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Discussion Starter #1
Hello everyone,

I've been sick in the past few days and was just sitting on my couch resting all day every day! so to kill some time I've started googling around about tq and hp and read about cars that have different engine setups. My simplistic view of tq is that tq moves mass, hp is how the car speeds up. I found 3 different engines in 3 different cars that kind of show which is the more significant measure of power. The 3 engines are:

Cadillac CTS-V : SC'ed V8 556 hp / 551 tq
BMW M5 : V10 N/A 500 hp / 383 tq
Challenger 392: V8 N/A 475 hp / 470 tq

Getting 1/4 info from motortrend's tests:

CTS-V: 12.30 @ 117
M5 : 12.50 @ 115.3
392 : 13.00 @ 111.3

Now I know some people here might feel offended by MT's 1/4 result for the 392 (I found a video where it made 12.44 @ 110 still trap speed is less than MT's) but for consistency I chose MT's numbers.

Now taking the M5 V10 engine as the base for comparison, all three cars are in the same weight range. What strikes me is that even though the CTS-V has 170 Ib-ft tq more than the M5, they are still comparable and close. the 392 has about 90 Ib-ft tq more than the M5 but its also comparable and the M5 has better 1/4 results. my conclusion was that what makes the CTS-V faster is the 51 hp advantage over the the M5. and what makes the M5 faster than the 392 is the 25 hp advantage over the 392.

I read so many posts stressing on tq, but from the above numbers it seems like hp is more significant than tq. I think tq to a certain level becomes irrelevant and maybe pose more traction issues. both the 6.1 & 5.7 hemi's have about 25 Ib-ft & 40 Ib-ft tq mow than the M5 respectively but neither stand a chance against the M5.

I hear that what makes the 392 a different beast is the tq across the power band, but I think what makes the 392 faster than the 6.1 is primarily because of the extra 50 hp. and what makes the 6.1 faster than the 5.7 is simply the extra 40 hp.

I thought maybe the M5's V10 is more sophisticated than the LSA on V and the 392, but it doesn't matter how the engine was built, hp and tq numbers are universal, right?

One last thought, If I am cruising and keeping the rpm at peak tq point and the and punch it, what role do the tq and hp play in this situation? I assume tq is what would push me back to my seat & hp is what would keep the car moving faster.

Please don't make this thread about your own experiences and 1/4 numbers, nor become defensive about the Hemi. I'm trying to understand theoretically how tq and hp factor in car performance.

Thank you,
Bader
 

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Interesting question and one that has been debated probably since the invention of motors (or engines). Hot Rod Magazine did an extensive explanation in this article. As to the car manufacturers claims, I would take those with a grain of salt. Car makers have been well know to underrate power in the past and I suspect overrate power when its a selling point for a car.

Another problem... even with our guys on this forum that do extensive mods its pretty well known that different dyno's are going to yield different results even on the same cars.

With the 1/4 mile times you noted there was a .7 difference between the three cars. 7/10th could be the result of the environment they were run in, different tracks, different traction issues, driver skill, any number of things that could skew the results. Even Motor Trend has different numbers for the same car depending on which article you read and what the comparisons are being made to.




http://www.hotrod.com/techarticles/hrdp_0401_torque_horsepower_guide/index.html
 

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Torque is what moves your car, Hp is a product of torque. There are so many variables it's ridiculous but it's about how much power, where it is and how you use it. The driver is a HUGE part of it too.
Also wouldn't think much of those 1/4 times in those magazines, they get those cars for a few hours at the track one day and have to spend that time learning how to drive it.
 

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Discussion Starter #4
That hotrod mag article had a great perspective on tq and hp. I just want to say I gain the purpose is not telling which car is faster, may be the CTS-V is the fastest but the M5 and the 392 are comparable are comparable. the reason I picked these cars is that they all about the same weight, M5 41**, CTS-V & 392 42**. the difference is in the hp/tq numbers. specially the torque. the M5 is way behind the other two yet it pulls as hard as both the 392 and the CTS-V.
 

