DQ, Whats the difference between a Mustang dyno and a dynojet?

[Fast_351]

Here's why a Mustang Dyno is more accurate in simulating track conditions than a DynoJet. First, lets all agree on one thing. The rate at which an engine increases RPM DOES matter to tuning (an engine increasing 1000 RPM/sec sees completely different fuel and air demands than an engine increasing at 200 RPM/sec).

That said, the Dynojet uses a fixed weight drum. With the same amount of RWHP, it will accelerate at the same speed regarless of whether you have a 1000# rail or at 5000# heavy street car sitting on it. The dynojet would have you put the same tune on either engine. However, in real life, the RPMs on the 1000# rail increase way faster than the 5000# street car. The rail needs a different tune than the street car.

Now on a Mustang Dyno, the rate of acceleration is controlled by the weight of the vehicle (and perhaps wind speed, I don't know). This will result in a tune that is tailored to the actual RPM increase rate vs an increase rate that is seen when on the dyno.

-Mike


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[Rev]

OK, can we just simplify this? The Mustang dyno tests cars and the DynoJet tests engines. Which do you want? The DynoJet is proven. I have a lot of questions as to the Mustang dyno's (and the operator's)ability to simulate a car.

Rev

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'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

[Unit 5302]

Originally posted by turbolx:
Not to start a flame war here, but please don't throw out misinformation like this. We use chassis dynos to tune the whole car, not just the engine. (that's what engine dynos are for!) The primary purpose of any chassis dyno is to try to accurately simulate what's happening on the road or at the drag strip, which should include wind drag, especially with trap speeds in the 1/4 over 100mph.

Ah, a Mustang Dyno owner.

Anyway, you're wrong. But that's okay. Hyping your product is cool. Dyno's were meant to do exactly what their name imply's. Measure horspower.

The weight of a vehicle can be completely offset with gears. If you change the gear ratio in your car, your weight information becomes completely distorted. There is something called a computer to adjust air/fuel ratio's if the tuner doesn't know what he's doing. Tune it on the ragged edge, you get what you asked for. As far as putting your Mustang Dyno up against a Dynojet car, both with 400hp measured, yeah, you're car is going to win. Know why? Cause your dyno is wrong. Take your car with 400hp (setup with your BS parameters) then send the guy to a Dynojet and voila, he's got more. 420, whatever. Why is it that so many people who tune their vehicles on a Dynojet experiance no problems with their cars? Cause you are floating hype. If a tuner knows what he's doing, your car will be setup right. As far as tuning, since the car isn't run in the same gear for tune purposes, the engine is placed under different load conditions (called gears). A 3rd gear run won't put as much load on an engine as a 4th gear run. It's called torque multiplication. If a car is properly tuned, the 3rd gear pull, and the 4th gear pull should appear almost exactly the same. Making up some make believe weight number (cause you really don't know, and the load on the engine is changed by gearing) for a car won't help you tune it.

Furthermore, a coefficient of drag is NOT a constant number at all velocities. Take a look at the Ferrari Testarossa. It has a god awful Cd of drag, at measured wind tunnel speeds. But, dispite that fact, it manages a very high top speed. That's because airflow changes and creates pressure zones where air builds up forming a barrier around the object. Take a look at your rear window and watch the changing patterns as your speed increases and decreases on a rainy/snowy day. That correlates to a direct change in drag coefficient.

All your engineering is partially right. Under 1 set of circumstances. Applying them to the real world is another thing altogether.

[exgmguy]

OK, relax guys! I see where you are coming from. If I had a car that was struggling to get into the 13's i'd want Dynojet numbers too.

[Rev]

LOL, I do struggle, but I don't always make it. Sometimes (often) I run low 14's. I somehow doubt that a Mustang dyno will help much there. I need my TFTW heads bad. To heck with the dynos.

Rev

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'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

[Vector]

My comments will be enclosed with ***

Originally posted by Unit 5302:
Ah, a Mustang Dyno owner.

