sdminus

I m about to get a digital egt gauge to assist my tuning. I was thinking of tuning to my presumed max egt with lambda in mind. What is idea peak exhaust temp i want to see. Also would this temp be universal to all rotaries ( i would think it would be ) ie all types of port.



Scott

Lynn E. Hanover

It is a function of everything that is going on during the combustion process, including when and how it got started. It is used along with an oxygen sensor to quickly get into the "sweet spot" power wise, where the best performance for that time and day may be recovered.



Since it is the end result of a bunch of inputs it changes with air temp, density, pressure and ignition advance, split if any, RPM and of course mixture. If there is a turbo involved, then turbine inlet temp, or TIT. My favorite temperature.



So once you have such a gage, how do you tune with it?



Can you tune at all? You must have a carb or if injected, a method of controlling the mixture at points along the RPM range. I would limit this tuning to full throttle tuning only where you show off the equipment.



EGT equipment is of little value in the part throttle situation. There is just very little information to be recovered. The first thing you notice is that the gage goes up and down just like the tachometer. And just as fast. So, you need help with data recovery. A friend to watch the gage for you, and, or, a movie camera to record EGT and tach at the same time. In the race car I have a small dash and gage set on the passenger side just for the movie camera to watch. The driver will not bring back any usefull data about the engine.



You can run up the revs to whatever the test RPM is, say in third gear, and left foot brake to hold that RPM for a second at full throttle. It may be that this will upset the car so badly as to make it dangerous, so tune it on a dyno if at all possible, or with the camera idea.



I have been instructed by a world famous engine builder that NA readings above 1600 degrees are not usefull for long term reliabillity. So I don't do that. There are some who go well above that and the apex seals are fine, and then one day the engine goes soft with a warpped seal, and then who do you call?



Don't call me. I told you not to do that.



Here are some example numbers from a NA 12A with bridgeports and a free flowing exhaust. Note the relationship between EGT and mixture ratios.



6500 173.3 HP 1515 front 1491 rear A/F 12.3

7000 196.9 HP 1518 front 1489 rear A/F 12.0

7500 218.2 HP 1517 front 1494 rear A/F 12.1

8000 233.9 HP 1522 front 1511 rear A/F 12.6

8500 239.2 HP 1543 front 1540 rear A/F 13.0

9000 241.9 HP 1583 front 1578 rear A/F 13.2 BSFC .662 oil temp 167 oil pressure 105. Timing is 25 degrees.



And this is with a carb! Note the A/F for each EGT. Note that the carb is going lean at the top, where injection should be dead on the tune all through the range around 12.7 or so, or whatever your builder wants you to run. Remember if you premix, leaning is removing top oil as well. Note also how low the EGTs for best power are.



Changing timing, mixture, RPM, air temp and whats in the glove box will change EGT. Just so you know, best power is just rich of peak EGT. And that can be real hot maybe 1800 degrees. It can also melt an apex seal and or detonate a turbo engine. I am always shooting for less than 1600 just before the driver shifts.

Peak power is 245 HP at 9,400 RPM.





Lynn E. Hanover

sdminus

Wow Fantastic write up



Im going to be tuning a turbo charged engine. The reason i want the egt is because im tuning with Lambda methanol injection. Im confident about my ratios but want to try and get the best from my set up with the additional safty of the egt gauge.



Im am hoping to hook the egt up to my datalogit so then i will have egt, Wideband 02, Knock etc



would you still reckomend just shy of 1600 degF at the shift point on a turbo rotary.



Im impressed with the power of the 12A motor you have. Do you have any pics of it

Scott

Lynn E. Hanover

Since the turbo adds back pressure, there may be room for a bit more temp across the apex seals. A rotary turbo expert can give you the range. They want extra energy to help spin up the hot side. The turbo MFR will have a limit for TIT Turbine Inlet Temperature for each unit. That limit may be more than the apex seals can deal with, so ceramics is the way to go. Or, perhaps RWS metals seals.





I only know about NA rotaries. The turbocharger makes it a different animal. If you followed my rant about the engine changing displacement while the head space stays the same. They are just dying to detonate all of the time the boost is up. Anyway the Methanol will be a big help for that. The fuel will be absorbing a bunch of the heat and you need about 30% more fuel to get the same BTUs. It also creates a lot of acid and washes down the oil film rather quickly. I don't know if it can carry any premix.



When I raced Karts we ran it with food coloring and nitro, or just bought model airplane fuel. Missile mist was my pet brand. Our fuel tanks were clear plastic, and it was a blast to show up with red gas or black gas. And the stuff runs real good. Caster bean oil and keep her rich or die.



It would be good if the controller could ****** away advance with each Lambda hit, so as to keep the apex seals in it. Ceramics if you can afford them.



The pictures are on discs all over here. Lost two hard drives and all of the picture files twice. There are pictures on Nopistons, but where I don't know.





Lynn E. Hanover