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Is this a good rule of thumb for engine exhaust temperature

  1. Mar 19, 2011 #1
    I have done a basic test on my car at idle and have found that the exhaust pipe temperature just hits 100 deg C eg boiling point of water 1050mm away from the exhaust port.

    Is this a good guide to exhaust gas temperature?
    Can you compare other engines using this method?

    I also can hang on the the exhaust pipe for about 1 second at a distance of 2450mm.
    At the end of the system the pipe is just warm eg you can hold continuously.
    From other information on another forum the temperature at the exhaust pipe exit will burn you hand and mine does not.

    PS I am claiming about a 78% increase in mpg.
    Its been said here in this forum that I might be lucky to get another 5 % in thermal efficiency.
  2. jcsd
  3. Mar 19, 2011 #2
    The exhaust pipe temperature is NOT what matters most. What you want is the temperature of the gasses inside. Some headers have coatings inside and out that are designed to keep the gasses hot, and minimize transfer to the metal so that the gasses are less dense and in theory easier to push through the exhaust system. You can drill a hole in your header, weld on a temperature probe, and accurately measure the heat of the exhaust gasses probably a good bit better than your current method.

    What methods are you using to increase fuel efficiency?

    here is an EGT probe you can use: the clamp on one down the page a little:


    then weld up the hole you made when you're done.
    I don't believe measuring the outside heat is the best basis for comparison because in my experience it can vary a lot based on many factors. When I had a stock exhaust it would be SO hot it would burn the skin right off me. I switched to a carbon fiber slip on exhaust and I can hold it all day.
  4. Jan 7, 2012 #3

    My header's have no coatings as far as I know.

    My method involves raising the compression to about what todays engines are running.
    You could say I have made minor changes to the inlet port but thats all I am saying, But the information is on the net of what I have been up to..But the pics are no longer there.

    You can still have a look at my strange engine timing graphs.
    As far as I can tell the curve runs a pretty straigth line, unlike a normal engine where the timing reaches its maximum at around 1/2 red line revs.
    This roughtly linear timing thing, I am not sure if is good or bad though but it is different.
    Second engine timing graphs
    Note: most of the graphs go to 10 000 rpm my engine only does 7300 rpm with valves bouncing.

    Is this a slight improvment on using my hand to test exhaust temperture?
    I know its not as good as EGT probe though.
    Testing the external tempreture of the manifold near the head with 60/40 solder any sort of indication of what is going on inside?

    The other problem is the 2 cars, one has extractors and mine has cast iron, if this makes the test invalid then don't bother with the links.

    Maybe someone with nothing to do could get some soft solder (60/40) and do a similar test on an engine with a cast manifold at idle after operating tempreture has been reached. Thanks in advance!

    The first test on wagon.

    The second test on wagon.

    Note: the patch of white on the exhaust manifold, used to be cheap blue spray paint about 3 years ago and hasent compeletly burnt off yet.

    The second test the on other engine.

    The third test on the other engine.

    The tests on this engine the solder melts really quicky and the flux smokes like its on a soldering iron unlike the wagon where it takes forever to just melt with very little flux fumes.
    Last edited by a moderator: Sep 25, 2014
  5. Jan 7, 2012 #4
    Proper ignition timing relies on numerous variables, not simply rpm.

    Exhaust temperature is influenced by many things, and trying to compare temperatures between different vehicles is pretty much meaningless.


    What are "extractors" -- tubular headers?
  6. Jan 8, 2012 #5
    Thanks for your answers pantaz
    Tubular headers is what I mean by extractors
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