posted August 20, 2003 02:13 PM
Straight talk about dynos can open... worms -- everywhere...
so i was doing some reading on dynos and how/why they come up with vastly different numbers and i'm left with more questions than answers. seems no-one can agree what the deal is, or at least not explain it clearly. seems there are alot of people with opinions and/or scienntifically sound (tho oversimplistic) musings, but few if any who really know what they're talking about.
so what i'm looking for is some straight talk from people who know, and know that they know. there's no way to say this without sounding rude, so please understand that i mean no offence to anyone: i'm not looking for opinions and responses from people who read a couple articles and now think they know everything. if u'v done extensive reading and are not fool enough to randomly choose any one source as the gospel, then that's something else. what i'm looking for here is a definitive collection of dyno knowledge to help curtail the rampant spreading of falacious knowledge about dynos. i'v gotten quite annoyed at all the BS i'v read (and not BS as in "it doesnt match my understanding or opinion", but obvious BS that doesnt even begin to compute).
i know there are some on this site who shoudl know their shit. experienced dyno operators who have taken the time to research dyno's and their capabilities (jsut being a dyno operator doesnt mean u know jack shit about the differences between dynos), people involved in their manufacturing, or people who just know alot about them, preferably with some first hand experience to backup their claims. links to good articles etc are also appreciated.
here's the thing that started it all: it's commonly said that Dynojet dynos read higher than all other dynos.
seems to be 2 issues here: inertia vs eddy current operation, and calculating the number presented to the user.
let's deal with the latter issue first. first let me say that i'v only heard this issue talked about in regards to inertia readings (sweep tests). seems Dynojet uses an average value for the inertia of the bike's moving parts (driveline only or engine too?) and adds the power required to spin up these parts the reading from the rear wheel. this is what is blamed for the dynojet's high readings. seems to me this would be an attempt to simulate steady state HP readings as u'r removing the effect of the driveline's inertial effect during acceleration. however, i'v read that engine performance during acceleration & steady state is not the same at any given RPM so there are other factors in play here. there was mention of some bikes having separate acceleration & steady state maps even. anyone know if this is true?
if this correction factor is the only difference between dynojet readings and others, seems that's no big deal. shoudl be possible to add hte same "correction" factor to any other dyno software or remove it from dynojet. perhaps all the confusion is there is no clear labeling as to what exact HP number is being presented. BHP (crank)? true RWHP? "driveline inertia compensated" RWHP? acceleration vs steady state HP?
the second issue is steady state vs acceleration test. obviously this overlaps with the previous issue as i'v already touched on it quite a bit. everything i'v read suggests steady state & acceleration HP is different, and in particular that steady state (only measurable via a loaded dyno, normally an eddy current one) readings are lower. i'm not sure this makes sense to me tho, as accelerating the driveline would rob power from the rear wheel (or from the contact patch to be precise), so acceleration tests ought to be lower. do engines put out less power during steady state than acceleration? i'd think the opposite would be true.
so the final question would be how come the numbers we see in magazines are pretty consistent, both compared to each other and consistently ~15% lower than crank horsepower numbers many manufacturers publish. any who publishes what numbers? do europeans (including brits) use crank numbers? seems in NA we all use rear wheel numbers, both in magazines and in most of the manufacturer's publications i'v seen, tho they rarely seem to publish HP. the magazine numbers i see are generally about 15% down from crank HP, so i'm thinking either they use RMHP from steady state tests or they use DJ numbers from sweep test, but since they seem more accurate than the ones "we" get when we take our bikes ot a dyno, i'm thinking they dont use the blanket "driveline inertia correction" values, but specific values per each model of bike.
so now that i'm finished shooting my inexperienced and unknowledgeable mouth off, who can tell me what the real deal is?!?
posted August 20, 2003 08:28 PM
yep, took me an hour on and off to say what i was really trying to say, and attempt to make it somewhat clear, which is part of what is missing from every other article and discussion on dynos i'v read.
posted August 20, 2003 09:14 PM
well you have a lot of questions
in the real world even engine builders & dyno operators have questions
why does 1 engine have more HP than another
that is questioned all the time
even tho the same builder assembled the same parts the same way
is said & has been proven to be a 2 to 5% variance
some nascar engine builders are completely baffled at times
the 1 they massage.....does not seem to respond or live up tro the extra effort
& expectations.... they pick 1 at random......Bingo it lites up the dyno
they race it....runs well has good speed... as good or better just like the dyno
predicts..... does not blow
they bring it back ... tear it down
find nothing any different that they can do
change.... upgrade
in the future
nascar uses engine & chassis dynos....... go figure
inertia dynos will never be the same.....
