DynoJet vs Mustang Dynos
Melting Slicks
Joined: May 2007
Posts: 2,533
Likes: 1
From: North Aurora IL
Mustang Dyno is lower.....a little more realistic numbers to the ground due to the fact that the mustang dyno applies a load resistance to the rear tires during the run as if you where actually on the street.....as the dynojets are almost free spinning wheels thus get bigger numbers...
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Le Mans Master
Joined: Aug 2005
Posts: 5,130
Likes: 3
From: Winter Park FL
One thing I want to know is how does a mustang dyno determine its resistance? Is it a set amount or a calculation?
Le Mans Master
Joined: Nov 2005
Posts: 5,451
Likes: 2
From: East Peoria Illinois
Only numbers that tell me how my car really feels are track numbers. It doesn't matter if its a mustang or dynojet, they can all be fudged and may not reflect what a car "really feels like". Neither should be relied on to tell you how a car will perform, it's just a tuning tool.
One thing I want to know is how does a mustang dyno determine its resistance? Is it a set amount or a calculation?
One thing I want to know is how does a mustang dyno determine its resistance? Is it a set amount or a calculation?
Le Mans Master
Joined: Aug 2005
Posts: 5,130
Likes: 3
From: Winter Park FL
Are you saying RWHP will tell you how hard a car will pull 3rd and 4th on the street but not on the track? If a car makes nice dyno numbers but can't get out of its own way on the track what makes you think it will be able to get out of its own way on the street? Dyno numbers are all just a bunch of fluff anyways, to many variables and ways to cheat the system.
Le Mans Master
Joined: Nov 2005
Posts: 5,451
Likes: 2
From: East Peoria Illinois
Are you saying RWHP will tell you how hard a car will pull 3rd and 4th on the street but not on the track? If a car makes nice dyno numbers but can't get out of its own way on the track what makes you think it will be able to get out of its own way on the street? Dyno numbers are all just a bunch of fluff anyways, to many variables and ways to cheat the system.
Melting Slicks
Joined: May 2007
Posts: 2,533
Likes: 1
From: North Aurora IL
Yes a dyno is a tuning tool to get the most out of your set combo and make sure everything is working within the areas it should be....the track tells you how fast it will do the 60ft 1/8th, 1/4 and speed...It helps you also learn the car better and what works and what dont....each balances as tuning and getting the most of the car.....the difference in dynos is that dyno jets do not put a load on the rear wheels and it gives out a higher number to the ground....the mustang dyno...correct me if Im wrong puts a resistance as if you where driving down the street and not on rollers....giving you resistance.....and it is set but caculated out by the company that figured what the resistance is.....So the mustang dyno is perferred when finding out what you actually have to the ground on the street/track......Dyno numbers are not a bunch of "fluff" I have been all around to many different race tracks and each of the tracks are different as far as the time clocks, lenght, and speeds....there is always human errors and difference between each electrical machine....but each gives that person a better understanding what the machine they are driving is doing and able to do.....
Pro
Joined: Mar 2005
Posts: 623
Likes: 7
From: Bakersfield CA
First off tuning is for the street, or on a real race track.
Second Mustang dynos create load via weighting and electro-magnets, due to calibration and maintenance they are some of the most inconsistent numbers you will see.
The dynojet may be a freewheeling design but it creates the best opportunity to compare apples to apples.
Lastly the comments about a mustang being for tuning and dynojets is for big numbers is comical, they are both for numbers only.
Max RWHP #'s are garbage anyways any good racer will tell you the shape of the curve is more important than how high it goes, just ask anyone with a huge cam who lost to a guy with a little 224 or 228 cam.
Second Mustang dynos create load via weighting and electro-magnets, due to calibration and maintenance they are some of the most inconsistent numbers you will see.
The dynojet may be a freewheeling design but it creates the best opportunity to compare apples to apples.
Lastly the comments about a mustang being for tuning and dynojets is for big numbers is comical, they are both for numbers only.
Max RWHP #'s are garbage anyways any good racer will tell you the shape of the curve is more important than how high it goes, just ask anyone with a huge cam who lost to a guy with a little 224 or 228 cam.
Pro
Joined: Feb 2007
Posts: 702
Likes: 1
From: Frankfort Il
Here's a write up I did for another thread. Hex had a lot of good things to say as well. And here's the thread:
http://forums.corvetteforum.com/show....php?t=1691817
http://forums.corvetteforum.com/show....php?t=1691817
HEX has been all over this one, and for the most part I agree with his answers. The basic reasons for the difference is in part on how the power is calculated, and partially due to the amount of "load" the vehicle "sees" during the pull.
DynoJets measure horsepower and derive torque from that. Loaded Dyno's have a load sensor, and actually measure the torque being applied to the drums (it's a little 5volt reference load sensor). Horsepower is then derived from that information. Torque is an actual force (like gravity), where as Horsepower by definition is a derivited of torque (work over time).
The load sensor data is then sent to the computer where it takes two constants, vehicle weight and Hp@50mph (aerodynamic coefficient used by the EPA) where the computer then calculates the amount of resistance to be applied to the vehicle (PAU force).