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This may be easier to wrap your mind around, by considering that hp and torque are not entirely different things:

Big torque is what moves the car, while big hp is just the presence of that same torque moving the car on the top end of the engine's powerband (high rpm).

Torque is responsible for lurching the car off the line, while hp is what keeps the car pulling hard as rpm's rise all the way to redline.
 

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Torque gets you moving...

Horsepower keeps you moving...

You can't have one without the other, they will always balance out at 5250RPM

But you take a diesel that makes 800LB FT of torque and weighs in at nearly 8000LBS and run 11's in the 1/4 mile.... "Torque makes weight disappear"
 

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Gearing makes a difference too. The 1/4 only gives one metric of performance. One can tune a car specifically for the 1/4 and sacrifice everything else. The balance is why we have so many different cars/performance. Torque is what gives you the insane Gs at launch without having to wait for the engine to build RPM as much. Just look at the old 440s, they had 390hp and 490torque! And its generally underrated!
 

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Discussion Starter #9
Gearing makes a difference too. The 1/4 only gives one metric of performance. One can tune a car specifically for the 1/4 and sacrifice everything else. The balance is why we have so many different cars/performance. Torque is what gives you the insane Gs at launch without having to wait for the engine to build RPM as much. Just look at the old 440s, they had 390hp and 490torque! And its generally underrated!
Maybe thats better a setup for race cars, but for street cars with street tires you can't utilize all that torque at launch. even on our stock SRT's we have to ease up on the throttle to keep the tires from spinning. I saw reviews for the 6.1 where their best 0-60 was 5.5 sec! in other reviews the car made 4.7 sec. I know friends who have moded SRT's 6.1 street race the M5 and they can only keep up with it in one gear. thats rolling from 50 or 30mph. After the M5 flies away. though the more than 40 Ib-ft torque should atlas give the hem a head start but it doesn't do much in reality. Same thing with the CTS-V, a 170 Ib-ft of torque should kill the M5, but if you see 1/4 numbers or 80 to 120mph acceleration they are pretty much comparable.

so I'm thinking a 500tq 600 hp car is easier to drive than a 600 tq 600 hp car and it would be as fast. I wonder if I put the M5 V10 engine and its drivetrain on my car, It would be as fast as the 392.
 

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Maybe thats better a setup for race cars, but for street cars with street tires you can't utilize all that torque at launch. even on our stock SRT's we have to ease up on the throttle to keep the tires from spinning. I saw reviews for the 6.1 where their best 0-60 was 5.5 sec! in other reviews the car made 4.7 sec. I know friends who have moded SRT's 6.1 street race the M5 and they can only keep up with it in one gear. thats rolling from 50 or 30mph. After the M5 flies away. though the more than 40 Ib-ft torque should atlas give the hem a head start but it doesn't do much in reality. Same thing with the CTS-V, a 170 Ib-ft of torque should kill the M5, but if you see 1/4 numbers or 80 to 120mph acceleration they are pretty much comparable.

so I'm thinking a 500tq 600 hp car is easier to drive than a 600 tq 600 hp car and it would be as fast. I wonder if I put the M5 V10 engine and its drivetrain on my car, It would be as fast as the 392.
You need to factor in tires and tire size. The SRT for its HP/tq has rather narrow tires in my opinion. You can easily spin these, and with a much wider tire, that wouldn't be as easy.

I had an 05 GTO, 400 HP/tq, and an 07 Corvette, same 400 Hp/tq, and while the Vette weighed way less, it also had huge tires in comparison. The Vette would just launch itself, and was actually hard to spin the tires. That car just took off as soon as you gave it gas. The GTO, would just spin and spin - and if you weren't pointed straight, it wasn't pretty!

You're right that in a street car, too much tq or HP and its a waste. And of course, how much do you really need to drive to work or go to the store? Its fun to have, but really, there is a limit where you really can't use any more for a pure street car. On the track, thats different.
 

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Torque gets you moving...

Horsepower keeps you moving...

