HP vs TQ question

[Dwight]

I have done a search but have not found the threads I was looking for. So I'll ask the question.
Can someone explain the relationship of HP / TQ? A commend was made about HP being more important at the drag strip. Another commend about Nascar engines have 800 HP and 400 foot lb. of TQ. I understand that if you want to go 200 mph you need an engine that will turn high rpms to get you to 200 mph but you need TQ to push the car to that speed. What is the ratio?
Thanks
Dwight

[Bob In Ct]

For racing purposes, especially oval racing, it's all about HP! Torque defines the ability of an engine to do a certain job, HP defines how fast it can do it. 300 FT-LBS of torque is far more valuable at 5,500 RPM than it is at 2,500 RPM.

HP = (torque X RPM) / 5252

Bob

[DAVID GAGNARD]

I posed a similar question years ago to an ole mechanic and asked him to give me a answer that a dumb a$$ like myself would understand, he thought for a second and then said;

You know when your on the entrance ramp to an interstate doing about 20 mph???? then you accelerate to say 70 mph and blend in???? Torque gets you to 70 mph, horse power keeps you there once you hit your speed and level off...............

makes since to me..............

David

[richsd]

An favorite quote on the subject from a friend on another forum.

"Horsepower is how fast you hit the wall, torque is how far you take the wall with you."

Along those same lines:

"Understeer is when you hit the wall with the front of the car and oversteer is when you hit the wall with the rear of the car."

[Bob In Ct]

Torque has no time function, HP does! It's all about HP. Transmissions and differentials can always increase torque but they don't increase HP. 800 Ft-LBS is not very useful at 100 RPM (waterwheel effect). 400 FT-LBS at 6,000 RPM is far more valuable.

Bob

[xlr8or]

Originally Posted by Bob In Ct

Torque has no time function, HP does! It's all about HP. Transmissions and differentials can always increase torque but they don't increase HP. 800 Ft-LBS is not very useful at 100 RPM (waterwheel effect). 400 FT-LBS at 6,000 RPM is far more valuable.

Bob

Tell that to a guy with a diesel hauling 40,000 lbs in the trailer.

Both are very useful when used in the appropriate application. If the car is primarily street driven I prefer a wide torque band over a peaky horsepower curve. The track is a different animal and you want the HP up high in the RPM range where you will be running the engine.

[Jac Mac]

You cannot measure HP without knowing what Torque you have first.

Lets say for some crazy reason you decide you need 800 HP @ 7000rpm.
To obtain that you simply just keep developing the combination until you have
600 ft/lb of torque @ 7000rpm, you only get torque readings from the dyno, the HP is simply a calculation from that reading in conjunction with RPM with allowances for Temp-Humidity etc.

BHP = [(RPM x Torque) divided by 5250]

Torque= [(BHP x 5250) divided by RPM]

Jac Mac

[RedBarchetta]

I recall someone once telling me that "Torque gets you up to a certain speed and Horsepower keeps you there." Works in NASCAR.

[lovehamr]

In this same vein someone once told me this;

“You feel torque from the seat of your pants much more than you feel horsepower.”

The human butt can no more distinguish torque from HP than it can blue light from red light. In simplest terms we are dealing with power or energy, a force that moves you. These forces are expressed in mathematical terms thusly;

1 HP = 33,000 foot-pounds per minute (there’s that over time thing that Bob mentioned)
Or it could be P/hp=[T/(ft lb)][w/(r/min)]
5252
By the way, that 5252 is why nearly all dyno charts show the HP and torque curves crossing at that RPM.
Or it could be 746 watts
Or maybe 2,545 BTUs (British thermal units)
One BTU being equal to 1,055 joules, or 252 gram-calories or 0.252 food calories.
This means that 1 HP is also equal to 2684975 joules, or 63504 gram-calories, or 641.34 food calories
Presumably, a horse producing 1 horsepower would burn about 641 Calories in one hour if it were 100% efficient.

