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Magazine Dyno Charts, what do they really say?
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Posted by: mxpaul
I am really sceptical of the dyno charts posted in magazines. Mainly because they don't give the conditions, dates and times of the actual runs on the bikes. It seems to me that the only way it could be accurate is if they did all of the tests under the exact same conditions with all of the bikes preped in the exact same way.
When they are comparing prior year models to current models dyno charts, do they have both bikes on hand with the same # hours on them and test them back to back or are they just going back to some dyno run they did the prior year or something. I don't know whether it makes since to even consider these dyno charts at all.
Here is an example that really confuses me: In the current issue of mxracer they have dyno charts of all of the 00' and 01' bikes and on the 01' yz125(I have one) they talk about the fact that yamaha took a little bottom end away and added some mid/top, but when you look at the dyno chart between the 00' and 01' the exact opposite is indicated. Did they get the 2 charts reversed, or does this indicate the inaccuracy of the dyno charts in the first place?
Paul
Posted by: dirt bike dave
Paul - dyno readings are supposed to be 'corrected' for standard atmospheric conditions using a formula. In other words, if the air is great that day (better than 'standard') the actual dyno reading is supposed to be adjusted downward. Atmospheric conditions make a BIG difference in actual power.
The dyno doesn't tell you about part throttle behavior, and that's where most of us ride almost all the time. It seems possible that a bike that has good part throttle low end power might not compare well with another engine at low rpm wide open throttle on the dyno.
Posted by: Nucklehead
In talking about the posting of the graph dynos I find one aspect misleading and at the same time annoying. The scale changes like the wheather, and the last 500 rpm is present some years or left out on others giving the impression of more or less overrev. Same thing with the top 5hp of the graph. It makes it difficult when you try to compare the graph from last years mag. At first glance it looks as if there's been some big changes until you put them both to scale and then you notice there isn't much of nothing. I was checking out the FMF website recently and same thing. Many diff. dynos and so many diff. scales. Some tiny some big.
Posted by: marcusgunby
Ive seen a change of 2hp on a 125 by changing the main by 2 sizes.Unless each bike was jetted very close the graphs are only a guide.Also with one engine it rode like a kart engine all top no bottom at all.With some alterations that made a small difference on a dyno it was like a different bike to ride.
Posted by: KDXIdaho
Dyno charts in magazines are effective for one reason - To eat up page space so they don't have to write so much.
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Peace,
KDXIdaho
Posted by: Eric Gorr
Perfect KDXIdaho, the fact that those dyno charts don't show typical noise in the form of torque troughs and such shows that they're artist renderings. When the editors can't fill the pages the artists have to put it all together.
Posted by: Buzz Bomb
Yeah, plus they have a different amount of HP listed for each bike whenever its listed. It varies from issue to issue if you save back issues.
Posted by: Tennessee Thumper
Have you ever noticed how the pipe shootout's never come out and say this pipe is no better than stock.You pretty much know the pipe's worthless when all they have too say is "It went on easily".The sad part is 2 yr's ago I actually thought those chart's meant something. http://dirtrider.net/ubb2/smile.gif
Posted by: Yogurt
It used to be when you put on an aftermarket pipe, and you actually did notice the difference. The gap between production and works is so close right now, it's hardley noticable.
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-Ryan
'00 CR 133
Posted by: Vic
A few years ago, Dirt Rider magazine was publishing torque graphs, for a while. That was more useful (though not necessarily accurate) information, but I guess people didn't appreciate it, because it soon stopped.
Posted by: steve125
And thats to bad because in the case of the yz250f the torque curve is the big gain over a 125 not the hp.So only half the story gets told.
Posted by: mxpaul
Actually Torque is easy to calculate if you know the RPM's and HP. There are several shareware engine/performance programs that are made for drag racing that will let you plug in the HP or Torque numbers and will calculate the other of HP or Torque.
My biggest problem with all of this is that it seems that "perception" of power from these MX motors must be based on many other factors other than a WOT sweep through the RPM's on a Dyno. Thus the typical 1, 2, or 3 HP difference at various RPM's that these dyno charts show doesn't really mean too much.
From what I can gather, each person or tester has a different definition for what the terms "bottom, mid, and top" mean.
Posted by: John K
Where can I find these programs?
Posted by: spanky250
Torque and horsepower can be calculated if you know one of them. The formula to calculate horsepower is Torque x Rpm divided by 5150. This is why the torque curve and horsepower curve always intersect at 5150 rpm on a dyno chart. A dyno does not measure horsepower, only torque, horsepower is calculated. Simply reverse this formula to calculate torque from a horsepower reading in a magazine. As for the magazine charts, they only mean something for that particular bike, as all engines are different, even on the same model, due to tolerences. Some will run better than others. Factory race bikes (and probably magazine test bikes as well)start off better than all but a tiny fraction of production bikes because they hand-pick the closest-to-design-perfect parts with the most perfect tolerances to assemble these engines.
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1992 KDX 250-FMF porting,two-stage power reeds, Fatty pipe, Power Core silencer,titanium rod,Wiseco Ultra-lite, Pro-Action suspension...Why didn't I take the blue pill???
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