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Dyno vs. Track Testing

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Posted by: theMotoMan

After doing much comparison of yz250f pipe reviews in recent magazines, I came to the realization that I really don't understand why a pipe with a great dyno chart doesn't perform well as others on the track. I'll give an example here from Dirt Bike magazine.

Both FMF pipes (MX & SX) and both WB pipes (E & R series) produce nice dyno graphs that have HP increase over the whole power band; they are nice and smooth. These pipes were rated 'B' and 'C'. The 'track test' showed mediocre throttle response and 'willingness' to rev.

On the flip side, The Dr. Dubach pipe and the Pro Circuit pipe dyno graph appear to mimic the stock curve through the low and mid range, then produce more top end. These pipes got an 'A' rating and the 'track test' showed better low end and throttle response even though they had less hp at low rpm.

Is this paradox the result of the torque curve the magazines failed to display? Inquiring minds want to know!


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01 YZ250F
00 TTR-125L
00 TTR-90
00 PW-50


Posted by: MXN4FUN

Simple, Pro Circuit advertises more in the mags. Dubach pipe is made by Pro Circuit. But in all fairness the Dubach pipe does rip. Seriously, the pipes with big numbers on the dynos usually fall flat somewhere in the torque curve. They produce the numbers but fail to produce a broad usable power delivery. This forces the rider to be perfect or be penalized. The more forgiving pipes rate higher. A constant crescendo of power is what should be strived for not hit and miss peak numbers. This is my story and I'm stickin' with it.


Posted by: marcusgunby

I adgree with the previous comment.We have found on the CR125 engine the parts that poduce the most Hp feel the worst on the track.It a balancing act, the dyno is only a tool.


Posted by: weimedog

I hate to say it but MXN4FUN hit the nail on the head...hard. After a few years you can read between the lines with most of the magazines. The rating between those who advertize heavily usually is fair.

My wake up call....Dirt Bike Magazine editor gets a TM to ride at the ISDE, TWS the TM distributer, advertises in Dirt Bike for a variety of things. TWS used to be VOR's distributer. VOR get slammed for having a way too soft fork relative to all and especially the Yamaha. I ride brand new Yamaha and find the exact opposite to be true. How can this be?

I happen to think Dirt Rider the magazine is the best of the publication lot. A coincidence.

This is why DRN and the like is so valuable to folks.

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2001 VOR503 V-Cross
1982 husqvarna XC430
1974 Bultaco Frontera 360
6 Kids, Four Ride, 3 race. (cr125, yz80, 2 KX125's)
Case 780, INT 1066, Ford LTL9000...and a Percheron

[This message has been edited by weimedog (edited 04-07-2001).]


Posted by: Ol'89r

IMO, you shouldn't tune for HP unless you are trying to sell parts.

What really matters is the torque curve. You can have very high HP figures on a dyno, but, if you don't have a usable torque curve to go along with it, you won't be able to get the power to the ground.

Most aftermarket manufactures try to get the highest HP figures they can on a dyno. This is because a high HP number sells parts. Most of them don't show the torque curve, only the HP curve.

Normally, as the HP curve goes up, the torque curve drops off. To get an engine that will perform well on a race track you would want to set it up to have the torque curve match the HP curve as much as possible.

Just my $ .02

Ol'89r


Posted by: Eric Gorr

I think I can shed some light on this discussion. Dynojet dynos, the rig that all the big aftermarket companies and magazines generate their numbers from, is an inertia dyno. The motorcycle spins a big drum and sensors measures the acceleration of the drum and interpolate crankshaft horsepower. In other words, this dyno doesn't have a load cell to measure torque, instead it uses an algorithm to infer crankshaft horsepower. The dyno doesn't distinguish between a KX65 and a big Harley Hog, its the same algorithm. Factors like the weight of the operator, the angle of the swingarm and the tension on the tie-downs securing the rear wheel to the chassis of the dyno, the shock spring tension, and a zillion other factors are not actually accounted for on these types of dynos.
I've tried jetting a motorcycle on a Dynojet by exhaust gas temperature, then running the bike on a race track and re-adjusting the jetting in the same way, guess what? The dyno exerts a much greater load on the motorcycle than knobbies in the dirt.
When I see pictures in magazines of Dynojets being run in an open wharehouses with no air control by so-called 2-stroke tuning gurus I laugh and feel embarrassed for them. For anyone interested in learning about real engine testing, buy this book from the SAE "ENGINE TESTING - THEORY AND PRACTICE" by Plint and Martyr available from the SAE book store at www.sae.org
My testing methods include running simulations on a computer with a number of excellent programs, then putting it on the track with a rider under the scrutiny of the clock. Because the bottom line is, all that matters is how fast a guy gets around the race track.



