From a drag racing perspective and simplified:

More torque = lower ET's in the quarter mile
More HP = higher MPH at the end of the quarter mile

 

i agree. full torque at ZERO RPM has some interesting possibilities....

 

Since we are into analogies...

You can also think of it this way:

Say you have a powerlifter and an olympic sprinter.
They both need to carry 500 gallons of beer from point "a" to point "b".
The powerlifter slowly carries keg after keg from a to b.
The sprinter quickly carries twelve pack after twelve pack from a to b.
After one hour, they both have delivered 500 gallons to point a.
The powerlifter and the sprinter are rated the same horsepower.
The powerlifter did it with strength ("torque"), but less speed ("rpm").
The sprinter did it with less strength but more speed.

Now if the powerlifter could run with the kegs as fast as the sprinter with a twelve pack, you would have some serious horsepower. (Or if the sprinter could run as fast with a keg as with the twelve pack, again major horsepower, same thing).

Now if you forced the powerlifter to only carry twelve packs or the sprinter to carry kegs, they wouldn't be able to get as much done in an hour. This is the same as screwed up gearing in a car.

As far as racing goes, horsepower combined with proper gearing is what it comes down to. On the street, a wimpy fast sprinter running around like a maniac is annoying compared to a powerlifter slowly carrying a bigger load.


[Modified by Vince Ivanc, 10:17 PM 6/5/2002]

 

Uggg.....

what HE said...

:)

 

Vince, Nice!!

But I would take the beer from the sprinter because it will be colder, he got it there quicker. :lol:

 

Everything makes more sense with beer :lol: . :cheers:

 

i love this analogy...i have a friend who uses beer to explain just about everything! i own a chassis dyno,what i tell my customers is this..torque is measured and horsepower is calculated..but now that i have this analogy they'll probably relate! good subject and good content! :)

 

Heck...I'm smarter than I tought. Because I already knew that. :yesnod:

But very well said. :smash: :cheers:

 

Thanks guys....great explanations and analogies...I'll be ready for anyone at the local cruise nights now!!! :cheers: (I think the little guy on the right holding the beer is the sprinter :lol: )

 

I'm glad you brought up cruise nights. I think the local hot rodders (non-vette drivers) think we have more money than brains and buy an "already" fast car because we don't know how to mod one.


I used to drive my 86 maro around with a 550HP motor and I got a lot of respect from these guys. Now tha I am rolling with class in my 94 vette I notice they are a lot less "friendly".

:mad

 

Red, we have a few of these at our cruise...affectionately known as "gearheads"...guys who pursue HP at all costs...including comfort, class, and driveability (ie tubbing, blowers, etc). But hey, to each his own I say. Its equivalent to a body builder and an athlete...sure you can outlift me but meet me at the oval for a few laps :D . I used to stop and look at their cars just for the sake of the hobby but when I noticed they just kept walking past mine, I stopped giving them the satisfaction...takes all kinds I guess

 

Red94Vette,

""Deep breath….

I can write a program that simulates a car accelerating without using one single horsepower number, not one. I use the torque curve to calculate the acceleration. So if it’s torque that moves our car, why do we throw around horsepower figures?""

Then you have started out all wrong because your aren't using TQ to find acceleration you are using HP already from the get go. A TQ curve with rpm is a HP curve actually. You are plotting TQ AND RPM which is HP. On this curve you can see the elements of TQ and RPM separately but together they represent HP.

If I just give you TQ by itself you can figure nothing. If I give you a chart of TQ vs RPM I have given you a POWER curve.

I'll just give you TQ by itself and then see how you figure acceleration. One car has 300 ft pounds of TQ and the other has 400 foot pounds of TQ They are at a 60 mph roll. Which will accelerate faster? They are outfitted identically with 6 speed transmissions with normal gears and weigh the same and have the same aero drag. Like any car you can use different gears at the same speed depending on how you drive etc.

