Thats what's weird about the dynopack.
The other time i went on it the shop owner and friend did it at 3.375 a per factory final drive. But this time the dyno operator matched the reading on the dynopack rpm readout to the rpm gauge in the car. To match it he put it at 3.510
I am going to see them next week to find out why he changed it.
I don't know if he change the ratio in a saved run if it will convert the #'s ?
I will find out and give you guys an answer.

 

Uhh...ok..

So what?

Engine RPM is calculated from that ratio...if it is not correct your dyno results on a dynapack are not correct.

 

they all get corrected.

 

How would they get properly corrected with the wrong ratio?

In case you didnt know, a dynapack calculates engine RPM based on rear wheel speed unlike a dynojet or similar which reads RPM directly from the engine from the coil/a spark plug wire.

 

thats probably why we have our wires crossed......all my dyno's I have ever done were on a dynojet. I will have to get with robert and ask him about our corrected setting's.


How do you know what's proper and what's not? on a dynojet I thought there was only a couple of way's to have to setup is there more?

 

Torque dropping off beginning at 4200rpm, horsepower peak at 5200rpm with the run ending at 5900rpm is enough to show that the dynapack operator calibrated it wrong . I've only seen the dynapack in action once, and have no clue which way the results would go if the gear ratios are wrong. Maybe it'll show more power? heh.

 

Edman,

When the operator uses 'calculate gear ratio' mode on the dynapak, he's matching the rpms of the rear drums to the rpm's indiciated on the car's tach. The car's tach is notoriously inaccrurate; this is a 'backup' tool if someone does know what the correct ratio is. On my run, they did the same thing; I looked at the value that they were going to use (it was something like 3.20!) and just told them the correct number. It should be 3.375 (rear end ratio) x 1.034 (4th gear) = 3.489.

 

I just spoke with the shop owner and he said the #'s shouldn't change with a different ratio.
Only the curve would be changed to the correct rpm.
He said the best way to get the right ratio is to match the wheel speed to the tach in the car.
Unless you can tap the wire in the ecu and get a digital read out.
But the difference in rpm is not much.
He says it can only cause a tuning problem to a car with a standalone because the dyno rpm could be off by a few rpm. But not much since most standalne are tune at 250 rpm zone.
And the difference is probable not that much.
Rage, On my old run the dyno was set to stop at 6000 rpm.
For the reguler guys that just want hp #, its plenty accurate.
Hope this clear it up a bit.

 

Dynopacks are weird in that the proper ratio IS required or the numbers all come out funky. If you look at your TQ vs HP graph, the numbers don't even make sense.

HP is a function of TQ... basically, TQ over a period of time. The formula to calculate HP is :

HP = (TQ*RPM)/5252

Which means TQ and HP *always* cross at 5252rpm. No ifs, ands, or buts.

So, if you look at your chart here :

http://www.geocities.com/edman951/dyno301rwhp-2.jpg

Here's the RWTQ that I read off the graph, and the proper corresponding HP from RPM. I've also included the TQ peak:

3500 - 304rwtq = 203rwhp
4000 - 306rwtq = 233rwhp
4148 - 311rwtq = 246rwhp
4500 - 298rwtq = 255rwhp
5000 - 283rwtq = 269rwhp
5500 - 265rwtq = 278rwhp

So if you look at your HP curve, it's totally different. Now, the dyno claims that you made 302rwhp@5259rpm. To achieve that HP figure, you work with the reverse formula :

TQ = (HP/RPM) * 5252

And get 302rwtq at 5259rpm. You're about 20 away at that RPM.

 

OK its getting more technical.
You really took the time to calculate it. Cool.
It's really interesting, you have opened my eye to the math of engine power.
Thanks

So if what you say is true. ( not saying you are wrong)
Can we even trust the tq # i got on that run ?
Are the hp# you calculated accurate?
But if the dynopack calculates it like you. Why don't my tq to hp # match?

