The Story Behind the Dynojet

[Tom03es]

http://www.hotrod.com/thehistoryof/113_0603_dynojet_chassis_dyno/index.html

Pretty good read. This article was taken from a post from the eddy current dyno owner whose shop the local Mazda club is having a dyno day at in March.

Here's his post regarding the differences between a Dynojet and a Dyno Dynamics (eddy current dyno):

What's up with our dyno:
We did our homework up and down before making a dyno purchase. Between Adam and I we have personally used (not just dyno'd one of our cars on, but hoodwinked a shop owner into actually letting us play with the software/controls for awhile) every type of dyno on the market. We went with a Dyno Dynamics because it simply blows every other dyno on the market out of the water. I could go on for pages on the specifics of why. I'm more than happy to answer any specific questions. It's also the only chassis dyno out there that can deal with some of the exotic AWD systems that Porsche/Lambo/etc. can test on without causing the stability control stuff to have a heart attack.

Does it read "lower" than other dyno's out there?

Absolutely. It's not that our dyno reads "lower" it has more to do with industry standards in this country and every other dyno reading "higher". By far the most popular dyno in this country is a dynojet. Why? They are cheap and have an amazing marketing department. For example. An AWD dynojet costs about 1/3 of what ours does. We were having to beat away their factory reps with a stick. Whereas with our Dyno Dynamics we had to chase down a rep ourselves and deal with a huge headache of actually getting a unit. For a shop that doesn't do their research a Dyno Jet is an obvious choice. The problem is that the Dyno Jets read very high (typically 15-20% higher than what a car really makes). For more on this go here:

http://www.hotrod.com/thehistoryof/113_060...dyno/index.html

The issue is that you have a situation where the majority of the shops in this country are using a dyno that reads high. This has resulted in the power expectations for the entire American aftermarket to be skewed about 15-20% high. The best example I can think of recently is the Ford GT500. Ford rates that car at 500 horsepower. On our dyno they put down ~360. Thing is, if you ask any old hot rodder... the truest measure of horsepower out there is your trap speed in the 1/4 mile. A totally ham fisted driver really can't throw this number off too much. The numbers that come off our dyno jive almost perfectly with 1/4 mile trap speed math. Dyno Jet numbers... not so much. On the GT500 1/4 mile trap speeds are typically 106-108mph. Curb weight is 3950.

http://www.4lo.com/calc/dynocalc.htm

Go there. The math adds up with the numbers off our dyno. This is something we have proven time and time again.

The thing that makes dyno jet numbers extra stupid in Colorado is the correction factors on forced induction cars. SAE correction on our dyno is typically around 30%. Problem is that a turbo or supercharged car really doesn't loose 30% of their power at this altitude. They lose about half that due to pressure ratio in-efficiencies and the like. So for a FI vehicle we take whatever SAE number the dyno calculates at the time and cut it in half (another feature we like about our dyno, with other systems you are stuck with either SAE or no correction). We have found this method to be extremely accurate. We have had customers use our dyno, move to sea level and use an identical Dyno Dynamics unit. Numbers at sea level were 5hp lower on a car that had driven 30,000 miles between testing on our dyno and at sea level. We'd like to think our method is pretty good.

With a dynojet in Colorado you have about 15% more correction on a turbo car than you should have on top of the built in 15% "we suck at math" correction those dyno's have built in.

Personally I'd rather give "low" numbers to a customer and have them stomp someones brains in that is making "much more power".

 

[BinoMP5]

nice info... thanks

 

[JasonLHall]

ah...any dyno can be adjusted to make almost any number. In my experience, the truest dyno is the mustang dyno.

Dyno Jets are good for industry standards such as doing a run on a dyno jet in CA and doing the same car in NY with the same settings, you should get the same number.

In otherwords, you can brag to one another as long as each other was on a dyno jet.

Mustang tends to be the most accurate hence the nick name "Heartbreaker"

Also, think about how a Dyno Jet is attached to your car. You are skuing the HP numbers at the wheel because well...you don't have your wheel on the car. Wheels add weight (depending on type) that can reduce the WHP number.

 

[niky]

Actually, it's the Dynapack that has the wheels off... The Dynapack should technically be the most accurate, as it removes slipping losses from the tires not being able to bite the rollers... but the numbers don't jive 1:1 with other dynos... and the "correction factor", which is inputted manually by the operator, is a fudge factor that allows for some truly silly numbers... and should have been left off the system. Plus, the drivetrain losses introduced by heavier wheels (which really affects accceleration on weaker cars) is not taken into account.

But in my experience, the Dynapack gives nice, very consistent numbers, a very detailed dynograph read-out, and is not affected by a change in mags or tire compounds, and has none of the strap-down issues other dynos have. But since no one uses it... it sucks for comparison purposes. It's a great tuning tool, though.

The one I'm using now is a Dastek. It's a brake dyno, just like the 'Pack and the DynoDynamics, but numbers are, obviously, different... the shop has had it calibrated to Dynojet correction factor merely for the simplicity of use. I'm using this one simply because this is what the guy tuning my motor has.

As long as you're comparing Dynojet run to Dynojet run, it's all good and well. The point is: you know how much power the car is making compared to other cars on the same machine. Screw it if it's "wrong"... as long as you know what you're making compared to stock and the competition, it's all well and good.