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Old 10-25-2002, 03:04 PM   #136
Scottycs
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200 hp is still more than m3s put down in 5th. You produce more torque because of the driveline Ratio but that is divded out, (Torque/(trans gear ratio*rear end)). Therefore in each gear you produce same wheel torque.

200 * 1.21= 240 whoopie

hence stock m3 is 200 wheel hp *1.21 and you get 242. WOW!

I will be calling you tomarrow afternoon.
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Last edited by Scottycs; 10-25-2002 at 03:07 PM.
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Old 10-25-2002, 04:35 PM   #137
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Actually, the torque isn't divided out. Your Dynapack (like any dyno) really has no idea what the final gear ratio is.

So it measures the torque available at the rear wheels for each gear, calculates the current speed and RPM, and the software in the dyno makes it's calculations from there.

When you're in 3rd gear, you're effectively trading RPM for more torque, as you do in 4th gear. In 5th gear, the transmission is essentially a pass through device, which means you're not losing any power through it (minus what the bearings absorb, and gears flowing through fluid). Fluid and bearing loss is about 1% max (based on information from ZF; I'll assume Getrag is just as efficient).

So while I don't doubt your 200 rwhp in 5th gear, I STILL doubt the 17% driveline losses.

This is especially true with the Dynapack, as you no longer have to contend with friction (tires) and tire flex losses. If anything, your driveline losses should be even LESS than the 12% I'm suggesting.

I really don't have any doubts about the Dynapack unit; it certainly seems to perform well. The driveline losses are something I still take issue with.


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Old 10-25-2002, 04:37 PM   #138
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No, it does not measure rpm, It divides wheel torque by the final gear ratio BC YOU MUST enter that in and it takes NO rpm reading. That is how wheel torque is calculated. Trust me, I know more than you on the subject!

As I said before, I will be calling you later on. No need for you to make remarks on subjects you are not familiar with.

Also the peak numbers are similar to your other roller dynos, though mustang dynos tend to be lower than dynapacks/dynojets.



Quote:
Originally posted by GR8 Ride
Actually, the torque isn't divided out. Your Dynapack (like any dyno) really has no idea what the final gear ratio is.

So it measures the torque available at the rear wheels for each gear, calculates the current speed and RPM, and the software in the dyno makes it's calculations from there.

When you're in 3rd gear, you're effectively trading RPM for more torque, as you do in 4th gear. In 5th gear, the transmission is essentially a pass through device, which means you're not losing any power through it (minus what the bearings absorb, and gears flowing through fluid). Fluid and bearing loss is about 1% max (based on information from ZF; I'll assume Getrag is just as efficient).

So while I don't doubt your 200 rwhp in 5th gear, I STILL doubt the 17% driveline losses.

This is especially true with the Dynapack, as you no longer have to contend with friction (tires) and tire flex losses. If anything, your driveline losses should be even LESS than the 12% I'm suggesting.

I really don't have any doubts about the Dynapack unit; it certainly seems to perform well. The driveline losses are something I still take issue with.


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Last edited by Scottycs; 10-25-2002 at 04:40 PM.
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Old 10-25-2002, 06:10 PM   #139
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Quote:
Originally posted by Scottycs
No, it does not measure rpm, It divides wheel torque by the final gear ratio BC YOU MUST enter that in and it takes NO rpm reading. That is how wheel torque is calculated. Trust me, I know more than you on the subject!

As I said before, I will be calling you later on. No need for you to make remarks on subjects you are not familiar with.

Also the peak numbers are similar to your other roller dynos, though mustang dynos tend to be lower than dynapacks/dynojets.



You know what...don't bother. If you're gonna be an ass, there is no point. You obviously don't understand anything about driveline losses, REGARDLESS of how your Dynapack measures it.

Ever taken an engineering class? I'll admit I don't know much about your Dynapack dyno (though I'll give it credit, it certainly seems like a good package), but you don't know much about the driveline of a car.

I'm not debating the accuracy of your Dynapack; I'm debating the accuracy of your driveline losses, which even Dynapack says are minimal.

What difference would it make if it measured engine RPM via coil pickup of some sort, or calculated it by entering final drive ratio? So what? It *still* needs to know engine RPM to plot a curve. I have no experience with the Dynapack, so I'm going based on what Mustang dyno requires, which is merely the engine RPM (off coil), and all other measurements are made from the roller.

There should be no need to *calculate* wheel torque, as if it's a true loading dyno (which it is), then it should just be able to measure the torque, and go from there. All it needs engine RPM for it to plot the curve, and make HP calculations from.

Why does Dynapack calculate engine RPM from final drive ratio, rather than just picking it up from the coil? This seems like an opportunity to introduce error into the system, rather than taking an accurate number right off one of the coils.

What other calculations does the Dynapack software make, other than corrections for atmospheric conditions?

Correct me if I'm wrong, but if you enter the final drive ratio, AND the Dynapack is measuring the rear wheel torque and dividing it by the final drive ratio, wouldn't that *effectively* be estimating the flywheel torque, and NOT the rear wheel torque (minus some driveline losses)?

And since we can't actually *measure* HP, is it basing it's HP calculations on the corrected torque values?

Without reading the manual, something seems odd here...it's the first dyno I've seen which *cares* about final drive ratio, and I'm trying to figure out why (other than to calculate engine RPM).

