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Discussion Starter #1
Finally got my 2013 GT up on a Mustang Dyno. Only made 321 RWHP and 302 LB FT of torque at 6800 RPM (limiter about to kick in), but the HP was still steadily going up. I doubt my exhaust mods did much in the way of power, so this is pretty much my stock baseline. The guys were telling me that a Mustang Dyno tends to give lower numbers and that I'd probably be closer to 335-340 RWHP on other brands (20% loss). I'm not too concerned about the difference though.2013 Mustang GT 4/6/2013 Dyno Run #3 - YouTube
 

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that seems REALLY low...360-380 ish is what most are putting down, so yeah a 20% fudge factor would put you in the ballpark...what's the point of using a dyno that reads inaccurately?
 

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Even if he was able to take it past 6800 RPM, I think I would have only gotten maybe another 2-5 HP. Everyone seemed to be lower than expected on this Dyno. It is an auto, so I'm not sure if that has anything to do with it. Once I get it tuned and do a couple more mods, I'll probably try it out on a different kind of Dyno. The shop was having a Dyno Day and it was $40 off the original price, so I couldn't pass that up.
 

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is yours an automatic? if it is then your numbers are ok. Automatic loss is calculated somwhere between 75-80% whereby it is 85% for manuals. with 75% loss you'd be at 428hp at the crank.
 

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even if it's free what is the point if it doesn't read accurately? The app for iphone would probably be a better reading
 

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is yours an automatic? if it is then your numbers are ok. Automatic loss is calculated somwhere between 75-80% whereby it is 85% for manuals. with 75% loss you'd be at 428hp at the crank.
Yea, it's an auto. I think he had it in drive too versus the select shift. That makes a little more sense with the percentage, thanks. I guess that would mean I actually gained a little from the exhaust, maybe because I have the side pipes wide open.
 
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even if it's free what is the point if it doesn't read accurately? The app for iphone would probably be a better reading


There is no such thing as an accurate dyno. All that matters is consistency for tuning purposes and showing gains after mods.
 

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Found this from a tuner on a Vette forum; definitely helps knowing the differences:

"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."
 

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Use it for what it is worth...... a tuning tool.

Now that you have a baseline you can use that number against future mods.

If that shop doesn't know about mustangs I would probably find another and get another baseline tho.
 

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Discussion Starter #11
Use it for what it is worth...... a tuning tool.

Now that you have a baseline you can use that number against future mods.

If that shop doesn't know about mustangs I would probably find another and get another baseline tho.
From what I've heard, they get a lot of Mustangs through there, but there are also other shops that are heavily used by club members. It'll be a while before any other mods, so I'll cross that road when I get there.
 

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that seems REALLY low...360-380 ish is what most are putting down, so yeah a 20% fudge factor would put you in the ballpark...what's the point of using a dyno that reads inaccurately?
It might be the dyno or it might be the car. One should use a Dyno as a baseline for mods. Now you have it and can now compare mods so long as you use the same Dyno
 

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It might be the dyno or it might be the car. One should use a Dyno as a baseline for mods. Now you have it and can now compare mods so long as you use the same Dyno
I'm thinking it's a mixture of the auto and the dyno. Definitely plan on sticking with the same one though so I get accurate increases on future mods.
 

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Discussion Starter #17
The drag strip is the place to tell what kinda power it's making.


Sent from AutoGuide.com App
I agree. They just opened the track this past weekend, but I'm going to wait for it to warm up a bit before I take the car out there.
 
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That DYNO operator should have had your car set to whatever the 1:1 Gear ratio is (now its usually 3rd gear in the 4 speed autos, not sure about the new autos though) and he should most certainly should have the TC/AdvanceTrac set to OFF!.......And I do believe that I read that when you use the "Select-Shift" in manual, it LOCKS the Torque Converter up so you wont burn any of the Clutch Pack Bands up in the new automatics when you hold it in any gear!..........Your analysis of the different Dynos is spot on:bigthumbsup. As "Mustang" Dynos do read quite a bit lower than inertia dynos........But the REAL Heartbreaker in the Dyno world are those manufactured by "DYNO-DYNAMICS" As these tell the whole truth, and use "Tractive-Force" (the same measurement that they use to calculate Railroad Locomotives usable HP) as the one thing that the MD dynos calculate into the formula is "Tire slippage, and friction loss at the contact patch"............I do have to say that the Mustang Dyno that you used did infact read on the LOW side though............Was your engine heat soaked?......Was it hot inside the shop?........There are many different variables that could have caused a low read on that run!.......As far as Manual trannys go, it is well known that it is hard to get a correct read with these funky MT-82's as opposed to the Tremec 6 speeds because the MT-82 does NOT have a gear that is a "True" 1:1 ratio, so with it you have to do a pull in 5th gear as opposed to 4th (as 4th gear in just about every manual known is a 1:1 ratio regardless if it is a 5 or 6 speed) ...........You should take it back and make sure the dyno operator has your tranny set in select-shift (whatever the gear ratio that is closest to 1:1) And that the "Nannies" are set to OFF:bigthumbsup. ........................Sean
 

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Discussion Starter #19
It wasn't too hot in the garage, so that didn't play a factor. I don't think they had the traction control off or used the select shift, so definitely try that next time.
 
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That DYNO operator should have had your car set to whatever the 1:1 Gear ratio is (now its usually 3rd gear in the 4 speed autos, not sure about the new autos though)
To do this reliably with the 6R80 auto trans you would need a specific tune for the dyno. It can be done but it's not like dynoing a manual.


As far as Manual trannys go, it is well known that it is hard to get a correct read with these funky MT-82's as opposed to the Tremec 6 speeds because the MT-82 does NOT have a gear that is a "True" 1:1 ratio, so with it you have to do a pull in 5th gear as opposed to 4th (as 4th gear in just about every manual known is a 1:1 ratio regardless if it is a 5 or 6 speed)

This is incorrect. 5th gear in the MT-82 is in fact 1:1. There is nothing special about having a 1:1 gear ratio, it is simply the gear where the input shaft and output shaft are locked together, hence the name 'direct drive'. While most American cars with manual transmissions had 4th being direct drive, most Japanese and European cars with 6-speeds had 5th being direct(BMW M3, Toyota Supra). Audi's with Quattro are a notable exception as they don't have direct drive gear ratios.


Automatic transmissions are unique as in the manufacturer's attempts to increase the number of available ratios they made the transmissions with multiple planetary gear-sets so they can alter the ratios and get more forward gears. The 6R80 has 3 gearsets so a direct drive was not practical. The closest gear to direct drive is 4th at 1.14:1.
 
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