I have written pages and pages of posts on this topic on various forums. Here's a little write up I did a few weeks ago. . .
DynoJets are inertia dynos, and have been around for years, much longer than any type of load cell dyno. Inertia dyno's work on the principle of the acceleration of a known mass over time. Their rollers are the known mass. Weighing in at over 2500lbs or so. Your car gets strapped down to the machine, and the dyno collects it's data. It is able to calculate horsepower by measuring the acceleration in rpm of the rollers in regards to RPM. This is why gearing can affect the dyno results, more on that in a bit. Now that the dyno has recorded the horsepower curve, it can take the integral of that curve and get the torque curve. Since the dyno’s power calculations are based on the acceleration of mass over time in regards to RPM, gearing is very important. Since a vehicle with a lower gear ratio can accelerate the mass to a higher speed using less engine RPM, it will show a higher horsepower number than a car with a higher gear ratio. If a car is able to accelerate the dyno’s rollers from 200rpm (roller) to 300rpm (roller)in 1500rpm (engine), then the dyno is going to record more power than a car that did that in 2000rpm (engine).
Now we go to Mustang dyno’s and other loaded dyno’s. Our Mustang MD-1100SE dyno’s rollers weigh 2560lbs. That is the actual mass of the rollers, much like the DynoJet. That’s about where all the similarities end. When we get a car on our dyno, we enter two constants for the dyno’s algorithms. One being the vehicle weight, the other being what’s called “Horsepower At 50mph”. This is a number that represents how much horsepower it takes for the vehicle to push the air to maintain 50mph. This is used as the aerodynamic force. Mustang dyno’s are also equipped with a eddy currant load cell. Think of a magnetic brake from a freight train. This magnetic brake can apply enough resistance to stall a big rig. Off one side of the eddy currant load cell, there is a cantilever with a 5volt reference load sensor (strain gage). As the rollers are spinning this load sensor is measuring the actual torque being applied. So as the rollers spin, the load sensor is measuring the force being applied, sending that information to the dyno computer, taking into account the two constants entered earlier, computing the amount of resistance needed to be applied to the rollers to load the car so that the force of the rollers resistance is as close to the force the car sees on the street. The dyno is then able to calculate the total force being applied to the rollers in torque, and then taking the derivative of that torque curve to arrive at the horsepower curve. Since torque is an actual force of nature, like gravity and electricity, it can be directly measured. Horsepower is an idea that was thought up by man, and cannot be directly measured, only calculated.
I like to state it like this. . . I start by asking how much your car weighs, lets say 3500lbs. Now you take your car and you make a make a WOT rip in your tallest non overdrive gear, how much mass is your engine working against? 3500lbs right? Now you strap your car on a DynoJet and you make a WOT in the same gear, how much mass is your engine working against? 2500lbs right? Now you strap your car on a Mustang dyno, how much mass is your engine working against? 2500lbs. Plus the resistance being applied by the eddy current generator. We’ve seen anywhere for 470lbs of resistance to over 700lbs of resistance as measured in PAU force in the data logs. So which one is more accurate? Well they their both accurate. If a DynoJet dyno says you made 460rwhp, then you made 460rwhp. If a Mustang dyno says you made 460rwhp, you also made 460rwhp. Now which one of those numbers best represents what your car is doing when its on the street. That’s a different question.
The most important thing to remember is that a dyno is a testing tool. If the numbers keep increasing, then you’re doing the right thing. We try to look over at NET gain, instead of Peak HP numbers. A 30rwhp increase is a 30rwhp increase regardless of what dyno it is on.
Now I can address how to calculate the difference between one type of dyno and another. Simply put, you can’t. Because Mustang dyno’s have so many more variables, it’s not a simple percentage difference. We’ve had cars that made 422rwhp on our Dyno, two days later make 458rwhp on a DynoJet the next day. We’ve also had cars that made 550rwhp on our dyno, make 650+rwhp on a DynoJet a few days later at another shops Dyno Day. For instance, my 2002 Z28 with a forged internal LS6 Heads/Cam/Intake, makes 460rwhp on our dyno. I thought that was a little low, since I’ve had cam only LS6 Z06 vettes make 450rwhp. So I overlaid the dyno graphs. Guess what, the PAU force for my car was almost 200lbs more than the C5Z06 that made 450rwhp with cam only. So I entered the weight and horsepower at 50 number for a C5Z06 and did another horsepower rip with my car. The only reason I did that was to compare Apples to Apples. This time my car made 490rwhp, no other changes. Now I don’t go around saying my car made 490rwhp, I say what it actually did with the correct information entered into the computer. It made 460rwhp. Now if I ever get a chance to take it on a DynoJet (which I plan to in the spring), I have no doubts it’ll be over 500rwhp. I know this based on airflow and fuel consumption on the data logs.
