Lower hp ratings in HD trucks

I know it has been discussed here before, but I found a real answer so thought I'd bring it up.

Example, the Ford 6.2L V8 and the RAM 6.4L Hemi are both rated for less power when the truck's GVWR exceeds 10K #.

Ram 6.4L Hemi in a 2500 - 410 hp, in a 3500 Megacab - 367 hp
Ford 6.2L V8 in an F250 - 385 hp, in an F350 DRW - 316 hp

The question is WHY?

Most will answer that it's due to different engine calibrations for more durability. That's incorrect.

The real reason is NOISE and the EPA.

I was following this thread called: "Ask the engineer" where the engineer that designed Ford's 6.2L V8 (Mike - V8 Ford) was answering questions.
Here's a link to the page where this question is addressed.
LINK

His response is broken into a few posts as people ask clarifying questions. I'll copy and paste here.
--------------------------------------------------------------------
"Originally Posted by boatwon
Hey Mike,

What is the difference in the 6.2 for a dually application? Or is it same engine at a lower RPM rating? Will it still rev to 6000 RPM? Same power through whole range or different programing?

thanks, Doug"

Reply: "Same engine, same calibration, same everything, except that power is declared at a lower speed, resulting in a lower power rating."

Quote:
Originally Posted by Crazy001 View Post
It's rated at a different RPM.

If I remember right it's rated at the torque peak rather than the HP peak.

So the same engine will perform the exact same way, but for reasons I don't understand rated HP is different from peak HP.

As an example, consider your van. It makes 410 ft-lbs @ 2,700 RPMs. If it were rated the same way the new engines are in dually applications it would NOT be referred to as a 265 HP engine. It would be a 210 HP engine(410 x 2,700)/5252.

Same engine, same peak HP, just rated differently.

Reply: The power and torque for the over 10k GVWR Superduty 6.2L is rated at 4200 rpm (hence the lower power number versus the F250). The engine still redlines at 6000 rpm.

On the F250 the peak horsepower is at 5500rpm and the peak torque at 4500 rpm.

Thanks for the correction, Mike!

Sorry to confuse things, Bill. I read about this awhile ago and I thought it was at the torque peak. Looking back I'm seeing 316 HP and 397 TQ, both rated at 4,179 RPMs.

So not quite torque peak, but both numbers are rated at the same RPM for some reason. Why is this?
__________________
Tom

Reply:
Compliance with EPA noise requirement

Tow Vehicles

22 Replies

FishOnOne
Nomad
Feb 12, 2015
Lessmore wrote:
Sounds like the way Chevy rated the old L-88 427 Rat motor in the late '60's. This engine was not really for the street, more of a semi race engine. Chevy rated it lower at 430 hp, than their 427 , 3X2 barrel carb 427 which was rated at 435 hp.

The 427-435 HP engine was an engine that ran well on the street and was not in the same high state of tune as the venerable L-88. Also the L-88 was very expensive and not many were made.

The reason, GM didn't want customers buying the L-88 because it was the top power rated engine in the line, then be unhappy with it, while trying to run this hopped engine on the street.

So....my understanding is that they also rated the 427 L-88's HP, not at the peak rpm where it developed it's top HP (some say around 560 HP) , but at a lower rpm, where it did, indeed develop 430 hp.

I'm sure there will be a few posters that will say...no...none of this happened.

But there you go.:D

Agreed... I know all very well what it's like to have a hoped up engine in your daily driver.

I'm lucky to be alive....:B
FishOnOne
Nomad
Feb 12, 2015
I'm just impressed that a Ford engineer would spend the time on an internet forum and answer technical questions about a particular engine. Equally impressive is to know the name and face of the engineer who played a significant role with the design.
Learjet
Explorer
Feb 12, 2015
blame it on the old loud oil burners :)
steve-n-vicki
Explorer
Feb 11, 2015
look at the fan size , more blades ,bigger diameter = more noise, hence lower RPM , less noise, its all about heat rejection under sustained high engine loads
RoyJ
Explorer
Feb 11, 2015
VERY interesting!

I always knew they rated it at the torque peak rpm, but I thought they artificially chopped the redline to that rpm as well.

Good to know the engine is exactly the same as a <10k lbs version, just that the rating occurs at a lower rpm.

So I guess if you wanted to, you can put your foot down, and rev to the exact same hp peak as a 3/4 ton truck. Only you're technically "over-revving".
Bedlam
Moderator
Feb 11, 2015
That may be happening within the pickup line. Once you get to the chassis cabs, they run a different tune on the engine to allow longer duty cycles at full output. Look at 6.7 specifications on Powerstroke and Cummins diesels in the pickups and then look at them on the chassis cabs - They did not derate these engines due to noise or EPA. I posted Hemi numbers before when the same engine is used for different platforms - You cannot tell me that all the engines were tuned the same and the measurements were taken differently for each one.
ib516
Explorer II
Feb 11, 2015
mabynack wrote:
fla-gypsy wrote:
The Ford engineer stated quite clearly there was no difference in the Ford motors they rated differently. They were not de-tuned, etc. They simply measured the HP/Tq at a lower RPM to meet the silly EPA noise regulations. If you own one of these de-rated motors rest assured it makes the same power at the same RPM as the higher rated motor.

I've been searching around the internet and found several references that say the same thing. Apparently they run the engine up on the dyno until the noise level gets to the limit and that's the point where the peak HP reading is measured.

Exactly what I found.
mabynack
Explorer II
Feb 11, 2015
fla-gypsy wrote:
The Ford engineer stated quite clearly there was no difference in the Ford motors they rated differently. They were not de-tuned, etc. They simply measured the HP/Tq at a lower RPM to meet the silly EPA noise regulations. If you own one of these de-rated motors rest assured it makes the same power at the same RPM as the higher rated motor.

I've been searching around the internet and found several references that say the same thing. Apparently they run the engine up on the dyno until the noise level gets to the limit and that's the point where the peak HP reading is measured.
ib516
Explorer II
Feb 11, 2015
Yes, the hp rating for the F350 DRW version was at 4197 RPM or some silly number like that, and the F250 version was rated at it's real peak hp at 5500 RPM or thereabouts.
fla-gypsy
Explorer
Feb 11, 2015
The Ford engineer stated quite clearly there was no difference in the Ford motors they rated differently. They were not de-tuned, etc. They simply measured the HP/Tq at a lower RPM to meet the silly EPA noise regulations. If you own one of these de-rated motors rest assured it makes the same power at the same RPM as the higher rated motor.