That is not so.

The F-350 is expected to have a duty cycle of around 25-40% of rated 350hp.

The F-550 is expected to have a duty cycle of 50-70% of 325hp.

You are comparing peaks, not average.

Cooling have to be sized for average, not peak.

When there is a peak cooling need, there is a degree of "overhead" before the system gets overwhelmed (aka rad boil over).

The overhead can be improved simply by adding a bigger tank of coolant, e.g. a 5 gallon aux tank.



That is not a directly comparable measure, though it is indeed the case that the 6.7 cooling capacity is bigger.

Cooling capacity is not just a function of radiator size and depth.

A more accurate measure is the surface area exposed, which require a measure of the total fin area --- that require measuring the dimension of individual fins and multiplying.

A certain amount of tweaking also need to be made for the closeness / density of the fins (e.g. if the fins are too close, they radiate heat at each other and do not allow enough air flow and vice versa).

Then there is the real big difference --- the size, power, and programming of the fan.

That, in the shroud, and with some calculation of force air flow (from the vehicle at speed) gets you the airflow across the radiator.

A far more complex calculation than just comparing radiator sq. in. and thickness.

If you want to get real cute, aerodynamics of the underhood, air flow under vehicle, underhood temperature, ambient temp, etc. all make a difference....

 

It's not true?

Then how can an F-250 pull a hill like Veil Pass or the one leading up to the Eisenhower tunnel at full throttle without overheating?

This is NOT cooling the average engine load, but rather the peak engine load. For a relatively extended period of time.

 

The question is, peak for how long?

That is where reserve capacity comes in.

Reserve capacity is a totally different thing.

Think of it as thermal mass.

Suppose vehicle A and B both have an identical heat dissipation capacity in the rad.

A has 50% more power than B (and generate 50% more heat to dissipate).

Theoretically, A should overheat first, all other things equal, right?

OK, now, hook up a 50 gallon tank of coolant to Vehicle A, vs. the standard 8 gallon of coolant.

You have now added roughly 6 times the "reserve capacity" to A.

It will eventually overheat, but not before heating up 58 gallons of coolant.

That is reserve capacity or a lot of thermal mass.

You cannot know that without knowing the other parameters of design.

Including the programming / clutching / of the Fan.

As simple a thing as turning on the fan sooner can majorly impact the "reserve capacity" of the cooling system.

A software tweak...

 

Thermal mass lesson:

Remember the runaway cars?

The manufacturer insist that brakes always overpower the engine.

That is true for the first 2 or 3 stops (from cold).

Once the brakes heated up, they fade.

Thus, thermal mass (reserve capacity) vs. peak capacity... in a different sense.

Their peak capacity from cold generates a braking force more powerful than the engine / transmission the first few times.

But once they "soak up" heat, they are weaker than the engine...

The same story, applied to brakes.

 

Nope, this is where experience comes in.

I agree with your point about reserve capacity, but remember we're not talking about lawnmower engines here. These things put out a LOT of heat, and are capable of heating all 1,100 lbs of engine, coolant, and oil to operating temperature and beyond VERY quickly.

Now for that part about experience...

From our meets we've had in OH lugging 11,000 lbs up hills at full throttle repeatedly, I can say conclusively that under full throttle pulling the hill at ~35 MPH the coolant temperature goes DOWN when the cooling fan comes on. This at 70° F.

Now there is a temperature point where this will no longer be the case, but for the vast majority of situations these trucks can cool well under full load. This was further demonstrated in the "rumble in the rockies" test. Full load for over 10 minutes in thin air, and it did NOT overheat. While belting out 400 horsepower.

 

You are measuring the temperature at one sensor at one location.

The observation that the temperature measured goes down do not say much except to say that the cooling fan do move air across the rad, and in doing so, the liquid temperature is cooler at the place it is measured.

Thermodynamics and heat is well understood in terms of physics, and vague terms like "a lot of heat" is not helpful when what is needed is to nail down specifics (calories, etc.) as to how much heat is generated, how much is being dissipated (via the cooling system), etc.

To see the temp gauge move down when the fan comes on tell you not much.

It does not ask or answer the question of how much energy has the coolant soaked up in the entire system.

In order to answer the question, you have to get a weighted average temperature of the coolant in the entire system, and then pose / answer the question of what is the total caloric capacity before and after your tow, how much was "cooled" by the rad etc. and lost, and then to ask, how much reserve capacity (defined by how much more heat can be introduced into the cooling system given the rate of cooling / dissipation) is left before it boils given the pressure / temperature in the system.

Unfortunately, doing that require laboratory / engineering validation equipment, not a crude mass market temperature gauge at one point.

If I took the same temp gauge, and moved the sense point to a different location, (e.g. closer to the cooled coolant intake on the engine; or conversely, at the hot coolant exit to the radiator), I would get totally different measures.