But since we’re asked this question constantly we're fairly conservative, and hence tell our customers that the difference is closer to 6-7%, but as you make more power, and the more your car weighs, the difference increases as well. You must remember, Dyno's regardless of the type are tuning tools, and are in no means meant 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 intergalactic racing in space, use a DynoJet. If your car sees gravity, and has an aerodynamic coefficient, and you race on a planet called Earth, then use a Mustang Dyno
Let me start by saying great writeup. I love the input on this topic as no two dyno's read the same, the most important things that you can look at is calculated airflow and fuel consumption (when accurately tuned). As those two values will tell you more than any dyno will when it comes to how much air the engine is moving at a given RPM. Dyno's are a tuning tool and nothing more! Who cares what it makes on one dyno compared to another as long as it makes what it is capable of. If your tuner is good and comfortable with their dyno they will let you know if there is an issue holding your setup back. Dyno numbers have a place but it should be placed well behind track numbers and real world results.
The most important thing to remember is that a dyno is a testing tool. If the numbers keep increasing, then you’re doing the right thing. We try to look over at NET gain, instead of Peak HP numbers. A 30rwhp increase is a 30rwhp increase regardless of what dyno it is on.
... and that is the thing that alot of people will forget here.
__________________ 1998 Camaro Z-28 M/6: Under Construction Just a tiny 224/230 Pat G cam;LS6 intake;Hooker LTs; stock 98 heads; UPD lid; JF tune; ect...ect...ect
394rwhp/381rwtq (100 degree temp.)
I have written pages and pages of posts on this topic on various forums. Here's a little write up I did a few weeks ago. . .
DynoJets are inertia dynos, and have been around for years, much longer than any type of load cell dyno. Inertia dyno's work on the principle of the acceleration of a known mass over time. Their rollers are the known mass. Weighing in at over 2500lbs or so. Your car gets strapped down to the machine, and the dyno collects it's data. It is able to calculate horsepower by measuring the acceleration in rpm of the rollers in regards to RPM. This is why gearing can affect the dyno results, more on that in a bit. Now that the dyno has recorded the horsepower curve, it can take the integral of that curve and get the torque curve. Since the dyno’s power calculations are based on the acceleration of mass over time in regards to RPM, gearing is very important. Since a vehicle with a lower gear ratio can accelerate the mass to a higher speed using less engine RPM, it will show a higher horsepower number than a car with a higher gear ratio. If a car is able to accelerate the dyno’s rollers from 200rpm (roller) to 300rpm (roller)in 1500rpm (engine), then the dyno is going to record more power than a car that did that in 2000rpm (engine).
Now we go to Mustang dyno’s and other loaded dyno’s. Our Mustang MD-1100SE dyno’s rollers weigh 2560lbs. That is the actual mass of the rollers, much like the DynoJet. That’s about where all the similarities end. When we get a car on our dyno, we enter two constants for the dyno’s algorithms. One being the vehicle weight, the other being what’s called “Horsepower At 50mph”. This is a number that represents how much horsepower it takes for the vehicle to push the air to maintain 50mph. This is used as the aerodynamic force. Mustang dyno’s are also equipped with a eddy currant load cell. Think of a magnetic brake from a freight train. This magnetic brake can apply enough resistance to stall a big rig. Off one side of the eddy currant load cell, there is a cantilever with a 5volt reference load sensor (strain gage). As the rollers are spinning this load sensor is measuring the actual torque being applied. So as the rollers spin, the load sensor is measuring the force being applied, sending that information to the dyno computer, taking into account the two constants entered earlier, computing the amount of resistance needed to be applied to the rollers to load the car so that the force of the rollers resistance is as close to the force the car sees on the street. The dyno is then able to calculate the total force being applied to the rollers in torque, and then taking the derivative of that torque curve to arrive at the horsepower curve. Since torque is an actual force of nature, like gravity and electricity, it can be directly measured. Horsepower is an idea that was thought up by man, and cannot be directly measured, only calculated.
