My reaction to your points:

1. In theory, it is possible purchase an AWD dynojet using 224 or 248 rollers all around. The only problem is that every AWD dynojet I've used is not so equipped. If you know of an AWD dynojet that uses the same rollers front and back, let me know. I'm sure they are out there by now but I doubt they are very popular due to cost and packaging issues.

Last time I checked with Dynojet (about a year ag) regarding this fore/aft mis-match issue they didn't quite understand what a problem this poses with AWD drivetrains. Nor did the see the problem with their "Dyno Trac" loading feature only applying load to only one of the two rollers . Of course, in time, their dynos destroyed enough Porsche and Volvo transmission. So I'm sure they know of the potential problems by now.

2. Rolling a fixed mass is an accurate way of measuring hp indeed. That's why there are such things as inertial dynos. Of course, they aren't populatr anywhere else in the world due to their limitions. But US carfolk tend to love them because they are the official dyno of NASCAR and give bigger numbers than those dynos across the pond from Bosche, Maha, Superflow and the like.

3. You might want to do some more research this topic. There are more destroyed AWD porsche and volvo transmissions than I could shake a stick at. This is from normal dyno testing and not Dyno Trac usage. These cars, in particular, are less tolerant of for/aft wheel speed differentials due to their clutch-pack/dog design. The Volvo tranny, in particular, uses dog teeth that engage immediately when fore/aft slippage is detected. When these teeth engage, they usually snap off since the big fat dynojet roller can't accelerate instantly. And yes, viscous coupled diffs (like what you have in an EVO or WRX) are also subject to the same speed mismatch stresses. Of course, viscous goo doesn't snap like a dog tooth. Instead, it just heats up like the dickens and will gradually lose its viscous coupling effect in time. Not only does this suck for the center differential, it also taints wheel hp measurement by adding a power-absorbing variable that isn't there when driving your car on the street. And the dyno still reads higher than any other dyno in the world... go figure

My dyno, and EVERY other load bearing dyno in the world, will give lower numbers in higher gears (all other things kept equal). After all, the faster you spin the driveshaft, axles, wheels, tires, brake rotors, hubs, output shaft, etc,. the more inertial and frictional losses there will be. This is fact.

Dynojets pose an interesting dilemma when it comes to gear selection. For one, you can't hold everything else equal . That is, the lower gear, the shorter the run lasts. The shorter the run lasts, the less load your putting on the engine. The less load you are putting on the engine, the less boost your going to make. The less boost you are going to make, the less power you are going to put down to the ground. Then again, there are factors which can work in the other direction as well. That is, the shorter the run lasts, the less heatsoak affects incurred by the intercooler. The less heatsoak, the greater charge density. The greater charge density, the more power. So very quickly, we see that different cars, with different engine configurations, will react to gear selection differently when it comes to Dynojets. So your statement isn't correct.

As of last year, there were 5 AWD Dynojets in the world. Last I checked, there is over a hundred AWD Dyno Dynamics dynos in the world. And yes, they all agree with each other. So I guess I'm in good company. And they all measure wheel hp-- not wheel hp tainted with ever-changing center diff power absorbsion

Cheers,
shiv

 

Well I still like my 145 hp Evo (or whatever it REALLY makes).

 

...and on the best comment of the evening, I'm headed down stairs for a and back to see what a much more level headed Claudius had to say today. I can only handle so much from the vendors here these days... to bad it's not my site as I'd have already banned a few.

 

Thats interesting. When I removed the lid off the air box the a/f richen about .2 everywhere but I left the filter in. I wonder if a conical filter leans out the a/f?

 

11.9:1 and 12.0:1 A/F's .... wow you are brave man! I made 32 whp, with 20 psi tapering to 18 psi on my EVC, and at 11.5-11.6:1 here in FL with the heat and humidity.

Hmmmmm ... maybe I should try running a little lower boost, but with a bit leaner map?

 

Shiv wrote:
Now your not going to start dissing NASCAR on an open forum are you? You don't want to **** off Billy Bob and Bubba do you?

For comparisons sake, as long as everyone is getting similiar consistent numbers, does it really matter?

Dynamic load dyno's such as yours have many advantages regarding test and tune, especially at variable load conditions. I am not arguing that point, that is probably also why most manufacturer's would use them. That does not necessarily indicate that they are more accurate at WOT maximum HP acceleration testing.

Shiv writes:
Even though we are not talking about Porsches or Volvo's, perhaps you could point your stick at one or two verifiable tests performed by a credible source? I looked and couldn't find any, I even sent an email to Dyno Jet, haven't heard back yet.
No offense but for the momment this is all just assumptions and hear say, the ownice is really on you to provide credible proof to back up your statements.

Shiv writes:
This is actually not true. My own testing done on a Mustang AWD dyno and the AWD Dyno Jet showed the Dyno Jet actually reads slightly lower,(same gear, same car, similiar conditions). Also did you see this; http://www.turbomagazine.com/tech/0306tur_dynodash/

The Dyno Jets actually put out some of the lowest numbers in this test.

