Timing vs EGT's vs rpm and towing

[AH64ID]

I was wondering if anyone has come up with a rough max EGT for "x" timing. We know a stock 04.5-07 will run 1450°+ when towing and not melt a thing, but the timing has a lot of heat rejection to the piston. So when we bump the timing we get more heat to the cylinder, and less out the exhaust so we need to decrease our safe EGT's when towing.

In looking at Rich's "gift tune" and rpms he has a max of 14.8° at 2,000 rpms and 16.2° at 2,200 rpms, which is range many people like to tow in. But then at 2600+ it's 20°. Based on that I would think you could handle more EGT's at lower rpms than upper rpms, yet EGT's aren't referred to that way. It's usually 1300° continuous, 1350° max, or 1350°-1400° 1 minute out of 5, etc.. But looking at dynamic timing the rpm and load would seem to have a huge impact. I don't even want to look at stock tables, as we all know those were not designed with power/performance in mind.

Airflow has to have an impact too, but I am not sure how much as 1200° out the exhaust is still 1200° at 10 psi or 40 psi.

Any input, or experience?

[killerbee]

The first thing that is clear to me, is that EGT is a very widely misused parameter. Also, it is very innacurately reported in many thermocouple/gauge combinations, unfortunately, making any kind of comparison difficult.

One other tradeoff is important. Lowering of EGT with advance comes at the expense of head pressure and resulting gasket issues. Lower egt isn't always better.

Airflow increase, if you mean by increasing compressor output, is also a double edge sword. It can create ambient air dilution to help lower EGT, but that could mean a higher stress on head parts as well as turbo.

Correct (safe) timing is highly subjective, and highly dynamic, changing with many changing conditions. I know that is not much help to you, sorry.

[AH64ID]

Unless I am missing something EGT's are what we have to go by. We know it's not a true correlation to cylinder temps as timing plays a huge role in that, but we should be able to infer something in the safe realm.

We can counter the effects of cylinder pressures with better studs, and compressors by staying in the MAP, but what is a "safe" EGT at a given load/timing?

The big difference between towing and a street truck is heat soak, a street truck can survive 1600° runs, but the same EGT's pulling a 7° grade for 6 miles would melt a piston or six.

[FUBAR]

I agree with the difference in trucks being able to sustain different conditions. Sounds to me the both of you are on the same page, just a different language. I too have wondered how to find the sweet spot between running too high/low egt's vs cylinder temps and pressure other than strapping it to a dyno. When you speak of factoring load% into this topic, I have not been able to come up with an accurate value for the 5.9L

[Dmaxink]

Only way to tell on cyl press other than heresay at this early on in tuning is by an actual cyl press monitor..

[DoghouseDiesel]

Cylinder pressure is why we used good fasteners and o-rings.

Nothing new there.

[THEFERMANATOR]

I know it's not scientific, but I like to set my tunes up to where the EGT's run close to what I consider high on the safe end, and balance the timing percentage so that engine temps run middle of the road. ZTo much timing and your EGT's go down, btu engine temps go up. Not enough timing and engine temps stay safe, but EGT's skyrocket. I have found 40-45% to work well as a starting point, and go from there.

[AH64ID]

But what is considered safe? Is 1300° safe all day long at 15° of timing, or is it safe all day long at 20° of timing, and you can go to 1350° or higher at 15° of timing?

I'm not worried about cylinder pressure, as Rich said that's easy to take care of. What I don't know is how hot is too hot with "x" timing.

I'd like to see a scan of this motor and tweak it for towing! 480/940 at 34psi and 1301°. http://www.cmdmarine.com/Products/Commercial%20Propulsion/qsb/FR92283.pdf

[MQ105]

Wouldn't be a good comparison due to the marine engine's sea water cooling.

[AH64ID]

Wouldn't be a good comparison due to the marine engine's sea water cooling.

I don't see how that would make any difference on cylinder temps, it does have a 25° cooler thermostat but that's not going to make a noticeable difference in cylinder temps, which is what were trying to protect with pyro's. Sea water cooling does allow for greater sustained hp for a given engine size as cooling is unlimited. In fact that's an aftercooled motor and the aftercooling happens with the coolant so the intake charge will be hotter than what we put into our cylinders which will have a greater effect on EGT's.