I prefer brake(hydraulic) dynos where you pull the engine back under load
there again i dont like electric/"eddy" dynos
all of them are subject to heat soak.... to the engines & to the dynos
ambient temps....Altitude..... humidity..... fuel density....
VARIABLES..... the #'s will always be different
if you are looking for 1 rule of thumb
there aint one
if you have a dyno at your disposal..... use & enjoy
it will tell you when you are right.... wrong.... gaining/losing
it wont tell you if it is reading comparing to another dyno
tharts what racing is for
ciao
____________
bend your mind.....
or break your ass...!!
posted August 21, 2003 04:44 PM
Edited By: necro on 21 Aug 2003 17:47
I am glad I didn't stay out of this and contributed to the "straight talk". ____________
3829
posted August 22, 2003 08:08 PM
My brain hurts just reading your thread. But I'll give you this, you've got some fair questions and issues. While I'm not going to pretend to bullshit you, as you requested, know this; flite leader and his last paragraph is a fair summation.
We use the Dynojet dyno because it's easy to use, it's repeatable, it's easy on the motor, and it's by far the accepted standard in the industry for numbers. Operative word, "accepted standard." If you use the Superflow or the Factory dyno, people simply question those numbers because they relate to the most widely used numbers; that being Dynojet (like it or not). As an industry, we really don't have much choice in the aftermarket. We must use the most widely used dyno to have our "claims" make sense to the consumer. Believe me, if everyone started using another type of dyno, so would we. Dynojet being the case currently. But all that matters is testing bikes on the same dyno to correlate numbers consistently.
I'll tell you this, as far as roadrace engines are concerned, the dyno is simply one "tool" we use. Developing exhaust for Team Honda, we've made stuff on the dyno that really looks good. Real eye-bleeders. Give it to the riders, they may turn their noses up at it. Believe me, we see it weekly. So you simply use it as a base, get your numbers, and go test. There is only one thing that really matters, it's lap times. We don't win races on the dyno. If a particular motor feels good at where a particular rider likes to operate, then you've accomplished your goal. Some riders like big hp on top. Some like mid-range. Some like low-end. Some like no sliding and big torque. Some want to back it out of every corner so they want a motor that revs freely. The powerbands may be completely different. It may be down 10 hp on top, but since he gets the big drive out of the corner, they equal out. Then you take how hard that engine may be on the rider, suspension, tires, fuel mileage, etc. Depending on gearbox selection, you may run into limitations on what final gearing may be. That opens another can of worms on sprocket selection and whether it may require more/less chain slack because of bigger/smaller sprockets, where the wheelbase ends up because of the sprockets you may or may not run. The rider will whine if you're a half a tooth off because he can't draft or he's hitting the rev-limiter when he does draft. He'll whine because you changed the wheelbase 3 mm. He'll whine because you've fixed the drive in 4th gear onto the banking, but now 2nd gear coming out of turn 2 sucks because you dropped/raised 200 rpm and he don't like it. Don't get me wrong, they have every right to whine at the level they ride at and I love the challange at getting them exactly what they want. I won't even get into mapping, cams, cam timing, crank weight, and oh my god suspension and tires....
