High stall converters and dyno's, is it worth it??

[TC]

I've been doing some reading on converters and came across this.

THE TRUTH ABOUT DYNAMOMETER READINGS AND HIGH STALL TORQUE CONVERTERS
There is a misconception and a lot of misinformation about the poor vehicle performance numbers that are generated by testing a car with a high stall torque converter on a dynamometer. Most people that are not familiar with how a torque converter operates will automatically think that the torque converter is inefficient. This is totally false and the following facts are why you should not believe the dynamometer numbers while using an unlocked
high stall torque converter. All late model dynamometers have a software program that commands the loading and speed of the vehicle over a certain period of time while making a test pull. The software used in these dynamometers is setup to be used with a locked 1:1 connection between the engine and the rear wheels, such as using a standard shift transmission in 3rd gear or when an automatic transmission has the torque converter clutch
locked. When an unlocked high stall torque converter is used to make the pull and the dynamometer software has not been changed to allow for the fluid coupling differences the dynamometer readings will all be bogus. For instance, the low rpm torque readings will be high due to the torque multiplication of the torque converter being run in partial stall. Likewise,
the high rpm torque readings will be low due to the long period of time the dynamometer takes to allow the torque converter to transition from partial torque multiplication to a hydraulic locked condition. The only cure for this phenomenon is to rewrite the dynamometer software to prevent this from happening. Torque converters with a low STR or low stall are not as adversely affected by this phenomenon. The high rpm transition problems
never occur when the vehicle is being driven or raced normally. Therefore, worrying about what the dynamometer numbers are is a total waste of time. If your dynamometer operator refuses to alter the software to give correct readings then the only things you can do is (1.) lock the torque converter clutch and do the testing, (2.) use the readings you get with an unlocked torque converter as a baseline and continue to tune the car like normal
until you get the best numbers remembering these are just numbers and not the actual horsepower and torque or (3.) use a dynamometer shop that gives you the service you deserve for your hard earned money. The only really true test of the performance of a vehicle is to take it to the track and see what
ET and MPH the car will run.

So what's your take on the subject, is it worth paying the big bucks to have your car dyno'd, knowing that the numbers are going to be off??

[TC]

Re: High stall converters and dyno's, is it worth it??

And then there's the rebuttal.

No "software changes" are required to read accurate delivered power ? regardless of the level of convertor slippage. I assume this article?s author was reacting to guys complaining about their low rear-wheel dyno power. Most often these are builders that ?just know? their engine makes ?XX Hp? so that either the convertor or dyno ?must? be the issue.

The most common reason for low dyno power readings is an engine that simply does not have any more to deliver. That said, a high-stall convertor (un-locked) is inherently going to waste a bit more power (as slippage heat) than a low-slip version (of equivalent quality).

Perhaps by software changes, this writer is suggesting adjustments to those "estimated flywheel power" equations that some dynos love to report. While it is easy to squirt in larger ?loss factors? that better estimate the power lost in the converter, keep in mind that only the un-factored dyno-measured wheel power is what is available to push the car down the track.
Note: While our official position is that such ?flywheel estimates? are not particularly useful, DYNO-MAX 2000 ?Pro? software does allow users to output (and modify) both Estimated Flywheel Power and Estimated Torque formulas.

The writer implies that, with a high-stall convertor, a chassis dyno?s power reading will be wrong. Yet, the subsequent examples are for torque readings. Almost by definition, a chassis dyno measures delivered power at the ground (roller). Discussing a chassis dyno?s delivered power (or tractive effort) data is, therefore, unambiguous. However, when quoting chassis dyno torque results we must state them in terms of a driveline location. Unlike power, torque multiplies directly as a function of gear ratio. If I tell you that a vehicle tested at 500 ft-lbs of torque, it means nothing - unless I also reveal whether that number is in terms of the absorber, roller-shaft, axle-hub, tail-shaft, input-shat (convertor output), or crankshaft?s RPM.

