Mustang Dyno vs DynoJet

[Fuzz]

Kinda wondering if it is possible for someone to explain why one would be better than the other.

Do they both give out the same data?The guys owning one or the other seem to think theres is the best.

Just wondering. . DYNO 101 huh?

Fuzz

 

[Don M]

All dynojets use a simple formula to calculate HP. They have known slugs of inertia and they calculate HP by measuring the time to accellerate the roller or slugs of inertia. This is the simplest dyno of all to calculate HP without using several different formulas to get to ultimate HP like the majority of Mustangs.



Mustangs measure twisting force or torque with their rollers. Many Mustang dynos have a limit at which the tires will stick to the roller before traction becomes an issue. This can cause in-accurate readings. Further, once the Mustang has a torque number the software goes through several complicated algorithms to finally get you a HP number. The level of complication is far greater than a simple inertia type dyno like the Dynojet. Not to be unfair there are a few other brands that can be used as an inertia dyno as well, but there are differences in them that will ultimatley make them less viable than the Nascar Dynojet in the long run for turbo diesels.



Don~

 

[drawson]

Here is my take. The mustang is a great dyno for doing R&D work the DynoJet is the dynos for putting down some big numbers. There is too much tire slippage on the mustang after 375 HP.

 

[JGK]

I asked one of the guys running the Mustang dyno at the Edge at the Utah Dyno Day on Saturday what the difference was. He said their Mustang measures HP and calculates torque, whereas the Dynojet measures torque and calculates HP. One spins a massive 500lb drum while the other has a lever arm that applies a load (can't remember which one uses which).



Does that sound right to you, Don, or am I out in left field again?



-Jay

 

[Don M]

Originally posted by JGK

I asked one of the guys running the Mustang dyno at the Edge at the Utah Dyno Day on Saturday what the difference was. He said their Mustang measures HP and calculates torque, whereas the Dynojet measures torque and calculates HP. One spins a massive 500lb drum while the other has a lever arm that applies a load (can't remember which one uses which).



Does that sound right to you, Don, or am I out in left field again?



-Jay

Jay,



The Dynojet measures HP first and if you have the special adaptor you can measure torque as well on 12 valves. Ford PS trucks have a tach signal that can be read without the special pick-up. Remember the Dynojet will measure HP without the pick-up for torque on any truck, car, etc.



The Nascar Dynojet has a 5000lb drum or slug of inertia that the trucks accellerate while the time the drum takes to spin is measured. This a simple one step calculation to get HP.



Most Mustangs use torque to get HP through a mathematical calculation. Some Mustang dynos are inertia type dynos too though. Most are not.



Like Dee stated the Mustang run into traction problems after about 350HP and you get a bunch of tire spin. Making the readings skewed IMO.



Don~

 

[JGK]

Don,



OK, so I had it basically right but just backwards, and I dropped a '0' in the drum weight. Thanks for the clarifications.



I had mine dyno'd in Utah on Saturday (Mustang). There's a local shop that has a Dynojet and I think I'll have a run on that one to compare numbers.



-Jay

 

[Amianthus]

Most dyno's fall into two categories. Inertia and applied load (?). There are several ways to apply load using a water brake, electric brake, generator, and so on.



The Dynojet is an inertial dyno that calculates HP based on the acceleration of the weight and the time it takes to do said work. From that, you can extrapolate torque using the HP=Torque * RPM / 5252 equation. For RPM you need to have either a pickup from the engine or calculate it based on tire size, gear ratio, transmission ratio, and speed of the roller. Obviously, the engine input would be the best.

There are some good and bad of the dynojet. First the good. Traction is rarely a problem and operation is easy. And operator error is minimized because of it's simplicity. The bad is that you can't change load to get maximum power at all levels of the graph. You are assuming that you are going to be at maximum power when you put your foot in it, but a diesel's power lags behind it's acceleration. So the numbers may become skewed and may not give a representative example of the engine's true potential.



An applied load dyno works like this. You spin a set of rollers that has a brake attached to it. You load the brake and the brake deflects against a counter force (spring, lever, or fixed weight). As the brake resists the motion of the rollers, it moves against this weight. The distance it moves is measured by a strain gauge. This is converted into torque against the rollers (tractive effort). The machine then calculates HP based on the speed of the rollers and the tractive effort being applied at that speed using the equation HP=tractive effort * speed (mph) / 375. Based on HP you can extrapolate torque using the equation above. Of course, getting your input for RPM in one of the above manners.