The point is that its energy, a force, what moves you, not some nebulous calculation as others have postulated.

Torque is the force applied to a lever, multiplied by its distance from the lever's fulcrum in our case a theoretical lever and a rotating fulcrum, or more simply:
T = r x F (whadaya know another calculated theoretical number)
Which is linier force multiplied by a radius. Of course this formula always assumes a perpendicular force axis to the fulcrum, something that just doesn’t happen in a reciprocating engine for more than a millisecond at a time.

From the Ole mechanic “You know when your on the entrance ramp to an interstate doing about 20 mph???? then you accelerate to say 70 mph and blend in???? Torque gets you to 70 mph, horse power keeps you there once you hit your speed and level off...............”

To put this into perspective the next time you want to accelerate really fast try shifting at your engine’s torque peak rather than the HP peak. It doesn’t take a rocket scientist figure out using which shift point will accelerate the car faster. This is because we’re talking about energy expended over time not a static applied force. To say that another way; I could put 84 pounds (that’s a Buell motorcycle’s peak output) of torque on the bike’s crank shaft with a ratchet handle, but I don’t think it’s going to accelerate too quickly and I doubt that the rider’d feel it to much in the seat of his pants either.

I find the whole argument over HP vs. Torque to be silly in the extreme because they are really one and the same, just expressed differently to show how the power is produced in any given engine for any given application. For instance a tow vehicle was mentioned; do we want high RPM power for our tow rig? I think not, we want it down low so that it’s managable and produces minimum wear on moving parts. How about the drag car? We want as much power as possible and since an internal combustion engine is in effect an air pump then we want as much air as possible to pass through the engine. All things being equal, the faster the engine is turned, the more air goes through it, the more power is made over any given period of time.

In summary, to disassociate HP and bow to torque is like saying that you really like chocolate cake but that chocolate is over rated. It just doesn’t make sense.

Steve

[Dwight]

OK Steve

Why is my Tq more than my hp? Would you look at my dyno chart and tell me what is happening and why?

Dwight
I hope you can see the picture of the chart

[Bob In Ct]

So I guess both tractors and bulldozers will be good at getting up to speed on entrance ramps. The Formula 1 guys are making a mistake winding their engines up to 19,000 RPM.

I can produce 300 FT-LBS of torque on my bicycle, why is it I can only get up to 25 MPH?

Bob

[Jac Mac]

Originally Posted by Bob In Ct

So I guess both tractors and bulldozers will be good at getting up to speed on entrance ramps. The Formula 1 guys are making a mistake winding their engines up to 19,000 RPM.

I can produce 300 FT-LBS of torque on my bicycle, why is it I can only get up to 25 MPH?

Bob

Do you really want my thoughts on this????

Jac Mac

[CSX 4027]

I just had this discussion with Tom Kirkham. At both VIR and Watkins Glen, the fastest 427 Cobra I have seen runs in the 2.08 - 2.09. We all know what the car weighs. The Gt 350's also run around the same. When I had 4027, my best time was in the high 2.12's at The Glen. My former Winston Cup car has run The Glen and VIR at 1.58 - 1.59. That's a whole lot faster and a whole lot heavier. It was 780hp/500tq.
I think most buidt Cobra's as street monsters with way too much torque. The last 427 we built as a standard bore/standard stroke dynoed at 551hp and 565 tq. The motor is a killer on the street but I would have preferred to kill the torque a bit, like to under 500 and bring up the hp. That would have taken a bigger cam making it less streetable. You can't have everything.
The cup motors are set up great. It would be neat to see what a well set up Cobra would do with real Cup Power and not a version of.
But.........going that fast in a car as unsafe as a Cobra as opposed to a cup car is a bit nuts also.
Cheaper,safer,faster to have a Cup Car

[Dwight]

OK It took a while but I found this link to a site that was posted on the FFR Form. With our Cobras there are other factor to consider, like aerodynamic, HP, torque and lots of other things that make us go fast. I think Mr. L.E. Mayfield has very interesting information for us.


