VAP

whether diesel, gasoline or Wankle/rotary... modded or stock, fuel injected or carbureted, turbo'd/supercharged or normally aspirated?

I just figured this out on the software that came with the Dynorad while playing with it on the computer. Then I went into my Desktop Dyno software and it confirms the same thing. How/why is this possible and how/why have I never known this before!?!

JWG

While I have forgotten the specifics (do a search in the A4 forum under "5250"), the mathematical formulas for hp and torque always have the same value at 5250.

Basically, it seems counter intuitive, because we generally think of hp and torque as natural forces that obey the laws of physics rather than contrived mathematical formulas that artificially quantify the natural physical forces.

In a way, it makes perfect sense. How else would we measure the forces generated from a spinning piece of metal, i.e., the crankshaft, other than through taking known values and performing mathematics on them?

VAP

how/why while HP can be corrected and torque can't due to not having a "formula", their paths still cross at the same 5250 intersection.

I shoulda paid more attention in those classes.

But thanks for the confirmation and explanation. Tho I still don't fully understand it's nice having the confirmation/corraboration that my "theoretical" data corrections are not faulty.

A6Gary

Here is the reason for why the two factors are related:

T=(63,000)(P)/n

where:
T = torque, lbf-in (pound force-in)
P = power, hp
n = shaft speed, rpm

Power is computer as a function of force and velocity (i.e., piston speed and stroke):

P = (F)(V)/33,000

where:
F = force, lbf
V = velocity, ft/min

In general, an in-line engine produces its peak torque at about 1/2 of the speed of a V engine since the in-line usually has a stroke that is ~twice of the V. Also, an in-line engine that has multiples of six cylinders (e.g., 6, 12, 18) will be harmonically smoother than any other engine.

Hope this info helps you.

JWG

63000=5250*12; why is your figure 12 times bigger? Instead of 5250 Revolutions per minute, you have 63,000 revolutions every 12 minutes or 1/5 hour.

Otherwise, assuming an engine makes 100 hp at 5250 RPM, you will make 1200 lbft of torque using your T=(63,000)(P)/n. Using T=(5250)(P)/n, the engine making 100 hp at 5250 makes exactly 100 lbft of torque.

Decades have passed since I took a math or physics class at the university and I do nothing more complex than add, subtract, multiply, and divide in my job, but I did pay attention in class.

Help?

A6Gary

Engineering Design", by Shigley. If you mulitply your 5,250 by 12, you get the 63,000. The factor of 12 is needed to switch the units from "feet" to "inches" to come out with torque in "lbf-in" in these equations. One horsepower is equal to 550 ft-lbs/sec or 745.7 Watts.

JWG

"In general, an in-line engine produces its peak torque at about 1/2 of the speed of a V engine since the in-line usually has a stroke that is ~twice of the V."

Why would the I-6 have a 2x longer stroke than the V-6? That does not make any sense to me. Both engines would seem to need to make a similar length stroke; the V vs. I configuration only has to do with proportions not power. A V-6 is much shorter than an I-6 but correspondingly much wider.

12v stroke = 3.40 in. (86.4 mm)
12v Max torque 184 @ 3000 RPM
BMW 3.0 I-6 stroke = 3.53 in. (89.66 mm)
3.0 I-6 Max torque 214 @ 3500 RPM
BMW 2.5 I-6 stroke = 2.95 in. (74.93 mm)
2.5 I-6 Max torque 175 @ 3500 RPM

With all due respect, your statement does not appear true.

Audiboy

should be 5252 but close enough. Watts his name? Watt? :P

xr4tic

HP = Torque * RPM / 5252

So at 5252 RPM, HP = Torque. Above 5252 RPM, HP is always more than Torque, and below 5252 RPM, Torque is always more than HP.

Get any numbers from the Dynorad yet?<ul><li><a href="http://vettenet.org/torquehp.html">http://vettenet.org/torquehp.html</a></li></ul>

A6Gary

For these two engines, the peak torque of the 3.9L V-6 was at ~2x the peak torque of the Chev 250 cu in I-6. Obviously, I didn't take a look at BMW's in-lines vs. the Audi's V-6s. I believe that the engine designers/engrs reduce the stroke of V engines because of the eccentric loads that would be increased due to the piston on one journal being much further from the other piston on the same journal (hence, greater forces on the block &amp; crank). Also, having a shorter stroke allows the engine to rev up faster than it would with a longer stroke. But the trade-off is a longer stroke increases torque. So, it's a balancing act between increased RPMs vs. increased torque, which is up to the engine designer/engr.