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Creaks When Walks...
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172 Posts
Discussion Starter #1
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Here's the new "Horsepower" section of the forum, and certainly everybody's interested and excited to start seeing all sorts of dyno charts detailing baselines, modifications, etc. That's natural, but... Well, let me start this another way.

I have been a bit hesitant to post something like this, but the more I thought about it the more I thought it was important before all sorts of dyno results did get posted... and perhaps confused the issue more than they enlightened it. Essentially one has to ask a few questions, and remember a few points, before ever trying to evaluate, and more importantly compare, dyno results. We already have some dyno sheets posted, but with each of those I have yet to see the single most important piece of information that should go along with them.

What kind of dyno were they done on?

Were the runs done on a water-brake/hydraulic dynamometer? Or were they done on an electric AC (alternating current), or a DC (direct current), or eddy current rig? Or more commonly these days, were they done on a inertia/flywheel/accelerometer dyno?

This is way, way more important than most people realize, because each type will give you significantly different results... i.e. for instance a "Mustang" water brake will always show you lower numbers than a "DynoJet" accelerometer rig will, but may actually be more accurate.

To add even more confusion there is not just differences between brands and types of dyno's, but there are often even extreme differences between two individual dyno's of the very same type and brand. The installations are almost always different shop-to-shop, and even the size of the room they are installed in, how they get their airflow, how they get rid of the engine exhaust, how solidly they are mounted, how old they are, how well they are maintained, etc. can all make a difference.

Then there is their calibration... And their software from the given manufacturer, and what version it is.

And, of course, there is temperature, altitude, air density, etc. that have to be considered.

So far no one has ever been able to come up with any sort of truly reliable set of compensation, comparison, or equivalency formulas to compare dyno's to each other, and so the only real way to compare dyno results is to run on the same dyno, and preferably on the same day. Needless to say this is rarely practical for when you are doing mods, but it is still best to go back to the same dyno you ran on before. Most dyno shops do have correction factors for their own dyno's that will work quite well accounting for running on different days of varying atmospheric conditions, but it really is almost impossible to accurately compare figures obtained on different dyno's in different places.

That may not be what anyone wants to hear, but... it's pretty much the way it is.

Another thing to remember is that "horsepower" is really just a man-made mathematical construct to try and measure work over time. Torque is actually what a dyno measures...

Here's a trivia question for you... Why is it that the torque curve and the horsepower curve on a dyno run ALWAYS cross at 5252 RPM?

(That is, if they do cross... some engines don't turn as fast as 5252 RPM, and with those engines the two curves will NEVER cross...)

The answer is simple. The mathematical formula for computing horsepower is:

Torque x RPM / 5252 - (torque times RPM divided by 5252)

Torque is the force exerted in trying to twist the crankshaft. Some much torque is exerted in each rotation of the crank. So to attempt to figure the amount of "work" that force (measured torque) can do over a period of time you take the number of times the crank rotates over, say, one minute, and multiply the force by those number of times in that minute and divide by a constant.

As you can see, one can directly measure the force (torque), but there is really no way to directly measure how much that force (torque) can actually get done (work) over time, so a mathematical formula was constructed to try and do so.

There are lots of other ways to measure engine output, and some that even work much better to compare different size engines to each other (like BMEP), but somehow torque and horsepower together seemed to become the standard for motorsports engines.

I won't even mention the differences between DIN and SAE horsepower figures... As this has already gone on long enough and is probably boring too many of you.

However, there are still a lot of other factors one should keep in mind when discussing power output of our engines. We may all want to discuss some of those factors so we can all decide on what standards we want to all set here for what's posted and what's not, etc. No doubt some will scoff or laugh, or maybe even try to say dyno differences, correction factors, calibration methods and standards, etc. should be ignored, rather than address the matter... But until we all settle on what details should be included in the dyno posts then by and large those posts and charts will not give anyone here data they can use.

At the very least the type of dyno, the brand of dyno, what software is being used, and what conditions were the runs made under should be included with any dyno post.

But that's just my opinion... What do each of you think???

Thanks!

Dallara


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Warning! Fat people are harder to kidnap.
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1,373 Posts
Dallara is correct, there are a bunch of variables. Is your tachometer digital or run by a cable off the cams, is your oil pressure guage electric or is there a mechanical oil tube coming from the crank case? Every measurement has a degree of error.
I used a Dyno-Jet dyno to get the chart I posted. I listed the dyno settings for the base line. All a dyno is for is to see gains or losses. If you use the same dyno and settings the results will show. I don't care the horsepower amount just the plus or minus. The temp. and humidity do matter also. That's why I listed mine but we aren't talking road racing air cooled two strokes and I didn't spin a manual humidity guage I used the weather service.
My only desire is to measure improvement not amount. I don't use the dynos at bike events to see who has the most and blow up my engine in Hooters parking lot on a mobile dyno. Oh damn I'm starting to ramble. Good thing the internet provider allows unlimited key strokes. :p Later,
 

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Gimme fuel gimme fire gimme that which I desire
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51 Posts
Good post, Dallara. Dyno print outs are nice to have in a "mine is bigger than yours" argument, but they aren't written in stone (and would be a bitch to carry around if they were). Besides, mod your XR as much as you like, Rossi will still beat you around Laguna Seca on a VStar650.

furyus
 

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My giant goes with me wherever I go.
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14,911 Posts
its all relative

Good post Dallara! The value of dyno comparisons from various locations tells us little.

