Power Band

[FB71]

OCD or just joking? I take some wonderful meds for mine!

[blkfordsedan]

Thanks Jim. That helps explains a couple things. Now I just have to figure out the math behind it so I can quit thinking about it.....and check to make sure the oven's turned off......3 times.......while only trying to rotate the knobs counter-clockwise...........and counting the steps from the computer to the stove.................

[FB71]

I may be wrong, but the dyno actually measures Torque (force) & RPM and calculates HP, right?

correct. HP is work over time.

The mathematical correlation between them doesn't change. In theory, you should be able to calculate HP at any given RPM if you know the Torque. What's the difference between the dyno taking readings at the crank vs. at the wheels (other than being less)? Obviously, you have a torque converter and tires than can slip and absorb varying amounts of torque, but that's the whole point of a Chassis Dyno. It measures the bottom line force that the wheels put to the pavement and takes all other factors out of the equation? I guess I can't visualize how a chassis dyno would have any effect on the 5250 point.....I would say that the only factor would be the accuracy of the dyno and procedure.

If the gearing is not accounted for by the dyno operator, the crossing will move on the readout. Most operators properly account for final drive, and direct drive thru the trans is assumed. However, transaxles never have a 1:1 gear, to eliminate hunting gearsets. Its always a tad higher or lower (0.97:1, 1.04:1, etc.). This will move the crossing on the graph. If the crossing is nowhere near 5252rpm, then the pull was done in a gear other than 'direct'. A common trick for a local Aisan/Euro tuner is to do dyno pulls in 3rd to falsly inflate their tq claims.

[FestYboy]

dropping 200 lbs on a 1900 lb car will make a notable differance (follow: 63hp into 1900lbs = 30.16lbs/hp, 63hp into 1700lbs = 26.98lbs/hp. that is a 10% loss of weight (give or take) and will net better accel and economy.) totally worth it as it's "free" were a cam runs about $150 and you're still draging that weight around with only 6 more hp to help it out (27.5lbs/hp). now on that thread, we'll go one better, weight loss AND mods... so, 1700lbs + 63hp + ~6hp for the cam, + 2hp for catback exhaust, + 4hp for header and +2 for modded intake = 1700lbs + ~77hp: that's 22lbs/hp (much better)

[smokeshow]

odds on, you are probably right PWGUS... but I would be interested to see someone to post data to back up my statements...

[pwgus]

well what do we have, rear seats, air bags on the aspire, air conditioning, passenger seat, that probably only amounts to 100-250 lbs, not worth it in my book, the ac maybe but the others are too much for me justify. if it was whole seconds that would be one thing, but completely stripping down the car for .1-.2, maybe .4 s at tops of an increase seems unjustifiable

[smokeshow]

Going completely outside this spectrum of engine, but still on same topic.. but on low torque vehicles ( i.e. Festiva ) weight reduction is usually the best/cheapest way to make a car quicker.. Because you are changing the power/torque to weight ratio.. The old rule of thumb being 1/10 off of the ¼ mile time for every 100 lbs you lose.. but this is different and actually somewhat increased on low torque vehicles, because you will bigger changes when you drop 100 lbs.. due to the lower torque ratings...

My 2¢

[smokeshow]

I agree with your thoughts on the 5252 rpms... It was just my personal observation that 99% of the time on chasis dyno's they still cross at 5252.. ( I just put 5250, because on most dyno screens you can't visably see 2 rpm).. but yes, physics/math never lies!

[blkfordsedan]

Guess I never actually thought about it, but it seems to me that although drive train losses reduce efficiency, but both HP & Torque are reduced.

I may be wrong, but the dyno actually measures Torque (force) & RPM and calculates HP, right? The mathematical correlation between them doesn't change. In theory, you should be able to calculate HP at any given RPM if you know the Torque. What's the difference between the dyno taking readings at the crank vs. at the wheels (other than being less)? Obviously, you have a torque converter and tires than can slip and absorb varying amounts of torque, but that's the whole point of a Chassis Dyno. It measures the bottom line force that the wheels put to the pavement and takes all other factors out of the equation? I guess I can't visualize how a chassis dyno would have any effect on the 5250 point.....I would say that the only factor would be the accuracy of the dyno and procedure.

I know it's pointless, but to me this is a very interesting query and I am a self-admitted Geek!

[pwgus]

Tq and Hp, as measured at the crankshaft, will ALWAYS cross at 5252rpm. No outside influence affects this constant. Now, as measured at the wheels, is a completely different story. Drivetrain losses must be accounted for.

That I can agree with I think

[FB71]

Tq and Hp, as measured at the crankshaft, will ALWAYS cross at 5252rpm. No outside influence affects this constant. Now, as measured at the wheels, is a completely different story. Drivetrain losses must be accounted for.

[pwgus]

I didn't mean for it to sound demeaning/offensive/condisending... Just inquizitive, and I tend to type faster than I think

I have done this more times than I can think of in my life lol

HP & Torque will ALWAYS be the same at 5250 rpm. It is a law of Physics!

I contend this in that in a perfect physics law system you may be correct, but like I say, other real world infinite variables will always present themselves, throwing our wonderfull calculated numbers into chaos (enter quantum physics, but thats somewhere I don't want to go lol) I liked the lower paragraph, tho most interesting. I just doubt that in practical aplication your always going to end up getting HP & Torque to cross perfectly at 5250 rpm's.

[smokeshow]

I didn't mean for it to sound demeaning/offensive/condisending... Just inquizitive, and I tend to type faster than I think... LOL...


Rock on!!!

[blkfordsedan]

I am not questioning the theory, I know that what is it supposed to be. If need be, I will post pics of the dyno sheets... I am just curious as to what causes the numbers not to be correct... Anyways.. I think we are still following the lil white rabbit.

Sorry Smokeshow, wasn't questioning your knowledge specifically. I was just trying to shed some light for some of the less experienced guys who were asking. Your statement was just the most direct to the subject.

As for why they don't cross on some of the Dyno sheets, I don't understand that one either. Has to be a difference in the RPM scale between the HP & Torque? If you find an old sheet, I'm sure you'll notice right away.

[smokeshow]

I am not questioning the theory, I know that what is it supposed to be. If need be, I will post pics of the dyno sheets... I am just curious as to what causes the numbers not to be correct... Anyways.. I think we are still following the lil white rabbit.