Ok, I think I'm getting off the subject maybe. Again, good questions. I'm an operator of this tool. And that's all I use it for, just one tool to making a winning combination.
posted August 23, 2003 12:05 AM
thx bryant. i was hopin u'd way in as i expected u'd have plenty of experience with more than one type of dyno given ur position.
everything u say certainly makes sense, including the "industry accepted" numbers. tho i ask u this: since the different numbers are (far as i know) simply an issue of software, and other dynos (liek teh superflow) can give u dynojet numbers if u ask it to, why still stick to the dynojet? i assume it just happens to be the dyno u have or the one u prefer based on all teh _other_ reasons (quality, price, service, etc). other than the software, every inertia or loading (to be more general than "eddy current") dyno is gonna do the same job right? of course i realize there are differences like roller inertia (factory pro has a very low inertia roller for example). but i'm still left wondering exactly HOW dynojet arrives at their numbers?
interesting u mentioning the dynojet bein easy on teh motor. why u say that?
u also touch at length on the point of how the dyno is meaning full and how it should be used as a tool. this is something that bothered me a bit when reading some written material both from users/joe blows and fomr some manufacturers. they argued that using sweep tests (unloaded dyno) is useless cause of it not behaving the same as steady state. so they said for mapping (and other work i guess) u NEED a loadded (normally eddy current) dyno, otherwise a dyno is quite wasted. first off i disagree with going as far as "wasted" regardless of any other factors. anyway, the point was i thought this was pretty stupid because how often is a bike engine in steady state while making power? if ur applying full power, u'r accelerating, unless u'r doing a top speed run. considering this, i'd say a sweep test would be better than running several hundred steady state tests. who cares how the engine makes it's power during steady state (again, except for top speed). this is of course esp true for drag racers. if u have a drum with enough inertia, or better yet an eddy current in partial sweep test mode, such that ur pull takes about the same time as first gear in a race, then u have a nearly exact duplication of a real drag race to work with. i'd wanna tune power for the highest area under the graph under that set of conditions rather than doing steady state tuning at every 250rpm interval (or whatever). be much more telling for a drag race methinks. which of course also touches on what u mentioned about low & mid range hit. it's not always about peak HP. if u can lose a little up top but gain a bunch down low, then the choice is obvious. hell, look at the 12 vs busa. if it were all about peak, then the 12 shoudl blow the busa away. but it dont. so am i dull of crap on the sweep vs steady state test thing? or does it actualyl work that way? if a big time racer like Gadson's team is tuning, do they use sweep tests or steady state?
oh, i fergot to ask, what model of DJ u use? i tend to assume it is the 250, which i beleive is an eddy current model right? tho it has a "retarder" rather than a "brake" if i remember correctly, tho i have no idea what the diff is.
oh yeah, jon & turbo, if i need "straight talk" i sure wouldnt be askin u too. unless of course it's straight talk about dealing with ur pimp and i'll ask necro for straight talk about post whoring
posted August 23, 2003 07:03 AM
The best dyno that I've come across so far is the MJP (www.mjpeng.dk), this is an "Engine Development Dyno". The one major thing it can do that a DJ250 cannot is to measure H.P & TQ while the break is on and the engine is loaded. Now you can adjust A/F under load to find what your engine combo likes at all throttle positions and rpm's.
DJ250's usually set up maps TOO LEAN on most modified engines!!
My 1270 produced over 200 h.p. on this dyno running 91 octane pump gas!
HOW?! It is so happy and SMOOTH running at 12.7- 1 A/F ratio. 13.0-13.2 is WAY TOO LEAN......That's what a DJ250 would run you at.
Note: my 1270 runs a compression ratio of 13.8 and the "correct" A/F allows the combustion chamber to run cooler w/o risk of detonation.
Check out MJP's site.
____________
You say PSYCHO like it's a BAD thing!!
posted August 23, 2003 10:59 AM
You hit it on the head as to why we use the DJ. "Quality, price, service", ease of operation, industry standard, etc. Honestly, I'm not a programmer, so I don't know how DJ came up with their conclusions. You'd have to ask Mark Dobeck that question. But they make sense to me. Basically you build up a certain amount of energy in the drum as you are turning it. Since the softward knows the mass of the drum, it makes sense that a program could be written to transfer that info into a viable, repeatable number. There are 3 things that can change this number or "fool" it; the tire spinning on the drum; more or less air pressure in the tire; a heavier or lighter operator on the bike. I simply try and keep those consistent. We normally don't have a problem with wheel spin except on Turbo bikes (250-450 hp). In that case, we use some tie-downs to keep the tire from spinning on the drum. We may also start the run at a higher RPM. So instead of our "normal" start at 2 - 2500rpm, we may start at 3 or 3500, but that's in real extreme cases. But whatever dyno is used, the most important aspect is keeping things consistent.
