5250 Rule Attn: Cuda

[gsmopar]

Cuda,

A while back you mentioned a dyno rule of I think 5250. You said that the torque and HP graphs should cross at I think 5250 RPM's or the graph is BS. I noticed all of the graphs in my magazines seem to cross at about 5250. The graphs on the Hughes page look kind of funky to me (big torque swing) and they don't cross at a consistent rpm graph to graph. You think they're bs'ing us?

Dyno Pulls <-- link here

PS: I've been on shift at work and won't get to pull my oil pan until tomorrow sometime (Posted a thread a while back about a clanking noise when I flipped the engine on the stand!)

Thanks,

Greg

[cuda66273]

The rule of 5250 is pretty much etched in stone, I believe that you could vary it by adding an un-natural element like NOS or a blower.

Maybe Dynorad will chime in here and clearify this as I've not seen the Hughs dyno sheets to make a judgement.

I'll drop him an email and see if he wants to comment

Lemme know about the clank thing....

[gsmopar]

I added a link above if you want to check them out. No nitrous on any of these runs. They say it's "Corrected." May be running at high altitude?

[cuda66273]

I would need a detailed explaination of how they got the tork curve to do that on #1 and 2

#3 looks pretty good as it's corrected HP and tork and very normal.
#4....again I'd like to hear the details before I passed judgement....to me it doesn't seem right???

Dynorad....what do you think?

[cuda66273]

In reading their discription I see they spec a "Rewoked manifold with plenum modifications"

I wonder if they used a $1000 Wilson manifold to achieve those numbers....that $1000 doesn't include the manifiold.....just the re-work.

[dewme5]

it's 5252rpm that the crossover point occurs. HP is just a factor of torque over time.

TQ X Rpm / 5252 = HP

400ftlb x 5000 / 5252 = 380.8hp

400ftlb x 5500 / 5252 = 418.9hp

you will frequently see dyno graphs that don't cross at 5252 graphically.. that is, they alter the graphs so that you get the biggest visual impact, but these graphs have HP labels on one side, and TQ labels on the other side.

if you take a look at dyno pull number 4 from the links provided above, you see that the two lines cross at approx. 4500rpm, but the scale on the left goes to 600 (HP), and the scale on the right goes to 700 (ftlb) But, if you follow the rpm on the bottom over to 5252, and then straight up to the orange line and straight over to the right, you see it's at about 545ftlb, and then follow 5252 up to the blue line, and then all the way to the left, it again comes out to about 545 HP.

Hope that makes some sense of it for you

[dynorad]

Dewme5 is exactly right.

There is nothing you can do to an engine that will make the HP and torque curves not match at 5252 RPM assuming that your units of power are HP and your units of torque are ft-lbs.

When your power and torque curves are corrected to standard conditions (29.235 in Hg, 77F, 0%RH) both curves are scaled by the same factor. So correction will have no effect on where the curves cross.

If your test is run at more favorable conditions than standard, the uncorrected power numbers are reduced to achieve corrected HP, and if you are running at conditions that are worse than standard (more likely), the uncorrected power numbers are increased to achieve corrected HP.

Here in the Denver area our uncorrected numbers typically have to be increased by 20-25% to account for the low air density.

Correction is useful for comparing runs on different days or for comparing one car to another, but have no bearing on the actual 1/4 mile performance of your car. The uncorrected number is more useful for predictiing actual performance.

[cuda66273]

I see now what Dewme5 is talking about...just seems a little bit deceptive to me, could lead the unknowing into believing something that's not quite correct.

[CudaMike]

Dewme5 is correct. If the same vertical scale is used for both TQ and HP then they will cross at 5252 rpm on a graph. If they use different scales (fairly common), they won't. You can multiply out the numbers at a given rpm to see if a graph has been doctored.

[Eric Strong]

When I first saw this formula for 5252, I was very suprised. I thought it was a hoax, so I tried a few combos on the Desktop Dyno and to my surprise it checked out every time. I think this could be a great benefit to those of us who question dyno graphs like those from Hughes.

Quick Claims Adjuster!!!

[mtrv8n]

OK, guys..how many feet in a mile???


OH!!!!!!!
Thats where the number comes from, because torque is calculated in Ft - lbs, and HP is time and miles...

[gsmopar]

5280

[dynorad]

One of the definitions of power:

Power(ft lbs/sec) = Torque(ft lbs)*rotational speed (radians/sec)

1 HP is 550 ft lb/sec

1 RPM is 60/(2*PI) radians/sec

So after the unit conversions and algebra:

HP=(Torque*RPM)/ 5252.1131

People round it to 5252 or sometimes 5250.

[gsmopar]

You guys and this board rule!