Anyway, you're wrong. ***and so are you*** But that's okay. Hyping your product is cool. Dyno's were meant to do exactly what their name imply's. Measure horspower. ***yeah horsepower at the engine or horsepower at the track? hmm which do you want... tough choice there!***

The weight of a vehicle can be completely offset with gears. If you change the gear ratio in your car, your weight information becomes completely distorted. ***wtf? a vehicle weighs the same going 100mph in 4th gear as it does going 2 mph with the engine off*** There is something called a computer to adjust air/fuel ratio's if the tuner doesn't know what he's doing. Tune it on the ragged edge, you get what you asked for. As far as putting your Mustang Dyno up against a Dynojet car, both with 400hp measured, yeah, you're car is going to win. Know why? ***um because the car tuned on the MustangDyno is tuned for more usable on-track horsepower than your car which is tuned for the most horsepower it can just fling out there as fast as it can*** Cause your dyno is wrong. ***no you are*** Take your car with 400hp (setup with your BS parameters) then send the guy to a Dynojet and voila, he's got more. 420, whatever. ***he's got more real, usable hp*** Why is it that so many people who tune their vehicles on a Dynojet experiance no problems with their cars? ***who, what people? I want names*** Cause you are floating hype. ***and you are floating BS*** If a tuner knows what he's doing, your car will be setup right. ***so you don't think that turbolx knows what he's doing? How can you know that anyone knows what they are doing?*** As far as tuning, since the car isn't run in the same gear for tune purposes, the engine is placed under different load conditions (called gears). A 3rd gear run won't put as much load on an engine as a 4th gear run. It's called torque multiplication. If a car is properly tuned, the 3rd gear pull, and the 4th gear pull should appear almost exactly the same. Making up some make believe weight number (cause you really don't know, and the load on the engine is changed by gearing) for a car won't help you tune it. ***the load on the engine is changed by gearing, the load on the WHEELS isn't!!!! wow is that a new concept for you? I wonder! The MustangDyno simulates VEHICLE weight, your VEHICLE weight does not CHANGE depending on gearing or it would be MAGIC. The engine, regardless of gearing, fights against the same weight inflicted on the wheels all throughout any speed range you could think of (without going into the realm of relativity here). So why would putting resistance on the rear wheels to simulate vehicle weight be innacurate because of the engine gearing? Think about this a little more... come on now, it's not tough.***

Furthermore, a coefficient of drag is NOT a constant number at all velocities. Take a look at the Ferrari Testarossa. It has a god awful Cd of drag, at measured wind tunnel speeds. But, dispite that fact, it manages a very high top speed. That's because airflow changes and creates pressure zones where air builds up forming a barrier around the object. Take a look at your rear window and watch the changing patterns as your speed increases and decreases on a rainy/snowy day. That correlates to a direct change in drag coefficient. ***we are not talking about increases and decreases in speed in rainy snowy weather. We are talking about a very predictable acceleration curve over a 1/4 mile distance which we deffinately can calculate the drag factor.***

All your engineering is partially right. Under 1 set of circumstances. Applying them to the real world is another thing altogether. ***ironicaly enough, that's exactly what the Dynojet doesn't do***

Flame me all you want, I find it fun to shoot you down Unit as you seem to like doing it to me.

[This message has been edited by Vector (edited 08-18-2001).]

[jimberg]

A chassis dynamometer's first function is to measure the amount of mechanical energy available at the rear wheels. This is what a DynoJet does very well. It's probably a good bet that you can turn off all the simulation crap on a Mustang Dyno and get the same exact numbers.

My problem with what I've been reading is that it sounds like tuners are misusing the intent of the simulation. I agree with turbolx's idea of simulating load for the purpose of finding issues with pinging and such. What I disagree with is the idea of measuring horsepower during a simulation. The reason you're getting lower numbers is that you have two sources of mechanical power pushing against each other. The first is the REAL output of the motor. The second is the SIMULATED output of the dyno itself. It sounds like you are basically reporting the net horsepower between the two. That's a worthless number since you're mixing actual data with simulated data. OR (maybe turbolx can answer this) the Mustang Dyno knows exactly how much force it is applying against the engine and can make adjustments to the drive wheel horsepower accordingly. That would be better, of course, but if the simulation isn't accurate and simulates too much resistance, you're potentially tuning out power that you would have otherwise had.

