Turbo with 42RLE (overdrive question)

MikeE024

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My transmission goes into overdrive & lockup around 42 mph which drops my RPMs to about 1600.

I read that lugging your engine is bad for a turbo, but I'm not sure how that rule plays into in-town driving where load varies.

Should I drive with OD off for in-town driving? At 45 mph, the RPMs are at 1627 (OD on) or 2358 (OD off). It seems that I could keep OD off until I approach around 55mph.

I'll likely be in boost more often if I have OD off in town. I don't have enough experience to know if that's good, bad, or doesn't matter. The Banks turbo is set to 6 psi of boost.

Here's a visual from Grimm Jeeper showing the engine RPMs when in 3rd versus 4th gear at different speeds.


Screen Shot 2023-02-08 at 4.46.39 PM.png


Screen Shot 2023-02-08 at 4.49.25 PM.png


Screen Shot 2023-02-08 at 4.51.44 PM.png
 
I don't think you are going to hurt anything. It might all be academic anyways, but I'm assuming you are only going to be in OD at that low of rpm at very light throttle loads anyways, so probably not building boost anyways, right?
 
I don't think you are going to hurt anything. It might all be academic anyways, but I'm assuming you are only going to be in OD at that low of rpm at very light throttle loads anyways, so probably not building boost anyways, right?

I noticed that boost would build as I pushed the gas pedal while the engine was still lugging in OD (before the transmission kicked out of OD).

There's a good amount of load on the engine right before it kicks out of OD with the pedal method. I'm worried about potentially stressing the turbo by being in boost before the transition out of OD.

Staying out of OD would be the simplest way to eliminate this scenario, but I'm green when it comes to the turbo stuff so I don't know if I'm making something out of nothing or if staying out of OD in town could cause a problem I haven't considered.
 
I wouldn't worry too much about it. I have never heard that lugging the engine could cause turbo damage. The 42RLE has a crap shift schedule stock. They are factory tuned for economy. The overdrive is ambitious and resistant to downshifts. You can tune the shift points in HP Tuners, but it requires a MPVI2 and an extra credit for the TCM IIRC. I tuned mine in the LJ before going to the 6 speed auto. It made driving the 4 speed much more tolerable.
 
I wouldn't worry too much about it. I have never heard that lugging the engine could cause turbo damage. The 42RLE has a crap shift schedule stock. They are factory tuned for economy. The overdrive is ambitious and resistant to downshifts. You can tune the shift points in HP Tuners, but it requires a MPVI2 and an extra credit for the TCM IIRC. I tuned mine in the LJ before going to the 6 speed auto. It made driving the 4 speed much more tolerable.

Thanks for that info. I agree the schedule is bad and the OD is a bit annoying to deal with.

I have an HP Tuners MPVi2 I would just need to get credits. I wanted to pull the Banks tune anyways to have a copy.

Would it possible for me to emulate your shifting schedule? I’d like to improve it if I can once I’m back to the rig full time in the early summer. I’ll try to learn more on how to use the device between now and then.
 
Thanks for that info. I agree the schedule is bad and the OD is a bit annoying to deal with.

I have an HP Tuners MPVi2 I would just need to get credits. I wanted to pull the Banks tune anyways to have a copy.

Would it possible for me to emulate your shifting schedule? I’d like to improve it if I can once I’m back to the rig full time in the early summer. I’ll try to learn more on how to use the device between now and then.

I can send you what I had. I was running 4.56 gears and 35s, so it may be a bit different for your setup. The tables are easy to tune, you just have to remember that the RPM is for the transmission shaft speed not engine speed.
 
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I wouldn't worry too much about it. I have never heard that lugging the engine could cause turbo damage.

I messed this up. The damage i read about would be to the engine due to low rpm pre-ignition.

And I think it would only be an issue if I slammed the throttle super aggressively, and even that isn’t a practical issue bc the auto-trans would kick me down to third.

Thanks for your input and patience with me on this. I have lots to learn.
 
I can send you what I had. I was running 4.56 gears and 35s, so it may be a bit different for your setup. The tables are easy to tune, you just have to remember that the RPM is for the transmission shaft speed not engine speed.

That would be super awesome to look at.

I’ll do some searches to help guide me I know there have been discussions on this before.

You’ve been in some discussions that were way over my head when I read them and still are but I’ll see what I can learn. And there were discussions on this near the tail end of a giant turbo thread from a couple years back in the other forum.

Iirc it’s the RPMs are for the output shaft speed (I’ll double check).
 
I read that lugging your engine is bad for a turbo, but I'm not sure how that rule plays into in-town driving where load varies.
I wouldn't worry too much about it. I have never heard that lugging the engine could cause turbo damage.
I messed this up. The damage i read about would be to the engine due to low rpm pre-ignition.

Just found a screenshot on a different computer...this is the post talking about turbo damage that caused me to start this thread.

Screen Shot 2023-03-03 at 5.37.24 PM.png


I believe this post was speaking to someone who's running larger tires with higher gearing. I don't think it applies when running 35s with 5.38s and a 42RLE.
 
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Not anything to worry about. Also not sure how lugging the motor destroys a turbo. Lugging a motor is theoretically hard on but in practice as much as it gets done, it's not really a factor.
 
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I wouldn't worry about it too much. Also, if you find that the 42RLE is lugging often you can tune the shift points to downshift sooner.
 
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Not quite sure why this is a question. Unless you are on the highway, there is simply no reason to allow the 42 to go into OD. Stop being silly.
 
The short answer is that I'm learning.

Power adders make no difference to how you have to drive the 42. It is a shit transmission with terrible response to being in a TJ. You drove it before the turbo, nothing about the turbo changes how you drive the 42. When your hand grabs the shifter to take it out of park, extend your index finger and hit the OD off button. Unless your garage is on a freeway onramp, that doesn't change.
 
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There is also a mod that automatically turns off the OD switch on startup if you can't be bothered to do it.
 
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There is also a mod that automatically turns off the OD switch on startup if you can't be bothered to do it.

Yes sir, I had the mod but removed it because I didn't like where I tapped into the reverse. Maybe reinstall it later.
 
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There is also a mod that automatically turns off the OD switch on startup if you can't be bothered to do it.

I have filed that stupid alteration under my list of shit that people too dumb to breathe do. Your extended index finger literally points right at that switch when you shift out of park and you're too silly to just move it 1/2" and punch the switch? Give me a fucking break. Do it 3 times in a row the next 3 times you drive your rig and it becomes automatic after that.
 
It probably depends in a lot of factors, especially how the engine is tuned. OEM turbocharged gas engines like the Ford Ecoboosts will run 20PSI of boost at around 2,000 RPM, and will run modest boost (~10 PSI) as low as 1,200 RPM. Granted, the OEM systems are significantly more refined, and have a number of additional safeguards to prevent damage to turbos or catalytic converters.

I would say the biggest thing to watch would be the exhaust gas temperature (EGT). Diesels monitor these heavily, and these temperatures can be far higher in gas turbocharged engines, especially under load. Commercial diesel drivers will actually watch the EGT and use it as a shift indicator. EGT too high? Downshift to protect the engine. EGT well below the limit? Upshift and save some fuel.

How much heat the turbo can handle will vastly depend on its construction. If it is designed for higher temperatures (like a Ecoboost turbo as opposed to a Powerstroke turbo), you can usually be far more aggressive with it. It will also depend upon the consistency of the coolant (or oil) flow through the turbo. One of the reasons OEM turbocharged cars have auxiliary water pumps is to keep coolant flowing through the turbos after shutdown, especially when in auto stop-start conditions.