HP/TQ Graph

kenkillsr · 12-30-2007, 04:44 AM

Tech's;
I recently read an item in TL wherein the tech stated; "the most efficient operation, {sweet spot}, is where the HP and TQ curves intersect."
Since reading this, I've been searching for the chart/graph relating to my 2005 E350 6.0L PSTD.
Anyone know where I can find one or more?

**BroncoHauler** · 12-30-2007, 09:21 AM

I don't know if that makes any sense. You're plotting two different variables on one graph, so you can pick completely different scales. As a matter of fact, you can pick scales where the plots will never intersect.

Herb

scatter · 12-30-2007, 09:58 AM

Ken, here's the HP vs Torque graph that was in the 2007 E-350 brochure.

I always thot that the HP and Torque intersected closer to 2,000 rpm, but I guess not. I don't know if the above graph is valid for every year of 6.0, but I'm guessing it is or at least very close.

Herb, you're right that they are different values/scales, but both HP and Torque are rated against RPM so can be ploted on the same graph against RPM. Anyway, that's what they do as can be seen above.

mmocken · 12-30-2007, 11:59 AM

There is no 'sweet spot' on modern diesels.

Older diesels did have peak torques at 1500 RPM and also peak firing pressure.
-This was to give minimal engine noise/peak fuel efficiency
-Mechanical fuel injection was tuned for performance at lower rpms
- 2 valves/cylinder and high weight internally prevented higher rpms

On the PSD, the peak HP occurs at 3000 rpm, this also coincides with the drop off of torque. The torque drop is due to the ECM limiting turbo pressure and fuel.
- I'm sure this engine could produce up to 4000 rpms. Of course at 4000 you have to worry about valve bounce and overheating components.
- I would never chip a modern engine....there is not enough design margin today.

**BroncoHauler** · 12-30-2007, 12:04 PM

True, they can be plotted on the same graph, but if I change the scale for Torque on the left hand Y-axis to read between 250 and 500 ft-lbs instead of 200-450 ft-lbs, it will in essence move the torque curve downward in relation to the HP curve, thereby making the two plots intersect near 2000 rpm.

The horsepower at 2000rpm is still around 180HP, and the torque is still around 440 ft-lbs, but I've changed where the plots intersect. Actually in this scenario, they will intersect near 700 rpm as well.

I'll admit that I've been more of a Power Point engineer that electrical engineer for some time, but I think I have that right.

Herb

scatter · 12-30-2007, 06:04 PM

You've got it right Herb, at least right enough for me. What the graph is set up to show is where the max torque and max HP intersect. In this case around 230 HP and 440 lb-ft torque when turning out 3000 rpms. If you run at 2,000 rpm you'll have around 175 hp and 440 lb-ft. The graph is good to see what power you'll be developing at what rpm. As you pointed out, you can make it intersect wherever you want by changing the scale. Based on the proverbial "sweet spot" of max torque and HP, the 6.0 should be run at around 3000 rpm. Way too high for me!! Mmocken spells it out pretty well.
I'm turning 2000 rpm at 70 mph with 315 tires and 4.10 gearing. Sounds and feels good there. Nice thing on the diesel is that max torque is available from 1250-3000 rpms! Gassers are great engines too, just don't have that broad, flat torque curve. Did that keep me out of trouble??

JoeyNick · 12-30-2007, 07:55 PM

I have a PDF of the 6L Shootout Report, compiled in September 2005. A bunch of power programmers (chips) were compared head to head on a dyno, including stock programming. It's run on a truck vs. the van but you get a good idea with the numerous graphs.

Let me know where to send it or if there's a way we can post it on this web site.