If I would tune my car on a Mustang Dyno, I would at the very least expect that my final horsepower numbers come from the drive wheels and that the simulation stuff is turned off at the time.

As far as turbolx's comments about air/fuel ratios being different under certain loads I would agree and the computer does have tables based on varying loads at different RPMs. I hope, however, he wasn't implying that there is a way that he can tune that without burning a custom chip or using a completely programmable ECM.

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351W 89 Mustang GT Convertible

[Unit 5302]

Vector, the comment you re-quoted wasn't directed at you. I had no idea you owned a Mustang Dyno.

Anyway, you didn't simply slide into a heated debate, you cannonballed in. Your first comment was that I (part of the "you guys") didn't know what horsepower really was. Also, your examples were flawed.

If you step into those kinds of debates here, you need to be ready to back what you say up, and be pretty sure what you are saying is standing on solid ground.

I, as noted by me in the past, can be pretty quick on the trigger, especially when I feel directly confronted. Expect if you step into a hot debate and take the opposite side of me and make an error, that I will point it out. If you've stated something to the effect of me not knowing what I'm talking about and you make an error, that I may be a little abrasive on my rebuttal.

[Vector]

I understand Unit, and I too apologize for being a bit trigger happy. The "you guys" comment was being way to general as I do realize a lot of people know what horsepower means (as they've been tunning cars for many many years). Although I still feel my argument is perfectly solid.

[This message has been edited by Vector (edited 08-20-2001).]

[turbolx]

Well, since people here seem to be more content racing their dyno sheets than actaully going to the track to find out who's quicker, I don't see why I should bother with this debate much further.

I guess I wasted all that time in engineering school too, because someone says I'm wrong on the internet.

The bottom line is as I stated before. The dyno (either one) is a tuning tool, not the ultimate judge of vehicle performance. That's why we go to the track. A competent tuner can certainly tune a car well using either type of dyno, I know I could. The trick is that the load bearing dynos can do a few more things that make the tuning process much easier when it comes to keeping motors together on the track.

If you wish to disagree with me on the merits of load bearing and vehicle simulation, fine. Just realize that this does not make me wrong. Do the homework and actually read some automotive engineering textbooks AND go to the track more often and you'll start to understand a little more. I am confident that I am short on neither technical expertise nor practical "real world" experience on this one, folks.

Your mileage may vary. You wanted my opinion, you got it!

/me hi-fives Fast_351

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Greg Banish
President, Detroit Speedworks, Inc.
'93 LX Turbocharged Road Racer
'00 Bad-Ass F150

[jimberg]

Originally posted by turbolx:
Well, since people here seem to be more content racing their dyno sheets than actaully going to the track to find out who's quicker, I don't see why I should bother with this debate much further.

One of the problems with making such vague statements is that anyone involved in the thread will take it to mean it was themselves to which you were referring. The quoting feature exists so that we can direct our responses to an individual. A good example is Vector's blanket statement, "You guys don't seem to understand what horsepower really is." I took this to mean that he felt I didn't understand what horsepower means. Then proceeded to give examples that were just wrong.

Originally posted by turbolx:I guess I wasted all that time in engineering school too, because someone says I'm wrong on the internet.

This is simply the nature of the Internet. I don't know you. I have no clue about what's in your mind other than what you communicate via messages. If I feel that someone makes a statement that is inaccurate or doesn't make sense I will challenge it. I expect them to do the same about anything I write, but they better be prepared to back up their challenge with some facts. Do you know that I'm not an engineer? That Unit's not an engineer? Maybe we are, just bad ones. Just having a degrees doesn't impress me that much since I don't have one and I still program circles around people who have them (Yeah, I'm not an engineer). This doesn't mean I have disrespect for a person who has a degree, just that I don't assume someone knows what they are talking about because they claim to have one.

Originally posted by turbolx:
The bottom line is as I stated before. The dyno (either one) is a tuning tool, not the ultimate judge of vehicle performance.