DYNOmite dynamometer systems can capture multiple RPM and torque sources for real-time calculation of shift-ratios and driveline efficiencies. For example, place an RPM pick-up on the engine and a rotary torque transducer on (both) the convertor flex-plate and tail-shaft yoke. Now input (engine) power, along with transmission output torque, will simultaneously display alongside the chassis dynamometer?s wheel data. Transmission efficiency is read directly in this case.
Note: DYNOmite stand-alone torque converter and CVT transmission dynamometers are equipped as described above. Except that they end at the transmission output shaft ? and sometimes substitute a large AC motor (for the internal-combustion engine) as the power source

Most, hot-rod level, chassis dynamometer tests will not invest in rotary torque transducers. Some will not even bother with a secondary RPM pick-up on the engine. Instead, they enter a fixed ratio to correlate the monitored roller?s speed to the engine?s RPM. I think this is what your article?s writer was complaining about in regards to reported torque with high-stall convertors. If the dyno operator matches the ratios at low torque loads load (less convertor slip) reported engine RPM will be off (slightly) under high-slip conditions (and vice versa). Therefore the rpm and ratios used to state the measured roller torque (which is still accurate) in terms of ?engine RPM? will off by the same error. In these cases, just consider the reported ?engine RPM and torque? as ?converter-output RPM and torque? ? still totally usable data.
Note: Our DYNO-MAX 2000 ?Pro? software reports the true delivered power so that the above described ratio errors do not affect its reported results! It even allows users to enter convertor slippage vs, torque RPM curves to compensate for the slight ratio errors (but most simply use an engine RPM input).

Instead of getting defensive, and resorting to inaccurate dyno disinformation the convertor company should have been upfront. The author should have written that they make their slippage/efficiency trade to gain extra off-the-line torque multiplication and engine RPM for added launch power at the wheels. They could have further explained that, in the right car, this earns it quicker ETs ? in spite of some efficiency loss (pre lock-up).

The facts are:


1) An accurate* chassis dynamometer will monitor and record the total power delivered to the rolls from the rear wheels ? no matter what convertor is in use.
*Note: excluding the use of popular "Dynojet" power inflation factors.

2) A chassis dynamometer will also monitor and record all increases (if any) in delivered power at low (vehicle) speeds from a high-stall converter effectively acting as a (somewhat inefficient) gear reduction.

3) At higher vehicle speeds the dynamometer will monitor and record the proof that (compared to their locked-up state) high-stall convertors waste a bit more some power (generating heat) due to higher internal slippage.

4) When the convertor goes into lock-up mode, the dynamometer will monitor and record the increase in delivered power - as the convertor slippage ends.

Further, dyno operators running careful tests can evaluate the differences in "net power (vs. time) under the curve." This allows them to evaluate the likely affects on ET of various convertors. In other words, a drag-race road load simulation will return a quicker elapsed time if the convertor delivers more low speed power than it inevitably trades off at higher speeds.

The one real-world caveat is that dyno simulations do not take into account how the vehicle's tires and suspension react to differnces between convertors. Test that at the track. After much combined track and dyno experience, for a single car, it is possible to estimate ET changes from subsequent dyno convertor experiments alone.

Sorry to be so long winded, but oversimplified answers lead readers to incorrect conclusions. I do agree that convertor performance should not be judged solely by its peak rear-wheel dyno power. I think that is what the article?s author was really trying to get across, but it sure needs to be re-written for a fairer technical accuracy.

[calico camaro]

Re: High stall converters and dyno's, is it worth it??

well i think we have all figured out there will never be a consistancy between dyno numbers. IF your paying just to get a hp reading then yes you are waisting your money. not saying that dyno days are not fun since you can compare between other cars and have bragging rites or what not. but to use them to get a acurate hp number is vain at best. they are a tuning tool. and used properly are a good tool. but thats where it ends. i could care less about the total number it puts out, just the gains i get from tuning, and where the gains are.

[DanStokes]

Re: High stall converters and dyno's, is it worth it??

