6.2 Dyno

[MarkT]

20% is on the very high side for losses... I imagine that some of the loss can be attributed to the larger wheels and tires... big wheels lead to low dyno numbers... also it is a brand new motor so is probably not broken in...

Frog... a few times I've seen the claim that a dyno can only measure torque (and that horsepower is not "real" but calculated...) then how would bigger wheels and tires result in lower numbers on a dyno?

The only way I can see bigger wheels making a difference in the numbers is if the dyno is measuring the time required to accelerate a known load... such as the inertia of a flywheel. Wheels and tires act as flywheels themselves... so adding bigger tires and wheels add to the (unknown) load the engine sees. This added load will increase the amount of time to accelerate the known load which makes the output numbers smaller. Clear as mud?

My point is that if a dyno reading is affected by the size of the wheels, that dyno is directly measuring the rate of doing work... in other words horsepower. The torque numbers are then calculated from the HP readings... HP is not calculated from torque in this case.

Just wondering what your thoughts are on this... Why would bigger wheels result in lower chassis dyno readings?

 

[frogslinger]

F=MA

torque = F*r where r is a constant (for our purposes)

therefore Torque/r=MA

R is determined by the machine by comparing engine speed to dyno speed (less computation is required if you use the 1 to 1 gearing)
mass is the weight being accelerated
acceleration is acceleration

force is determined...

add heavier wheels...

M is thrown off
therefore F is thrown off.

No P.

Note... it is not so much that HP does not exist... it is just that it has as much practical use as a Rankine to the day to day user. If you are building a lightbuld or an electric motor... ok but that is why we have watts...
Because of this contrived standard we get the 5252 by simplifying (33,000 ft·lbf/min)/(2π rad./rev.) ... so now we have a number made to correspond to a standardized fictional horse, which it doesn't, so that a defunct technology can be compared inaccurately to a largely outmoded pack animal. It is a stupid measure, which sells poor parts and causes people with badly designed motors to brag in bars and get beaten on the streets...

Ask the average guy what a HP is... they will not know. Ask them to demonstrate a foot pound... good chance they can.

Now I suppose you can say that given the ease of torque multiplication you can make a s2000 motor tow a semi trailer... ok fair enough... but that does not make the argument any less made up. And it is still the torque moving the train.

Given the other definition of power you could say that Horsepower should be an accurate predictor of gas mileage (conversion of chemical to kinetic energy)... it doesn't do that worth a hoot either though...

The only practical use that I can find in the auto sphere for HP is to describe the TQ curve... if a motor makes 750 TQ and 300 HP it will not rev above about 4K... if it makes 190 HP and 70 tq it will have no bottom end...

 

[Frivol]

My thoughts on this are with frog. When i checked the math i only did it on the torque and it came out about right. i wasnt able to watch the video so i dont know if they ran it in 4wd or not. but anything past the motor is going to take power away untill it's transfered to the ground. any added weight/distance and/or transfer case will lead to the power difference. and also this motor only has 100ish miles on it.

 

[frogslinger]

prettty sure it is not in 4wd... what with the front wheels not turning

 

[Frivol]

ahh you got me with the turning of the wheels ><
:doh:

 

[Raptor1]

I used to run a dyno for engine testing for the big three in Detroit. Frog is correct on his math. A dyno operator can adjust the way he runs the test and vary the results from one run to another. A company of Henesy's reputation may test and show low numbers, 1. to get us to buy thier equipment 2. to show bigger HP and torque gains,so you think thier parts are better than they really are.
You can take the same truck and dyno operator and take them to another shop and run the test the same way and get different results. It is variables in the type and brand of dynos that make the difference. So research the shop you are going to deal with and make sure thier reputation is solid and stay with one shop and one operator.
Big heavy trucks like ours, are as a general statement going to perform better on the street and low speeds with mods that will increase torque. bUILD A TORQUE MONSTER AND YOU WILL BE HAPPY WHEN YOU MASH THE LOUD PEDAL! REMEMBER WHEN IN DOUBT POWER OUT !

