Anyone have experience with an ATV on a dyno? If so, since some atv's "last gear" is lower than a 1 to 1 ratio, do you use the gear closest to a 1 to 1 ratio? Example....Raptor 4th gear ratio is 1.047 and the 5th gear ratio retio is .904. 5th gear should would produce less HP and Torque than 4th gear since 5th gear is basically overdriven (overall drivetrain rotation faster than the engine RPM). All comments appreciated.

 

Gearing does not affect HP, only torque multiplication.

Dyno's use an RPM input, so the rotation of the chassis dyno's drum is calculated against the RPM to account for tire size and gearing differences.

 

With "high" gear below 1/1, to get a realistic reading, the drum would be traveling faster than the engine RPM at any specified RPM and back-calculating to a 1/1 ratio. So for an engine making peak torque at 5000 rpm's, with a fifth gear of .9, the dyno drum would be turning 5,556 rpm's and the dyno would calculate back to 5,000 = 5,000 rpm's (1/1), and then calculate peak torque? I know automotive applications are usually not dyno'd in overdrive (under 1/1). Anyway...keep 'um commin' guys.

 

"Not exactly," garyc660R.

Even if the quad's transmission is 1:1 in high gear, the final drive (rear pumpkin) or sprocket set provides a considerable gear reduction between crankshaft revolutions and wheel revolutions.

Horsepower on a dyno can be measured at any gear ratio, although some are more convenient than others. An engine produces the same horsepower at the same rpm, regardless of the final drive ratio. Gears cannot multiply (or divide) horsepower.

Dynos actually measure torque against a load (water brake or electrical generator) and convert the output reading to horsepower, taking the maximum reading. The conversion formula involves engine rpm; all practical engines produce their maximum horsepower at a higher rpm than the torque peak rpm.

Diogenes

 

The shop I go to has a Dynojet chassis dynamometer it is an inertia type chassis dynamometer.
What it means is that it calculates horsepower and torque based on how quickly the rollers move in a given inertia, in this case, a set of rollers of a given mass and dimension is accelerated.
The length of time it takes to accelerate from one rpm level to the next is the sweep time and the rate that you accelerate from one rpm to the next is the sweep speed or sweep rate. Cuz it takes more power to accelerate the mass faster, you will see lower horsepower figures when an atv is tested in a lower gear. This is cuz at higher speeds and higher gears, it takes longer to accelerate from one rpm level to another for example, 2000 rpm to 6000 rpm.
This stands until the gains in horsepower from increased sweep time are offset by the increased frictional losses of the gearbox, gearing and tires.
As speeds increase, the frictional losses in the gearbox, gearing and tires increase. The higher the horsepower of the atv, the faster it will accelerate the roller and the higher the speed will need to get the sweep time long enough to give an accurate reading. Cuz the Dynojet chassis dynamometer is an inertia type chassis dynamometer it does not allow you to perform fixed rpm or step type horsepower tests you can not hold the atv at a given rpm or speed and check the horsepower level.
The inertia type dynamometers gives you a very accurate measurement of what the atv see's in "real world situations". An inertia type dynamometer will show the effects of reduced weight such as lightweight flywheels, gearing and wheels while a steady state test does not show these improvements.

2000 SCRAMBLER 400 2X4

SCRAMDADDY400

 

Diogenes....I understand you have a magnification at the rear of the vehicle and basic engine principles, but was trying to stray away from a long and complicated post..so I assumed a simple overall 1/1 ratio, which would be ideal for getting the dyno info. that I was looking for. The question is..when the transmission output speed is higher than engine operating rpm's, does the dyno accomodate for this loss? There is a loss...why don't drag race cars use an overdrive transmission? Less power being transmitted to the rear tires is why. Thanks for the reply.

 

The law of conservation of energy suggests that energy cannot be created or destroyed. There is no loss other than the frictional losses in the tranny that are there in any gear.

There are many 9 sec Grand Nationals out there using the TH200R4 tranny.

Looking at what drag racers use and don't use is not a valid way to determine how HP and torque is affected by certain pieces of equipment. There are many more factors that come into play.

What would the difference be between a 1:1 tranny pushing 27" tires and a .7:1 tranny pushing 19" tires? (assuming any reduction after the tranny was the same)

 

Gearing multiplies torque....what happens when the torque is factored by .9 instead of 1? The torque is less at that point. Then after the other gearing factors are added in, the end result is less torque when comparing .9 to 1 at the rear wheels.
I agree, poor comparism on the auto, but the basic principles are the same. I have been around quite a few Grand Nationals and have a bud that still owns one, and have yet to see a 200r4 stay in one that is even slightly modified. A built 700r4 is normally the choice for racers that do the street thing, but the car is normally set up for around peak power at the finish line in the 1/1 gear, not overdrive.
Assuming a 3/1 primary reduction ratio and a 3/1 secondary reduction ratio, with .7/1 top gear and 19" tires, axle revolutions would be 7,102 feet per minute. With 1/1 top gear and 27" tires, axle revolutions would be 7,065 feet per minute. Basically the same length and gearing. The only problem is the machine with 19" tires would be applying roughly (meaning other factors I don't wanna get into) 30% less torque to the rear tires in high gear. Thanks for reply's in advance!

 

It's all relative, tire size is part of the gearing equasion. There is no free lunch. That is what your tire size analogy implies in reference to torque. It all factors in to torque multiplication. From what you say at the end, when geared equally (for equal RPMs at equal speeds), the taller tire example provides 30% more torque, that is not possible, it violates the law of conservation of energy.

If you measured torque at the axle, you'd be correct, but when it gets to the ground, the tire diameter puts the torque back to equal levels.

For instance: (this experiment can be done with the butt-o-meter) take your Raptor, install a set of 18" tires. Note the acceleration & top speed. Next install a set of 25" tires, note acceleration and top speed. Now, compensate for the 25" tires with appropriate gearing (sprocket) changes, it will accelerate and have the same top speed as it did with the 18" tires (less the loss from the heavier tires/rotational mass).

As far as the GM OD tranny's go, the TH200R4 (the TH200 was a POS) has a better gearset for performance use. I have been told by several drag racers with vehicles in the 9sec range (using these tranny's) that the 200R4 can be built as strong as and in many cases stronger than a 700R4. I am also on an e-mail list with several of these GN owners that like to program their own fuel injection systems and really tweak on these things. I believe the biggest problem with not using OD in a GM tranny'd car is that the gear itself is not very strong and there are circuits within the transmission itself that prevent it's engagement under high load and RPM.

 

Primary gearing along with each gear ratio multiply torque (possible increase or decrease in torque) and transfer that amount of torque to secondary gearing and tires. Tire size and secondary gearing cannot alter torque, so the torque remains constant after it is multiplied by the individual gear ratio's. So the law of conservation is not being violated.

I agree, if the secondary gearing and the tire sizes are varied, but the secondary + tire ratio is the same, acceleration and top speed should be roughly the same.

If overdrive was desirable at the strip, the GN guys (and anyone else with OD) would definately have the transmission problem taken care of.

Wanna talk about oil/oil properties and manufacturers recommendations Gabe?