 

I love this place...Thermodynamics 101...when can I apply for my diploma?

 

When you have them hot flashes.

 

Words of wisdom:

Arguing with an engineeer is like wrestling with a pig in mud, after about 30 minutes you realize that the pig is enjoying it!

Interruption complete - please carry on.

 

Who's the engineer?

 

I'd be willing to bet that the 550 is expected to have a significantly lower average vehicle speed during its life, which _could_ (I don't claim it does or does not) significantly impact how much cooling/hp is required. The fan is an excellent mover of air, but not remotely close to driving down the road @ 50+ mph.

There was a comment about the RiR test requiring full-power towing at high alt for a fair while. One of the things I've wondered is whether Ford's liquid-to-air intercooler might be a significant liability under high sustained loads. LTA coolers are inherently less efficient than ATA, simply because you have to move heat across 2 barriers instead of just one. OTOH, LTA coolers are much more consistent (or should be if they're tied to engine coolant temps) because you don't have nearly the temp fluctuations involved (ambient fluctuates much more than engine coolant, unless you're trying to overheat).

So, in a high sustained load situation, the intercooling system can overheat more easily in a LTA cooler than an ATA system of the same size. This would result in Ford's hp declining, even if the ECU _wasn't_ adjusting. The ECU will have to adjust, though, to prevent blowing the engine apart eventually. I don't claim this is all a factor in the RiR test, but it's a very real possibility. The ECU adjustments are also the one thing that all of gearloose1's naysayers are continuously ignoring.

Again, I don't claim I know what's being done, but I know what _has_ to be done (for the reasons already explained in this thread).

 

You make a great point about the CAC efficiency. I don't know the effect it has on IATs, but it would be curious to be able to read the intake temps.

I have it from a credible authority that turbo capacity was likely the limiting factor in the RiR test.

But that's for another thread, this is about possible capacity. I brought up cooling because I think that's a tough thing to overcome when we're already pushing 400 HP. Then GL started talking about how it can only cool 300, and the debate ensued.

 

Indeed it did.

I am quite comfortable with the notion that the 550's engine is de-rated for durability reasons. Many, many factors or systems may be a part of the overall durability equation, but the basic durability issue isn't to do with the emissions system. To claim the contrary is genuinely silly, for the reason(s) I pointed out in my first reply. The O.P.'s question is thus incomplete; he needs to answer my question about 'for how long.'

 

Torque likely theoretical maximum (before crankshaft / bearings / connecting rods / cylinder walls fail....

I would thumbnail 2,000 ft lbs instantaneous for not more than 5 seconds.

HP... I would guess 1,000 hp for not more than 5 seconds.

Then a cooling rest cycle of 20 minutes...

Don't know how many cycles you can do this before it blows.


What we now need is a Ford test engineer to sneak a comment as to what is the "break" point.


Rules of thumb... quite often the safety factor is 2X the maximum expected stress.

I guess there is some leeway in the block for growth, so I stretched it a bit.

 

I really don't see a huge drop when the tuck is empty on flat ground, or on Teton Pass in Jackson Wy.

I do however see a noticeable difference towing 15,000 around. Of coarse you should notice that there is a load back there, not my point. The 6.7 seems to do well on relatively flat terrain at 6200-7500ft.

Here is what I have experienced with 3 separate trucks all F-350 long box crew cab 4x4 single rear wheels all towing the exact same load and trailer up the same mountain pass.

2001 f 350 3.73 gears, 16" rims 265/75/r16 tires, Banks power pack 120 hp chip. Towing 15,000 50mph all the way to the top with 1000-1100 degree exhaust. Yet still managed 18-20 mpg empty around 15 towing

2008 6.4 stock 3.73 gears 20" rims 275/65/r20 tires, same load same mountain pass, 25 mph.

Tuned the 6.4, 1300-1400 degree exhaust, 30mph no matter the tune.

2011 stock 3.55 gears, 20" rims 275/65/r20, towing the same load same mountain pass 38-40 mph.

So on the steep mountain passes I see a big difference between the trucks. Keep in mind that Teton pass starts out at around 6200 ft and tops out about ft. the road is a 2 lane with 10% grades and several switch backs all with in about a 3-4 mile stretch.

On flat ground I think the 6.7 is just as good or better than my 7.3 was.

Now I am sure that there will be someone come tell me that there is no way a 7.3 would do that, maybe I had a good one because mine would.

If anyone is in the area with there similarly 6.7 please get a hold of me and you are more than welcome to tow that same load up Teton pass and you tell me how well your truck does. I will say more than likely not a whole lot better than 38-40 mph.

I have noticed that once the motor oil temp reaches 230 degrees I feel a very noticeable drop in power out put. Maybe that could be remedied. I also feel that the motor wants to run more but is being held back by electronics.

I hope this helps answer you question.