Thanks

 

hehe, that's why I said I have no idea what's right and what's wrong with your graphs. If you assume the TQ curve to be correct, then your HP reading is wrong (on the high side). If you assume the HP curve to be correct, then your TQ reading is wrong (on the low side). I don't have enough experience with Dynapack dynos, only used it once, so I dunno what's right, what's wrong, what it measures, how it calculates the other using what factors...

In my calculations, I assumed TQ curve to be correct because it pretty much matches every other K26/6 TQ curve I've seen.

One final note, all dynos measure things a bit differently. Even identical model dynojets at different shops can vary by a few %. Dyno numbers are really only used for bragging rights, selling parts, and forum arguments (the best part!) . The most important aspect of dyno testing is that you should stick with one dyno shop for all your tuning, and look at the change between the runs. That will tell you if you have more power or not with your new tune/parts.

The whole 300whp debate stems from the fact that that K26/6 turbo can only flow enough air for around 310hp flywheel, and that's with EVERYTHING being perfect, so even with variations on the high side, it's very unlikely someone can show a 300whp dynosheet without cheating .

 

I would say that both are reading high as the lower than actual ratio would cause the dynapack computer to correct for you being in a higher "gear" than you really are. Imagine doing a dyno run in 4th, but doing the calculations assuming you're in 5th.

Lower gears produce more torque at the wheels, so you would be putting a whole lot of torque to the ground in 4th and then the calculations would think that you put that amount of torque down in 5th...thus giving you optimistic flywheel torque numbers.

The discrepency between the horsepower/torque curves I think may stem from the SAE corrections. If the sensor is placed in a hot area...near the computer exhaust fan for example....you would get a large correction and thus "higher" horsepower numbers.

Hope that made sense...

 

Well I used the same dyno as Edman last year, with my Vitesse stage 1 Kit, and got 337rwhp at 17psi. When the operator tried using Edman's gear ratio, we noticed that the rpms from the dyno weren't matching with the SMT5 (ECU) rpms. So we adjusted the gear ratio accordingly. So I was also led to believe that if the wrong gear ratio is used,you will get different hp and TQ # on the same car.

 

Steven, what was the ratio when you did your run?
Can you e-mail me your sheet i'd like to compare it to mine.
Thanks

Rage,
I agree, all dyno's are different and comparing charts is only cool on the forum.
The dyno i use is setup in a closed tempeture controlled room. The shop built it for R&D and not as a drive truw dyno shop. And since i trust the shop and since they are friends of mine, its even better.
For the past 2 years that's where i do all my dyno runs. And i have gained power everytime i go for a run after a good mod. So in the end its like you said rage.
"The most important aspect of dyno testing is that you should stick with one dyno shop for all your tuning, and look at the change between the runs. That will tell you if you have more power or not with your new tune/parts."

Can't wait to get my car on it.

 

As I understand it the dynapack measures torque at the wheels and wheel rpm. From this it calculates wheel hp. So far there should not be any errors apart from measuring accuracy.
To convert rwhp to engine power you just divide by transmission efficieny. Again there should be no errors apart from the fact that drivline efficieny is just a guess.
Where it get's tricky is converting torque and rpm. To convert them you divide wheel torque with gearing and you multiply wheel rpm with gearing. If the gearing is wrong then torque and the rpm it's at will be wrong. As stated above hp will be correct but the rpm where it's at will be wrong. However since both torque is wrong and the rpm figures are wrong with the same amount they will cancel out when you calculate hp from rpm and tq and you still should get curves that cross at 5252 rpm. Therefore these errors seem very strange.

In the compressor map I've seen for a 951 K26, the air flow limit were at a level capable of supporting 330-340 flywheel hp in a well tuned engine. The efficiency was not good at these flow levels and you are very close to overrevving the turbo. It should be possible to get 300 rwhp but then you are right at the edge and reliability will suffer, especially if you have a K26/6.

Tomas