General [M]ayhem

Go Back   General [M]ayhem > General [M]ayhem > Automotive [M]ayhem
Register Members List Mark Forums Read [M]erchandise Calendar

Reply
 
Thread Tools
Tex Arcana
I am a mean disrespectful person hiding anonymously and need an attitude adjustment.
 
Tex Arcana's Avatar
 
Quote:
Originally Posted by FlyNavy
No one gives two shits because the reason people use chassis dynos is to know how much driveline loss they're incurring. It's not to measure the exact amount of torque that the tires are putting to the ground because that's pretty close to impossible to measure with current technology because of the innaccuracy of how a dyno works.

Actually, people use chassis dynos because there is no other alternative without lost of cost and effort. THey also use them to evaluate mods and tunes, to be sure the work done enabled gains. So it's reasonable to expect that the dyno produces accurate results, irrelevant of the method used.
__________________
People should not be afraid of their governments. Governments should be afraid of their people.--V


Men heap together the mistakes of their lives, and create a monster they call destiny.
--John Hobbs


~~~ ~~~ Tea[m] Pyratex ~~~ ~~~
Old 08-30-2004, 09:02 PM Tex Arcana is offline  
Reply With Quote
#226  

Advertisement [Remove Advertisement]

LagPenguin
 
LagPenguin's Avatar
 
Yeah, he said it's not a cracked rotor.
Old 08-30-2004, 09:02 PM LagPenguin is offline  
Reply With Quote
#227  

Tex Arcana
I am a mean disrespectful person hiding anonymously and need an attitude adjustment.
 
Tex Arcana's Avatar
 
Quote:
Originally Posted by BlazerLT
Can we get back on topic

I could care less about your fucking torque talk.

Did the thread starter come in here yet to explain the cracked rotor?

Um, no. On both counts.
__________________
People should not be afraid of their governments. Governments should be afraid of their people.--V


Men heap together the mistakes of their lives, and create a monster they call destiny.
--John Hobbs


~~~ ~~~ Tea[m] Pyratex ~~~ ~~~
Old 08-30-2004, 09:02 PM Tex Arcana is offline  
Reply With Quote
#228  

Tex Arcana
I am a mean disrespectful person hiding anonymously and need an attitude adjustment.
 
Tex Arcana's Avatar
 
Quote:
Originally Posted by FlyNavy
Those are pretty underrated as well, right? I drove my buddy's Cobra when I lived in Florida...put a nice grin on my face

Ford may have had their own reasons to underrate the Cobras and for all I know they rated them at the rear wheels instead. Just like it's rumored that GM did with the 4th gen F-bodies so they wouldn't look as powerful as the Vette. But typically when a car company releases power figures they're advertising them at the flywheel so the numbers look bigger.

Do you concur, Dr Tex?

No, Ford stated a horsepower number for the '99 Cobras, and when the chassis dyno numbers didn't jive with the stated numbers, a number of owners pulled theire engines and put them on chassis dynos, and got an average of 35hp less than stated. The word spread, the lawsuits spooled up, and Ford was stuck modifying the existing cars with revised intakes, exhausts, and heads to get the power up, and it cost so much that they had to kill production of 2000 Cobras just to pay for the recalls (and a good percentage of '99s never made it in for recall, most ending up in storage).

Since then, Ford has always understated engine power numbers, which are borne out (at least as I understand it) by the dyno numbers. Waht I'm trying to do is understand how the discrepancy works, especially when one takes into account torque multilication thru the gearing.

SAE standard is to rate engine output at the crank; the new method (begun in 1972) forces manufacturers to base these numbers off a motor that is like it is in the car, with all accesories (power steering, water pump, air conditioning, air pump, etc), unlike pre-'71, when they measured engine output with a motor that had NO accessories (even the waterpump was off the block).
__________________
People should not be afraid of their governments. Governments should be afraid of their people.--V