Of course not. There's power transfer from the wheels to the track which would be different based on the weight of the vehicle, suspension components, tire size, tire compound, track materials, track temperature, wind resistance, etc. All of which you are implying that the Mustang Dyno can simulate accurately. Will a Mustang Dyno allow the car to do a wheel stand or a burnout?

Originally posted by turbolx:
The trick is that the load bearing dynos can do a few more things that make the tuning process much easier when it comes to keeping motors together on the track.

If you wish to disagree with me on the merits of load bearing and vehicle simulation, fine. Just realize that this does not make me wrong.

I can only assume that this is directed at someone other than myself since I didn't disagree with you on this particular point other than the fact that it is possible that if the simulation could be flawed to the point that too much load is put on the car causing you to tune out performance that didn't need to be tuned out.

My other problem is with a prior statement of yours where you said "I will gladly put a car that makes 400rwhp on my MD1750 up against any car that makes 400rwhp Dynojet in a race." If you're implying that your car will win, tell us how it could with less actual horsepower. I'd say it can't unless it was inaccurately reporting power.

A dynamometer is a measuring device much like a torque wrench or a thermometer. No matter what torque wrench or thermometer you use, the readings they return should be the same when measuring the same thing. I suppose this doesn't really matter, though, if your only purpose is to make changes to the point that you know if you make more power than you did on a previous run.

It becomes a problem, though, if you are trying to make a statement about how much power you are able to gain by your tuning when comparing it to results of other tuners.

I guess the lesson to be gained from this debate is that if you tune your vehicle on a dyno to always tune it on the same dyno unless you're only concerned about the gains you make during the dyno session.

Oh, and about debating. Simple "I'm right, you're wrong" arguments don't really do much to further the knowledge of the readers. If I'm wrong, I like to be told why I'm wrong. Then I understand why and the people reading will understand why. If someone doesn't take the time to tell me why, I just assume that they don't know themselves.

I think I still have some questions on the table for turbolx. If you don't mind, I would like your learned response. See my previous message.



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351W 89 Mustang GT Convertible

[turbolx]

Originally posted by jimberg:
I can only assume that this is directed at someone other than myself since I didn't disagree with you on this particular point other than the fact that it is possible that if the simulation could be flawed to the point that too much load is put on the car causing you to tune out performance that didn't need to be tuned out.

Perhaps, but this is where the experience of the person doing the tuning comes into play again. Given the choice, most of my customers would prefer a tune that gives up 10-20hp vs. one that has them changing gaskets all summer instead of driving.

My other problem is with a prior statement of yours where you said "I will gladly put a car that makes 400rwhp on my MD1750 up against any car that makes 400rwhp Dynojet in a race." If you're implying that your car will win, tell us how it could with less actual horsepower. I'd say it can't unless it was inaccurately reporting power.

How do we know that the Dynojet is not artificially high is some applications? Just because a larger number of them are in service (probably because they are literally half the price of a load bearing unit) does not mean they are more accurate. Turbo cars in particular are incredibly sensitive to loading for their tune. I have seen turbo 5.0L cars spin the hell out of a Dynojet, but for some reason run mediocre at best at the track. There is a reason for this.

Granted, for the garden variety N/A motor car, a Dynojet isn't half bad at all.

A dynamometer is a measuring device much like a torque wrench or a thermometer. No matter what torque wrench or thermometer you use, the readings they return should be the same when measuring the same thing. I suppose this doesn't really matter, though, if your only purpose is to make changes to the point that you know if you make more power than you did on a previous run.

...and much like a good torque wrench, one should be able to calibrate the dyne AND verify torque readings vs. a known force. Since Mustang dynos measure torque directly with a load cell (strain gauges) that can be calibrated and certified, I have a higher confidence in them than a dynamometer that gets torque by extrapolating HP from roller acceleration and again extrapolating with respect to engine speed. Dynojet claim to "measure HP directly", but I have yet to ever see a "horsepower meter" in any instrumentation catalog. Every other accurate engineering power measurement I have ever seen deals with measuring force directly at a fixed distance (torque) and multiplying by speed to find power. Look into how power outputs of turbines, generators, and engine dynamometers are measured...