I alluded to this earlier and have posted on it in the past, but you should see the process the OEM's have to go thru to get SAE verified HP numbers. First of all these numbers are always generated on an engine dyno - there are just too many variables on a chassis unit. A team from SAE descends on the site and begins a days-long process of verifying the dyno - load cell cals, speed readout cals, temp and pressure cals. The entire software system is analyzed to assure that all the input data is measured correctly and is then input correctly into the appropriate calculations. The engine has to be analyzed to assure that the engine "as tested" is consistent with the engine that the manufacturer has claimed that they want to sell. And on and on. The actual dyno runs are an anticlimax.

My point is that, unless your shop is willing to go thru all this (and it ain't cheap), any HP numbers you get are essentially for comparison purposes only. Some shops do a pretty good job of coming close to the SAE requirements while most don't even have the equipment to do the necessary steps ("What's an ice point cell?"). It takes several thousand dollars of equipment to just properly measure dew point and verify the measurement - get the picture? A sling psychrometer can get you pretty close if you can't or don't want to spend the big bucks. I could go on and on - this is something I actually know something about.

All this said, I dyno a combination whenever possible, if I can afford it. The "afford it" part gets me to a chassis dyno - engine dyno time is pricey, even if just because of the time required to build a set up (remember, I'm not running a SBC). The HP numbers are worthless but interesting. What I really can learn is AFR at WOT, PDQ. And Wayne can adjust those AFRs to assure that I won't fry the motor. The HP numbers will tell if the new combo is better or worse than the old one, and by about how much - that's useful.

In other words, ALL dyno data has merit as long as you know what you're getting - and what you're not. Bragging about your HP dyno numbers is like bragging about your tire pressure - it's a big SO WHAT. USING the dyno results to tune and tweak and improve your combination - now you're talking.

Dan

[BlackoutSteve]

Re: High stall converters and dyno's, is it worth it??

As I've mentioned before, I used a Dynapack hub mounted chassis dyno. It knows engine speed via a spark plug wire sensor, and knows wheel speed on it's hub. So knowing how much the converter slips is a no brainer..

It's my belief that if a dyno can't measure power accurately via a torque converter, then it's not an accurate dyno, and/or it's method of measuring power is unrealistic.
Torque converters transfer a consistant amount of power when propelling a vehicle at the track. The vehicle weight is always the same, and the ET/MPH repeatable. So why can't that same power that the wheels see be measured accurately?

Perhaps slipping stall converters reveal the apparent shortcomings of how dynos measure power..

[Eric68]

Re: High stall converters and dyno's, is it worth it??

IMO Chassis dynos are best for making comparative measurements, not absolute HP tests. In other words, use a chassis dyno to get a baseline power number, then make a change and see if power increases or decreases. They are best used for tuning, not an accurate HP number.

I think if you hold to the same theory as me it really makes all this hubbub about TQ converters and accuracy a mute point. You just need measurement consistency run-to-run, who cares about the actual number?

[DanStokes]

Re: High stall converters and dyno's, is it worth it??

Steve - Never used a hub dyno but the concept certainly has merit. Is the Dynopack a water brake, Eddy current, or ??? Any pics? When I wrote my dyno article I researched them a bit but was unable to find anyone with hands on experience. Evidently I've never lived close to a facility that used this device so I can't track one down. I would certainly be willing to run the Buzz Bomb on one if it was available.

Dan

As I've mentioned before, I used a Dynapack hub mounted chassis dyno. It knows engine speed via a spark plug wire sensor, and knows wheel speed on it's hub. So knowing how much the converter slips is a no brainer..

[CDMBill]

Re: High stall converters and dyno's, is it worth it??

One other benefit of the chassis dyno is opportunity to get full power cycle pulls without going a 100 mph or whatever as this is also how you can test cooling system integrity, identify leaks that only show up under pressure and generally see how the drive line behaves. This is particularly useful in these days where many parts of the country have fewer tracks and opportunities for on track testing. There is no substitute for on track testing as that is what we are preparing for usually, but I like having a safe baseline tune and knowing that I'm not going to dump something under the tires at the top end of the track.

