Looks like the new 2017 6.7 will make 925 lb ft of torque. I wonder would anyone be more willing (and able) to buy it instead of the 6.2 gas if they shrunk it by 25%. So instead of 925 lb ft and roughly 18 mpg (empty) you would have just over 690 lb ft and perhaps 22 mpg (with 5.0 liters). Also, the $8500 premium charge for the diesel engine could be lowered to maybe $6500ish. And maybe many engine repairs could be done without pulling the cab.

I was just thinking if I had to replace my 2002, would I actually go for a new diesel. It'd be more enticing if was scaled down a little and still have plenty of grunt for a pickup truck. I realize shrinking the displacement by 25% doesn't mean all the dollars and power shrinks by the same amount but hypothetically speaking...

 

There is an argument for a smaller diesel out there.


The F150 fits the idea you have. There are some test mules floating around right now. I think the motor will be in the 3.0 liter range though.


Super Duty needs to stay where it is in terms of power and capabilities.

 

that would give you a 5.4 diesel.


I would rather have them upsize it 25% and have a 9.0 diesel.


my reasoning is if they made everything bigger....it might not break as much as the 6.0, 6.4 and 6.7 has.

 

I'm sure there are good reasons for this (otherwise Ford wouldn't do it), but I don't understand it. The F450, 550, 650 and 750 are detuned to under 700 lb ft. Does the market not support the same performance, but with more fuel economy, easier maintenance, and lower up front cost for a pickup?

 

When is more not better ? LOL ! As for less breaking, I didn't think the 6.7 has strength issues; I thought it was more computer and emissions issues.

 

I'd be interested, but I'm not sure how much market demand there is. I think the majority of private owners would prefer more power, but it could be a huge benefit to fleets and those of us who don't need a 440HP pickup truck.

I'd love one...so much that the new Titan XD is gonna be on my list to check out when it's time for the next truck. I'd love to see that 5.0L mill in a Super Duty.

 

You're assuming that fuel economy would be better. The engine doesn't make it's max power output constantly nor does it run at it's most efficient point all the time. Fuel consumption is largely set by the fact that the truck has frontal area of X that requires Y amount of power at Z speed, and the gearing is fixed based on towing power at that level and not max fuel economy. If you kept everything else on the truck the same there's no guarantee that the new engine would be at a more efficient point than the current one. Diesel has a finite energy content, it's physically impossible to get some of these economy levels people want in an engine with so much thermal energy loss at the weights of these vehicles in a form people are willing to drive on the highway.

That's why gearing transmissions are the next big step forward, matching engine outputs more closely with actual energy requirements (ie the 2nd OD we're seeing commonly now), and dual-dry-clutch cars with no torque converter losses. There's no need for a smaller diesel in the Super Duty because it wouldn't actually BE any better necessarily unless they changed the rest of the driveline, and at that point the larger/higher rated engine might actually be more efficient. The next step after that is energy preservation, things like regenerative braking to store instead of burn off energy used to attain speed. I don't think thermal efficiency is going to take a huge jump because an internal combustion engine directly powering a vehicles wheels will never be at it's peak efficiency point. Diesel-electric hybrids like locomotives have a lot of potential, and electric motor and battery technology are currently progressing to where it might be viable in passenger cars. That's when you'll see a big efficiency jump: using a gas turbine to run a generator part-time to charge the battery bank actually running the motors in the wheels.

 

I agree with a lot of what you're saying. Basically it takes X amount of fuel to move X amount of weight no matter what the engine size is. So if you're always loaded heavy, your mpg will be about the same regardless of engine displacement.

However, I believe there is also fuel economy to be gained when not towing heavily (driving empty) and idling (like sitting at stop lights). Big displacement engines drink big all the time. Smaller displacement engines drink less unless they're working hard.

 

Eh, sort of. Fuel consumption is directly related to power output in all cases. Put a 6.7L engine in a smaller vehicle and you could see substantially better fuel economy if geared right.

There is a LOT that goes into engine design and calculating efficiency, but engine size is one of them. There's a reason the 6.2L engine was only rated at 12/16 MPG in the F150, whereas the smaller V8 was rated at 14/19. You don't think engine size had anything to do with that?

 

What's that now?

 

I realize shaving 25% displacement will not boost mpg by 25%...fuel economy is more complex than that but it would save some. Taking the V8 6.7 and shaving off 2 cylinders would also save some money in parts and engine compartment space. So if two F250's or F350's were sitting side/side and identical except one had the 6.7 making 925 lb ft and the other had a 5.0 making 700 lb ft (more than the F650 by the way), I'd take the truck with the 5.0 diesel. Its 700 lb ft would be more than plenty and that would be money saved.

I have to wonder where will the power race stop? Power is great for toys, but there comes a time when money is important too.

 

You're making a comparison for GASOLINE powered engines, not diesels which is what the OP seemed to be looking at. Gas engine fueling is based on a stoichiometric mixture so obviously a larger displacement engine will burn more fuel since it has to in order to prevent damage.

A diesel on the other hand can be run with significantly more air than the fuel volume requires to burn, meaning the displacement of the engine is more analogous to a power cap at the maximum level of airflow based on how much fuel can be pushed into the cylinder and still burn without burning up the exhaust. Gas engines essentially have a fuel economy floor created by the stoichiometric ratio required to run the motor without burning the valves and pistons. Diesels have a minimum amount of fuel required to idle the engine, but they also typically consume less at idle that gas motors so the idle fuel requirements of the smaller diesel is less of a concern than power output at driving speeds.

Yes engine size matters, A LOT, but in this small example of paring down the displacement of a diesel engine by 25% without changing the rest of the design of the truck, there is no guarantee that fuel economy would increase with the smaller motor. It would most likely be very similar in most situations, more dependent tuning of the torque peak related to vehicle speed than displacement of the engine.

 

BTW, Texastech diesel....pretty interesting idea of a diesel over electric hybrid pickup. I ain't saying it's practical today, but definitely would be cool if it could cut fuel, save weight, etc, etc.

 

I would take a detuned 6.7 over smaller displacement. When I drove for a living, we had Cummins that were rated at 1100tq and 330hp, with a gross weight of 101,500lbs we still got 5.9mpg on average. Yes, we were slow up the mountains, but we made it almost every time (barring the sporadic failures). We didn't put a truck out of service until it hit 1 million miles. The only reason manufacturers are putting so much tq and hp into trucks today is because of the consumer. Most people want to compensate for their insecurities by driving 70mph up a hill with a trailer rated to run 65mph, to prove how awesome they are; Then complain about engine failure. I guess I don't get it, or I have an old school mindset.

 

How many gears in the transmission?

It's not about the HP, it's all about how you use the torque.

Tom - this isn't meant to be flippant, I really think there's an underlying issue here. To get cylinder deactivation on a gas motor GM had to install HPO activated collapsible push tubes, that turned cylinders in to air springs so that they didn't move any air through the engine each compression cycle. I think there is a ton of potential in forced-induction gas powered motors, direct injectors, and cylinder deactivation, I was just saying that in the narrow slice the OP brought up that engine displacement is not the only, or even primary, issue.