Possible new class 5 rig. Am I nut's to choose gas motor ?

[klahanie]

Long McArthur Ford does a great weekly update of Ford’s production capacity for all of their various models. According to their most recent update (week of 7/8), the order banks for regular Super Duties (not 450/550) are still open. I’ve been watching them a bit this past year and it seems like 450s are rarer than hen’s teeth; they have never commented on 550s.

No relationship w/ these guys; sharing only because it seems like a handy thing to know if you’re considering ordering a Ford Super Duty.

To answer the original question of this thread: I’d get the 7.3L. I agree that the 6.7L has tremendous chooch and would be fun to have crossing mountain passes, etc. However, I think diesel is gross. Fueling it, dealing with DEF and associated emission controls, diesel fumes at slow trail speeds are all things I would want to avoid. Modern diesels are way cleaner and quieter than my old 7.3 but as a $13,000 option, the HO 6.7L (I mean, if you’re going to get one, get the good one) just doesn’t have enough value to justify it to me. This opinion is worth that you paid for it.

Thx for the tip. Figure I have ~ a month to decide.

If this was, money no object, I'd still go diesel, I think it would drive noticeably better (no one saying otherwise) and I really like that optional aux fuel tank easy button. Some state they like to stop for gas every few hours ... take a pee, get a coffee etc. I don't. The less time at a gas station for me the better.

I'll admit tho, diesel fills can be messy.

As for off highway I actually prefer the diesel for slow stuff or cruising FSRs vs our previous gas truck (all that extra torque).

But every rig is a compromise. Some things have to give.

 

[rruff]

No you're most certainly not affecting just first gear. Wow. If a 3.73 truck turns 1900rpm at 75mph, a 4.30 truck would turn approx 2200 rpm. Massive difference. Same goes for every gear.

Why are you stuck in a particular gear? These trucks have 10 gears, and if you are climbing a pass or accelerating or doing something else where power is needed, it will pick the optimal one.

Maybe with a regear you'll climb that pass in 7th at 4500 rpm, instead of 5th at 4700 rpm. No benefit whatsoever.

In your example above you could just shift the 3.73 to a lower gear and run similar rpm if you want.

 

[Buddha.]

Why are you stuck in a particular gear? These trucks have 10 gears, and if you are climbing a pass or accelerating or doing something else where power is needed, it will pick the optimal one.

Maybe with a regear you'll climb that pass in 7th at 4500 rpm, instead of 5th at 4700 rpm. No benefit whatsoever.

In your example above you could just shift the 3.73 to a lower gear and run similar rpm if you want.

It’s not just about changing rpms. You get more torque in every gear. More gear reduction (bigger gears) get you more torque at lower output speed(higher input speed).

 

[IdaSHO]

With regards to gearing, how hard the engine works for a given load, or how much power that gets to the ground thats required for that load, is a combination of trans gears and gearing, and axle gearing.

So saying you “get more power” with lower gears is just ignorant. Depending upon trans gearing, dropping a gear will likely net you more power to the ground than lower axle gears.

And we are not talking about a 3 or 4 speed auto. We are talking about the typical 10-speed autos. With such a selection, rear end ratios are not nearly as critical as they once were. Especially talking about gassers with a larger useable rpm range than many low reving diesels.

Further…. lets make clear that MAX power anywhere is irrelevant. Sure, you could have max power at a certain rpm and certain speed, but all that will do is result in poor fuel economy. It really doesnt take much power to maintain highway speeds once up to that speed. Far less than max.

At the end of the day you want a USEABLE power band, that provides low enough rpm on the highway for quiet cruising, enough gears to manage grades safely, and enough grunt to safely pull from a stop loaded.

 

[andy_b]

Why are you stuck in a particular gear? These trucks have 10 gears, and if you are climbing a pass or accelerating or doing something else where power is needed, it will pick the optimal one.

Maybe with a regear you'll climb that pass in 7th at 4500 rpm, instead of 5th at 4700 rpm. No benefit whatsoever.

In your example above you could just shift the 3.73 to a lower gear and run similar rpm if you want.

You’re of course partially correct - with more ratios, a 10spd is more likely to find the right gear without adjusting the final drive.

For me, the biggest issue being undergeared and its associated loss of torque and engine braking is at slow speeds off-road. At those speeds, the transmission is already going to be starting off in 1st or 2nd and then there isn’t much more it can do to minimize the effects of a higher effective final drive caused by larger tires and unchanged factory gearing. Of course you can engage low-range but it is still compromised. It isn’t the end of the world but it is noticeable and for vehicles designed for off-road use, it should be taken into account.

...

I'll admit tho, diesel fills can be messy.

