virtual dyno only measures acceleration based on how fast the rpms go up (basically) factoring in gearing and this and that...

real dynos actually measure the force that the car puts down to the rollers.

that said, i use virtual dyno all the time just to look at a rough estimate of the car performance.

ps if your clutch is slipping its gonna say you're making like 600 lb ft of torque

 

Is jerking off the real or virtual dyno??

 

And unless I'm mistaken, they measure the force the car puts down to the rollers by seeing how fast the rollers accelerate, while knowing the mass of the rollers. Virtual dynos measure the force the car puts down to the road by seeing how fast the car accelerates, while knowing the mass of the car, gearing and all that other fun stuff.

Sounds similar to me...

 

Its all arbitrary. The true measure is really on a flat road though. So if the math in the VD is accurate, and the input are accurate it should technically be more real world accurate than a dyno which simulates.

 

virtual dynos don't measure how fast the car accelerates, it measure how fast the engine rpms accelerate, and works backwards from there to calculate a wheel horsepower.

thats why i mentioned slipping clutch. basically virtual dynos add in a lot of factors to the equation.

real dynos yes measure the acceleration of the rollers, which are directly forced by the actual wheel horsepower (torque, w/e)


:: and because what we are looking for from a dyno is the whp/wtq, that's what makes a real dyno "better". if you're curious of an estimate of that based on engine rpm acceleration, then virtual dyno is fine.

 

the measure of acceleration would be more accurate, provided it accounted for every factor possible.. wind speed, Cd, etc etc.

the individual measure of how much horsepower/torque that reaches the wheels is still more accurately calculated by the dyno.

that said, we dont REALLY care about the "horsepower" we care about the acceleration. a real dyno is just a way of comparing two different cars in terms of engine output and how much that goes to the wheels.

i could be mistaken but i doubt any virtual dyno program factors in Cd. if they do, color me impressed


all this said, i note i think i've been on a real dyno ONCE in my car's life. who cares if you're making 330wtq or 325wtq or w/e.. car accelerates well, and is comparable to cars with similar mods. that's all that really matters

 

Knowing gear ratios, tire size, etc, you can translate engine rpm -> speed very accurately, you just have to tell the VD what gear you were in. And IMO a slipping clutch isn't a valid argument "against" virtual dynos.

Real dynos add their own share of factors, like heatsoak and simulated load. Pick your poison

Both VD and VDR store Cd and frontal area for every car, so I would suppose that they do factor that in.

 

A "Virtual Dyno" is just as good as a dynomometer when used correctly. If you do consistent pulls with the weight of the car the same and on the same stretch of road, you will get repeatable results. This allows proper tuning, and is just as accurate as a dyno. Both will see slight variation. I would honestly venture to say that a virutal dyno reading is more reliable than, say, a non-load bearing DynoJet or DynoPak, as it utilizes real-world resistances on the drivetrain and tires.

As far as giving "accurate" power numbers, they are also equal. A Mustang reads different than a Dyno Dynamics and a DynoJet or a DynoPak. Which is "accurate?" I don't know. The virtual numbers based on logs are just as "accurate" as any of these others as it is comparable to itself as noted above.

 

"Real" dynos also reference engine RPM, so a slipping clutch would still throw off the graphs produced ... just in a different way.

 

Totally agree!

 

To me this thread seems to be people that want to be able to brag about their numbers on the boards using VD plots.

Lets be real here, when we post our dyno numbers online we are just happy we got a high number and want to share it with all that we are happy and maybe brag a bit.

All dynos are just tools and numbers should be irrelevant except comparing your own car to itself after further modification to see what your gains were. The VD works just as well as a regular dyno when used "perfectly" (which to me i don't think most people do) for that purpose. However I don't think thats what the OP wants out of this thread he wants to be able to compare his numbers to a regular dynojet user or other dynos as well as others lobbying the software plots.

If you really want to compare numbers go to a dyno day, they happen all the time, spend 50 bucks and get some numbers. Comparing real dynos to each other are hard enough so why make it worse comparing it to software numbers.

So in short, all it takes are people going down a slight hill to raise their numbers so no I don't think we should look at these the same, just use them to tune and be happy. And if you want to post for bragging rights, hit up a real dyno.

 

Kyooch, what is your rebuttal to some dynos using the weight of the roller as the resistance calculation rather than the weight of the vehicle itself (as a "virtual" version does)? To me, that says that the reading from the dyno is only "accurate" when the vehicle weight exactly matches the weight of the roller. The further off the weight, the less accurate it becomes. It would read high for a heavier car and lower for a lighter car.

I think way too many people are stuck on dyno numbers. That's not what a dyno is for. The reading are used to simulate road conditions so it can be tuned in a safe environment. Dynos aren't meant to be "accurate" in relation to the car ... they are meant to be accurate in relation to themselves. That's all that matters.

 

Beat me to it---saw the Title line and all I could think is

"Is your virtual girlfriend as nasty as your real girlfriend!"

 

To start, yes I still stand by my position.

Again, I think the point may be being missed here. You guys are trying to argue that the virtual dyno program is as accurate as a real dyno.. which is crazy talk

Real dynos measure the actual output to the wheels alone. Attempting to measure how much power is going to the wheels based on the acceleration of the car throws in soooo many more factors.. yes - many are accounted for - weight, gearing etc.. but there's more than that, and enough to throw off the numbers

Yes, "logically," if every single factor is the same and accounted for in a virtual dyno program, then it will be precise. It may or may not necessarily be accurate, and that depends on the formula and how well it factors in EVERY SINGLE factorable difference that you may run into in outside conditions - which you guys are putting a lot of faith in.

Virtual dyno is good for getting a rough estimate of what your powerband is. That's about it. However, running a log outside to throw into a dyno program introduces so many variables that may or may not be accounted for. You guys do understand that right?

The point I'm making is, the good thing about a real dyno is that more factors are eliminated. Period. Runs on a real dyno are going to be both more accurate and more precise.

Honestly, I have to agree with what someone else said. It seems like some people are trying to preserve the accuracy of their precious virtual dyno numbers. Yea I range 370-400whp on virtual dyno, same road, car, mods, conditions etc. Truth be told, I probably make 340whp. I'm not saying virtual dyno is bad, most I've seen are just simply way too optimistic. Sometimes aren't even all that precise either.

 

I'm not talking about the weight - which come on how many of you have actually weighed your car to begin with? Here's another point to make - how much gas do you have in the car when you take your logs? As real dynos measure the force generated by the wheels to turn the rollers, that's not something that matters for a real dyno. It does matter for a virtual one.

In terms of the weight of the roller resistance thing - are you saying that heavier cars produce more power on a real dyno?

It really comes down to roller acceleration vs car acceleration - which do you think is a more accurate estimate of the whp?

Like I said, otherwise virtual dyno is great for getting an estimate of the powerband