 

[MarkT]

F=MA

torque = F*r where r is a constant (for our purposes)

therefore Torque/r=MA

R is determined by the machine by comparing engine speed to dyno speed (less computation is required if you use the 1 to 1 gearing)
mass is the weight being accelerated
acceleration is acceleration

force is determined...

add heavier wheels...

M is thrown off
therefore F is thrown off. SNIP

I'm not exactly sure how you would calculate "r" (the radius or "lever arm length") by comparing rpm of the dyno and engine... but it really doesn't matter for purposes of the point I want to make...

SNIP

Ask the average guy what a HP is... they will not know. Ask them to demonstrate a foot pound... good chance they can.

Just because the average guy doesn't know what a HP is, doesn't make the unit of measure unimportant!

Now I suppose you can say that given the ease of torque multiplication you can make a s2000 motor tow a semi trailer... ok fair enough... but that does not make the argument any less made up. And it is still the torque moving the train.

You are making my point for me here. Torque numbers mean ABSOLUTELY NOTHING if you don't include two other important factors: Distance and time. (Knowing the RPM at which the torque is being delivered adds in these necessary factors.)

I can take a wrench with a really long handle and apply 499 lb-ft of torque to a shaft that will move a vehicle. If that shaft does not move, I have done exactly zero work and the vehicle hasn't moved... but I'm still exerting 499 lb-ft of torque!

But now let's say the shaft starts to turn at 500 lb-ft of torque... and with my wrench I can turn the shaft at a rate of one rpm. The vehicle is going to move slowly.

So now I hook up a small engine that puts out 50 ft-lb of torque at 5000 rpm. Way short of the 500 ft-lb required. So I add a bunch of gears to multiply that torque and (ignoring losses) I can put out 500 ft-lb of torque at 500 rpm. The shaft (and the vehicle) is going to move a lot faster than with my wrench at one rpm... 500 times faster.

So now I hook up a big engine that puts out 500 ft-lb of torque at 5000 rpm. That engine will turn the shaft at 5000 rpm! Now our vehicle is moving really fast! 5000 times faster than I could move it with my wrench!

But notice the one thing that is constant. The torque is still the same 500 ft-lb. But the faster the power source can apply the required torque to the shaft, the faster the vehicle will move.

Now look at the calculated HP for each example power source:

Wrench = 0.09 HP

Small engine = 47.6 HP

Large engine = 476 HP

Ultimate output torque remains the same at 500 ft-lbs but the HP numbers directly reflect the ability of each power source to move the vehicle... that's very meaningful IMHO.

Bottom line:

Torque is a static force measurement and useless for comparing engines without knowing the rpm at which the torque is being delivered.. And once you start talking about the rpm at which the torque is delivered, you are looking at the rate that torque can be applied and now, like it or not, you're actually talking about HP.

HP is a unit of measurement that tells you the rate at which you can apply the torque and is extremely meaningful.

Given the other definition of power you could say that Horsepower should be an accurate predictor of gas mileage (conversion of chemical to kinetic energy)... it doesn't do that worth a hoot either though...

I'm not sure what "other definition of power" you are talking about... but it doesn't matter. Fuel economy is a solely measure of the engine's efficiency. (How efficiently does the engine convert the chemical energy into mechanical energy?) Fuel economy has nothing... zero, zip, nada... nothing to do with HP.

The only practical use that I can find in the auto sphere for HP is to describe the TQ curve... if a motor makes 750 TQ and 300 HP it will not rev above about 4K... if it makes 190 HP and 70 tq it will have no bottom end...

I'm not exactly sure what you're saying here... not enough info...

Anyway... here's the real point about this type of chassis dyno reading: If the mass (weight) of the wheels changes the output readings that particular dyno is not measuring torque...

As you've said yourself, this type of dyno is measuring acceleration of a mass and calculating torque.

You can just as correctly (and actually more easily) measure the acceleration of the mass and calculate HP!

 

[frogslinger]

HP=work done/time taken

work attempted... trying to explain this to you...

time taken... way to long...

HP=0

(same argument turns a 411 HP 6.2 motor into a 0 HP motor when you get stuck in the mud and cannot turn your wheels)...

You know what I am saying I know what you are saying.

Deciding not to debate it anymore.

 

[Madcowranch]

 

[Xjrguy]

Need no holds barred steel cage match to solve this.