avatar
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    I ran my ski this weekend and my findings at WOT:

    AFR 11.9 - 12.4
    EGT 1,620 to 1,650

    That sure seems hot to me per my air fuel ratio readings.
    Looks like i need to set up my AFR at like 11.0 to 11.5 to bring my EGT temp down to a safe level or do i need to go the other way.

    Those findings were on stage 3 with 2rude at 8,550 rpm with 15.4 psi boost.

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    rxpblast's Avatar
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    where is a good spot to install the probe for this on a stock exhaust manifold?

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    West Texas RXP skoepp's Avatar
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    Quote Originally Posted by rxpblast View Post
    where is a good spot to install the probe for this on a stock exhaust manifold?
    I was told as close to the exhuast port on head as possible. Since i am running the jacketed header I had to install mine right after the header pipe next to the AFR bung.

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    Moderator beerdart's Avatar
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    I drilled mine at the flange it is not jacketed for the first 1/2" or so.
    Out of the water at idle stock fuel system stock supercharger external IC. I was seeing EGT all three 980 +/- 50 deg F
    AFR average 11.5
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    Moderator beerdart's Avatar
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    EGT Explained

    EGT (Exhaust Gas Temperature) is a very useful tuning tool when combined with a wideband O2 sensor. EGT seemed to get a bad rap when used to try and determine actual AFR (Air Fuel Ratio) because it is influenced by many other factors as well. A rich mixture will see high EGT temps because the air fuel is still burning as it gets pushed out the exhaust valve. As the AF gets leaned out the EGT will drop, but then around 14.6 it will start to go up again and even faster till the motor gets so lean it will barely run. Ignition timing also plays a major role in EGT temperatures. An overly retarded timing at a safe AFR will give incredibly high EGTs, just as overly advanced timing will also do. Excessively high EGTs can help the exhaust valves smash into the head causing deformations in the valve seat, and or burning holes in the valves. Usually a temperature of 1800F (982C) is considered to be the max upper limit and is too hot for nearly any combination. Steel will take on a reddish tint and begin to slightly soften if heated to this point. Remember that just because the exhaust temperature is that hot does not mean your headers or exhaust valves are that hot, but that they will be quickly approaching those temperatures unless the EGTs are reduced. You will also begin damage O2 and WO2 sensors at about 1650F (900C) and therefore should use this value as the upper limit when dealing with a street car with O2 and or WO2 sensors. The melting point of mild steel is about 2730F (1515C) and your headers will be dripping at that point, but you should never see EGTs anywhere near that point. Typical EGT values should be between about 1250 and 1600 at WOT. Most engines will make max power at an AF ratio between 12.0 and 13.5:1 but should be lower sometimes if detonation is a problem or high IATs are expected from a forced induction application. There is no “ideal” EGT. The optimal EGT values will change with engine combinations (cams, pistons, headers, etc). Raising the compression with no other changes will drop the EGT at the same AFR. Many times a decrease in EGT is the result of detonation. It seems counter intuitive, but all the extra heat from the detonation gets absorbed by the combustion chamber so there is less heat transferred to the exhaust.

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    West Texas RXP skoepp's Avatar
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    Quote Originally Posted by skoepp View Post
    I ran my ski this weekend and my findings at WOT:

    AFR 11.9 - 12.4
    EGT 1,620 to 1,650

    That sure seems hot to me per my air fuel ratio readings.
    Looks like i need to set up my AFR at like 11.0 to 11.5 to bring my EGT temp down to a safe level or do i need to go the other way.

    Those findings were on stage 3 with 2rude at 8,550 rpm with 15.4 psi boost.

    THanks BEERDART, excellent info.

    I am still confused on my findings. If you look at my readings at wot you would think that adding fuel will decrease temp but will then also make it too rich.

    One thing i failed to mention is i was running premium pump gas which is only 90 octane in my area.
    I just hung up with the owner of www.bndautomotive.com and he thinks by running his fuel additive (1 oz. per 6 gallons of 90 octane) will bring up the octane to 97 and I would be able to take fuel away from engine and burn more effeicently with better lower egt.

    One thing for sure, my ski is not running very efficent at those kind of egt's for what ever the reason being.

    She is not going to last very long at those temps.

  8. #8
    Ride Hard! aha's Avatar
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    Hey Beerdart thats some great info!

    Question for ya... because you have your AFR sensor mounted on your exhaust manifold do you find that your burning out AFR sensors?

    According to what you posted 900 is the upper limit for the AFR sensor but your running around 980. So I would think this would fry the AFR sensor.

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    Moderator beerdart's Avatar
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    My EGT was 980F or 526C

  10. #10
    suck my wake's Avatar
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    Quote Originally Posted by skoepp View Post
    I was told as close to the exhuast port on head as possible. Since i am running the jacketed header I had to install mine right after the header pipe next to the AFR bung.
    Beerdart's location is correct , if you put it further away like after the manifold you will get a "general" EGT temp but you won't be able to see the temps of each cylinder and that is what you really want. If you have a bad injector you will know it right away, if you put it past the manifold you won't know whats causing a high temp.

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