Dyno figures

[SYT_Shadow]

Dynos are most useful for measuring deltas in power, not as a way to estimate crank power.

Wheel dynos are not the best devices on the planet to measure output, but dynojets with STD correction have proven to be relatively consistent.

A stock F8X dynos around 400whp.
A ZCP around 420whp.
A CS around 430whp.
A GTS around 470whp.

BMW, like other european manufacturers, takes 8h to dyno a single car. It's done on an engine dyno (not in the car) and it's done in static conditions, not accelerating through a gear in 10 seconds.

[Ed_rx7]

So are we saying transmission loss is roughly equating to about 30 hp? So roughly 8% ?

[AlejoEvo]

Originally Posted by Ed_rx7

F80 paul, my friend probably has the logs yes.

What would the logs show, that would be relevant to this conversation though!

Originally Posted by Ed_rx7

F80 paul, my friend probably has the logs yes.

What would the logs show, that would be relevant to this conversation though!

Logs says a lot about the tunning style. Take AFR by example: some tuners like rich and some more lean! And that says a lot about the car performance.

[Ed_rx7]

F80paul has tuned cars with a silo at spec which make over 700 whp ( supposedly) on US dyno’s . So tuning style etc isn’t an issue.

I’m trying to get to the bottom of rated power difference of cars with similar spec, running similar times

[E92inSG]

My car (f80paul tune) Dyno-ed 510whp on a Mustang Dyno this week and just clocked 6.1s 100-200

https://www.bootmod3.net/log?id=5e7f...0b430c46472bc4

This was the actual log from the 6.1s run

[Ed_rx7]

What’s your mod list?

[Ed_rx7]

So. An anyone tell me why mustangs read lower than dynojet dynos?
And whilst the variance is so vast it seems with the figures, which ones to people think are true !?

Curious

[E92inSG]

from another forum:

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.

[E92inSG]

Originally Posted by Ed_rx7

So. An anyone tell me why mustangs read lower than dynojet dynos?
And whilst the variance is so vast it seems with the figures, which ones to people think are true !?

Curious

there are no "true" numbers, you use the same dyno to find out % gains from certain mods.

even 100-200 which is a pretty accurate, can have many variables. same hp cars may still run diff timings depending on car weight, slight up/ down slope, shift points, torque curve, wheel weight etc.

my own car has done 5.19s 100-200 on a different map with E85 and catless downpipes.

[Ed_rx7]

Very informative...thanks .!

So is a mustang a load dyno rather than inertia?

[CanAutM3]

Originally Posted by Ed_rx7

So. An anyone tell me why mustangs read lower than dynojet dynos?
And whilst the variance is so vast it seems with the figures, which ones to people think are true !?

Curious

None of them are "true" per se, they just measure differently.

Originally Posted by Ed_rx7

He is running, sSp clutches , Hybrid turbos, Meth and 93 fuel( 98/99RON )
So I would say it mirrors your setup
Making 556 whp on a MAHA dyno

The Maha is another type of dyno altogether than the Mustang and Dynojet. It is more sophisticated because it measures drivetrain loss to establish power at the crank. Because of the way the Maha operates, the whp it generates cannot be compared to other types of dynos.

Originally Posted by Ed_rx7

Very informative...thanks .!

So is a mustang a load dyno rather than inertia?

Mustang is both: partial load and partial inertia.

Originally Posted by Ed_rx7

Also considering our cars came from the factory with corrected figures in DIN ... why are they all being compared to other correction factors?....
surely it makes sense to use the same or similar corrections and possibly dyno to measure true increases?
I know people will say there are other factors ... altitude blah blah.... but surely you would try and keep things as simple as possible?... discuss

Sadly, it cannot be kept simple, simply because it is not .

DIN and SAE testing standards are very similar, they however use a different horsepower unit (1hp DIN = 0.98632hp SAE), this is why DIN and SAE power ratings show slightly different numbers.

Another important point is that an engine's power output will vary with acceleration rate. This is why most manufacturers test in steady state (constant RPM) because it yields more accurate and repeatable results. It is also important to realize that the test cells used by car manufacturers are multi-million dollar pieces of equipment and are therefore much more accurate and reliable than the relatively cheap dynos (dynojet, mustang, etc) found at local shops.

Further, regarding correction factors, both DIN and SAE standards specify that NO correction factors should be used for engines that auto-correct for ambient conditions. Most modern forced induction engines, like the S55, can correct for ambient by adjusting boost targets, hence correcting the numbers further with correction factors falsifies the results. It's also important to point out that correction factors also have their limit and remain only relatively accurate for slight variations from the standard athmosphere. This is why SAE and DIN testing standards both specify that engines should be tested in conditions that are closest as possible to the standard atmosphere, regardless if correction factors are needed or not.

Originally Posted by Ed_rx7

So are we saying transmission loss is roughly equating to about 30 hp? So roughly 8% ?

Making blanket statements like this regarding losses is the biggest mistake one can do. Losses are very complex.

There are many other variables that come into play when installing and running a car on a chassis dyno. How tightly the car is strapped down, for example, will affect tire rolling losses. What gear is used also has an effect. Most manual and DCT transmission have a direct drive gear, when that gear is used, there is much less drivetrain loss compared to other gears (as much as 2-3% difference). Just to state a few...

[CanAutM3]

Originally Posted by E92inSG

from another forum:

While most of the article shares pertinent information, there is a rather fundamental flaw in the excerpt above which invalidates a big part of their argument: from a pure physics standpoint, in itself, the transmission gearing has no DIRECT effect on the power readout of the roller dyno. The dyno's computer factors the roller's acceleration rate as well as the roller's speed to calculate the power being generated (Power = Roller's Moment of inertia * angular acceleration * angular velocity), which inherently nets out the effect of the vehicle's gearing. If the engine makes 400hp @ 6000rpm, the dyno will read 400hp minus losses at the wheels regardless of the gearing.

However, gearing will have an INDIRECT effect on the power reading due to its impact on the various other factors: the effect on the effective mass of the powertrain inertia (the faster the powertrain is accelerated, the more power being consumed to accelerate the rotating mass), tire rolling losses varying with the cube of speed, engine power output varying with acceleration rate from tuning, and drivetrain loss being much lower if a direct drive gear is used.

[Ed_rx7]

Thanks for your input

[Smee]

ed are we talking about Steve here?

[Ed_rx7]

We are indeed