2700 RPM all day?

[jspringator]

My truck did not like towing in OD (9,000 lbs.). Sometimes it wouldn't shift into OD, and finally set a code. It really seemed to like towing in 3rd, with RPM's up to 3000, but averaging 2750. Is this OK?

[Brandon]

2700 is just fine. That is when it is comfortable towing.

[CleviteKid]

Your engine, as well as mine, could run against the governor all day (about 3600 rpm) with no ill effects. As you observed, turning higher revs in a lower gear makes the same power with less torque, therefore less heat input per cycle, more airflow, cooler temperatures, etc. etc. etc. The engine can take it if your ears can stand the extra noise.

Dr. Lee :cool:

[rjschoolcraft]

I have to respectfully disagree with Dr. Lee. Since you have gages (I assume an egt gage), you can decide from what they tell you.

My Suburban, especially in stock trim, ran much higher egts at high rpm, or in third vs. fourth gear. This is because the computer severely limits boost available at the higher rpm. The 6.5 really needs boost to keep egt's in check. When stock, my boost would fall off to about 3 psi above 2700 rpm... you could watch the egt gage steadily climb out of control.

The basic fundamentals should be as Dr. Lee stated. Before I installed gages, I operated my engine the way he suggests. The problem is that GM designed logic into the control system that makes these engines behave in a counter intuitive manner.

Mechanically speaking, he's right. The engine can run against the governor without concern. If you modify the system to make more boost at high rpm, as I have, then you can control egt at the higher rpm and use that range more. However, my computer still clips boost back at 70 mph from 18 psi in OD to 10-11 psi in third (direct) when towing heavy, so the egt runs hotter, but not dangerous.

[Billman]

Wouldn't trans temps become a problem?

[jspringator]

I have my boost cranked up pretty good. EGT's were not in the "yellow" zone. Sometimes it was locked in 3rd (at least above 50 or so), I thought this would limit high tranny temps. However, sometimes it was not locked. I would like to plumb in a transmission cooler, with fan, that could fit between the frame rails. A manual on off or bypass valve would be nice so you could turn it on only when towing. I suppose the fan would be controlled by a thermostat. Anyone knoew where I can get such a beast? BTW, I didn't have much choice but tow in 3rd. The transmission wouldn't let it shift to OD sometimes.

[JohnC]

Originally posted by James Springate:
A manual on off or bypass valve would be nice so you could turn it on only when towing. I suppose the fan would be controlled by a thermostat. Thermostatic bypass valves used to be common for oil and trans coolers. Check around. If you can't find one, try a place that deals in parts for "baja bugs"

[JeepSJ]

Ronniejoe - you are seeing different results due to the stupid programming of the stock computer. Take away the computer and you will see that you get the same results as Dr. Lee. A simple TurboMaster from Heath would give you the same result. Take away the air and I would expect EGT's to rise. This is a man-made problem, caused by the way the computer is programmed. Don't mistake human-induced problems for the way things really work.

[rjschoolcraft]

Now, isn't that exactly what I said? I used the term "counter-intuitive" to describe the behavior, right? Springate has a 99 with an electronic boost control. My comments were very relevant. I melted my first engine down within 8,000 miles and 2 months of purchase because I drove it that way without gages installed.

Springate has provided more information since that post. His boost control keeps boost up and keeps egt down. He should be OK.

Controlling boost on turbo backpressure is the wrong way to do it. With the modifications I've installed, my computer controlled system is better than what the turbomaster can do.

[tom.mcinerney]

James,
As John C said, "Thermostatic bypass valves used to be common for oil and trans coolers. Check around."

Try Perma Cool and Earl's Performance.

[JohnC]

Click here for Cooler thermostats (http://www.perma-cool.com/Catalog/Cat_page14.html)

[dieseldummy]

JS, I have run my 6.5 at 3200 rpm's for thousands of miles and countless hours and never hurt it. My trouble came from pushing to much boost on the stock turbo and pushing to much fuel. All it created was heat, so watch coolant and intake temps. and you'll be allright.

Also, on a side note, RJ I must disagree with your theory about regulating boost. Backpressure is critical to engine life, run too much backpressure for too long and you elevate temperatures and run against the "choke" point of the turbo. I know you will tell the tell of running sustained boost pressures of 15-17 psi or whatever the number is, and you have gotten a lot of miles out of your 6.5 this way. I commend you on this great accomplishment. My personal experience has stated the opposite of yours which is why I dissagree about boost control.
Justin
P.S. In addition to the '93 listed in my sig. I have a plethera of experience with a '95 & '96 which are electronicly controlled.

[rjschoolcraft]

To each his own. Mine works. It's been on JK's Superflow lie detector as well.