I like to state it like this. . . I start by asking how much your car weighs, lets say 3500lbs. Now you take your car and you make a make a WOT rip in your tallest non overdrive gear, how much mass is your engine working against? 3500lbs right? Now you strap your car on a DynoJet and you make a WOT in the same gear, how much mass is your engine working against? 2500lbs right? Now you strap your car on a Mustang dyno, how much mass is your engine working against? 2500lbs. Plus the resistance being applied by the eddy current generator. We’ve seen anywhere for 470lbs of resistance to over 700lbs of resistance as measured in PAU force in the data logs. So which one is more accurate? Well they their both accurate. If a DynoJet dyno says you made 460rwhp, then you made 460rwhp. If a Mustang dyno says you made 460rwhp, you also made 460rwhp. Now which one of those numbers best represents what your car is doing when its on the street. That’s a different question.
The most important thing to remember is that a dyno is a testing tool. If the numbers keep increasing, then you’re doing the right thing. We try to look over at NET gain, instead of Peak HP numbers. A 30rwhp increase is a 30rwhp increase regardless of what dyno it is on.
Now I can address how to calculate the difference between one type of dyno and another. Simply put, you can’t. Because Mustang dyno’s have so many more variables, it’s not a simple percentage difference. We’ve had cars that made 422rwhp on our Dyno, two days later make 458rwhp on a DynoJet the next day. We’ve also had cars that made 550rwhp on our dyno, make 650+rwhp on a DynoJet a few days later at another shops Dyno Day. For instance, my 2002 Z28 with a forged internal LS6 Heads/Cam/Intake, makes 460rwhp on our dyno. I thought that was a little low, since I’ve had cam only LS6 Z06 vettes make 450rwhp. So I overlaid the dyno graphs. Guess what, the PAU force for my car was almost 200lbs more than the C5Z06 that made 450rwhp with cam only. So I entered the weight and horsepower at 50 number for a C5Z06 and did another horsepower rip with my car. The only reason I did that was to compare Apples to Apples. This time my car made 490rwhp, no other changes. Now I don’t go around saying my car made 490rwhp, I say what it actually did with the correct information entered into the computer. It made 460rwhp. Now if I ever get a chance to take it on a DynoJet (which I plan to in the spring), I have no doubts it’ll be over 500rwhp. I know this based on airflow and fuel consumption on the data logs.
But since we’re asked this question constantly we're fairly conservative, and hence tell our customers that the difference is closer to 6-7%, but as you make more power, and the more your car weighs, the difference increases as well. You must remember, Dyno's regardless of the type are tuning tools, and are in no means meant 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 intergalactic racing in space, use a DynoJet. If your car sees gravity, and has an aerodynamic coefficient, and you race on a planet called Earth, then use a Mustang Dyno
My 427LSX 11.5:1 CR, 235/250 .65X, LS7 heads/intake made 450hp 400trq with the cutout closed through my 9"/M6/heavy rims in my TA. Opened up the cutout, and it was making 30 more hp and 25rwtrq through most the rpms at 14:1 AFR until we cut the run early. Numbers appear low, but a C6ZO6 ported heads/intake/cam made 450 as well. This was all on a MD, with vehicles that "should" be making ~530-550rwhp
When I first set up my Mustang MD-500, it was about 13% less than a DJ, I know this because my own car was run on two different DJ 248s, within 2HP of each other, then on my Mustang. I redid my parasitic curve, (they come with a generic curve), which put it closer, I tweaked the calibration a little, about 5% less than a DJ, while slightly optimistic, IMO, close enough. I figure the higher the numbers, the customers are happier, the actual numbers aren't that important other than bragging rights, a dyno is a tool, a ruler, different rulers give different readings measuring the same thing. The important thing is are you gaining or losing from the tuning/mods you have done. If all you are interested in is 1/4 mile, then an inertia dyno is fine. A street car or a road race car needs a loaded dyno to be able to simulate all throttle openings, engine loads and rpms to get the entire fuel map correct.
When I first set up my Mustang MD-500, it was about 13% less than a DJ, I know this because my own car was run on two different DJ 248s, within 2HP of each other, then on my Mustang. I redid my parasitic curve, (they come with a generic curve), which put it closer, I tweaked the calibration a little, about 5% less than a DJ, while slightly optimistic, IMO, close enough. I figure the higher the numbers, the customers are happier, the actual numbers aren't that important other than bragging rights, a dyno is a tool, a ruler, different rulers give different readings measuring the same thing. The important thing is are you gaining or losing from the tuning/mods you have done. If all you are interested in is 1/4 mile, then an inertia dyno is fine. A street car or a road race car needs a loaded dyno to be able to simulate all throttle openings, engine loads and rpms to get the entire fuel map correct.
