Why the different ratings: under/over 10K GVWR Gas

[slarsen]

I have a 2012 Gasser, and I'm about to take a trip that will put me on the Rockies more than once. I was looking up the ratings to find the 'sweet spot' RPM's, and this is what Ford lists:


Horsepower 385 @ 5500 rpm (6.2L V8 under 10K GVWR); 316 @ 4179 rpm (6.2L V8 over 10K GVWR)

Torque 405 @ 4500 rpm (6.2L V8 under 10K GVWR; 397 @ 4179 rpm (6.2L V8 over 10K GVWR)


So my question is: why is the 10K GVWR rated so differently? What does this mean? I don't even quite get why there is a 10K rating vs. 9.9K rating in the first place.

Anyone?

[elkhornsun]

I would expect that with the 6-speed transmission and a tow load over 10K that the trans is in a lower gear (and have the engine at a higher RPM) than at the same speed with a lighter load. That would affect the engine RPMs and in turn the power output.

[slarsen]

I looked up the sources you referenced, ib516, and I am greatly reassured. Thanks for your wisdom and the response. And thanks to the others that went to the trouble of responding. I love this site.

[bmanning]

I remember discovering the de-tuning thing years ago while researching MD trucks; IIRC even some class 5&6 trucks run tunes in the 200-240hp & 500-600tq range.

If you look at MD & HD build sheets, there are usually multiple power levels to choose from, with quite a broad range.

As already pointed out, reliability & duty cycle expectations go up and there's still enough performance to get the job done at reasonable speeds. An inner-city delivery van that'll never tow and rarely even see the freeway just has no need for 350hp.

[ib516]

From what I read, the engines are exactly the same, with the same tune.

The power is measured differently in different weight classes, hence the different ratings.

The reason for the different ratings is for licencing and insurance purposes. Some take a big jump when GVWR exceeds 10,000#, so they rate one at just under that to save people money. Again, the trucks are identical AFAIK.

LINK #1

LINK #2

[JIMNLIN]

Reliability.
Truck makers have generally always (detune) used lower hp numbers in the HD (3/4 and one ton) versions.
There also can be a lot of difference in the engines internals in some cases.
Example is GM 5.7 they used for years would get things like flat top pistons with a 4 bolt main with lowered compression in the higher GVWR trucks vs two bolt mains/higher compression and domed pistons in the lower GVWR trucks.
All done in the name of longer term reliability. What Ford does with the 6.2 could only be answered by their tech folks or a web for the 6.2 internals and spec sheets.

Ford gives the 6.2 17 different GVWR's from 9900 up to 14000 lbs in the F250/F350 SRW and DRW trucks.

[Denny___Jami]

Same motor same tune it's just a wieght rating thing to make the goverment happy.

Denny

[Groover]

I have been trying to get the answer to that question for two years. From what I have found out the motors are identical with identical performance but rated to different specs. I have not been able to find a copy of the rating specs without paying several hundred dollars to SAE and no-one has volunteered to get a copy for me. No dealers I have talked with are even aware of the different ratings and cannot explain it when I ask. They also cannot explain why the diesel has the same rating in both trucks if it is just a GVWR issue. To further confuse the issue, the same motor in the F150 gets a third set of ratings and again I am told that it is the same motor.

[transamz9]

Benk is right, they de-tune the trucks they know is going to work for a living. CC truck most always have a lighter tune. They still have the power to do the work just slower.

[BenK]

Assume software to protect the ICE (internal combustion engine) for the higher
class trucks...because they are not grocery getter's, but WORK trucks

Duty cycle is the key for most things as you go higher in class into 'work'
vs grocery getter's or 'cars'

Oh...also assume 'duty cycle' is understood and know what that means

[rhagfo]

slarsen wrote:
I have a 2012 Gasser, and I'm about to take a trip that will put me on the Rockies more than once. I was looking up the ratings to find the 'sweet spot' RPM's, and this is what Ford lists:


Horsepower 385 @ 5500 rpm (6.2L V8 under 10K GVWR); 316 @ 4179 rpm (6.2L V8 over 10K GVWR)

Torque 405 @ 4500 rpm (6.2L V8 under 10K GVWR; 397 @ 4179 rpm (6.2L V8 over 10K GVWR)


So my question is: why is the 10K GVWR rated so differently? What does this mean? I don't even quite get why there is a 10K rating vs. 9.9K rating in the first place.

Anyone?

If you have that right, it is strange that the under 10K has a higher HP and torque than the over 10K. It is stating lower RPMs, so likely the same tune on the engine, just weird.