Mustang vs Dynojet comparison article

[larryc7777]

Here's an article I found that was done by Chevy High Performance comparing the results of testing the same car on both types of dynos. The article covers a lot of questions that have been raised lately on this board. Hope you enjoy the reading.

http://www.mustangdyne.com/Articles/CHP0603-article-01.htm

 

[KosherCobra]

Good article. Alot has been said about my HP/TQ. The % are varying for the conversion. An 03 Cobra on REM Mustang Dyne only produced 320 HP Compared to a few people that have 03 and got 360 on the Dynojet. That's more than the 5.1% the the article printed for the SS. I'm making a Dynojet run later this week after my final tune. and compare them the same day.

 

[larryc7777]

Originally posted by KosherCobra
Good article. Alot has been said about my HP/TQ. The % are varying for the conversion. An 03 Cobra on REM Mustang Dyne only produced 320 HP Compared to a few people that have 03 and got 360 on the Dynojet. That's more than the 5.1% the the article printed for the SS. I'm making a Dynojet run later this week after my final tune. and compare them the same day.

5.1% sounded low to me also, but I have never been to a Mustang dyno so I don't have any knowledge about them. I do have about 30 runs on Dynojet dynos, though. That's probably why my poor SC belt is going away.:rollseyes

 

[FKing1]

From the tuner of my Vette on a Mustang Dyno, it reads 30 to 40 HP less than Dynojet. Livernois has a new Mustang and says it reads about 320 for 03/04 Cobras.
Fred K.

 

[APTEN]

Good article. Alot has been said about my HP/TQ. The % are varying for the conversion. An 03 Cobra on REM Mustang Dyne only produced 320 HP Compared to a few people that have 03 and got 360 on the Dynojet. That's more than the 5.1% the the article printed for the SS. I'm making a Dynojet run later this week after my final tune. and compare them the same day.

I've had stock 03 cobras read as low as 340RWHP on a dynojet, and as high as 400RWHP on a dynojet. Each car is different.

Even MD quotes a comversion percentage around 5%.

 

[davidmax]

Dyno's are 95% tunning! Show me the 1/4 mile slip.Real world conditions could dictae who wins.Tires Gears etc...I use a Dyno Jet, because its sanctioned by NHRA,SCCA,and many other governing race orginazations,matter of fact I have never seen mustang #'s used by NHRA/SCCA Etc...Gotta be a reason,and when I spend 70large on a Dyno I get the best Dyno Jet.
There both excellent for tunning which is the issue and as far as whp and rwtqe DONT MEAN A THING!!! I have seen some wild stuff on #'s,Good Luck,Dave Smilovic

 

[APTEN]

Dyno's are 95% tunning! Show me the 1/4 mile slip.Real world conditions could dictae who wins.Tires Gears etc...I use a Dyno Jet, because its sanctioned by NHRA,SCCA,and many other governing race orginazations,matter of fact I have never seen mustang #'s used by NHRA/SCCA Etc...Gotta be a reason,and when I spend 70large on a Dyno I get the best Dyno Jet.

bottom line, I agree. The main usage for a dyno is tuning. The other is to make comparsions for before and after you make changes. That is the only thing they are good for if you want to be scientific. The other usage is to get an idea of how much power you are making, but in no means is that going to be a precise number that you can use on the internet to compare against others. Even SAE is not that accurate between different conditions.

Brian

 

[Robertson Racin]

Well put guys..

 

[Black2003Cobra]

larryc7777– I have seen that article before, and thought it was pretty good. I understand how the Dynojet works, (since it’s nice and simple), but I too, am unfamiliar with the Mustang dyno. The article helps, but it leaves me with more questions about the Mustang dyno. Accordingly, they use an eddy-current brake (in addition to a drum as an inertial load) to simulate aerodynamic and rolling resistance losses. As the drag force goes as velocity squared (and hence, power as velocity cubed), and since rolling resistance is typically modeled as a 3rd or 4th order polynomial, it stands to reason that the difference between a Dynojet and Mustang dyno would not be a fixed percentage (as would be the case for, say, simple frictional losses). Including these two effects would certainly result in less net power recorded, however, so that explains why the Mustang dyno would report lower HP numbers (in addition to the effect of electronic controls on timing, etc for varying loads). My first question is, since drag depends on the coefficient of drag and frontal area of the vehicle, how would the dyno know what these are for any given vehicle - does it have some set of look-up tables, or does it just use some default numbers for all cars? My second question is, since rolling resistance depends on vehicle weight, the weight distribution, tire pressure, etc, again…how does the dyno know what these things are so it can know how much load to apply to the eddy-current brakes? Does anyone know how they deal with these things? Just curious (and bored waiting for all the snow to melt!)

 

[Rev]

Black2003Cobra I will be RIGHT back! I am going to get my physics degree, then I will reply to your post.