It becomes a problem, though, if you are trying to make a statement about how much power you are able to gain by your tuning when comparing it to results of other tuners.

In all honesty, I'm not too worried about this. We keep a database of all previous runs on our dyno and when a customer returns here, we have no problem showing them gains vs. earlier runs or during a given tuning session. I can assure you that it is very real HP we find when tuning cars on our dyno too.

Once again (and I think I'm repeating myself here), we use the chassis dyno as a tuning tool. Our results do the talking for us at the track and on the street where it matters.

------------------
Greg Banish
President, Detroit Speedworks, Inc.
'93 LX Turbocharged Road Racer
'00 Bad-Ass F150

[jimberg]

How do we know that the Dynojet is not artificially high is some applications?Just because a larger number of them are in service (probably because they are literally half the price of a load bearing unit) does not mean they are more accurate.

We don't, actually. DynoJets may be less expensive since they sell more. That doesn't mean they are of lesser quality.

Turbo cars in particular are incredibly sensitive to loading for their tune. I have seen turbo 5.0L cars spin the hell out of a Dynojet, but for some reason run mediocre at best at the track. There is a reason for this.

Probably because turbo lag is an issue and since the DynoJet can spin up faster into the powerband of the car it will overcome lag sooner. The exhaust gas velocity is probably also higher so it can transfer more energy to the turbines.

I suppose this could even be an issue on NA cars. Hmmm...

This, by the way, is an excellent point in favor of a Mustang Dyno.

...and much like a good torque wrench, one should be able to calibrate the dyne AND verify torque readings vs. a known force.

The weight of the roller is a known force.

Since Mustang dynos measure torque directly with a load cell (strain gauges) that can be calibrated and certified, I have a higher confidence in them than a dynamometer that gets torque by extrapolating HP from roller acceleration and again extrapolating with respect to engine speed.

You're essentially comparing a balance (DynoJet) with a spring scale (Mustang Dyno). I'm saying that the DynoJet is like a balance since the wheels are moving an actual known mass, the roller. A known mass doesn't really need to be calibrated unless you're worried that it will lose a signifcant amount of mass on its own. The electronics that measure the acceleration of the roller would have to be calibrated, of course.

On a Mustang dyno you have two points of potential failure instead of one. The strain gauge which can be off, and which will more likely be off than a known mass, and then the same electronics used to measure acceleration of the drum. This is what makes it like a spring scale. I, as most scientists, would prefer a balance over a scale for making accurate measurements.

Dynojet claim to "measure HP directly", but I have yet to ever see a "horsepower meter" in any instrumentation catalog.

Horsepower isn't really measured directly since it is a measure of work over time. Dynamometers measure torque which has to be factored into an equation to determine horsepower based on the rpms. That's the formula that Unit 5302 used above.

Every other accurate engineering power measurement I have ever seen deals with measuring force directly at a fixed distance (torque) and multiplying by speed to find power.

This IS what a DynoJet does. See above.

Thanks for taking the time to discuss this. I have to do some more thinking about the positives and negatives of both.

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351W 89 Mustang GT Convertible

[This message has been edited by jimberg (edited 08-20-2001).]

[OneHotLX]

I have only two questions. First, on a Mustang Dyno can the simulations be turned off to get just a direct reading of horsepower like a DynoJet? Second, Turbolx, have you or anyone else actually had one car with the same tune on both a Dynojet and a MD? Did you see a difference in the HP ratings?(Note: I'm not asking whether the car was tuned on one or the other but whether there was a difference between the two dyno's HP numbers on a particular vehicle.)

Tony

[turbolx]

Tony,

Yes, we can adjust the loading to some extent. We are able to change the sweep control method on our dyno from "vehicle simulation" to "controlled sweep rate" with the latter being relatively close to Dynojet sweep rates. The result is reduced loading and often another 10hp or so. However, we also see that when we take a car that pings in "vehicle simulation" mode (from having too much timing for the combo) and run it in "controlled sweep" with an artificially shorter sweep duration, the reduced loading masks the pinging and the car appears to "run just fine". Of course, now that it's not detonating, it also magically picks up another 20hp (the same way it would with the proper programming tweak under correct loading). This is precisely why I prefer to run all of our tuning in "vehicle simulation" to make sure we know if it's going to ping or not before delivering the vehicle to the customer.