Shiv writes:
This is also not true, my back to back 3rd/4th gear testing on a load bearing Mustang dyno actually showed more HP in fourth gear. Once again you don't have to take my word for it, there are several of these dyno's in the US (one very near you), take your car and try it for yourself.
I agree there is more friction, but in this case the added power due to additional load seems to be able to more than overcome the increased frictional/heat soak losses, accept for on you dyno(as far as I know).



Ther are actually 8 AWD Dyno Jet's (that I know of) operating in the US right now. According to Dyno Jet, there will be several more before the end of the year. They are cheap, low maintenance, reliable, and the standard in the US, (like it or not) that's a tough combination to beat.


Last I checked there was just you and Dyno Comp in the US, and you two did not agree. Can we see some test data from one of these other 98 systems?
I understand there is another one now operating in S CA, what about them?

I think this is a very interesting topic, and with more data comming in all the time, there is always more to learn. Perhaps we should get our own thread going (Chassis Dyno Testing Accuracy), before people start whinnning again about beating a dead horse, yata yata yata, you hi jacked my thread .

Kind regards,

Eric

 

Finally a post related to the AFRs, thank you! I must have missed your question when you asked the first time.

IMHO, whether aquired from p. 454 or through countless hours of actual research, development, testing, and evaluation, the reputable vendors developing maps for the Evos fully understand knock monitoring and detection. Some are actually working on solutions to mitigate the causes through a process called tuning!

My comment about the AFRs looking safe is based on comparisons to AFRs I have seen measured on other similarly modified Evo's that were tuned with the aid of Det cans.

Was my personal assessment of the posted AFR scientific? No. An estimate based on comparative analysis? Yes (well mabe a little scientific then). Conclusive? No. A calculated risk that I would assume for myself based on available information? Yes. Follow-up with Det can verification if installed on my car? Absolutely.

 

Eric,

I too find this subject of great interest and agree that it would make for an excellent topic in and of itself. I like your approach of seeking out independently verifiable data sources for comparison and analysis.

I better end it here before I start whining again about that dead horse and yada, yada, yada.......

regards,

 

Oh sorry, I wasn't referring to you JFH, you were just trying to keep tightly on subject, I can apriciate that.
I just know from previous exchanges that some people feel that it's all been said before and there is just no clear resolution, so why keep harping on it. I dissagree, but I was out of line calling them whiners, sorry if anyone was offended by that remark. I do feel somwhat guilty for going off on a tangent in the middle of some one elses thread, but it's not like it doesnt happen all the time, and at least in this case it is relative to the subject.

Kind regards,

Eric

 

I have some interesting info from Dyno Jet.

While the 248 and 224 rollers are different sizes, they essentially have the same mass, and it is the mass not the size of the roller that determines roller speed at a given load. The larger 248 drums provide a better tire contact surface area, which is not critical on relatively low HP AWD application.
Apparently roller drum mass on there systems can very up to 17%, so some of there AWD dyno's could have perfectly matched drum mass fore/aft, and others could be off up to 17%. The actual drum mass for a given dyno is programmed into each systems computer.


So the actual front to rear load differential on an AWD Dyno Jet is going to be something less than 17%. Knowing this, I have a real hard time believing that a few 10-15 second pulls will cause any significant wear, let alone damage to the center diff. Based on this information, and my own testing/comparisons with a Mustang dyno (which would have absolutely no additional center diff loses) I do not see any reason to believe there is any accuracy issues due to the minor load variations that you might experience on the AWD Dyno Jet. (Man these guys should be paying me!)

They currently have (10) 248/224, (4) 248/248, and (3) 224/224 combos out there in the world.


Basically any AWD dyno where the fore/aft rollers are not physically connected COULD POTENTIALY damage a center differential. The only known AWD dyno that actually connects the rollers is the Mustang.

In there testing, the only cars they have run into problems with is Porsche, something about the active electronic center diff and the torque split they use, can cause problems with there AWD dyno. If I am not mistaken the Porsche does not have a 50/50 torque split front to rear. Trying to rotate two similar independent masses/loads at the same speed under these conditions, I could see where that could cause a problem. If I had an AWD Porsche I would only attempt to dyno it on a Mustang system.

Regarding Shiv’s claim that Dyno Jets add 15% to there measured/calculated HP, they assure me that there is no such added values, other than the applied environmental correction selected by the operator.

I actually need to go to work now.

Kind regards,

Eric

 

That's funny. The next time you see an AWD dynojet pull on an EVO or a WRX, see which axle starts spinning first and how long it takes for the other one to catch up (not that it ever does completely, I suspect). Don't take my word for it, just look for yourself. It's obvious enought that you can eyeball it.

And then consider that the center differential is doing all the work to equalize fore/aft roller speed.

And then consider that the difference in roller diamter induces vastly different inertial characteristics and how that is going to effect your center differential. What is easier to spin: a little 4000lb can of tuna or a big 4000lb barrel of monkeys?

Also consider that those 10-15 seconds of speed mismatch is occuring at max torque output, not during simple cruise conditions where torque output is a few % of what it is at WOT.

