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EGT questions

Discussion in 'The Garage' started by m j, Jul 29, 2002.

  1. m j

    m j 1/2 ton status

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    subject is a drag car that runs 10.20
    SBC 950 Holley 3 speed auto
    EGT is exceeding 1400deg within 2" of the port
    have been trying to jet it up to reduce the temp
    what is a good EGT?
    is it possible to have gone too far in jetting and have the EGT probe reading excess fuel burning in the header? I think that this can be done in turbo cars but have my doubts in a NA with huge exhaust

    anyone have link to drag engine forums they could share? I only know Ford specific ones
     
  2. Twiz

    Twiz 1/2 ton status

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    Did you find anything on this?

    How actuarate are the EGT readings? Can they pick off a full A/F ratio change?

    A book I was reading, the guy had a I/R manifold and one of the carb jets was off (like a full 1 point off from the rest) - in the book he said the EGTs did not change in that cyl. (Take it for what it's worth, a quick blip in a book.)
     
  3. m j

    m j 1/2 ton status

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    I believe my friend bumped the timing back and has the combustion gases released before combustion is complete.
    EGT is only an indicator and by advancing timing you can reduce the readings, to a point.
    a real wide band O2 sensor is the correct way to read A/F ratios.
    as the car was recently converted to a 'street car' I need to ask more questions of him. I was supposed to be at a baby shower but had snuck over to go for a blast in his car when he was asking for my help.
    I have been studying suspensions for a long time and have not looked at engines for years.
    it was a bad thing to ride in that beast, I want I want I want.
     
  4. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    So maybe now the Rustang project will get back on track?/forums/images/icons/grin.gif

    Rene
     
  5. Twiz

    Twiz 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    a real wide band O2 sensor is the correct way to read A/F ratios

    [/ QUOTE ]
    Yeah, but you can't run raceing gas with 'em (as far as I know).
    Pretty much the same story here too, buddy's tring to dial in his nitrous system and was thinking about doing it with a some sort of EGT analizer. Sounded like an interesting way to go to me.

    Most O2 sensors (cheep ones that are most commonly used and avalible) are only acurate around the 14.5 ratio, that's all well and good. But what if your tring to dial in a richer ratio? Like 12:1.

    At some point I'd like to weld in some bungs in a set of junk headers and see how the A/F ratio is spread out across the engine. I would not be suprized to see it off by over a point or more. I think that is one of the main driveing forces behind the creation of the new genneration Vortec engines (ever see the cyl heads on 'em?).

    Just rambaling. no real point here.
     
  6. m j

    m j 1/2 ton status

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    the ones that look like ford heads?
    or are you talking combustion chambers?
     
  7. m j

    m j 1/2 ton status

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    you can run race fuel with some, that is the basis of one kinda high $$$ race ECU.
    the Speed pro one IIRC I dont recall what name it is under now
     
  8. m j

    m j 1/2 ton status

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    I am trying to keep the number of unfinished projects low(and failing)
    I decided the engine is the easy part a few years back and the chassis is where I have been trying to learn.
    the tools are the priority now.
    I think the welder was the big ticket item and the rest are a paycheck or 2 sized
    bender, notcher,
    I have the frame jig kinda covered
    the tranny is a huge $$$ item, I will probably settle for a 4 speed Jerico but build the chassis to fit a 5 speed
     
  9. Gandolf

    Gandolf 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    what is a good EGT?

    [/ QUOTE ]Engines normally operate in the Exhaust Gas Temperature range of 1,200 to 1,600 degrees F. For instance, the maximum desired EGT for turbocharged engines is normally 1,475 degrees F. So, it sounds like you may already be in the ballpark. When you say you are getting and EGT of 1,400 degrees, I'll assume you are talking F. Is this under load at full throttle, cruising on the freeway, or...? This makes a difference, but I'll throw out some theory without the answer.

    Optimum EGT with a carburetted engine is kinda a vague point because there is less efficient mixture distribution in a carbureted engine (compared with a fuel injected engine). As each cylinder receives unequal fuel charges, each cylinder operates at a different temperature. Because of this, the mixture must be sufficiently rich so the leanest cylinder does not misfire, run too hot burning the exhaust valve, or detonate.

    Unless you are reading EGT simultaneously from all the cylinders, the EGT reading should be taken from the leanest cylinder. If you could run the engine on a dyno, and adjust the mixture while it was running, you would want to lean the mixture until you achieved peak EGT (the point where the EGT temp stops rising), or until the engine begins to run rough (monitor RPM for even the slightest drop). Then, from peak EGT (or from just outside engine roughness), richen the mixture until you get a 50 degree decrease in EGT. This will be your the optimum EGT setting yielding best power and optimum fuel burn. Now, as the ambient temperature, pressure and humidity changes, the mixture setting would also need to be adjusted to maintain optimum EGT. Since re-adjusting all the time is not practical, expecially since the engine is being used in a daily driver, a conservatively rich mixture setting would be necessary to cover a wide range of conditions.

    I hope this helps you get closer to the answers to your questions.
     
  10. m j

    m j 1/2 ton status

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    good info
    I cant characterize a tubbed 10 sec car as 'daily driver'
    it spends most of its time parked in the shop and comes out to play on special occasions and for stress relief
     
  11. Gandolf

    Gandolf 1/2 ton status

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    </font><blockquote><font class="small">In reply to:</font><hr />
    ...as the car was recently converted to a 'street car'

    [/ QUOTE ]It was late and I was tired. My mind somehow converted 'street car' to 'daily driver' /forums/images/icons/grin.gif
     
  12. m j

    m j 1/2 ton status

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  13. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    I read it without registering...cool info!

    Rene
     
  14. Gandolf

    Gandolf 1/2 ton status

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    Thanks, the link worked. That guy knows his stuff. He has experience based knowledge.
     

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