 

[jtfx6552]

Originally posted by Black2003Cobra
larryc7777– I have seen that article before, and thought it was pretty good. I understand how the Dynojet works, (since it’s nice and simple), but I too, am unfamiliar with the Mustang dyno. The article helps, but it leaves me with more questions about the Mustang dyno. Accordingly, they use an eddy-current brake (in addition to a drum as an inertial load) to simulate aerodynamic and rolling resistance losses. As the drag force goes as velocity squared (and hence, power as velocity cubed), and since rolling resistance is typically modeled as a 3rd or 4th order polynomial, it stands to reason that the difference between a Dynojet and Mustang dyno would not be a fixed percentage (as would be the case for, say, simple frictional losses). Including these two effects would certainly result in less net power recorded, however, so that explains why the Mustang dyno would report lower HP numbers (in addition to the effect of electronic controls on timing, etc for varying loads). My first question is, since drag depends on the coefficient of drag and frontal area of the vehicle, how would the dyno know what these are for any given vehicle - does it have some set of look-up tables, or does it just use some default numbers for all cars? My second question is, since rolling resistance depends on vehicle weight, the weight distribution, tire pressure, etc, again…how does the dyno know what these things are so it can know how much load to apply to the eddy-current brakes? Does anyone know how they deal with these things? Just curious (and bored waiting for all the snow to melt!)

Are you saying that the Mustang dyno HP number is the power at the rear wheels minus the power to overcome rolling resistance and wind resistance to give the net power left to accelerate the car? I didn't get that from the article, maybe I should go reread it...

If that is true, I can see why the Mustang dyno number is lower. I really wouldn't want that, however. As you point out, how would the dyno "know" these things?

I want to know how much HP is put to the rear wheels, period, without any subtracting of arbitrary numbers.

The fact that the load can be increased to better match the real world load on the engine seems to be a real tuning advantage. In case of a car that is heavier than the Dynojets simulated load like an '03 Cobra. I would suspect that to result in a very slight decrease in HP. The only difference being the engine maybe reducing timing advance under the higher load. I would suspect that this small decrease in power would be offset by the fact that the increased load would have the rollers, and hence the drivetrain, accelerating at a lower rate.

If the driveline is accelerated slower, the power lost accelerating the driveline should be lower. To illustrate the point, what if the engine and load were in balance so that the driveline was not accelerating at all (the way the old superflow engine dyno's used to work). This scenario would have no power "lost" due to driveline acceleration. The only losses would be through the gears and friction in the bearings. The Mustang dyno is closer to that scenario than the dyno jet, so I am not sure why it does not have a higher HP reading?

Further, why do dynojet numbers correspond to engine numbers better than the Mustang numbers?

In 1999 ford's documented number for rwhp for a post fix cobra was 320*.85= 272. If they used a mustang dyno they would have had to say the driveline loss was 28%?

New Z06's which are not underated like the '03 Cobra show 350-365 on a dynojet with 410 fwhp, again around 15% (350= 15% loss). 360 *.87= 313? If I took a Z06 to a mustang dyno and came up with 313 rwhp out of 410, I'd say something wasn't right.

Anyway, that article raised more questions for me, too, than it answered.

 

[Black2003Cobra]

hey again larryc – yeah, that was the impression I got from that article. (That the Mustang dyno effectively subtracts the aero and rolling losses by applying that extra load via the eddy-current brake.) And I agree that for a power measurement, that isn’t the number I would want either. I guess I would have made that an "option" (to subtract it or not). They also mentioned since they can include those effects, they can simulate ¼ mile runs on them. I’d question that, as well, however, but again, it makes it sound like they do back those effects out. You make a good point about backing out the inertial losses of the driveline if they were to load the car so that the acceleration is zero. But in 4th gear, I suppose those losses would be rather small anyway, so if they’re backing out the aero and rolling losses, you’d still end up with less power compared to the Dynojet. What do you think? I also agree that the Dynojet numbers seem to match manufactures specs better. Thanks for the feedback, and let me know if you come across anything else that helps explain how these things really work. I would like to know. (Occupational hazard, I suppose! LOL).

 

[TORCH RED COBRA]

Originally posted by Black2003Cobra
larryc7777– My first question is, since drag depends on the coefficient of drag and frontal area of the vehicle, how would the dyno know what these are for any given vehicle - does it have some set of look-up tables, or does it just use some default numbers for all cars? My second question is, since rolling resistance depends on vehicle weight, the weight distribution, tire pressure, etc, again…how does the dyno know what these things are so it can know how much load to apply to the eddy-current brakes? Does anyone know how they deal with these things? Just curious (and bored waiting for all the snow to melt!)

I can help a little on question # 2. I will first say that I prefer the DYNOJET because the Mustang Dyno can not do a 1-1 mapping of the simple Air Fuel Ratio like the DynoJet does.

The Mustang Dyno and the SuperFlow Dyno both know the Vehicle weight, the weight over each axle, tire sizes, rear axle Ratio and so on. They are parameters. How sophisticated the calculations are is something I do not know.

My own testing of my 03 on a Mustang Dyno versus a DynoJet 248C is that the Mustang Dyno reads 11.8 % lower. 475 RWHP versus 420-425 RWHP (Mustang Dyno).

ROB