[This message has been edited by Eric Gorr (edited 04-15-2001).]


Posted by: kevkon

Motoman

I totally agree with the previous replys. Remember, a dynometer is a tool to help understand, track and compare engine performance under a controlled enviroment. However, the results are relative to the type of dyno used and the conditions of the tests (solid baseline, accurate recordings, etc.). Hopefully these results can then be correlated to actual performance. However, the dyno can't take into account the various riding styles and track conditions of everyone who will ride the bike.
Of course, I totally agree that the magazine "tests" are highly suspicious and are probably conduted in such a way as to stack the deck.

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Posted by: steve125

Before i dyno my bikes i try to get all of the track testing out of the way first. What matters to me most is how the bike feels on the track. Throttle response,power delivery,and power band width are far more important than any peak numbers on the dyno. When i'm happy on the track, i dyno a few of the close combo's to see where i'm at. I agree with Eric, there are a ton of uncontrollable factors when dynoing. I'm lucky because Pete of HDR is a superb dyno operator and his repeatability in our testing is excellent. I think the dyno is a good tool to use as a reference, but by no means is it the final answer!

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01yz250f/DR.D exhaust/01yz144/Eric Gorr


Posted by: theMotoMan

There seems to be a consensus that track testing is the best, but how can you assure that IT is done in a controlled and uniform manner? I think it would be pretty hard to compare 10 pipes and tell which added bottom, mid, or top and which one had the best of each.

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01 YZ250F
00 TTR-125L
00 TTR-90
00 PW-50


Posted by: Rich Rohrich

Quote:
Originally posted by theMotoMan:
I think it would be pretty hard to compare 10 pipes and tell which added bottom, mid, or top and which one had the best of each.


To a degree that is true, but a structured test plan can tell you a lot about how various mods effect performance. Unfortunately there is nothing REMOTELY structured about the way the dirt bike rags test http://dirtrider.net/ubb2/frown.gif



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Rich Rohrich
==

"Wisdom is not a product of schooling but of the life-long attempt to acquire it."
- Albert Einstein


Posted by: kevkon

"Structured" testing as Rich said is the key. Aim for consistentcy and make recordings of as many enviromental variables as possible. You would be surprised at how many people make multiple changes to their machine when they are supposedly testing a component modification.
The dyno is a great tool for testing specific performance enhancements and providing a solid baseline for performance. You can find out a lot of information in a relatively short time and narrow down the choices. Its just that you don't race on dynos. Do your dyno testing, if you can ,to give yourself a direction, then take this data to the track, test under actual conditions , record the variables, and compare to your dyno tests. After you get use to this process you will see the advantage of combining the two.

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Posted by: superstock327

I don't believe I took the time to register to this site just to post this for you BUT here goes. I have never been on a dirt bike but I have made a few thousand dyno pulls on engines. I had this conversation with a well known sprint car driver in the dyno room. After we spent the day extracting all the horsepower we could I made several changes to the motor that produced 45 ft lbs more trq. at 4500 rpm. mid range suffered and it killed top end. His response was OMG change it back. Mine was do you want to win? If you put a car length on a guy off the corner how much acceleration, mid-range or horse power does he need to catch you? To make up that car length and be able to put a move on you by the next corner. I know , I know there are all kinds of variables but it is a pretty dang good rule to try to follow. If you don't get the overall of my point - - nevermind the sharp ones will get it.. nuff said


Posted by: hot125mod

Eric you confused me i thought a dyno read wheel horse power. or actually torque and then has some number i think i remember it being 5650 or like a random rpm then it calculates it into horsepower. i was watching a car run on the dyno a while ago and a tech was explaining it to me. clarity?


Posted by: ericz103

Horsepower is a function of torque. HP=(tq x rpm)/5252
He is just saying different dynos function different ways.

Dynos with load cell actually measure the torque against them and then calculate hp from the torque they measured. (Can be off the wheel or from the crank or where ever depending on the type of dyno)

The inertia one he was talking about as he said just relies on math to get a hp number from how fast it can move something(very simply said, but correct I believe). It know it takes this much force to move this object at this speed in this amount of time.
Lot of factors can affect the outcome of that measurement, that the dyno does not take into account.

Hopefully that helps, and is all correct info.


Posted by: hot125mod

yeah thank you


Posted by: OHIOMOTOXER

WOW ......talk about thread CPR...

2001 to 2008 !



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