I've been reading through threads and noticing in signatures different dyno results. It seems like the higher hp trucks, while having amazing torque numbers, don't seem to be as high in relation to the hp. For example, when I had my truck dyno'd, it put 325 hp down. Torque wasn't reading right, but the operator said said roughly 850. That's 2.6 times the torque as HP. There was a PSD there that had sheets from a different day that were 285/1100. That is 3.85 times the torque as HP. I know diesels are torque monsters. But it seem like the trucks putting down 500-600 don't make more than about 1300, which is only about twice the numbers.

What causes the numbers to be so different? Timing, rpm, charger size? Just curious.

 

When I was at 320 it was 740 torque.
It sounds like your dyno operator fed you a bit of a line as all the ones I've done were very close to double? My 24v was always a little lower than the 12v at the same hp?

 

What would cause this? Is the anemic breathing 12 Valve that much better for torque? Or is it the variable timing in the 24 Valve that causes the difference?

As fas as the operator feeding me a line, maybe. I can't say for sure, it was my first time having a truck put on the dyno. I would tend to believe that he knows what he's talking about, but maybe he stretched it a little too.

 

Its the rpms. The equation is hp = (torque x rpms)/5252. So if you could run to 5252 rpms the torque and hp will be identical. You're making a lot of torque at low rpms, so even though the power is there the rpms hurt the hp number you'll see.

Lets say you make 1000 ft/ lbs at 2000 rpms. Using the above equation you end up with 381 hp. Now if you made 1000 ft/lbs at 3000 rpms then you end up with 571 hp even though the torque is identical!

So bottom line is if its a high horsepower number you want to see then you want to make power as high in the rpms as possible. GSK, timing bump, or even a big laggy turbo can do this for you.

-The one who knows nothing of 12v cummins

 

What he said

 

and I'd really put some doubt into a sheet that had a PSD making 1100 lb-ft and only 285hp...

 

4 sheets to be exact. 6 speed 01. Same dyno. He had done it one day when they had the floor to themselves, he was the only one on the dyno.

 

I understand the equation. But I'm talking about the differences in peak torque to hp. 381/1000 is not out of the question on any of these motors. 571/1000 seems unlikely due to the nature of the diesel. Those are just numbers that you threw out there, I understand.

But it doesn't illustrate the peak to peak differences. I'm not trying to get real technical, sorry if it seems to be like that.

 

I generally figure 2-2.5:1 torque:hp ratio for CTD's, but it varies based on many things (like timing, turbo size, governor spring(s)).

I also doubt 285/1100, unless the truck was heavily modified and they only ran to 1400 RPM, and that's highly unlikely. Stock 6.0's started at 325/560 at the crank...

 

The dyno my truck was on said 376hp and 1100 ft.-lbs of torque. The rollers weren't calibrated to engine speed, so the torque numbers were off for everyone. Your dyno chart should tell you how fast you were spinning (MPH) when you hit peak hp. Find out how many RPMs that is, and do the formula to find your torque.

 

So the timing does affect it, being fixed is probably why a 12valve generally peaks at higher torque than a 24valve of equal horsepower.

01 PSD is a 7.3, not a 6.0. The guy knows Garrett(Bobcat) pretty good, it's a black regular cab XL F250. I'm not trying to say it is the beat all number, but 4 dyno sheets all consistent sure is hard to argue with. 3100 rpm max on the dyno graphs IIRC.

 

Normally, bigger chargers are used on higher HP engines...they don't spool as well, and torque suffers Torque is all about getting the bottom end going...lag is bad for torque!

Chris

 

I dont think I have ever even seen a stroke break 1000 torque. He may have it on dyno sheets, but he was either in a real low gear, or the dyno was junk.

Eric

 

Good post!

Could be that 12v's put out more torque at a given horsepower... Or it could be that 24v's put out more horsepower at a given torque.

 

Another thing to remember also is this...
The higher the rpm is where the truck makes max torque at the lower the actual torque number is.Also if they are close together in rpm relationship(max hp and max tq) the torque number will suffer.

When your dynoing on a jet that measures the numbers while accelerating the numbers will differ greatly if the truck can strike the hides early.The faster the truck can get to max power and the lower the rpm your tq number can be made,the more it can be raised.

Using this formula...T=(5252xHP)/RPM's

Truck A Makes 500hp at 2700 rpms....The torque would be=972 ft lbs.

Take that same truck and make the power lower in the rpm band and watch the torque number elevate...

Truck A Makes 500hp at 2150 rpms...The torque would be=1221 ft lbs.

So when the torque number inflates your getting close with your tune as you have the truck making power early and in the powerband where its supposed to be made.I have seen many trucks on the dyno and when trucks make power late in the run they always are short on torque.This is also why you will see a elevated torque number on a drug truck as they can strike the hides hard and early which will have the max power made alot earlier than the same truck with no drugs.

The power we make with these trucks on a dyno is all based off of acceleration,if you can get it lit early it will make power and torque,lite it late and then the torque number will suffer but the hp will show itself late in the run.Does timing have something to do with it,of course as anything than will allow the motor to lite sooner will enhance the numbers.I'd love to see someone make us a box for the electronic trucks that has the advance early and then retards it late in the run as I know how much I have gained in other applications with a retard box.........Andy