Yes, we have run vehicles in identical trim to how they were run on a Dynojet earlier for the purpose of seeing the difference. Typically, we see about 20-30hp difference, but this depends on the combo.

------------------
Greg Banish
President, Detroit Speedworks, Inc.
'93 LX Turbocharged Road Racer
'00 Bad-Ass F150

[Rev]

It could be possible that an engine detonated on the Mustang Dyno due to increased loading when it did not do it at the track under real life conditions.

That might induce the tuner to take out timing that was correct to begin with, and therefore lose power from this "tuning" that was supposed to "save gaskets".

Rev

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'66 Coupe, 306, 300 HP, C-4, 13.97 e.t., 100.3 mph
1/4 mi.

[This message has been edited by Rev (edited 08-20-2001).]

[turbolx]

Rev, you are certainly correct that it is possible, but it is not usually the case. Using the EPA's published load tables for most cars has resulted in loading conditions that have been just about identical to actual road testing in our experience. Our own testing has shown that loaded a/f readings on our dyno are typically within 0.1 ratio of actual readings on the road under the same load where a dynojet would show anywhere from 0.5 to 1.0 a/f ratio difference (on the rich side on the dynojet). This is the reason that the EPA and companies like Roush use load bearing dynamometers to do research and engine development work. Again, this is where a tuner's experience comes into play. I have no doubt that an experienced tuner can recognize this quirk when tuning on an inertia only dyno, and can leave the appropriate amount of "safety factor" in the tune to keep it alive on the street. Knowing exactly how much safety factor room one has in such a tune is another story though.

------------------
Greg Banish
President, Detroit Speedworks, Inc.
'93 LX Turbocharged Road Racer
'00 Bad-Ass F150

[Unit 5302]

A proper tune on a non load bearing equipped dynojet should include a max hp run, and an all gear run.

When this is done different loads are placed on the engine, significant enough to show a loss in hp associated with pinging, or unmask the supposed masked pinging.

For example, a 3rd gear dyno pull on it's own should be identical to the 3rd gear run in the all gear, and the car should not detonate or ping when in 4th gear.

How in depth is the EPA load information? The difference in any given 1987-1993 model year 5.0 between stripped 5spd coupe, and auto aod vert could easily be 300 lbs. A difference of 10%

If a person has problems with detonating and pinging and continues to blow head gaskets, maybe they should think about a different tuner, not a different dyno.

Also, if it REALLY bothers you that much, you can order the load bearing attachment, the air fuel ratio monitor, and the rpm pickup for the Dynojet for a grand total of $4550, or the load bearing attachment for $1500 stand alone.

I've seen the results of a Mustang Dyno tune. 330rwhp and a 107mph trap in a lightened 89 Saleen 5spd.

[exgmguy]

Originally posted by Unit 5302:


I've seen the results of a Mustang Dyno tune. 330rwhp and a 107mph trap in a lightened 89 Saleen 5spd. [/B]

No you have not seen the results. You read them on the computer.

My car on motor has made 260 and 270 rwhp on 2 different Mustang Dyno's in the Detroit area. And it ran 12.80's trapping 110-111 mph. That is in a 3000 lb race weight. Admittantly a tad lighter than Skyler's.
He also has not had his car weighed so you do not know if it is "lightened up" or not.

The cage probably offsets the aluminum heads and the seats.

[Patrick Boetticher]

no affence Go To the Track... i can say I have a 300 rwhp car all i want even if i have charts... dont mean i can run the 1/4 worth a crap!!! i have personally seen a 390 RWHP stang run a pitiful 13.98...(dunno if it was mustang or dyno) ( it was dynoed at germason automotive in CA, help me sky, leon) he couldnt get the power to the pavement, no slicks no suspension ect...
say what ever you want if you cant get it to the pavement power is nothing...

my .02