Detuned 6.7 diesel in Ford Super C RV

[patperry2766]

I was looking online at a Super C based on the Ford F-550 chassis.

The specs on the Ford website are 330 HP/ 750 TQ, while the specs on a "non-commercial" F-350 are 440 HP & 925 TQ.

When a manufacturer detunes an engine, are there physical differences and different parts to the engine, or is it all in the software that can be altered either with a re-flash or a tuner such as Bullydog or some other brand?

[Bedlam]

4.88's are not friendly for extended freeway driving. I chose Ram's 4.44's which are close to Ford's 4.30's to get nice 65 mph cruising and still have capacity.

[patperry2766]

Per Ford's website, the rear axle ratios are 4.10, 4.30 & 4.88.

Would it be ridiculous to think that a RV builder would plan ahead and order with the tallest gear set available, or would something like that even cross their mind?

[blt2ski]

Actually, torque multiplication is what gets the load going! Hence why my MDT with a whopping 330 lb ft of torque can pull 30K up a 30% grade, meanwhile my 05 duramax was limited to around 25% with a 20K load before stalling out. Power was there, but gearing was not! A lot of times, for how some MDT's are used, the top speed is set at 55 based on gearing, then they figure out the HP needed to move that load, and put an engine in that has the HP needed from a speed stanpoint, but gear, tire diam and trans gears setup the how little or steep of a grade you can pull in 11st gear.

I have spent many miles with the pedal to the floor going up hill with my non turbo idi 7.3 with its whopping 175hp! But I do get there, never have I stalled the rig on a hill/grade. Meanwhile many of the 35 series rigs I have had, with higher HP and torque motors, due to the crummy, ie really tall gears in trans, and axels, I have not gotten to the top of a grade because I stalled out! Blew up an auto tranny or three this way too!

Hence why I have learned, it is better to be underpower slightly, with a proper geared rig, than an over powered rig, with incorrect gearing for the task at hand.

Marty

[Retired_JSO]

I believe the F 550 could be detuned for a reason. That being a more commercial large gvw truck having a rear gear somewhere in the 4:80 to 5:10 range. Therefore, no need for a bunch of torque or horsepower to get the job done.

[Bedlam]

The governor is doing a TV show now. On my chassis cab, governed speed was an option at purchase and can set/reset later by a dealer.

[carringb]

patperry2766 wrote:

This website shows the engine to be detuned to 300 HP & 660 TQ, which is even lower that what shows on the Ford Commercial website.

At 35K GCWR, wouldn't you have to be driving with a heavier/heavy right foot to keep rolling, especially once you start hitting the mountains....or would this still be a non-issue?

I think maybe Thor just hasn't updated their info. That was correct for older model years

But yes, there will be many times the "gas pedal" will be to the floor. But you can push the pedal to the floor 100% of the time and not hurt a thing. Of course, on flat ground you'd just end up running into the 75 MPH electronic governor.

[patperry2766]

BillyW wrote:
330 HP and 750 lbs of torque seems like plenty of power to me...

Thor

This website shows the engine to be detuned to 300 HP & 660 TQ, which is even lower that what shows on the Ford Commercial website.

At 35K GCWR, wouldn't you have to be driving with a heavier/heavy right foot to keep rolling, especially once you start hitting the mountains....or would this still be a non-issue?

[wanderingbob]

In the past we would detune a Jimmy by moving to smaller injectors , of course that was before computers !

[TurnThePage]

330 HP and 750 lbs of torque seems like plenty of power to me...

[4x4ord]

What Cumminsdriver said is right. The engines have different turbos. (There maybe other subtle differences as well) You cannot simply go to Ford and have them reflash the chassis cab to get the pickup truck power. An aftermarket programmer may do it but I would not be surprised if you discover that you need to have someone write a custom tune to alter the chassis cab's power.

[carringb]

patperry2766 wrote:
Hypothetically speaking, wouldn't it be more beneficial to give this medium duty chassis all the power available so it wasn't necessary to run at near max/max capacity for extended lengths of time?

Basically what they are doing is artificially limit it so it is never running near max output.

These rigs also have much lower gearing then light-duty trucks, to put more torque to the rear wheels. This improves acceleration and gradability, however HP is what matters for top speed up grades. These sacrifice some speed in order to gain longevity.

[hone_eagle]

more power needs bigger rad, might not be the room . imagine worst case
-full load
-climbing
-desert (air on full)
-summer
-head wind
all must be considered when designed and warranty costed in.

[patperry2766]

Hypothetically speaking, wouldn't it be more beneficial to give this medium duty chassis all the power available so it wasn't necessary to run at near max/max capacity for extended lengths of time?

With having to put more throttle into it to get the mass moving and to keep it moving vs the un-tuned diesel, it seems that would put extra stress on the engine and lead to excessive wear and tear.

Do they get around this by presumably putting taller rear-end gears to compensate for reduced engine output?

[theoldwizard1]

CumminsDriver wrote:
Detuned engine output also because of duty cycle requirements that the chassis cabs have that the pickups don't.

Hit the nail on the head !

"Medium duty" truck engines are run at/near max capacity for long periods of time. Cooling is key to pass this test. Less power, less heat.