Mustang Dyno's and dynojets can be calibrated any way you want them.I use to run a Dyno jet and now own a Mustang Dyno.My Dyno is calibrated to read within 5% of a Dynojet and I've seen some Mustang dyno's actually read higher than a Dynojet.It's all in the settings.
There is no definate percentage or number that you can go by. I bought a H/C motor from a guy that made 463 on a mustang dyno. I dyno'd it in my car on TWO different dynojets and I made 457 and 458. THEN went to a mustang dyno that was supposivly calibrated to read like a dynojet and I made 464 there.
Yep all depends on the particular mustang dyno. Ours is lower than a dynojet but have never been able to establish a set percentage. Ive also seen cars on other Mustang dynos read lower once on a dynojet
The local dyno that I just strapped my car to was a mustang dyno that he had "unloaded" to read similar to a dynojet. He said that it was still applying the load (cause he said the lower HP cars seem to really take forever) somewhat, but that it wasn't as low as a normal Mustang Dyno.....the car laid down 329/360 bone stock with a lid and paper filter.....only 21k miles....
__________________ Terry Spalding
2001 SS Camaro Vert #4498
The easiest way to make a Mustang Dyno read higher numbers is to change the "parasitic loss multiplier". A value of 1.00 is the default setting, increasing this value to result in a higher horsepower number, but it will also show that less load "PAU Force" was being applied as well.
__________________ Mike Hornback @ Straightline Performance
best write up on the difference between dynojets and mustang dyno's i've read on a forum in a while. i've tried explaining this to people on many forums over and over and people still don't get it. you'd be amazed (or maybe YOU wouldn't) at how many people don't get how dyno's work.
__________________ 2006 Lancer Evolution IX MR MODS: Ralliart CF lip, Seibon CF hood, Chargespeed CF trunk, Black painted roof/vg, JDM EVO IX rear, Black UK trunk badge, K&N drop in filter, HKS Carbon Ti exhaust, Buddy Club Racing Spec Coilovers, Stoptech Slotted rotors, ACT HDSS, ACT Streetlite Flywheel, Ingalls Stiffy engine tq damper, HKS Type-1 TT, Hawk HPS pads, tinted windows, honda element antenna
12.82@107.41
1.86 60'
best write up on the difference between dynojets and mustang dyno's i've read on a forum in a while. i've tried explaining this to people on many forums over and over and people still don't get it. you'd be amazed (or maybe YOU wouldn't) at how many people don't get how dyno's work.
Try explaining to customers why an unlocked TH400 car with a 5000rpm stall reades under 450rwhp, and runs low 10's-high 9's. . .
__________________ Mike Hornback @ Straightline Performance
Glad I saw this thread. I was SOOO upset today. Was at the dyno today for a tune and got 455/455 on my 408. Ok I'm not just focused on the #s but when my tunner says, oh yeah that hemi with H/C put down 430, I said WTF!!! Oh and that was a small cam, couldn't tell it had a cam!
Mustang Dyno's and dynojets can be calibrated any way you want them.I use to run a Dyno jet and now own a Mustang Dyno.My Dyno is calibrated to read within 5% of a Dynojet and I've seen some Mustang dyno's actually read higher than a Dynojet.It's all in the settings.
What values can you alter in a dynojet to adjust the power numbers? To my knowledge, there are none.
Your exactly right about once you start to alter settings and try to make a mustang dyno read like a dynojet, that you can get the numbers higher than a dynojet. These user adjustable options (and weight/hp@50 variables) are what makes the mustang dyno a great tuning tool, with great road simulation, but it prevents the numbers from being consistant from shop to shop comparisons.
Thanks,
Ryan
__________________ 2006 Quicksilver GTO, M6 Daily Driver 1998 WS6 TA M6 Bright Red. ASC #370 -- SOLD
01 Ws6, m6, ASC#618 of 1583, 40k Miles, Slp lid, 85mm Maf, Ported FAST 90, UMI 90mm TB, Lucas 38lb inj's, Trick Flow 220cc heads milled to 60cc's, 7.5 Comp Pr's, VRX5 cam, Ls7 lifters, H.S. 1.7 rockers, Ls2 TC, Melling HO OP, PB 25% UDP, Pace Lt's, Pace Y, UMI K-member, UMI T/A relocator, UMI SFC's, UMI LCA's, UMI adj. PHB, SLP T/A, Koni 4th Gen's, Eibach prokit, MagnaFlow CB, Tuned @ StraightLine 457 HP and 405 Ft Lbs