Men heap together the mistakes of their lives, and create a monster they call destiny.
--John Hobbs


~~~ ~~~ Tea[m] Pyratex ~~~ ~~~
Old 08-30-2004, 09:10 PM Tex Arcana is offline  
Reply With Quote
#229  

SemperFly
 
SemperFly's Avatar
 
Quote:
Originally Posted by Tex Arcana
Actually, people use chassis dynos because there is no other alternative without lost of cost and effort. THey also use them to evaluate mods and tunes, to be sure the work done enabled gains. So it's reasonable to expect that the dyno produces accurate results, irrelevant of the method used.
I see your point.
Old 08-30-2004, 09:12 PM SemperFly is offline  
Reply With Quote
#230  

SemperFly
 
SemperFly's Avatar
 
Quote:
Originally Posted by Tex Arcana
Waht I'm trying to do is understand how the discrepancy works, especially when one takes into account torque multilication thru the gearing.
What discrepancy? The torque multiplication through gearing is corrected by the dyno's computer.
Old 08-30-2004, 09:14 PM SemperFly is offline  
Reply With Quote
#231  

akromix
 
Quote:
Originally Posted by demosh
But I am talking about wheel torque. And those are the numbers at the wheels in first gear in Saab 900s when the engine is at its torque peak. I fail to see any mistakes in my calculations.

http://superstang.com/horsepower.htm

read up.

edit: fuck...beaten. Damn you SFC for being on another forum that I'm on as well!
__________________
2edd33cc552881e36186f70a03c5108f

Last edited by akromix; 08-30-2004 at 09:19 PM..
Old 08-30-2004, 09:14 PM akromix is offline  
Reply With Quote
#232  

Tex Arcana
I am a mean disrespectful person hiding anonymously and need an attitude adjustment.
 
Tex Arcana's Avatar
 
Quote:
Originally Posted by SFC
btw, I'm going to lift, but here's a webpage you can read if you really want to know how it all works out tex and demosh:


Gearing does not change how a dyno measures rear wheel torque. Because a dyno is measuring torque as a measurement of work, not force, lowering gears increases how quickly the work is done (the dyno spins up faster) but lowers the amount of work done (the increase in speed is not as great).

for a complete explanation see a web site I created a while back.

http://superstang.com/horsepower.htm





*and if you really want I can try and convince him to come over here if you decide you STILL want to argue after reading all of that page.

Excellent article, and I see the point. Especially this:
Quote:
Originally Posted by http://superstang.com/horsepower.htm
But the torque at the dyno and torque at the engine are 2 different things, and I think this may be where some confusion is. The dyno measures the applied torque at the drum, which is higher in first gear. But the speed at the drum is lower, so (again ignoring the losses) the HP *should be* the same. But then the dyno is also measuring the engine speed (RPM), so it takes the dyno measured power, then goes back and calculates the "engine torque" from the engine speed and dyno HP. The "torque" reported by a chassis dyno is really meaningless, since it's neither the torque measured at the engine (how could it be?), nor the actually torque measured at the dyno drum (that would include the gear multiplications, so unless you have a 1:1 rear axle ratio in addition to a 1:1 trans ratio, the rwtq reported is certainly NOT the actual torque at the rear wheels).

The real-world example he cites is an excellent method of pointing out the weakness of the chassis dynos. And shows how the torque numbers derived are almost bogus, especially in the face of gearing multiplication.

But, overall, it's an excellent read, and a great source for information.

And, fuck YES I want him to come over and jump into this. I wanna pick his brains...
__________________
People should not be afraid of their governments. Governments should be afraid of their people.--V


Men heap together the mistakes of their lives, and create a monster they call destiny.
--John Hobbs


~~~ ~~~ Tea[m] Pyratex ~~~ ~~~

Last edited by Tex Arcana; 08-30-2004 at 10:00 PM..
Old 08-30-2004, 09:57 PM Tex Arcana is offline  
Reply With Quote
#233  

Tex Arcana
I am a mean disrespectful person hiding anonymously and need an attitude adjustment.
 
Tex Arcana's Avatar
 
Quote:
Originally Posted by FlyNavy
What discrepancy? The torque multiplication through gearing is corrected by the dyno's computer.

So, we're getting rear-wheel horsepower, but crank torque?? No, not even close.

