Horsepower vs. Torque: Which one wins?

SeriousEric said:

Clint Sever said:

By the way - what does the dyno measure then? I know Vipers dyno in fourth cause the ratio is 1:1 - does that cancel the torque multiplication factor? In what gear would the RWTQ be 2456?

In my mind, if the ratio is 1:1 and the rear is a 3.07 then the dyno is measuring power at the 3.07 ratio - why then is the RWTQ 1000 ft/lbs less when measured on a dyno?

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Good question. The # that the dyno reports should actually be called flywheel torque as measured at the rear wheels. You are correct in that a stock viper making 500 lb.ft torque (at the flywheel) is actually putting down 1500 lb.ft. at the rear wheels (minus losses).

So how does the dyno *know* how to factor out such things as gearing (trans & diff) and wheel/tire size? It does that by a ratio of drum speed to known engine speed. They're measuring your rpm, right? And the dyno knows at any instant how fast the drum is turning and that allows them to factor out the mechanical advantage (torque multiplier) due to gearing etc.

Click to expand...

Wow, ok I think I got it :thumb:! So, Eric, does that mean when we ask how many RWHP/TQ a car is making, we are really referring to the amount of power being transferred to the wheels from the crank, rather then the actual amount of power at the wheels?

And if torque is a quantifiable, tangible 'thing', then is horsepower simply a function of torque relative to engine speed?

Sorry I missed your call last night, I didn't hear my damn phone! I will definitely get it tonight.

The Dynojet actually measures rw hp and is able to interpolate that info. into torque via the corresponding rpm. F=ma or rw hp = the mass of the dyno roller x its acceleration.

Getting a great dyno queen number is only the first step in getting your car to go fast at the dragstrip or from a roll.

Clint Sever said:

SeriousEric said:

Clint Sever said:

By the way - what does the dyno measure then? I know Vipers dyno in fourth cause the ratio is 1:1 - does that cancel the torque multiplication factor? In what gear would the RWTQ be 2456?

In my mind, if the ratio is 1:1 and the rear is a 3.07 then the dyno is measuring power at the 3.07 ratio - why then is the RWTQ 1000 ft/lbs less when measured on a dyno?

Click to expand...

Good question. The # that the dyno reports should actually be called flywheel torque as measured at the rear wheels. You are correct in that a stock viper making 500 lb.ft torque (at the flywheel) is actually putting down 1500 lb.ft. at the rear wheels (minus losses).

So how does the dyno *know* how to factor out such things as gearing (trans & diff) and wheel/tire size? It does that by a ratio of drum speed to known engine speed. They're measuring your rpm, right? And the dyno knows at any instant how fast the drum is turning and that allows them to factor out the mechanical advantage (torque multiplier) due to gearing etc.

Click to expand...

Wow, ok I think I got it :thumb:! So, Eric, does that mean when we ask how many RWHP/TQ a car is making, we are really referring to the amount of power being transferred to the wheels from the crank, rather then the actual amount of power at the wheels?

Click to expand...

Correct. The actual torque at the rear wheels is (trans gear ratio) X (rear gear ratio) X flywheel torque. Talking about 4,000 to 5,000 lb.ft in first gear.

SeriousEric said:

Jerome said:

Who wants to tackle this one, TM?

Why can you dyno one car with low profile 19's on it and then change them out to say 16's of the same overall rolling circ. and have the hp and tq readings be different? :idea:

All else being equal and the runs back to back with only the rim/tire change. And then switch back to see the same results the other way.

And who can tell me which will give the better readings?

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The readings should be the same. Tire size should have no affect. On the other hand, chassis dynos do not give repeatable results. Figure an error of +- 7%. That's probably what you're seeing.

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Size will be the same, circ. and width. Only change will be the sidewall height. Even keep the same compound and air pressure.

The results will change with the two sizes. I would like to hear who has what to say as to why it does.

One will give higher, the other lower. This will be repeatable, not to the exact number but in the same direction (up and down )

SeriousEric said:

Clint Sever said:

SeriousEric said:

Clint Sever said:

By the way - what does the dyno measure then? I know Vipers dyno in fourth cause the ratio is 1:1 - does that cancel the torque multiplication factor? In what gear would the RWTQ be 2456?

In my mind, if the ratio is 1:1 and the rear is a 3.07 then the dyno is measuring power at the 3.07 ratio - why then is the RWTQ 1000 ft/lbs less when measured on a dyno?

Click to expand...

Good question. The # that the dyno reports should actually be called flywheel torque as measured at the rear wheels. You are correct in that a stock viper making 500 lb.ft torque (at the flywheel) is actually putting down 1500 lb.ft. at the rear wheels (minus losses).

So how does the dyno *know* how to factor out such things as gearing (trans & diff) and wheel/tire size? It does that by a ratio of drum speed to known engine speed. They're measuring your rpm, right? And the dyno knows at any instant how fast the drum is turning and that allows them to factor out the mechanical advantage (torque multiplier) due to gearing etc.

Click to expand...

Wow, ok I think I got it :thumb:! So, Eric, does that mean when we ask how many RWHP/TQ a car is making, we are really referring to the amount of power being transferred to the wheels from the crank, rather then the actual amount of power at the wheels?

Click to expand...

