The utility of EGT depends on application. On the comp car I tuned the run was over in just over 7 seconds, and we shut the engine off at the end of the run so the plugs were a better indication of what was going on in the engine. The A/F was always rich, especially when running Q16, and the main issue was to avoid detonation. The EGT sensors told you if you were down a cylinder, but that was about it. In a different application (like towing, or in an aircraft), the EGT's would be at steady state and would provide much more useful information. In a drag race car, not so much. The conditions and loads are changing so quickly the EGT is "behind" where you should be looking.

One thing to clarify, though. Diesel engines control output by injecting fuel into very hot air, they do not detonate per se. They are compression ignition engines which do not have a knock limit because they only compress air, not air and fuel. Diesel engines are limited by mixing -- if too much fuel is injected during the cycle it cannot burn and you hit the "smoke limit" where black smoke comes out of the exhaust. Spark ignited engines compress a combustible mixture of air and fuel, and initiate the combustion event with a spark. If the pressure and temperature of an SI engine gets too high during compression, you will loose authority over the combustion event because the mixture will go off by itself, you've hit the knock limit. Different animals.

Both SI and CI engines will respond similarly if you retard combustion event. If you retard the injection timing in a diesel, or retard the spark timing in an SI engine, the exhaust temperature will increase because the burn is likely not complete. That is one way to spool a large turbo in some applications, but keep in mind that the combustion is controlled differently.

In the OP's application, it is pretty much steady state so the EGT information might be useful, but a wide band would be more so. A relatively small, low pressure turbo could spool quickly and help towing without killing gas mileage. A 6 liter LS motor should make around 400 ft-lbs, but with 7 psi you could see 550+. That would get you up the hills, just back off when your EGT gets too high.

 

Well I'm pretty sure he used the words "6.0L" and "towing" in the first post, so I assumed gasoline towing possibly a 8000lbs vehicle going uphill at 88 to 95mph was the application and utility of EGT I recommended based on those exact principles
{elaborate}
I build the truck in my head and drive it. I take it for a 10,000 mile drive, up and down hilly terrain at 6500 to 8500lbs with a good old 4l80e and some huge tires. 600ft*lbs of torque is nothing to this rig and I am watching the EGT gauge rise 12psi with E10, getting uncomfortable. I can see it needs oil temperature sensor and oil cooler for the engine and transmission, that data will be even more valuable than EGT. I want to try 15psi and 18psi hell- the turbos got the headroom and IAT is fine. But instead I reduce the boost to 8psi and wait a week for the water injection to arrive. Okay a week is done and I've got 100% distilled water injection. I start at 50cc/min and find that it takes about 95cc/min to bring EGT down a couple hundred degrees with a solid 18psi of boost assuming 650lbf-ft. Comfortable EGT, low timing and plenty of oil cooler to go around it might survive. Was that easy? Everything with the truck is good but at night I have recurring nightmares about alcohol. Now I'm OCD about checking water level, pump function, line clearedness, line filtering, test the system frequently, keep a spare pump handy, and I keep dreaming about E85 and being able to stop worrying about the water system and start worrying about the water in the air inside the fuel tank that the alcohol is trying to absorb.

On a gauge, you are correct. Be specific. No professional is using a EGT gauge lol.

We log the EGT data and review it later, sitting at the kitchen table. Information collected in the time domain- simply shift the domain on the x-axis to line up with the transient delay.

You must do this for Wideband Data AND EGT data, same principle, there is always some delay between sensor and ECU. The delay becomes integral to your tuning strategy for some decisions.

Every car gets a wideband. You can't really afford not to have one. We really shouldn't bring Widebands into this but whats done is done. Wideband and EGT data both has a delay and can be logged, and used to tune an engine while you sit at the kitchen table. No matter what application.

 

Thanks for the info folks. I appreciate the discussion. It is alot to take in. I was hoping to do a rear mount setup due to the fact that I could pre fab most of it and get it all put in in a weekends time. The folks in my other post have told me that I really need to do an under hood setup, and I am not ready to take that on right now. So, the project is kind of stalled right now. But i still need to learn how to tune it. So I appreciate the time taken to reply.

 

Maybe, but it does kind of stress the point that what he wants to do isn't cheap, simple, nor should it be entered into lightly. After reading the replies what I took away from it is have someone knowledgeable involved from the start and build the "package" to specs The tuner can get you a good, reliable result from. But maybe more so... Ask yourself why you don't see v8 turbo gas engines being offered from the big three. **(Not for the dually trucks made for towing) not talking about performance V8 cars** With unlimited budgets, and the ability to make minute changes to every facet of a V8 gasoline engine to make it live with turbocharging they do not offer it, and never have. That should have you questioning the long term reliability of a project like this, and the real cost of developing a reliable package.

 

Yet, they all offer a diesel for these applications, that have a proven track record, have been around long enough that their quirks and weak points are known, been addressed. No wonder you see so many dually Chevies with Cummins swaps. Or you see a 454 Chevy/460 Ford with 250-300 hp, decent torque, shit mileage and the owner just accepts the sub par mileage.. then one day they buy a diesel and are for the most part satisfied with the power, better fuel economy and they accept the noisey diesel knowing it will go 500,000 miles if it's quirks are addressed.