I just reand the superstangs article.. sheds alot of light. However, I'm not 100% satisfied, because I want accurate numbers on both ends. And Iw ill do my damnedest to push this until I find an accurate correllation, or a way toturn the observed numbers to decent crank numbers, within a reasonable deviation.
__________________
People should not be afraid of their governments. Governments should be afraid of their people.--V


Men heap together the mistakes of their lives, and create a monster they call destiny.
--John Hobbs


~~~ ~~~ Tea[m] Pyratex ~~~ ~~~
Old 08-30-2004, 10:04 PM Tex Arcana is offline  
Reply With Quote
#234  

SemperFly
 
SemperFly's Avatar
 
Quote:
Originally Posted by Tex Arcana
So, we're getting rear-wheel horsepower, but crank torque?? No, not even close.

I just reand the superstangs article.. sheds alot of light. However, I'm not 100% satisfied, because I want accurate numbers on both ends. And Iw ill do my damnedest to push this until I find an accurate correllation, or a way toturn the observed numbers to decent crank numbers, within a reasonable deviation.
What? When did I say you were getting wheel hp when getting crank torque?


You're right, that article does clarify things immensly. My suggestion is to call DynoJet and Mustang Dyno and talk to someone there. Ask for the email address of an engineer or a design head and pick their brains. No one knows how these systems work better than the guys who designed them, right?
Old 08-30-2004, 10:10 PM SemperFly is offline  
Reply With Quote
#235  

demosh
 
Quote:
Originally Posted by Tex Arcana
So, we're getting rear-wheel horsepower, but crank torque??

Youre getting an estimation of crank torque. A scientific guess based on observed facts.
__________________
[M] Finnish Crew
ME > You
Old 08-30-2004, 11:40 PM demosh is offline  
Reply With Quote
#236  

THE-SA1NT
 
16 pages for this?
__________________
1998 Crown Victoria P71 Police Interceptor 4.6L V8
1988 BMW 735i 3.5L I-6 *sold*
1989 Maserati TC 2.2L Turbocharged, Intercooled I-4
1977 Datsun 280Z 2.8L N/A I-6
1979 Corvette 350c.i. SBC
1982 Porsche 924 2.0L I-4
Old 08-31-2004, 07:44 AM THE-SA1NT is offline  
Reply With Quote
#237  

SFC
 
Quote:
Originally Posted by Tex Arcana
Excellent article, and I see the point. Especially this:


The real-world example he cites is an excellent method of pointing out the weakness of the chassis dynos. And shows how the torque numbers derived are almost bogus, especially in the face of gearing multiplication.

But, overall, it's an excellent read, and a great source for information.

And, fuck YES I want him to come over and jump into this. I wanna pick his brains...


I believe he did as nohuman or nonhuman or whatever? Or is that someone who was already here?
Old 08-31-2004, 10:12 AM SFC is offline  
Reply With Quote
#238  

SFC
 
Quote:
Originally Posted by demosh
Youre getting an estimation of crank torque. A scientific guess based on observed facts.


16 pages and you still don't get what EVERYONE has been saying, it isn't crank torque, it's wheel torque. it's an estimation of the torque the engine puts out minus the power robbed from the fucking drivetrane. It isn't crank, it won't ever be crank, give it up. You haven't read the page I posted, and you haven't called dynojet, until you do both, stop posting. You're just being a fag troll now.
Old 08-31-2004, 10:15 AM SFC is offline  
Reply With Quote
#239  

nonhuman
 
Quote:
Originally Posted by SFC
16 pages and you still don't get what EVERYONE has been saying, it isn't crank torque, it's wheel torque. it's an estimation of the torque the engine puts out minus the power robbed from the fucking drivetrane. It isn't crank, it won't ever be crank, give it up. You haven't read the page I posted, and you haven't called dynojet, until you do both, stop posting. You're just being a fag troll now.

It's an estimation of the torque the engine puts out (at the crank) minus the power robbed from the fucking drivetrane (sic).

...

That's what he meant by crank torque. Calm the fuck down. Remember that torque changes with gearing, so it can't be the torque at the wheels.

Once again, to quote that website:
Quote:
But the torque at the dyno and torque at the engine are 2 different things, and I think this may be where some confusion is. The dyno measures the applied torque at the drum, which is higher in first gear. But the speed at the drum is lower, so (again ignoring the losses) the HP *should be* the same. But then the dyno is also measuring the engine speed (RPM), so it takes the dyno measured power, then goes back and calculates the "engine torque" from the engine speed and dyno HP. The "torque" reported by a chassis dyno is really meaningless, since it's neither the torque measured at the engine (how could it be?), nor the actually torque measured at the dyno drum (that would include the gear multiplications, so unless you have a 1:1 rear axle ratio in addition to a 1:1 trans ratio, the rwtq reported is certainly NOT the actual torque at the rear wheels).
Old 08-31-2004, 12:42 PM nonhuman is offline  
Reply With Quote
#240  

Reply


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump



All times are GMT -7. The time now is 05:50 AM.



Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.