Anyone know if there are any noticeable diff's? Pro's and Cons?

 

yes. no. maybe.

dyno's are a crap shoot. no two are exactly alike - and that's within brands.

Your best bet, pick a local shop, and use it to compare against itself.

 

From what I read on here, it's just another one of those arguments with no clear answer. I sure don't know. But as Bogus said, if you do all your comparisions on one machine, you'll know where you stand.

 

I read an article from a fellow who owned both types of dyno. I believe he said the Dynojet would read 11% higher than the "true rear wheel horsepower" number from the Mustang Dyno.

 

I am a proud owner of a Mustang Model 600HP with dual power absorbers. If you go to this website:

www.mustangdyne.com

Then click on the link for "recent articles" there is a article that was printed last year in Chevrolet High Performance magazine comparing the Mustang to the DynoJet. It gives a very good and comprehensive comparison to the two dynamometers.

Both are very good systems. While I purchased the Mustang mainly because of its ability to allow me to tune in part throttle situations and also allows me to load the engine to any road speed or load setpoint. While a DynoJet dyno will load a engine, its capabilities are very limited and not very accurate when it comes to its loading aspects. Mind you this is my opinion and others may disagree, but I find a friction loading device (brake shoes) very unpredictable in the DynoJet system.

For one anytime you use a friction device to create a load or a tension and try to control it with a PID (porportional, intergal, derivative) controller there had better be some highly advanced alogrithms to counter the changes in coefficent of friction and such as the brake shoes heat up. And let me tell you under high power situations they will heat up rapidly.

My engineering background is mainly in the pulp and paper industry. And years ago on paper machine winders we used to use large (50" and up) disc brake rotors and multi-caliper set ups to control winder tension. You see, when we unwide a jumbo roll of paper (imagine a roll of white copy paper 330" wide, and 8 feet in diameter that weighs over 20 tons!) into finish rolls on the winder, it is imperative that the winder maintains a set tension to insure that the finish roll forms correctly. Otherwise when the finish rolls hits the converting plants where they are made into reams of paper we see at Office Max and other office suppy stores, they would not run on the converting machines. So one can imagine a tremendous amount of heat build up of a brake rotor during the unwind operation of a winder and its parent (jumbo roll). When things get hot the coefficient of friction changes and the tension is constantly changing, so the alogorithms in the control strategy is very complex in them old friction based tension control winders. Most have been retrofitted with high tech AC drives with regen sections to control tension these days.

A similar technology is also applied in chassis and engine dynos. Mustang also uses a AC drive with a braking resistor bank to abosorb the electrical energy as it "regens" during a power abosorbtion run on their chassis dyno. Mustang also uses a Eddy current power absorber which my dyno is equipped with.

A Eddy current absorber is a rotor made of a high-permeable magnetic material and enclosed by a stator. The cavity in which the rotor turns is usually air-filled (dry gap). The stator has a series of coils, which can be energized to produce an electric field around the rotor. As the rotor, driven by the wheels, turns in this electric field, small rotating electro-magnetic fields (called eddy currents) are generated, which oppose the rotation of the rotor and try to move the stator in the direction of rotation of the rotor. The stator is also held in position by a strain gauge (torque link) which will measure this force acting on the stator. If you seen my thread about my dyno last week there is a picture of me working on one the power absorbers. I was actually installing the strain gauge in that picture.

This strain gauge is what tells the dyno control PC what amount or torque is applied the the dyno. The dyno load is varied by varying the electric current through the coils. The control with a eddy current absorber is extremely fast and accurate as compared to that of a friction system.

Read that article at the Mustang Dyno website, theres more information than I can tell you here. I am still learning more about my new toy

 

 

Excellent tjwong!

Some numbers to extropolate...

Completely stock LT4's put down 260 WHP on Mustang 1750 Dyno
On a Dynojet...300 WHP.

I use the Mustang model for all the comparisons...

 

Depending on how the Mustang dyno operator configures the test. One of the reasons that the Mustang will give lower number is that it also takes into consideration the actual vehicle weight and the hp requirement at 50 MPH for wind drag and drag coefficient numbers. One a DynoJet neither of those two numbers are taken in consideration. You are just spinning up a known amount of inertia that is built into the dyno drums. The rate of which it takes a car to spin that inertial weight to the engines redline and the amount of pressure that is put upon the dyno's strain gauges is used to calculate Hp and torque.

The Mustang is also able to do a inertia only test as well. I can turn off my PAU's to do this. On this coming week, I will have a rental car to trash on my dyno (courtesy of a local Enterprise agency) so I will conduct mutiple tests to see what the differences are with and without the PAU's activated.