Here is the link to the site, http://www.mayfco.com/cobra.htm
Dwight


Automotive Analyses
Return to Mayfield Motor Sports Homepage
Return to Automotive Analyses Homepage

FFCobra Forum Question: How fast is my Cobra with this much horsepower?
This also works for all vehicles, shhhh!



INTRO


Once upon a time, in a land far away, I was a huge fan of the original Cobra and it's final originator, Shelby. I went to the plant is Southern California, but at the time was a starving student or just out of school at Cal Poly, SLO. I could not swing the 6 grand or so, so I quietly walked away. Then I bought a used Tiger. Jeeze, I am off track and have just started this. Well, anyway, I spent an entire career with the Boeing Company doing odd jobs. Some of them involved aerodynamics and such.


Now I know how you all feel about your cars, Cobras, whether or not original or a reproduction. I know that many of you are true performance fans and have hopped up your cars to the n th degree. But, after all that hopping up, you find that there is little in the way of knowing just how fast it is or can be. Roads with the public on them just aren't the way to go and the drag strip just isn't quite enough either. What I have done for my Tiger, I am gonna try and do for you. I am going to develop a set of tools that you can use to figure it all out: "Just how fast will my Cobra go?"


Now you will have to go to his site to finish reading the article. With the charts it was to large to post here. Dwight

[RICK LAKE]

CSX4027 Steve how can you compare the two?? A fly brick, or barn door to a Nascar cup car that has been in a wind tunnel?? Come on. What's the CD on a cobra with what windshield? stock or the comp one. What's it on your Nascar cup car. Down force, cobra not much with comp windshield, car starts lifting at 125mph, Nascar front chin spoiler, rear deck spoiler, every piece of the body rounded and smoothed. And the best for last, was a complete roll cage in the cobra like the nascar car?? You put Boris Said in both car and let him race road course, then let's see where we are. Sorry Steve You left out alot of varibles. I would put Morris C's car or Steve's car from Run and Gun against the nascar car and take the less HP. You didn't say what tires where on these cars. I am stopping. You have been with cars for how many years, and you compare a throughbred to a quarter horse in a 1 mile race. Rick Lake Ps when are we going to the Manor for the buffet

[CSX 4027]

Tom & I were just having a casual discussion about it.
All differences noted, the Cobra just looks like it should be faster. Not even the Shelby Challenge Cars would beat a Cup Car. That too looked like it should too.
I just like the idea of the cup motor with less torque, more horsepower and more rpm's for the Cobra. I bet most would feel it more driveable and predictable on the track

[Bob In Ct]

HP = TORQUE x RPM / 5252.

Notice where the lines cross.

Bob

[Dwight]

To go 200 mph your engine has to turn enough rpms. You have a transmission, rear end gears and tire size to help.

I know it takes a certain amount of torque to get you to speed and keep you there.
Dwight

Second Strike Gearing Calculator

Specify Transmission and Rear Axle Ratio

Tremec TKO-600 5-speed (0.64 5th) 3.55 Rear Axle Ratio

Specify Rear Tire Size

255 Rear Tire Width 50 Rear Tire Aspect Ratio 16 Rear Rim Diameter

Speed (MPH) in Gears at RPM

Gear 1st 2nd 3rd 4th 5th
Trans Ratio 2.87 1.89 1.28 1.00 0.64
Overall Ratio 10.19 6.71 4.54 3.55 2.27
Split 1.52 1.48 1.28 1.56
Rev/Mile 8,142 5,362 3,631 2,837 1,816
1500 11 17 25 32 50
2000 15 22 33 42 66
2500 18 28 41 53 83
3000 22 34 50 63 99
3500 26 39 58 74 116
4000 29 45 66 85 132
4500 33 50 74 95 149
5000 37 56 83 106 165
5500 41 62 91 116 182
6000 44 67 99 127 198
6500 48 73 107 137 215
7000 52 78 116 148 231