The real value of the dyno posts to us is in the relative measures before and after mods. I'm not so interested in comparing FatBillys numbers to Vecchio's numbers, my interest is in FatBilly's numbers before his mods to his numbers after his mods on the same dyno. And for that info it doesn't matter what make, model, or type of dyno produced the numbers. Its all about before and after.....and I'm very excited, waiting to see his numbers after his QD's are installed! [:)]
 

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It aint no good locking the doors, when the madnes
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7,305 Posts
Yea, yea, all that is a given, but the whole purpose of this aint a my dick is bigger than your dick contest, it is just to give us something to take a rough guide from as far as different mods go.
As long as we dont take ourselfs to seriously we get an idea of what is going on out there.
All these exhaust manufacturers who give hp and torque figures don't give any dyno details either so its all relative.

The only real way this sort of stuff works, is if anyone who dynos there bike and then goes on to do any more mods and dyno again is sensible enough to use the same dyno, which i see as common sense. Then we see pretty accurate differences, the issue need not be over complicated or a dick showing contest.

This isn't about who gets the big figures, its about which mods work and which mods dont!

For those of you who don't want to mod your bike it is not really of great interest, but for those of us who do, it is.

So lets not have the guys who are staying stock pissing on our chips. :D

In other words, what Mr Magoo said!!!!!!
 

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My giant goes with me wherever I go.
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14,911 Posts
Oh Scotty, you're a pip!

So lets not have the guys who are staying stock pissing on our chips. :D
Ha!! What the f**k does that mean? This board is so educational!:eek:
 

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Reputation points: -4
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My XR still has zero miles. If it will be of any value to you guys, I'll have them do a pull at the dealership. Lemme know.
 

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It aint no good locking the doors, when the madnes
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7,305 Posts
Ha!! What the f**k does that mean? This board is so educational!:eek:
:D It means dont go putting a downer on it for those of us who are into it.

Come on just imagine you are sitting there eating your favorite potato chips and some fusker comes along and pisses on em, its sorta gonna ruin your day :D
My XR still has zero miles. If it will be of any value to you guys, I'll have them do a pull at the dealership. Lemme know.
Yes Dybercyke, it would be of great value, then we would have a run on a US stock bike with no cat in the box. (Just remember to do a few hundred miles break-in on it first)
And if any of the European dudes could do the same thing with a totally stock bike with cat, that would be great. Even if you had fitted XIED's they can easily be disconnected for the run.
 

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Reputation points: -4
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1,205 Posts
Well...

It started snowing again today, so break in wont be until late March or early April.
 

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Creaks When Walks...
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172 Posts
Discussion Starter #11
Next it'll be tea & crumpets...

:D It means dont go putting a downer on it for those of us who are into it.

Come on just imagine you are sitting there eating your favorite potato chips and some fusker comes along and pisses on em, its sorta gonna ruin your day :D

C'mon, Scotty...

Don't be so sensitive. ;)

Nobody was trying to put a downer on anything. Nobody enjoys tweaking engines (and chassis, suspensions, etc.) more than I do, and I am very interested in where various mods might take the XR. I'm holding off modifying mine for the time being, but that doesn't mean I won't one day. Most of my bikes are heavily modded. As such I want to see what people do to their XR's and how effective each mod is, just like you.

I just want to make sure the data posted here is complete enough that reasonable, rational, and relevant conclusions can be drawn from it.

Please, keep a stiff upper lip and all that, wot... :D

Dallara


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Keeping Them Flying
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183 Posts

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Warning! Fat people are harder to kidnap.
Joined
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1,373 Posts
Out of left field and into the latrine we go. Will you guys please leave my tater tot out of this? Ok you want to talk about your johnson here we go. Mines only and inch long but it is the diameter on a hub cap. Ask the ladies the diameter means more than the length. Besides fat guys are required to have a cute dismount! :eek: Later,
 

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Keeping Them Flying
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183 Posts
Didn't realize we were whipin 'em out for size. I thought it was to see how could piss up the wall the farthest.
Shoudn't have brought a knife to a gun fight I guess.
 
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Didn't realize we were whipin 'em out for size. I thought it was to see how could piss up the wall the farthest.
Shoudn't have brought a knife to a gun fight I guess.
I lose on all counts here. My wife has had mine locked away since we got married 25 years ago and only let me have them so we could procreate.
 
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"Come on just imagine you are sitting there eating your favorite potato chips and some fusker comes along and pisses on em, its sorta gonna ruin your day"

...maybe....but for sure its going to ruin his day once I'm finished with him.

Oh yeah..the dyno...the best thing I ever did to my KTM Superduke was Akropovic exhausts, a Power Commander, and then pay for a serious day session on a dyno (run by an ex-factory superbike team mechanic who knows what he is doing)..I could care less what the HP readings are on paper...He told me he found horsepower "everywhere" on the curve and he did! When I first rode it after the tune up it was amazing...much more power and speed than before..exeptional...If you've never had your modified bike professionally remapped on a dyno I highly advise it.
 
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I have MOTO METER TEST BENCH a hydraulic brake dyno same brand that jemco exhaust used to make their exhaust dont know if they still have it or use it. just has a hydralic barrel about 30 gallons mounted on the side of the set up which has a miles per hour and a psi gauge and a turn knob which loads the break when the tire spins the roller there is a very large squirl cage fan thats in front the faster you go and the more the load you put on it the faster the fan turns cooling the engine. there is charts to for mph and psi and over lays you lay across the guages to convert so you can calculate torque and h.p
I just put my sprint on it to break the engine in and if i change to a different set up i will run it how it is and see how many psi it will pull then do my change if it will go past the initial test or point i know that i have increased if not then it has gone backwards i have only put my hd sprint flattracker on it so far.
 
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