As far as my opinion as being easy on the motor. If you think about it, all your doing is turning this known mass of 700 lb drum or so. It's spins very freely with your hand, but obviously to spin it faster, you need more strength. In our case, power. Without having to calculate for wind, front tire resistence, road condition resistance, etc., your keeping a fairly even and progressive "load" on the engine. Just like accelerating down the street. But the load isn't brutal on the engine, because it's got "enertia" and free spinning bearings. Personally, I don't like load dynos that "pull" back down on the engine. Oh man, those things can be brutal in unskilled hands! It's extremely hard on the engine (my opinion).
To answer one of your other questions, we use a DJ150 with the 200 software/modules. A few times a year, we take the Dyno on the road to some shows/events. When we do this, we switch back to the DOS software (150) because it seems to be more stable in a "generator" enviornment. When we test in-house, we use the Win Pep. I like the idea of the 250 and "retarder", but I'd mostly like to have it because it's easier to mount an ATV/Quad on it! We'll be getting one soon, but we'll be keeping the DJ150 as well.
You are correct, and I agree on the argument of loaded versus unloaded for mapping. As we are "sweeping" the run, we have enough experience to look at what the sniffer readout is telling us, and make an adjustment to the map/carbs to compensate the A/F mixture/map to where we want it. Is it trial and error? Sure, lot's of times. But that's because there are so many other variables. Maybe everyone doesn't have that experience. If they don't, then a "load, steady state, eddy current, brake, retarder," whatever term one chooses to use, may be best for them. Other than the big dump you get going to full rich (most cases), when whack open the throttle from 2000 rpm, the fuel curve will read accurately enough to make adjustments if you have the experience. Bottom line, I prefer the sweep test.
psycho1122 - I've never heard of the "MJP". If those numbers work for you, then that's all that matters and it's all good. But to the lay-men and/or industry standard, they just don't work. "Most" relate to DJ, Factory, or Superflow and have an understanding of what that number may mean to them. Throw something new in, and it's meaningless to most. Also, I don't agree with 13.0 -13.2 being WAY TO LEAN, though 12.7 is a good number, it's not necessarily the best number. I've got lot's of motors running in the 13.0 range at certain throttle positions and RPMs. Honestly though, the only way to settle the bench-racing, is to get out on the track and let your bike do the talking. Otherwise, all this stuff is smoke and mirrors that give you a base to work with and improve on. Nothing more or less. To this day, I still have not won any Nationals on the dyno...
posted August 24, 2003 10:13 AM
urs is a DJ250 right swft? how does the automatic mapping work exactly? u jsut control the throttle according to what the dyno tells u and it takes care of setting the load at each rpm & creates the map accordingly?
Needs a life
Full throttle!
Posts: One MEEEEEELLION
posted August 24, 2003 11:30 AM
That's right. Tuning link is the application that controls the dyno and maps the PC3 from the same window. There's distinct modes, such as warmup, steady-state, and accelleration, and you tune differently for each. By and large, it's simply setting the throttle position and letting the dyno control RPM via the eddy current brake. You'll hear a lot of discussion about engine load under brake, or just spinning the drum. I can tell you that no doubt, doing 80 and 100% throttle pulls and mapping the 3k - 12k rpm range for those throttle openings generates a LOT of heat. And can be hard on clutches!
posted August 24, 2003 11:39 AM
i assume u have to choose which mode u want to tune for no? the PC can't hodl separate maps for each of the three modes can it?
posted August 24, 2003 09:18 PM
You may want to RE-READ my reply carefully and check out the site before trying to discredit good information.
____________
You say PSYCHO like it's a BAD thing!!
posted August 24, 2003 09:42 PM
psycho, i dont follow. btw i did take a look at thier site but didnt find much info there. besides, i didnt see anyone discrediting what u said.
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posted August 20, 2003 02:13 PM
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posted August 22, 2003 08:08 PM