Oh and yes I have a medium stall converter in the car, 4200-4400, and everything came out just fine at Westech a week ago. Their Superflow does adjust for car weight, tire size, gear ratio, estimated stall speed and driveline efficiency etc. by looking at rpm via optical senor and wheel speed.

BTW the dyno said I would hit 139 MPH, and we actually ran 139's with one 140.

[dieselgeek]

Re: High stall converters and dyno's, is it worth it??

I wouldn't recommend doing to a dyno just to find "a horsepower number" but instead, use it as an opportunity to make sure your tune is correct at as many possible RPM and load points. As Bill points out, it's very handy to have a stationary car, hooked to as much datalogging of vital signs as possible, that you can run up to any MPH and load that you choose...

Now, as Eric points out, comparison pulls are vital to find out what parts and tune-up parameters put the most power to the wheel. Different converters will have different "efficiencies" but, all else being consistent on one car, a chassis dyno is very good at seeing how those changes affect power at the tires.


In the end, all the efforts no matter what tools are used, are (in this hobby) aimed at getting the car down the track quicker.

[dieselgeek]

Re: High stall converters and dyno's, is it worth it??

Steve - Never used a hub dyno but the concept certainly has merit. Is the Dynopack a water brake, Eddy current, or ??? Any pics? When I wrote my dyno article I researched them a bit but was unable to find anyone with hands on experience. Evidently I've never lived close to a facility that used this device so I can't track one down. I would certainly be willing to run the Buzz Bomb on one if it was available.

Dan

Dynapack is a "water brake" style of dyno, but it has a complex electronic conrol of some type that lets it behave like an Eddy Current dyno. Really neat stuff IMO.

[SpiderGearsMan]

Re: High stall converters and dyno's, is it worth it??

dyno's
rich guys getting egos stroked
at least going to the track , you get a nice tan

[DanStokes]

Re: High stall converters and dyno's, is it worth it??

Spidey - it's just a tool, like all other tools. Just happens that I worked on them for nearly my entire adult life so I know what they can do - and what they can't. As you and others have pointed out, they're only useful in what they allow you to accomplish on the road and/or track. They're kind of like a college education (which I lack) - condensed experience.

Dan

[TC]

Re: High stall converters and dyno's, is it worth it??

Spidey - it's just a tool, like all other tools. Just happens that I worked on them for nearly my entire adult life so I know what they can do - and what they can't. As you and others have pointed out, they're only useful in what they allow you to accomplish on the road and/or track. They're kind of like a college education (which I lack) - condensed experience.

Dan

But you do have to say dyno's have changed over the years. Like how different did they get from the time you started using them to the time you stopped.

[TheSilverBuick]

Re: High stall converters and dyno's, is it worth it??

Spidey - it's just a tool, like all other tools. Just happens that I worked on them for nearly my entire adult life so I know what they can do - and what they can't. As you and others have pointed out, they're only useful in what they allow you to accomplish on the road and/or track. They're kind of like a college education (which I lack) - condensed experience.

Dan

But you do have to say dyno's have changed over the years. Like how different did they get from the time you started using them to the time you stopped.

I want to see Dan's answer, but I'll wager the dyno's haven't really changed, they've just been computerized. The principal designs are the same.

[TC]

Re: High stall converters and dyno's, is it worth it??

Spidey - it's just a tool, like all other tools. Just happens that I worked on them for nearly my entire adult life so I know what they can do - and what they can't. As you and others have pointed out, they're only useful in what they allow you to accomplish on the road and/or track. They're kind of like a college education (which I lack) - condensed experience.

Dan

But you do have to say dyno's have changed over the years. Like how different did they get from the time you started using them to the time you stopped.

I want to see Dan's answer, but I'll wager the dyno's haven't really changed, they've just been computerized. The principal designs are the same.

That's what I was getting at how much figuring is done by computer now, compared to when he started.