Dyno Results

hotmustang331 · Jun 20, 2005

trinity_gt said:
Still don't understand why the MD cannot turn off this "tune mode" or whatever it is that's causing the error and simply measure and display the actual power being delivered to the wheels. The elegant simplicity and determinism of the Dynojet makes it the benchmark - at least compared to the MD - for showing what power is there at the wheels.

As if that car, with those mods, is actually making just 229. For deltas during tuning or measuring A/F at steady state load, I can see the MD being useful. But why would anyone want to use something that's clearly not reporting the correct numbers for determining absolute power at the wheels?

its reporting the ACTUAL HP thats propelling your car....the dynojet is doing about the same thing as this dyno, but it loads EVERY car equally at around 2K pounds. So your car is pulling on that dyno like it would if it weighed 2K. Really the dynojet isnt really displaying actual RWHP, more of a comparing tool so every car is equal. If you were to enter the weight on the mustang as 2k for her car it would post simular #s to a dyno jet. but i also belive it takes into account for wind resistance, but i am not 100% sure...so again it would be pretty close. its kinda odd, what weight is actually showing what power your putting down? I really dont know. The dyno has to have a load on it to measure your HP, so i guess 2K pounds is what they figured they shoudl load everyone to as most cars wont weigh under that.

trinity_gt · Jun 20, 2005

hotmustang331 said:
its reporting the ACTUAL HP thats propelling your car....

No, I don't think it is.

the dynojet is doing about the same thing as this dyno, but it loads EVERY car equally at around 2K pounds. So your car is pulling on that dyno like it would if it weighed 2K.

The DJ is doing nothing more than measuring the power that is accelerating those deterministic, calibrated masses. It's a classically simple example of Netonian physics involving moments of inertia, masses, angular accelerations and so on. Knowing the key parameters of the system allows one to deuce the exact power being fed in simply by watching how fast these rollers are accelerating.

Really the dynojet isnt really displaying actual RWHP, more of a comparing tool so every car is equal. If you were to enter the weight on the mustang as 2k for her car it would post simular #s to a dyno jet. but i also belive it takes into account for wind resistance, but i am not 100% sure...

But I don't want my Dyno making rough estimates about esoteric nonsense like "wind resistance" when I'm curious about the actual power at my wheels. I don't want guesstimates of vehicle weight, air resistance, coefficients of drags and all that. "Oh gee, I add a Mach 1 chin spoiler...better factor that into the wheel HP on a MD..."

See what I mean? That's crap. I want control over all variables that can be controlled. A GTech accelerometer on an open road is subject to way too many variables, like road gradient and wind speeds to be of any use to know if a particular mod added or lost power. The MD, in trying to be cute, adds ridiculous variables like wind speed when I'm trying to conduct a measurement? That's not science...it's marketing.

Mass too...again, I don't care. I want to strip away everything else and measure the torque at the wheel-road interface. Don't you worry, MD, about the car's mass or aero coefficient. Just tell me how much power I've got at the the wheels. I'll let track performance tell me how my aero is doing.

so again it would be pretty close. its kinda odd, what weight is actually showing what power your putting down? I really dont know. The dyno has to have a load on it to measure your HP, so i guess 2K pounds is what they figured they shoudl load everyone to as most cars wont weigh under that.

It's just an arbitrary but known, calibrated mass on low-friction roller bearings. The rate of angular acceleration resolves back to a torque after factoring in the moment of inertia and, knowing RPM, you have HP from RPM*T/5252. It doesn't matter if it's a 1000HP blown SBC or a 100HP Saturn...they will do as much work as they each can on those rollers and that's just that.

From the perspective of tuning, I like the MD because of it's ability to put a steady load on the drivetrain, allowing tuning at discrete points. But for the all-out "what's she got?" dyno that we're all interested in, it's really quite useless unless you're doing deltas only, from one run to the next and are not interested in absolute numbers.

hotmustang331 · Jun 20, 2005

Exatcly, the dyno is for comparing #s that we KNOW. Its consistent. MD dyno is the only way to tune and the ONLY dyno that will get REAL WORLD A/F #s and the such. Use its #s for an estamate of actual propelling force with all factors in. NO dyno is completely acurate, that small guess work is no big deal. What you car makes on a dyno doesnt meak squat...its just for fun and a comparison. My reasons were A. to check A/F #1 and B. to see how my car stacked up against other cars, to see if my car is performing like it should. I would also not go to a MD to compare #s. MD is absolutly the best for tuning though, cant beat it. Dyno jet lets you see how you stack up against everyone else...and see what HP your car is making as compared to what its advertised. they figured it out, as to if its accurate in terms of HP... not me, but by no means is any dyno 100% accurate...like I was saying there is no way to measure it 100% accuratly. I guess they got pretty close. LOL

Oh and that wind resistence is used to calculate actual real world conditions. Like flying down the highway at 100MPH...it gives a good guess as to what your A/F will be and how your car is running. A DJ cannot reproduce real world A/F #s and the such. The car usually runs on the rich side due to the car being under less load. Personally I am getting my car TUNED next month after the cams on a MD...but a few weeks after I am going back to the dodge DJ to see my GAINS. As i cannot see how much power I gained when on the MD.

trinity_gt · Jun 20, 2005

hotmustang331 said:
Exatcly, the dyno is for comparing #s that we KNOW. Its consistent.

