These are the dyno numbers from my emissions test today:

60 mph: force: 1266.612 HP: 202.787
50 mph: force: 1397.666 HP: 186.333
40 mph: force: 1416.457 HP: 151.066

I'm trying to get to some meaningful numbers both at the flywheel and rear wheels. Rear wheel HP is obvious and I believe I want to divide the force figures by my 3.54 rear ratio for rear wheel torque, correct? With a stock auto tranny is there general formula to convert all of this into flywheel HP and torque? Also, am I seeing what I should be with an EZ box set on pin set 3 and a turnbuckle? Altitude of the test was approximately 6000 ft.

Oh yeah, forgot to mention that the tech was a fairly attractive blonde gal with diesel soot smudges on her face....no kidding.

 

First, go back to the basic definition of horsepower.
1 HP + 33000 ft - lbs. per minute

At 60 MPH the truck travels 5280 feet per minute. It develops a force of 1267 pounds against the restraint on the dyno.

Compute 1267 pounds * 5280 feet per minute / 33000.

What a surprise -- 202 horsepower!

Getting torque is a little trickier.

If the truck is not moving, the tires are "pushing" with the same force that the dyno is "pulling" 1267 pounds.

Now, torque = Force * moment arm in feet.

If we imagine your truck has 30 inch diameter tires (just a guess -- also remember the diameter "grows" as the tire spins faster), then the moment arm is 15 inches or 1.25 feet.

So the torque at the rear wheels is 1267 * 1.25 or 1583 foot - lbs.

To get torque at the driveshaft, divide by the axle ratio of 3.54 or 447 ft-lbs.

Generally speaking, delivered rear wheel horsepower is about 20% less than flywheel horsepower, so that gives you effectively about 560 ft-lbs of torque if the engine were taken out of the truck and mounted on an engine dyno.

As a check, we can use another formula -- HP = Torque * RPM / 5252

If we imagine your engine running at 1700 RPM at 60 MPH and delivering 202 HP to the rear wheels, then it would have made about 250 HP on the engine dyno.

At 560 ft lbs and 250 HP, and assuming you had those 30 inch tall tires, the tach would have been indicating 2350 RPM, which sounds about right.

You can plug in your actual tire diameter to the method above, and also check the other speeds as well.

As to what you "should" get with your mods, I really don't know. That's why I'm reading this board.