For an example of why there's a difference due to load, imagine this. It takes less power (however you measure it) to accelerate the mass of a 2500lb roller from 300rpm to 400rpm in five seconds than accelerating the same roller (2500lbs) with 550lbs of resistance via load cell from 300rpm to 400rpm in the same amount of time (5 seconds). That's why if there's a car that made 425rwhp on our Mustang MD-1100SE dyno, it will be faster than a car that made 425rwhp on a DynoJet.
As far as the timing example that somebody brought up, I've found that to be true as well. Sometimes the cars are faster with 1 to 2 degrees less timing than they see on the Dyno. Best was without being at the track is to check the plugs. That's why, no matter how good the dyno is, the opperator, or the tuner is, it will really only get you about 95% there. The last 5% is going to be needed to be done at the track.
When it comes to manipulating dyno numbers, if there's ever any questions, all you need to do is ask these simple questions if it's a Mustang Dyno. What Parasitic Loss Multiplier are you using (easiest one to change), and ask to see what the weather station is reporting. All you have to do that is go under "calibrations" and weather station peramitors. I can't remember what the SAE values should be off the top of my head, but it's not too difficult to find. If the box check "User defined" is checked, then they might be playing around with the numbers.
Because of these reasons, it's like trying to compare apples to oranges. As far as the "10%-15%" difference, we've found that to be untrue. In our tests it doesn't seem to be a constant at all. At 390rwhp on our dyno, the same car makes about 405rwhp on a local DynoJet. At 422rwhp on our dyno, the same car on the same DynoJet made 458rwhp. I've witnessed cars seeing close to a 80rwhp difference between a Mustang Dyno and a DynoJet at 600rwhp (Mustang MD-1750SE), although I cannot verifiy that with our dyno.
We're fairly conservative, and hence tell our customers that the difference is closer to 6-7%, but as you make more power, the difference increases as well. You must remember, Dyno's regardless of the type are tuning tools, and are in no means ment to tell people how fast their car is. Now which one is more "real world" is a totally different question. I like to explain it like this..... If you drive your car in a situation in which you have no mass and you're in a vacuum, so basically if you do intergalatic racing in space, use a DynoJet. If your car sees gravity, and has an aerodynamic coeffecient, and you race on a planet called Earth, then use a Mustang Dyno.
DynoJets measure horsepower and derive torque from that. Loaded Dyno's have a load sensor, and actually measure the torque being applied to the drums (it's a little 5volt reference load sensor). Horsepower is then derived from that information. Torque is an actual force (like gravity), where as Horsepower by definition is a derivited of torque (work over time).
The load sensor data is then sent to the computer where it takes two constants, vehicle weight and Hp@50mph (aerodynamic coefficient used by the EPA) where the computer then calculates the amount of resistance to be applied to the vehicle (PAU force).
For an example of why there's a difference due to load, imagine this. It takes less power (however you measure it) to accelerate the mass of a 2500lb roller from 300rpm to 400rpm in five seconds than accelerating the same roller (2500lbs) with 550lbs of resistance via load cell from 300rpm to 400rpm in the same amount of time (5 seconds). That's why if there's a car that made 425rwhp on our Mustang MD-1100SE dyno, it will be faster than a car that made 425rwhp on a DynoJet.
As far as the timing example that somebody brought up, I've found that to be true as well. Sometimes the cars are faster with 1 to 2 degrees less timing than they see on the Dyno. Best was without being at the track is to check the plugs. That's why, no matter how good the dyno is, the opperator, or the tuner is, it will really only get you about 95% there. The last 5% is going to be needed to be done at the track.
When it comes to manipulating dyno numbers, if there's ever any questions, all you need to do is ask these simple questions if it's a Mustang Dyno. What Parasitic Loss Multiplier are you using (easiest one to change), and ask to see what the weather station is reporting. All you have to do that is go under "calibrations" and weather station peramitors. I can't remember what the SAE values should be off the top of my head, but it's not too difficult to find. If the box check "User defined" is checked, then they might be playing around with the numbers.
Because of these reasons, it's like trying to compare apples to oranges. As far as the "10%-15%" difference, we've found that to be untrue. In our tests it doesn't seem to be a constant at all. At 390rwhp on our dyno, the same car makes about 405rwhp on a local DynoJet. At 422rwhp on our dyno, the same car on the same DynoJet made 458rwhp. I've witnessed cars seeing close to a 80rwhp difference between a Mustang Dyno and a DynoJet at 600rwhp (Mustang MD-1750SE), although I cannot verifiy that with our dyno.
We're fairly conservative, and hence tell our customers that the difference is closer to 6-7%, but as you make more power, the difference increases as well. You must remember, Dyno's regardless of the type are tuning tools, and are in no means ment to tell people how fast their car is. Now which one is more "real world" is a totally different question. I like to explain it like this..... If you drive your car in a situation in which you have no mass and you're in a vacuum, so basically if you do intergalatic racing in space, use a DynoJet. If your car sees gravity, and has an aerodynamic coeffecient, and you race on a planet called Earth, then use a Mustang Dyno.