EGT and MPG

[RICE RACING]

Originally Posted by 88turboii

so i just got an EGT gauge and have been observing.. it runs pretty hot at cruise around 1600F. timing is about 25 deg at 2.5krpm to 30 deg at 3krpm

so is there a relationship between EGT and best gas mileage? or can you not detect a sweet spot with EGT?

My RICESP runs following:

Light cruise 780 to 840 deg C (in backwards English IMPERIAL scum units this is 1544 deg F

This is with an AFR of 14.7:1

There is a direct relationship between AFR and EGT (and fuel usage and BSFC < economy to power) I set my RX7 to between 15 and 14.7:1 up to 100kpa absolute (0kpa gauge pressure). This returns the lowest amount of fuel usage in my case.

IF you set the AFR from lean or stoich to slightly rich (excess fuel) you have far far worse BSCF but you have much lower EGT, to give you an example if you set the AFR to 13:1 you can drop the EGT around 100deg C.

For me on inclines where load goes to around 25kpa (gauge pressure) I can easily run stoich, but power suffers and also EGT goes much much higher (simple mass flow here, and not enough fuel cooling the motor & turbo) and the EGT will go to your kind of levels or even higher to 950degC, so what I do is progressive set the AFR rich to around 13.0:1 and keep the EGT constant at my target 780 to 840 degC or lower..... this while not giving MAXIMUM economy (lowest BSFC) it does give highest power and lowest stress on the turbine and engine... with very acceptable fuel economy

If you start dumping fuel at a higher rate you will watch the EGT fall drastically, but you will also watch your fuel gauge drop in a similar fashion