You mean the Dynojet, right?

MD dyno is the only way to tune and the ONLY dyno that will get REAL WORLD A/F #s and the such.

I've said that I think the MD is useful for, and IMHO only for, tuning becuase of its ability to load the drivetrain, allowing a wide range of throttle inputs for a fixed engine RPM allowing fine tuning. An inertia dyno, even with creative use of the brakes, cannot mimic this.

Use its #s for an estamate of actual propelling force with all factors in.

If I want that I'll just go to a track. They have correction factors, the track is consistent etc. No, I just want to know how much power is available at the hubs, pure and simple. No wind this, no drag that, no weight the other...just power.

rwHP = HubTorque*HubRPM/5252.

The DJ gives that, the MD for whatever reasons does not.

NO dyno is completely acurate, that small guess work is no big deal.

I agree that there's uncertainties in everything. Even two DJ may give slightly different readings...like every scientific instrument, they rely on calibrations, maintenance and the like to give optimal results. However, in principle, the DJ is about the simplest, most determinist way to measure the work your engine can do via the road wheels.

What you car makes on a dyno doesnt meak squat...its just for fun and a comparison.

Well, my Ford Probe GT put down a whole 135 front-wheel HP. That's just how fast it could spin those 2000-lb rollers up to speed. It's directly comparable to my 268 rear-wheel HP Mustang or the 1500HP blower BBC that was on my favorite dyno last weekend. In all instances these three powerplants are trying to do work on a known system. Their results are eminently comparable, in terms of power they put down.

My reasons were A. to check A/F #1

I agree: the MD is invaluable for tuning.

and B. to see how my car stacked up against other cars, to see if my car is performing like it should.

I can do this on the track or on the street once in a while though.

MD is absolutly the best for tuning though, cant beat it.

Agreed.

Dyno jet lets you see how you stack up against everyone else...and see what HP your car is making as compared to what its advertised.

They DJ is good for two reasons. First, as you note, it's "universal". A 248C with 2000# rollers in one site is pretty much the same deal everywhere else and as long as all units are calibrated and maintained, their numbers are directly comparable. Second, it's giving an accurate measure of the power available at your wheels. No fudges, no estimates, just power.

Oh and that wind resistence is used to calculate actual real world conditions.

But I can get real world conditions in the real world.

Like flying down the highway at 100MPH...it gives a good guess as to what your A/F will be and how your car is running. A DJ cannot reproduce real world A/F #s and the such.

Well "wind resistance" isn't needed to tune AFR. That can be done simply by loading the tires at any given RPM to allow tuning of the AFR at various throttle angles. If that means 4000RPM in 4th, so be it. It doesn't have to be masked under "wind resistance"...it's simply "load tuning."

And the DJ, being an interial unit, doesn't have to try to reproduce wind resistance when all I want it to tell me is power at the wheels.

The car usually runs on the rich side due to the car being under less load. Personally I am getting my car TUNED next month after the cams on a MD...

I wouldn't recommend any other way to tune it. MD rocks for that. But it, for whatever reason, will not give accurate, absolute power-at-the-wheels numbers if you want them.

but a few weeks after I am going back to the dodge DJ to see my GAINS. As i cannot see how much power I gained when on the MD.

hotmustang331 · Jun 20, 2005

Cool, we are on the same page....YES... But when i was talking about it loading for wind resistence, i was refering to that helping with determining real world A/F...not its HP #s. Cuz there is a lot more load at the end of the 1/4 mile in 4th gear at 100 with wind than doing the same thing with no wind factored in.....I think they do it just to add to its tuning capabilitys and to make sure people dont go lean when at the track. Oh and I agree, test it on teh track to see how it runs....thats exactly why i said that what your car maes on a dyno doesnt mean jack (please dont take that as I am meaning that a 120RWHP car is faster than a 400RWHP car with both at the same weight LOL....more as saying that I have seen 480RWHP cobras get pulled by 430RWHP machs LOL.....in the real world anything can happen and dont go on #s to say who is faster...thats all I was saying/meaning LOL.) You have alot of knowledge on this subject and how dynos really operate. Are you an engineer of some sort? or fresh out of college LOL?

BlackenedSVT · Jun 20, 2005

Chili said:
Good job on the math there!

I didn't say that there's a 15% drivetrain loss which equals 225.. I said that it is estimated at around 15% but most of the stock GT's that I have seen are right about 225.

I was agreeing with you BTW..

No i know. I just felt like getting an extra post count in there No need to roll your eyes at me

Chili · Jun 21, 2005

UDTBadkarma said:
No i know. I just felt like getting an extra post count in there No need to roll your eyes at me

That's what I suspected..

escudolm · Jun 21, 2005

My 2003 Mustang GT dynoed 237rwhp and 280rwtq with nothing but a MAC Prochamber and MAC Catback. Its an auto also.

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