 

Thanks Twong great explanation! The reason I ask is because I'm looking at purchasing one or the other and I seem to be more impressed with the Mustang than the Dynojet mostly because of the Eddy current option. Being able to hold at a steady rate would help with diagnosing and tuning versus just loading while going up the RPM range. I just want to know if there is any reason why I mostly see the Dynojet especially here in the North East! Thanks again I 'll throw you an e-mail or 2 as I get closer to purchase the Dyno!

 

We need some type of standard here.

260 rwHP vs. 300 is a big difference.

My question to you all is what is GM using (of course they dont do rear wheel HP).

WHat type of system?

Id rather tell my friends I made 300 rwHP on the dyno vs. 260 rwHP, and if it means going to the dynojet then so be it.

Its like Car and Driver vs. Motor Trend. C&D usually has the faster times (they test top speed regularly too).

All, Im saying is if the 03 Cobra people are bragging about their numbers on a dynojet, Im at a disadvantage if Im bragging about my numbers on a mustang.

Of course, its not about bragging, its about winning the race. I think either one will show you how much power you gained after a particular mod. Just test before and after on the same dyno.

 

The steady state function is one of the best tools for a tuner, and or a repair shop. Just imagine a customer comes to you and tells you that he has a misfire or loss of power pulling a 6% grade at 60 MPH. I can set the dyno up to simulate that exact load, all I have to do is to connect my diagnostic scope to the engine and see if there's a problem in the ignition system. I don't have to even leave the shop to find the problem!

Why is that you see mostly Dynojets in the NE, well one reason possibly is the cost. A Mustang is considerably more expensive than the Dyno Jet. Plus its sort of a marketing issue as well, becuase they have NASCAR using the Dyno Jet as a standard for all the teams. Feel free to email me, if you have any questions. I can give you the name of my sales rep at Mustang when you get ready.

DizWiz, numbers is a marketing issue. As long as a dyno is repeatable and that you go to the same shop. What ever changes that you make will show up on that dyno be it good or bad. I can change the testing correction factors in my Mustang so that it reads the same as a Dyno Jet. I guess in a sense if people see big numbers they are going to be happier. But isn't it a false sense of reality? I have a friend in California, I won't mention any names. He has a performance shop much like mine. He has a Dyno Dynamics (Austrailian) dyno which he purchased about 4 years ago. Much like the Mustang MD250 in design and with a single PAU. His dyno would often read lower than his competitions Dyno Jet. So what he did was to go around to a few Dyno Jet shops with his personal car. With several Dyno Jet curves in his hand he reset his Dyno Dynamics dyno correction factors to read the same as the local competitions Dyno Jet. So now all of his customers are happier now with the higher readings.

 

All I can say is that I prefer Dynojet numbers to get power to the rear wheels, over Mustang Dynos.

 

From a tuning view point, it can be done better on a Mustang or any other brand of measureable load bearing feedback chassis dyno. Anytime you can simulate the actual load to the engine, your can tune it better. Different loads require different fuel maps, timing tables, knock retard tables and will cause different TQ converter slippage, turbo boost, fuel delivery issues etc. Like I just posted on a different forum, people in our area have found which Dynojet gives the highest readings and will drive miles for them. But here we do most of the tuning with our Mustang MD 1750, possibly we each have a good thing going. I beleive that Dynojets read 10-20% higher then every currently marketed brand of chassis dyno that I know of and any independent test that I have ever studied concludes that they are very optimistic with their numbers. However,I would consider them the internet standard of HP due to their popularity, sad. The day that I am impatiently waiting for is the day that Dynojet adds measureable, feedback load control that should cause even higher readings. This has to be the only thing holding them back from adding this very important option because they quoted me back in '99' that they will soon have it, glad I'm not still waiting. Some say that they are gradually pulling back on their readings with their newer versions of software, possibly just rumor. Don't get me wrong, I am not pro Mustang, just very pro chassis dyno tuning with a properly loaded engine which many brands of chassis dynos are very capable of and I like to hand out the most accurate numbers that I am capable of, even if they are lower.

EJ

 

EJ, I am in 100% agreement with what you just said. Would you mind if I call you Monday and to ask you a few questions about what you and I had emailed back and forth about when I first purchased my dyno. It has been some time ago since that because it has taken me this long since then to get the dyno installed and running.

Mainly its about the MDSP7000 software that you and I both are running in our dyno PC's.

 

Tom, no problem, do you have my #?

 

A great read, thanks for all the info everyone.

Currently I'm interested in non-adjusted (for wind resistance) torque numbers, since that is all you need to calculate acceleration in any gear. Calculating wind resistance is easy enough on a C4 (it's been done before), so you can easily add that in later.

Thanks again for the descriptions.