Correct. The actual torque at the rear wheels is (trans gear ratio) X (rear gear ratio) X flywheel torque. Talking about 4,000 to 5,000 lb.ft in first gear.

Click to expand...

Isn't the transmissions gear ratios directly affected by the rear gear ratio (3.07)?

What I mean by that is in first gear, is the motor turning 3.07 times for every one time the wheels turn? What about second gear? Is fourth the only gear (at least in a T-56) that retains a true 3.07:1 ratio between revolutions of the motor and tire?

Torquemonster said:

/images/graemlins/laughing.gif I'm not touching this one! /images/graemlins/freak

because I haven't got a bloody clue :doh:

:lolcry:

But I have heard of this before - bugger it - here's an opinion then

I think the problem is that chassis dyno's are not as accurate as engine dynos - and therefore they are great for tuning but not the most reliable source for real life power. If they were dead accurate - as Eric says - there'd be no change by swapping gears or wheels. I have no idea which wheel size gave most power... which one?

And why do you think that is?

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Lower profile gives a lower reading. Sizes (width etc.), pressure, compound, etc. be equal

As to why, I can't really explain it. It is beyond my ability to put into words. :bonk:

I was hoping you could tell us in simple English.

I'm not sayin' you're wrong Jerome, I just don't think you're right.

Ok - here's a wild stab in the dark

maybe the bigger sidewalls twist more and this twisting when it reaches its limits provides a counter force that actually helps the power - kinda like a pendulum effect... kind of...

maybe not

:help:

:screwy:

:leaving:

John Hennessey said:

Getting a great dyno queen number is only the first step in getting your car to go fast at the dragstrip or from a roll.

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Hey Smokin' ? I think he's talking about you. :lolcry:

Torquemonster said:

Ok - here's a wild stab in the dark

maybe the bigger sidewalls twist more and this twisting when it reaches its limits provides a counter force that actually helps the power - kinda like a pendulum effect... kind of...

maybe not

:help:

:screwy:

:leaving:

Click to expand...

Sidewall flex = stored energy :nod: Think wrinkle walls

Keep goin' Barry, you are on a roll. :thumb:

Jerome said:

Torquemonster said:

Ok - here's a wild stab in the dark

maybe the bigger sidewalls twist more and this twisting when it reaches its limits provides a counter force that actually helps the power - kinda like a pendulum effect... kind of...

maybe not

:help:

:screwy:

:leaving:

Click to expand...

Sidewall flex = stored energy :nod: Think wrinkle walls

Keep goin' Barry, you are on a roll. :thumb:

Click to expand...

The dyno spins counterclockwise and the tire is spinning the opposite direction. When the operator hits it, the sidewall flex is going to pull power out of the reading because it doesn't trasmit the power as accurately to the drum.

Clint Sever said:

Jerome - if the rolling circumfrence remains constant, then the dyno doesn't know wether or not it's a lo-pro 19" or a 16" wheel/tire combo. If the total circumference is 3.14*19"= roughly 60" for both, then it should register the same. In fact, I would say that if anything, the 19" lo-pro, real stiff sidewalled tire would give a bigger reading, because of the low amount of sidewall flex and reduced loss of energy resulting from it.

But that's just something that popped into my head, so it could be /images/graemlins/bs

Click to expand...

Clint re-read what TM and I both put up in our last few posts. Does any of it make any sense to you?
If yes, please tell me what you think about it.
If no, tell me your take on it.
Not a dig at all, just want you ideas on this.

Thanks

All this thinking is giving me a headache :bonk:

:rofl:

Clint Sever said:

Jerome said:

Torquemonster said:

Ok - here's a wild stab in the dark

maybe the bigger sidewalls twist more and this twisting when it reaches its limits provides a counter force that actually helps the power - kinda like a pendulum effect... kind of...

maybe not

:help:

:screwy:

:leaving:

Click to expand...

Sidewall flex = stored energy :nod: Think wrinkle walls

Keep goin' Barry, you are on a roll. :thumb:

Click to expand...

The dyno spins counterclockwise and the tire is spinning the opposite direction. When the operator hits it, the sidewall flex is going to pull power out of the reading because it doesn't trasmit the power as accurately to the drum.

Click to expand...

Rotational direction has no bearing on this, the sidewalls are the "energy storage area" regardless of the direction.

John Hennessey said:

Different power adders have different pros/cons as they run down the track:

Click to expand...

Let's talk about air boxes then. I've dyno'd my GTS on 4 different machines since '99 and from 11k to 25k miles. With the exception of a mustang shop in SA that wasn't properly altitude corrected, every one indicated between 410 and 413hp with a fully warmed engine. New u-joints and diff made no measureable difference on my car from my March and December '03 pulls. Stock airbox with smoothies and K&Ns dyno'd the same on a hot, humid day in Houston as the HMS CF box did on a cold, dry day in SA. However, at TWS, my front straight speeds are about 4-6mph higher with the HMS box, and my trap speeds at the strip are up from ~116mph to consistently around 121+ mph. I don't give a rat's ass how much fan you blow at the front end, you will not duplicate the pressure differences at the airbox in real life. Saturday, my cool engine made 8hp more than my warm engine. It was the only time I've seen this "magic" 420hp number for my filters and tubes car.

BTW - why is 5252 the magic number in the relationship between horsepower and torque?