The good of this dyno is that you can fully load the engine to it's maximum power for a given speed (RPM). You will have full boost and fueling and be able to hold it there to allow the reading to stabilize for accuracy. The bad is that traction can be a big problem. The brake may function, but the friction required may not be sufficient and the wheels will slip. Obviously, this will screw your numbers up and ruin the test. Then you'll have to do it again. Our observation with our dyno (GB Transmissions RAM 11) is consistant that our trucks will start to slip around 350-375 HP (actually around 1800 Ft-lbs of TE). The other bad of this dyno, is that the operator must know what he is doing. We used a pre-loaded curve to simulate road load (same as they did in Muncie) and found that the power lags behind the curve (for the same reason as the Dynojet does). Also, every problem we ran into in NE IA, the guys in Muncie ran into. Not to mention, I don't think that the calibration was accurate for that brake, IMHO.

A good test with this dyno would work this way. Bring the engine to the governor at full fueling, and then apply the brake to take the enigne down to your idle speed (or something close) and then bring the engine RPM back up by releasing the brake taking data on the way back up. That way you'll have full fueling and boost for a given RPM when you take your data point. But again, you run into the evil traction issue and that make this test very hard to do. The whole test, as described above, should take no more than 30-45 seconds. But having not done a successfull test as described, I can only speculate.



So how's that? Did that answer your question adequately? If not, I'm sure someone else can correct me or add their 2 cents. Hopefully, I didn't muddy the waters on this too much.



BTW, thanks to docdyno and Sun diagnostic systems for explaining this stuff to me while we were getting our dyno "modernized".

 

[KLockliear]

Originally posted by Amianthus

The bad is that you can't change load to get maximum power at all levels of the graph. You are assuming that you are going to be at maximum power when you put your foot in it, but a diesel's power lags behind it's acceleration. So the numbers may become skewed and may not give a representative example of the engine's true potential.

Just remember that since the load is a constant and is NOT adjustable by the operator, every run, every time, has the same load. This yields very consistent and repeatable results.



While the numbers may not be the highest recordable values, if you see a change in those numbers at the same point on the graph, you've done something.

 

[M Barnett]

but a diesel's power lags behind it's acceleration. So the numbers may become skewed and may not give a representative example of the engine's true potential

So does this mean a Dynojet may give low HP readings?

Michael

 

[KLockliear]

At a low boost point, yes it could. On a Dynojet type dyno, with an automatic, you start at around 1900rpm locked up in OD. By 2000rpm, you're at full throttle, but may not yet have full boost. Each time you make the run, starting at the same point, you should be at the same point of boost and power.



On a load dyno, you may be able to add load and hold the engine right at that RPM point so that you may get full boost. If so, it may record higher numbers.

 

[Boldt's Wagon]

Does the Dynojet provide a correction for altitude and temperature? If so, what is the correction for the Las Vegas location?

 

[Amianthus]

KLocklier is right. Yes, it can give lower numbers than the engine can truly make. It's funny you bring up automatics. We really had a b***h of a time getting good numbers from them. balancing between fueling, lockup, downshifting, and tire slippage, it is pretty tough.



As far as temperature and pressure correction factors, all good dyno operators should be able to do this regardless of the type of dyno. Each dyno should have a supplement for correction factors.

 

[KLockliear]

Yes, the Dynojet software uses the SAE J1349 rev. June 1990 correction factor... however, it assumes 85% mechanical efficiency and is setup for gas motors which lose more due to altitude. I'm not aware personally of an SAE correction setup for diesels, but that would be nice.



We normally see between 1. 06 and 1. 11 correction factors here in Vegas.



One thing also, it's much easier to get the truck to do a run with acceleration (as far as keeping it in one gear, locked up without spin) than on a load dyno as well.

 

[M Barnett]

I had mine run on a Dynojet and the chart showed 403 HP at 85 MPH. I don't know what the boost was though. Its a five speed. He didn't have the adapter for the torque readings.

Michael

 

[KLockliear]

Do you know what gear you have in the truck? 3. 54 or 4. 10? Also, which gear did they dyno your truck in 4th or 5th?

 

[M Barnett]

KLockliear; I have 3:54 rear and believe it or not, I don't know which gear it was dynoed in. I thought the chart would show rpms and it didn't. With 3,000 gks springs, I don't know if it would run 85mph at 3000 or not in direct drive, but I think it would.

Michael