The 15% additional correction factor came directly from Dynojet tech papers which used to be on their website. They have taken it off in the last few years for some reason. I can probably guess why.

Now here's the fun part:
The DTS dyno tested by Turbo Mag reads much like a Dynojet because the folks at XS tweaked it. They were tired of having folks come in and say that the dyno sucked because it read too low. So they tweaked a sensor input so that it reads on line with Dynojet. Something similiar applies to the Dynapacks which used to read low upon initial release to the US, but now read as high or higher than Dynojets due to US-specific software revisions. Appearantly, they decided as well that reading high is what many people want. As for the Mustang Dyno, it is totally user configurable and can read as high or as low as the operater wishes. Some read high and other read low. Like the Dynojet, it's a US based company with little or no overseas presence.

Maybe Eric can address each of these points in his upcomiing post. Of course, there's really not much that can be said about the 15% correction that used to be in the Dynojet white papers since they are no longer available. So I guess we can forget about that one and just focus on the fact that the other dynos in the Turbo Magazine test were tweaked to read Dynojet high on purpose. It would also be neat if he could address the issue of fore/aft inertial differences between the two rollers. Of course, if you can't dyno a Porsche (or some Audi/VW as well) on an AWD Dynojet, imagine all the other clutchpack based transmission systems than can't be dynod without fear of transmission failure.

And if some AWD transmissions are failing by being put through conditions that they were not designed to encounter (like say having....hmmm... two independantly spinning 4000lbs rollers of different inertia strapped to each axle) what kind of stresses does this induce in other AWD systems, regardless of torque split. So many questions and so few answers

Cheers,
shiv

PS. Also, it took a little mental gymnasitics but I think I figured out why an AWD Dynojet might give higher readings in an EVO for 4th gear instead of 3rd:

Wheel torque (a multiple of engine output and gearing) is higher in 3rd gear than in 4th gear. This means that a fore/aft wheel speed mismatch is going to induce greater absolute center differential power absorbtion in 3rd gear. Voila... less power, all other things held equal (which, of course, is impossible to do on a Dynojet since ramp up rate is not controllable). But just something to think about.

 

Great point! But these days, there are something called computers. And they are cool. So cool, in fact, that they can control fore/aft wheelspeed differential by applying retarding force to each individual roller. In fact, this is what most AWD dynos do--- besides the AWD Mustang dyno, which uses a chain to attach the front and rear rollers and Dynojet, who doesn't seem to think that it's important ). FWIW, the Dyno Dynamics dyno software individually applies the fore/aft retarder to maintain a fore/aft wheelspeed mismatch of no more than 1.5mph. Also, before each session, the dyno software prompts the user to input what car is being dyno tested. There are a couple dozen choices (Porsche AWD, Nissan AWD, Subaru WRX AWD, VW AWD, and so on...) If the choise is not given, you can then chose though a more general selection which includes Open diff, viscous LSD, clutch LSD, locked LSD, etc,.) These features are there so the dyno knows what not to do to (as far as wheelspeed differential and loading is concerned) ensure safe operation of each individual system. You see, when a new AWD system comes out, the guys at DD actually to analysis to see what is needed for proper dyno testing. Pretty neat, eh? Appearantly, they realize that different AWD systems require different dyno logic for proper operation.

This is probably why the DD dyno is the one used at the Australian Summer Nationals for all the dyno shootouts where 1000+ hp Skylines go up against 1000+hp twin turbo Holdens and 1000+ hp Porsches. For those who don't know, Summer Nats is the biggest dick-swing hp competition in the world. It's like a giant dyno day expect that all the competitors enter homebrew street cars that make enough power to force Dyno manufacturers to design newer, higher capacity, dynos. Do a yahoo for Summer Nationals and to get an idea of its magnatude. Some of the participants makes those 1000 Dynojet HP Supras (which probably run deep in the 12s... j/k ) look a little weak-kneed in comparison.

BTW, it's also interesting to note that, from what I've heard through the grapevine, the new generation Mustang Dyno is also rumoured to employ a similar wheelspeed management system and do away with the old school chain drive which made it impossible to conduct center differential testing/diagnosis. You might want to call them up and ask.

Cheers,
Shiv

 

To everyone else who has been following this thread, don't despair. I think we're finally getting somewhere.

Cheers,
shiv

 

are we finally getting somewhere near discussing the A/F ratios of the brain flash, which is what everyone except shiv and silver surfer come to this post to read about... but I guess reading about differences in dyno's is also interesting.

 

Obviously the a/f is safeon the flash so why not talk about dyno's? It is great stuff.

I definitely think that two different diameter rollers regardless of mass would be hard on a center differential. I just hope that on our viscous coupling type, a few pulls won't cause any damage. I would definitely prefer a dynapack but don't have access. If the rollers were the same diameter on the DynoJets it would be ok I think. How can they think this isn't an issue?

Still no word back from mike at AA on what if any correction factors were used on these graphs. I got the read receipt two days ago for the e-mail. I guess he is too busy to do me the favor?