I haven't done any EGT measurements for the last 3 races, and then I broke a motor at Barber Motorsports Park on 3 April. The motor failure was because the epoxy plugging the stock intact port broke out in chunks, injested in the motor, and cracked the apex seals, so I rebuilt the motor. This time I decided I better monitor EGTs to make sure everything was all right.
The EGT's were pretty hot at the last race on my 13B peripheral port road race engine. It was leaning out from 8000 to 9000 rpm, and the EGT climbed to 1770 deg F. The EGT probes are about 12" downstream of the engine header flange. They are type K thermocouples, inserted to a depth of about 1/2" into the 2" stainless steel ISC header. I was using a Longacre digital readout, and I had the readout calibrated at our lab, so the data is real.
My buddy/competitor Dave Jones about fainted when I told him how high my EGTs were; he says his 12A pp motor makes best power with EGT below 1600 deg. Dave's engine builder, Jesse Prather was there too, and he couldn't believe how high my EGTs were.
Also at this race was Jim Downing and Rick Ingman; I asked them, and Rick said he preferred keeping it down around 1600 deg, but that it might be okay as high as I was running it.
My car made great power (300 rwhp) and ran strong, winning the HSR GTU class at the Mitty at Road Atlanta May1. We had 10 GTU (under 3 liter) cars show up this time, 7 Porsches and 3 pp Mazdas. I was even with or slightly faster than the best of my competition on the long back straight at Road Atlanta. Lap time was 1:36.4; not bad for a 26 year old tub chassis.

What does your PP 13B motor run for EGTs?

Am I about to overheat and overstress my motor internals?

Could my high EGTs be the result of combustion going on in the exhaust pipes due to exhaust over-extraction by my hand built collector?

Has anyone experimented with thermocouple location; how far downstream of exhaust flange; and what effect that has on EGT numbers?

I know I need to find some smaller air jets for my Weber, so that I can richen up the top end. I am running 270 main jets and 100 air jets; the 100 was the smallest size I could find so far.

 

Sorry, My PP is running yet, so I cant share any data. But I do appreciate the info you have provided.

Are you PP's MFR's or Homemade?

 

When dyno tuning i place the thermocouples about 2-3" from the exhaust flange to get a good reading.

Rotaries can have egt's in the 1600-1800 range so IMO your readings are normal but on the high side. If everyone is telling you that they make max power at 1600 then, with all things being equal, do what works for them.

 

I am outrunning the guys who have their EGT at 1600, so I would be backing up if I did what they did

 

i ran SCCA GT3 Nats for 22 years, the last 6 years ( 83-89 ) for Mazda. Roger Mandeville built my motors for 3 years and Daryl Drummond for 3 years... my motors were frontline big bridgeported drysumped etc.

they were dialed in on Roger and Daryl's dynos and made best power at 1750 measured 6 inches from the port.

power band 7000 to 10,000.

only one failure in 6 seasons when we went one click too much w the final gearing at Road Atlanta and popped an apex seal...

i don't see a problem. you might look very carefully at your timing... maybe a bit more advance.

good luck and keep on truckin'

howard coleman

 

i ran SCCA GT3 Nats for 22 years, the last 6 years ( 83-89 ) for Mazda. Roger Mandeville built my motors for 3 years and Daryl Drummond for 3 years... my motors were frontline big bridgeported drysumped etc.

they were dialed in on Roger and Daryl's dynos and made best power at 1750 measured 6 inches from the port.

power band 7000 to 10,000.

only one failure in 6 seasons when we went one click too much w the final gearing at Road Atlanta and popped an apex seal...

i don't see a problem. you might look very carefully at your timing... maybe a bit more advance.

good luck and keep on truckin'

howard coleman