frieed

Noticed this on my last trip with the trailer.
With cruise off, I accelerated to 60mph on a slight grade and hold there.
Truck stays in 5th at say 2100 rpm. Low boost
Engage cruise and truck immediately shifts to 6th at 1600 -ish rpm and I listen to the boost climb.

Turn cruise off again and the truck does not downshift until you need a little more throttle to maintain speed.

Was not a one-off event, I saw this scenario repeat many times during the 2500 miles towing the trailer.

Obviously this is an ecoboost.
I posted here since I've only noticed this happening while towing.
Please don't flame me for rpms-vs-gear-vs-speed, I didn't take notes so this is a generalization.

-frieed

93Cobra#2771

iTrader: (2)

Yes, it does exactly as you say. It will hold a gear longer and max the load to almost 100% prior to shifting.

Non cruise operation it will a barely hit 65% before unlocking the torque convertor and/or downshifting.

Did you have a particular concern or?

frieed

Nope, just an observation.

brulaz

Guess that's how the bi-turbo works? Just guessing here, but at lower rpms like 1600, it needs to spin up the low-rpm turbo and you can hear it?

Here's the the 2-part torque curve. I've always interpreted the "steady-state" part as the low part of the bi-turbo, but I'm not really sure how it all works.




Would love to have a boost meter to see if the "boost" sounds we hear actually correspond to the boost the engine feels.

Some guys here prefer to tow in 5th with 6th locked out and say they get better mpg. So do higher rpms with less boost give better mileage than low rpms with more boost? I tried it but couldn't really tell any diff with the instantaneous mpg meter.

frieed

I don't think this is a bi-turbo in the traditional sense. These are identical turbos in parallel rather than series.

In this case, the engine is using more boost at a lower RPM, so it must be venting when cruise is off and the RPM is higher.

I have the torque app for my phone but didn't have it running at the time. I can tell the amount boost from the sound of the exhaust note. Under boost, the lower tones of the exhaust note become more pronounced, not a drone, but just louder. Long gone are the days when I could have heard the turbo whine, although since they can reach almost 200,000 rpm (IIRC) while working, I doubt anyone can hear anything other the very first onset of boost.

I have another trip to the mountains planned for labor day weekend so I'll try to remember to turn on the app.