Is it true that Mustang dyno's are more accurate as far as exactly what your putting at the wheels and about a 50-60 hp difference between the two? Dynojet reading a lot higher.

 

Yes more or less, but no about the 50-60 hp difference. dynojets are higher than mustang dyno's by at least 20hp from what ive seen, but that varies. When i got mine tuned at 328 hp the tuner said that it would compare to 345-350 on a dyno that was in the area.

The main point is that a dyno is a tuning tool. What matters is your track times, you can verify hp numbers from there

 

so far the closest thing to a conversion for the numbers, is take your mustang dyno numbers and multiply by 1.07 and that should give you your numbers on a dynojet within a couple horsepower, works pretty well actually.

 

So you're talking a 7% correction...

 

6-7% was going to be my guess as well

 

the guy i bought my motor from dyno'd 463rwhp on a mustang dyno.
463 x 1.07 = 495rwhp? id be EXTREMEMLY suprised if I made 495 on a dynojet. I got his tuned PCM also with the motor so everything is already tuned. plus that was through a 12 bolt. I still have a 10 bolt so add another 12 rwhp for that. let me see here...495 + 12 = holy heck I got 507rwhp, wow!

 

We tell customers to multiply by 1.12 to compare our Mustang numbers to a certain Dynojet close to us which usually comes very close. It will vary from given Mustang and a given Dynojet. We've had customers that have been tuned on the Mustang then run to the Dynojet for numbers. Suggestion, if you ever introduce a new dyno, just make sure it reads the highest.

 

Wow, that is a low reading dyno.....or all the dynojets around read really high. Im going go with your 12%, lol

 

With that calculation that would put me about where a I think I should be with a tune which is 400rwhp. What do you mean by your last sentence?

 

The last sentence simply means that you will get more business if you have a dyno that reads higher. I know guys that have driven an extra 150 miles passing one DJ for another DJ only because it gives higher numbers. Most consumers could care less about accuracy which invites, stated kindly, optimistic numbers.

 

A Mustang dyno (eddy current) can actually load the driveline and measures torque from a deflecting sensor attached to the dyno. Most of the Dynojet models are inertia only and calculate power from the accelleration of the drum. This tends to smoothe the power delivery some and less data points are taken as hp increases due to the very short dyno run.

In general most tuners will prefer or demand an eddy current loading dyno because they are able to specify a specific repeatable (and adjustable) load which is especially important when tuning part throttle. An inertia only dyno has to rely on the drum brake shoes to apply a load which is a negative to the dyno operator because its a wear item and repeatability is iffy.

An eddy current dyno can be programmed for a specific drive cycle that will simulate road driving conditions. This helps to sort out the tuneup. A change can be made and then the exact cycle can be repeated.

I think most parts manfactuers, such as forced induction companies develop their systems exclusively on a Mustang (or any eddy current) dyno. This combined with road and track time helps ensure the canned tune performs as you would expect. The tests are very repeatable and extensible.
When the company advertises their power gains obtained with a Mustang they can be fairly certain that their customers will be able to repeat those numbers in the field. When that system is then dynoed on a Dynojet the customer is then even more pleased as they get the impression they have more power than what they expected.

Now in the converse if products are developed on a Dynojet, or those numbers are advertised there are bound to be people that will be disappointed if their car is tested on a more stingy system.

Both systems can be considered "accurate" in as much that you can generally believe a gain or loss on both systems assuming proper test conditions are adhered to.

A dyno pull on a Mustang generally takes longer than a Dynojet and for my money that's a good thing. More data points mean more information to consider and more opportunities to finesse the tune or system.

Sorry if some of the info wasn't relevant to your question.

 

No, thanks for all the info andereck!
I guess I could see that. Like my local dyno, it's a land & sea dyno which reads almost exactly on a mustang dyno. Were dynoing cars here and everyone is disapointed. IE, a Magnum thats advertised 425hp from the factory only put down 320rwhp on the dyno here...

 

You're welcome. The particular example you stated might be more related to it being a Dodge than the testing equipment itself. Their power numbers could be considered "best case" putting it nicely (open nitrous bottle in the corner of the dyno cell?). If you look at the afr it takes a total nosedive at WOT ending in the low mid 10's. I'd bet it didn't when the calibration engineers were deriving the marketing numbers. On the other hand GM is a bit conservative. Case in point LS7's make anywhere from 25-35 more hp than claimed and rwhp numbers average in the mid 460's for a claimed 505hp engine.

 

Actually, that Magnum is on target. If we dynoed it, using our X1.3 multiplier for autos, if unlocked TCC, that gives us 416 net FWHP, there is a 5-10% variance from car to car, he's OK. We have never found any GM cars to be conservatively rated, just the standard mass production variance like all domestics.

 

Your multiplier might be a bit aggressive, or optimistic depending on how you look at it.

 

Here's how I look at it, X1.2 for a auto drive train losses plus X1.1 for converting factory's RPM step testing to RPM sweep testing = X1.3. This has worked very well for us for many years for converting SAE RWHP to a known SAE Net FWHP on low and high HP examples. As indicated here, what most call drivetrain losses is only a part of the equation and why many accurate chassis dynos are considered to read too low.

 

I got my dyno on a mustang dyno and asked the tuner if he knew an estimate of the difference between mustang dyno number and dynojet numbers. he said they used the same car same day on their dyno and took it to a dynojet and saw a 10% difference. 430rwhp car gaining 45rwhp. I got tune on a mustang dyno and when i get my retune in a month or so i am going to put it on a dynojet to see the difference.

 

Here is what you do: For the tune, go find a good tuner with a Mustang dyno. Then when he is done, go find a guy with a dynojet and get your bragging rights numbers. There is no quick easy conversion, so you just have to go do it.

-Geoff

 

dyno jet vs mustang from what I have personally observed. Its disturbing but seems to be true.

MD vs dynojet
200hp x 1.08
300hp x 1.10
400hp x 1.12
500hp x 1.16
600hp x 1.20
700hp x 1.30
800hp x 1.45
900hp FORGET ABOUT IT !

This seems to be the rough average % error I see between dynojets and the mustang I use. You notice the error gets larger with more power. Dont be surprised the dynojet 248c and its variants don't have enough inertia to have that software accurately measure the delta for the acceleration rate.Not to mention that flywheels have this bizzare property about loosing mass as they store inertia an aspect of physics still being explored.

So the more power you make on a dynojet the bigger the error with accurate dynomometers.

 

there was a 25hp difference for me when i went from a dyno jet to a mustang dyno w/no mod changes.
30TH TA- 463hp on a mustang dyno from a wimpy 346ci? i don't believe it.