Well i've been slowly "street" tunning my GTU to increase my milage while I wait for my daily driver to arrive. At the moment I'm achieving about 20.05mpg right now. Today on the way to work driving on the highway i noticed that at 2300-2700rpm I get about 710 Celcius at WOT and a little higher(maybe 720) at low throttle(~29-35% throttle). I turned down the fuel using the AFC II i have installed 1% @ Hi and 2% @ Low throttle. It helped a bit but i'm still far from my personal target of 760 Celcius at WOT. My question is though since its rather low RPM does EGT cool-off in this range? I haven't got the time to dyno it yet with the local shop's sniffer so I don't have AFR readouts yet, though I plan to soon If you all have observed cooling of EGT readouts how far does it cool? BTW this is all with old spark plugs would replacing with new ones increase or decrease EGT?

 

i'm no expert by any means, but you've got a TII and are aiming for 760? from my understanding rotaries run EGT's a decent bit higher than piston engines, and i used to run 800-840 on a turbo DSM with no trouble. from what i know, i think 760 is way to low of an EGT for WOT(read: pig freaking rich)

 

its an N/A.

 

Yeah the boost is off for about another week. I'm just trying to refine the map for now.

 

Well I cut back another percent or two on each point in the relevant range I noted and its sounding/looking better. The exhaust note actually changed a bit.

 

760 is low?

well in my TII my EGT sensor is on the dp and at WOT it was about 670-720

at low around 30% as 1987RX7guy said it is usually at 550-600

 

Yeah my Probe is about 6-10" away from the exhaust port on my rear rotor housing.

I'm using Ted's numbers for TII as a base he said 740 was *probably* safe for a turbo ap. So for a non boosted N/a I figured another 20* celcius will be ok without AFR confirmation.

 

Damn, my GTUs ran around 780 at cruise, and WOT was damn near 840-860.

 

Well, in my opinion, in the 21st century we have much better data that we can use for tuning besides EGT's. Tuning by EGT's is so ridiculously pointless. But I'm sure there are people who will disagree with me on this one.

In my opinion, tuning via EGT's is right up there with logging AFR off the stock o2 sensor.

 

That is correct.


-Ted

 

Sorry, but I gotta call you a dumbass.

So tell me then...what other option do you have for monitoring the engine when tuning fuel and ignition timing?

Sorry, we can't afford combustion pressure tranducers that costs thousands of dollars!


-Ted

 

Owned by Ted. In all actuality, what are the benefits of tuning with an EGT vs a Wideband?

 

They both have their benefits, and usually should be used together. Generally a EGT is good for determining too much advance/etc (since it'll run considerably hotter/etc), which a wideband can't tell you.

 

What exactly is an EGT telling you? Certainly not combustion chamber temperature, since the temperature measured is probably almost 1000° lower than CC temperature. So you've got a read on exhaust gas temperature... I'm not sure I see the benefit in that. Considering that both changing the air fuel mixture and changing the timing will affect EGT, I don't see any useful info coming from the gauge, other than the rare event that EGT's skyrocket because something is majorly AFU. Add in the slow response and relatively poor accuracy of an EGT probe, and you've got one worthless gauge there. Like I said though, just my opinion.

To answer your question Ted, I'd use a wideband along with a knock sensor. Now I know on the TII the knock sensor isn't very good, so I guess I don't have a complete answer for you.

 

So you ran that hot at WOT how come it cooled when cruising? I doesn't make sense to me :/ Normally I see a temperature increase in all situations going from WOT to cruise.

 

FWIW i've always noted that Rotary engines need to run more fuel to run properly compared to piston engines. Which is one reason they use a lot of fuel.

 

EGT shows change with ignition timing changes.
EGT probes don't fail with leaded gas.
EGT probes will normally outlast any wideband sensor.

The wideband, when in good condition, will react faster to fuel delivery changes / problems - I give you that, but for total tuning, it's useless for adjusting ignition timing.


-Ted

 

Hey man.

You probably see your AFR getting hotter at cruise because the AFR is much leaner (Closed loop stoich!), and the timing is much much more advanced I dont know yet, I havent installed my EGT yet. I got the wideband in the car now, and I have the EGT sitting on my desk, so I'll get you some definitive answers later :O

The other thing to consider, still have an airpump in there? That will probably muck with EGTs :O