baronbob

I have flown airplanes with EGT's for 36 years. Here is what I know about combustion heat and mixture. Take one state of the engine for this discussion, W,O.T. Apart from detonation, excessive heat will kill your pistons and or your exhaust valves unless you are cooling with fuel. The temperature in your combustion chamber will go up with leaning to a point (happens to be the peak) then the temperature will go down with further leaning but you do not have enough mass flow to take the heat away from the two parts I mentioned (piston & exhaust valve) This latter state is called lean side of peak (bad side to be on). What you want is to be on the rich side of peak where you have Mass Flow (created by a richer mixture) to take the heat out the exhaust. The important fact is, where is the peak not what the temperature is. Here is why. You can't really properly measure the temperature due to thermo losses related to probe positioning and conductivity to surrounding heat sinks (metal). What you can do is to see where the peak is relative to leaning and once you find it then richen by 50deg or 100deg to be safe. The person who was testing with increased pressure and the temp was rising was on the right track as he was on the correct side of the curve. leaning made the temp rise. He might have been too close to peak however so you should keep leaning until the temp drops and then you know that you are on the lean side of peak. Now richen the mixture until you see the temp falling and you are now safe. These gages are not accurate enough to give you an exact temp, but you should not care because all you care about is peak and any Gage in most any location will show peak. The more expensive gages for airplanes only show a star near peak and no numbered gradations except bars on 50deg increments. If all this is too confusing call me @ 530 587 4700 Baronbob

mcollinstn

BaronBob

What about max cruise fuel economy. Where should
your EGT's be in relation to peak?

And on supercharged marine motors, many guys run too close to detonation to safely play with trying to find peak EGT since detonation will cause temp spikes that a cheap gauge won't identify properly.

boom

HPJunkie

I get 1350 on the # 2 cylinder at the port in the manifold and 1300 on the #7 in the mani at the port. At 3000 rpm the probes run about 1100 deg./1150 deg. The reason its on the 2and 7 ports is because those are the 2 pistons that melted last time. Greg

Nordicflame

I see about 1150-1200 at 3500 rpm and 1250-1300 at 5500 rpm.
This is at ~7.5 lbs gauge and ~5 lbs absolute manifold pressure due to altitude (5000 ft).
9.25:1 static compression ratio.
91 octane.
Timing vs absolute manifold pressure is 34 at 0 lbs, 33 at 1 lb, 32 at 2 lbs, 31 at 3 lbs, 30 at 4 lbs and 29 at 5 lbs.
A/F is 13.5:1 at idle and gradually ramps to 10.8:1 at WOT.

The beauty of a FAST ECU and wide band O2 sensor

1400 sounds a touch high. Follow Kanook's suggestion and up the fuel pressure on the one motor and see what it does.
Another twist is that I've also heard that too much fuel (and also lack of timing) can also cause excessive temps.

Dave

blown formula

This weekend I am going to have to check my EGT probes to see how far they are stuck into the manifolds.
At 3000 rpm there is about 300* difference between the two engines.... everything else is the same on both engines so maybe it is something along those lines. No other way to explain it that I can think of.

cobra marty

NordicHeat, Why so rich at WOT? How do you like the FAST ecu? What wiring harness did you use? Do you use the knock sensor? I think that it is my next venture.

Nordicflame

Marty,
I went with the suggestions of Dustin and a few others. It works out well and I have very little transom soot after WOT runs. I'd rather be a tad on the rich side anyway.
The harness came with the ECU and I use an aftermarket MPI set up.
I'll try and attach a picture...
PM me if you have any questions.
Dave

Kanookstr

Blown F. try swapping probes and swapping the wires on the guages, If the 300° swaps along with it. then you know its not the engine. It's either the probe or gauge. Then swap the gauge wires again, if it stayed on the same side, then you know it's the probe.If not, then it's the gauge.
Good luck

Bob280Silencer

Check your timing also.Late(retarded) will cause high egt.ALWAYS pull a plug to see if it agrees with your egt.Guages & egt probes are just for reference,plugs don't lie.Bob