Really, rear wheel torque *should be* rear wheel torque, regardless of the final drive ratio used to get there. When you change gears (or rear diff), you're effectively changing the torque output to the rear wheels (actually, you're changing the moment arm; torque itself doesn't really change). If all the Dynapack does is use it to calculate engine RPM, then that's fine. But if it factors into the calculation of torque somehow, then I'm starting to get confused.

Does anyone have a manual for one of these things in .PDF format?


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Old 10-25-2002, 06:23 PM   #140
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I understand perfectly.

Yes, I know quite a bit about the driveline of a car.

Minimal, hmm that doesn't bring a number to mine. Try calling dynapack and speak to greg, he is the one who trained us on the unit and told us the correction factors are about 15-20%.

Read this 2 times:
There are no calculations! Torque is a function, it measures real torque, but to get the actual torque from the engine you must divide by the final ratio. If your M3 has 200 pound feet of torque in 5th gear (1:1) and your rear end is 3.15, the torque you put to the wheels is 630. The dynapack divides to get the torque number for the engine, there is no error involved. Now roller dyno, its is ALL CALCULATION.

EVERY DYNO MAKES CALCULATION FOR ATMOSPHERIC CONDITIONS. Your Mustang dyno doesn't show it bc it is included in the original calculations. Mustang dyno DOES NOT MEASURE TORQUE NOR HORSEPOWER, it merely calculates it. They measure acceleration as a function of time. Also the weight of the rollers should be the same weight as your car, so that adds even more inconsistency.



Quote:
Originally posted by GR8 Ride


You know what...don't bother. If you're gonna be an ass, there is no point. You obviously don't understand anything about driveline losses, REGARDLESS of how your Dynapack measures it.

Ever taken an engineering class? I'll admit I don't know much about your Dynapack dyno (though I'll give it credit, it certainly seems like a good package), but you don't know much about the driveline of a car.

I'm not debating the accuracy of your Dynapack; I'm debating the accuracy of your driveline losses, which even Dynapack says are minimal.

What difference would it make if it measured engine RPM via coil pickup of some sort, or calculated it by entering final drive ratio? So what? It *still* needs to know engine RPM to plot a curve. I have no experience with the Dynapack, so I'm going based on what Mustang dyno requires, which is merely the engine RPM (off coil), and all other measurements are made from the roller.

There should be no need to *calculate* wheel torque, as if it's a true loading dyno (which it is), then it should just be able to measure the torque, and go from there. All it needs engine RPM for it to plot the curve, and make HP calculations from.

Why does Dynapack calculate engine RPM from final drive ratio, rather than just picking it up from the coil? This seems like an opportunity to introduce error into the system, rather than taking an accurate number right off one of the coils.

What other calculations does the Dynapack software make, other than corrections for atmospheric conditions?

Correct me if I'm wrong, but if you enter the final drive ratio, AND the Dynapack is measuring the rear wheel torque and dividing it by the final drive ratio, wouldn't that *effectively* be estimating the flywheel torque, and NOT the rear wheel torque (minus some driveline losses)?

And since we can't actually *measure* HP, is it basing it's HP calculations on the corrected torque values?

Without reading the manual, something seems odd here...it's the first dyno I've seen which *cares* about final drive ratio, and I'm trying to figure out why (other than to calculate engine RPM).

Really, rear wheel torque *should be* rear wheel torque, regardless of the final drive ratio used to get there. When you change gears (or rear diff), you're effectively changing the torque output to the rear wheels (actually, you're changing the moment arm; torque itself doesn't really change). If all the Dynapack does is use it to calculate engine RPM, then that's fine. But if it factors into the calculation of torque somehow, then I'm starting to get confused.

Does anyone have a manual for one of these things in .PDF format?


Pat
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Last edited by Scottycs; 10-25-2002 at 06:34 PM.
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Old 10-25-2002, 11:02 PM   #141
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Hmmm....interesting. So if you were to put in a final drive ratio of 1:1, would the Dynapack show 630 lb-ft of torque, and the RPM range being indicative of whatever the final drive ratio is (ie, engine RPM divided by 3.15)?

I'm not saying the Mustang is the cat's meow, as you said, it merely measures acceleration, and calculates the torque required to accelerate X mass over Y time (one of which is known, the mass, and Y which is measured). It's merely a loading dyno, as opposed to the Dynojet.

Darn, the more I learn about this dyno, the more I like about it. If I understand correctly, it's essentially measuring flywheel torque, MINUS any driveline losses (rear wheel torque divided by final drive ratio).

Well Chris, we'll have to agree to disagree on the driveline losses portion of it, as I just can't see a linear gearset contributing to 6 or 7 percent of power losses, particularly in fifth gear. There has been a lot of gibberish spouted for many years by dyno tuners (and engine tuners) about driveline losses, often being spread around as gospel. As I've said, the Dynapack should be at the low end of the spectrum, especially since you're taking one of the big factors out, the tires.

So, on that side note, you said you have slightly different output numbers in 3rd, 4th and 5th gears. Could that be merely rounding errors in terms of final drive ratio calculation? (since gears aren't generally EXACTLY 3.15:1 for example...).

Since the Dynapack actually takes that factor out (I'll never look at a Mustang Dyno the same again...), it *should* in theory be essentially 100% (or very near to it) accurate in any gear. Any ideas on this? I'm just wondering why you've seen that big of a difference.


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