As for off highway I actually prefer the diesel for slow stuff or cruising FSRs vs our previous gas truck (all that extra torque).

But every rig is a compromise. Some things have to give.

I agree that the extra torque at slow speeds is nice - my beef with diesel off-road is how much it stinks, especially for those following behind while moving at slow speeds. This is better with modern diesels and their emissions but they’re still smellier than modern gas engines. I get that this is just personal preference at this point; sharing my rationale for my choices.

 

[rruff]

For me, the biggest issue being undergeared and its associated loss of torque and engine braking is at slow speeds off-road.

If I'm going slow offroad, it's in 4lo. Gearing is plenty low in that case.

I'm sure I'm giving up a little acceleration, but pushing a little harder on the peddle would take care of that...

I'm just sharing my reason for not spending for a regear. If lower gears had been available stock, I would have gotten them.

 

[andy_b]

If I'm going slow offroad, it's in 4lo. Gearing is plenty low in that case.

I'm sure I'm giving up a little acceleration, but pushing a little harder on the peddle would take care of that...

I'm just sharing my reason for not spending for a regear. If lower gears had been available stock, I would have gotten them.

4-low will get you lower, but my point is it is not as low as stock would be (which often isn’t low enough anyhow for real off-road work). The ability to drive down and up obstacles as slowly as possible is key, especially on heavy and cumbersome trucks like those being discussed. It is easier on the drivetrain and the trail. Having higher-than-ideal gearing isn’t the end of the world, but having the right gearing is worth the small amount of effort at the front end to order them from factory (as the OP is doing). At $2-3k per axle, a regear may not be worth it to do in the aftermarket. In those scenarios, an aftermarket underdrive might be cheaper/easier to install and also keep the benefits of a higher final drive at highway speeds.

 

[NoDak]

Don’t fear the gear.

 

[86scotty]

But what if I do fear the gear? What do I do then?

 

[IdaSHO]

Personally, If I were to ever consider a re-gear, I would never have a shop do it.
Nor would I do it myself... Id be hunting factory built axles via junkyards.
Simply because I will place MUCH more faith in a factory axle than a re-geared one, especially in a heavy truck that works hard.

As far as new, tough call. But in my experience with full size Fords, diesel and gasser, its a toss up.
My 6.2 Gasser does great with the 3:73s, running heavy, even up and down some of the longest and steepest grades in the country.
But it certainly does it differently than the old 7.3 Powersroke we had.
It came with 4:10s, and I regeared with junkyard axles to tall 3:55s and it was the best thing Id ever done.
With the 4:10s it was gear bound, and we often hit the cruise at 55-60mph just so we could carry a conversation in the truck.
Ungearing to 3:55s reduced in cab noise a ton, allowing us to cruise with the came noise at proper 65-70mph, all without noticeably effecting available power or even MPG.
If anything, our MPG improved.

The 6.2 loves RPM. So drop a gear or two and let it eat.
The new 7.3, different animal as well. And while I dont have any first hand experience, on paper it looks to be a solid step up from the 6.2 for power,
but with a decent amount more low RPM torque. So while we can talk about gearing all day, looking at a dyno for the 7.3 may be more useful than anything

And the dyno vs the 6.2 is curious. With all the hype I would have expected a larger or more dramatic difference.
And keep in mind when you look at the dyno, this is a 7.3 with 4:30 gears vs a 6.2 and 3:73s

My take-away....

Even though there is a fatter amount of HP and Torque across the band, the single biggest difference I see,
and one you would notice all the time is how soon power comes on in the RPM range.

The 7.3 delivers power a good 500RPM sooner. But as a few have mentioned, these are things you will notice from a stop.
Once rolling and into gears, the difference is marginal. Unless you are running at MAX power all the time.
Which simply isnt normal case.

 

[rgv]

The discussion on re-gearing is interesting, particularly on how the newer 10 speeds are more forgiving.

In my own opinion, torque multiplication happening at the rear axle is torque multiplication that doesn’t happen between the crankshaft and axle input, and consequently should generate less heat and wear.

This may become important as you get near the max GVW rating of a transmission/t-case.

 

[rruff]

That being the case, does the diesel have a different transmission? If not, the one on the 7.3 must be overbuilt... ?

Apparently they are different: "Same basic transmission, same exterior size, same bellhousing bolt pattern(mod motor bolt pattern), only differences are for torque handling. Different converter, different clutch packs."

 

[klahanie]

Follow up time. And the winner is ....

Gas !

Finally was able to order. Gonna be next year, maybe April before we see it. I'll try to post up mpg etc when we ever get this rig put together (F550crew, 84 ca - gonna be a monster, oh well)

Thx again for all the input. 👍