You can't have one without the other, they will always balance out at 5250RPM

But you take a diesel that makes 800LB FT of torque and weighs in at nearly 8000LBS and run 11's in the 1/4 mile.... "Torque makes weight disappear"
Yes, beware the guys in "BOMBed"* diesel pickups. You're making me miss my 05 Ram. A 750 lb diesel engine can make insane power for less $, but it would be very easy to melt pistons with all that heat if you don't know what you're doing.

*Better Off Modified, Baby!
 

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Not to get all mathy on people here, but torque and HP are directly related, such that HP is a product of torque and engine RPM and nothing else. Meaning, if at a certain RPM two different engines produce the same torque, they will then be producing the same HP.

Kean's link above lays this out pretty nicely. In short, this is how it breaks down:

(Torque in ft/lbs. x RPM) / 5,252 = HP

The "5252" number is also explained in that article. It's a conversion factor that's the result of converting engine RPM from minutes into seconds in units of radians, along with the definition of HP being 550 foot-pounds per second.

tl;dr: you can learn everything you need to know about an engine's HP output by knowing the torque curve and vice versa.
 

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what you haven't considered in this comparison:
How that power is brought to the pavement.

A) The M5 has one of the most perfect launch controls available (like e.g. the Nissan GT-R)
B) The M5 has a sequential gearbox called SMG with 7 usable! gears.
==> Why usable? When you look at the Challenger automatic gearbox you have 5 usable gears. all close together. all good, but only 5.
When you look at the 6speed Challenger you don't have 6 but only 5 gears. 6th is far away from an usable gear - 5th nearly, too as the gap between 4th and 5th is very long (all 6speed Challengers reach their top speed in 5th)

Big gaps between gears costs you a lot of time.

AND:
C) Shift times. SMG is much faster than any auto or manual ever can be.

So yes. When you stay in one gear perhaps the CTS-V or the Challenger pull stronger than an M5. But the M5 has so many perfectly arranged gears that it will kill the other cars on the 1/4 mile - even worse on a 1mile race.
 

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Much of what torque does is part of the fact that a longer stroke on the same size bore will give you more torque (force multiplied by length of crank web on the crankshaft equals torque.) Higher torque, lower RPM engines require fewer gears (hence the 4+2 gearset on the TR-6060 in our cars) and should last longer, although that may be academic in most non-exotics. High rev racing engines are maintenance hogs by nature, due to the engine speeds and they tend to run high in that band to boot. We tend to run closer to the middle of the speed band, closer to our highest torque numbers on the highway.
 

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Torque is why my 1600cc Harley can beat most sport bikes off the line in traffic light to traffic light races. Horsepower is why those same sport bikes scream past me on the highway. In a country where most speed limits are set at 65 mph, I would sacrifice HP for TQ every day and twice on Sunday. My high comes from acceleration, not speed (though going really fast would be nice if the law permitted.)
 

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Discussion Starter #17
what you haven't considered in this comparison:
How that power is brought to the pavement.

A) The M5 has one of the most perfect launch controls available (like e.g. the Nissan GT-R)
B) The M5 has a sequential gearbox called SMG with 7 usable! gears.
==> Why usable? When you look at the Challenger automatic gearbox you have 5 usable gears. all close together. all good, but only 5.
When you look at the 6speed Challenger you don't have 6 but only 5 gears. 6th is far away from an usable gear - 5th nearly, too as the gap between 4th and 5th is very long (all 6speed Challengers reach their top speed in 5th)

Big gaps between gears costs you a lot of time.

AND:
C) Shift times. SMG is much faster than any auto or manual ever can be.

So yes. When you stay in one gear perhaps the CTS-V or the Challenger pull stronger than an M5. But the M5 has so many perfectly arranged gears that it will kill the other cars on the 1/4 mile - even worse on a 1mile race.
The M5 numbers I mentioned were from a 6 speed manual. I am not comparing cars here. My concern here is the hp/tq combination. The numbers basically say what makes the car go faster is hp. I guess the amount of torque needed depends on the weight of the car. based on the numbers in my post, 383/470/551 Ib-ft doesn't make much of a difference for a car that weighs 4k Ibs.

2009 BMW M5 vs 2009 Cadillac CTS-V - Specs - Comparison - Motor Trend
 
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