Like I said just tell me which one would accelerate faster since you know the TQ that both engines have? Tq figures by themselves are meaningless in general. HP which includes TQ AND RPM WILL tell you how hard a given car can accelerate because they tell you the work vs time potential of the powerplant. That fact sometimes confuses people but that's just the way it is unfortunately. Most racers DO understand this.

TQ is more of a reflection of the engine's size and it's volumetric efficiency. Big engine have more TQ than smaller ones in general but may or may not actually have more power. It is nicer to have bigger torquier engines since they do not need as much RPM to make the same power. They are more reliable and generally more impressive since they build power sooner and closer to off-idle than do smaller higher rpm powerplants. But remember that an F1 powerplant has virtually no TQ and yet is extremely fast since it can turn high rpm. The same goes for gas turbines and such which can fly helicopters and power tugboats but also have very low tq yet high rpm. You just have to gear them differently.

You can always gear your TQ up to what you need at the working end of the machine but you can't gear hp up!

 

The one with more torque will accelerate faster at the same speed with same gears.

Want to know the equation for acceleration?

Acceleration = [(Engine Torque * Tranny Gear * Rear Gear / Tire Radius) - Drag Force - Rolling Resistance)] / (mass of car + inertias)


No horsepower there my friend, no RPM in the equation. It's one torque value.


[Modified by Red94Vette, 12:17 PM 6/6/2002]

 

I'll just give you TQ by itself and then see how you figure acceleration. One car has 300 ft pounds of TQ and the other has 400 foot pounds of TQ They are at a 60 mph roll. Which will accelerate faster? They are outfitted identically with 6 speed transmissions with normal gears and weigh the same and have the same aero drag. Like any car you can use different gears at the same speed depending on how you drive etc.

Sure I can solve that problem (assuming you mean they are making that torque at this instant in time, side by side in 2nd gear).

Since you told me their speed I can figure out the drag force and the RPM.

At 60MPH with 3.45 gears in 2nd gear in a ZF 6spd you are at 5143 RPMs.
At 60 MPH you have 70.6 pounds of air resistance.

The car with 400 ft lbs will accelerate at .480 g's (this is 391.7 HP)

The car with 300 ft lbs will accelerate at .353 g's (this is 293.8 HP)





[Modified by Red94Vette, 2:31 PM 6/6/2002]

 

Red , you are assuming that the two engines are the same or can turn the same rpms, Racer 7088 said nothing about the type or size or rpm capability of either engine. Look at what he said again....... :seeya

 

Here's what I assumed in the example above. They are at the same RPM. IF they are at the same speed with same gearing their RPMs will be the same.

Now when he told me one made 400 and the other 300 lbs of torque I took it that they are making that at the instant in time we are talking. What good is that information if he told me it made that at some arbitrary RPM that has nothing to do with this example?

Now that was his point of posting this, is to prove that... But, on my original post I said I use a torque curve to accelerate a car, not just torque. By torque curve I mean a plot of torque at different engine speeds. He is saying that is the same thing has horsepower.

I am saying there is no way to measure horsepower directly, that it is calculated and my drag race program doesn't use horsepower numbers, it uses torque vs rpm which the product of that is horsepower.

:seeya

 

You are assuming they are racing at the same rpm in the same GEAR (second) - gearing overall and in each gear is the same but each engine is capable of different rpm and power., I think he was saying you could have a much higher hp car with "only" 300 ft/lb of torque easily outrun the 400ft/lb car from 60 up because it has much more HORSEPOWER.

No flames.....and I liked your explanation and program......just trying to clarify...... :seeya

 

No flames.

I do understand his point. If you made 200 ft lbs of torque at 10,000RPM that is 380 HP. 200 ft lbs isn't a lot and if he didn't have a low gear that car would be a dog and a half.

The point he was making was he listed two different torque figures that could happen at any RPM.


I was being a little cranky and made a quick assumtion of they made that torque at the same RPM, just because I'm hard headed :lol:

Now here is the overall idea that he is saying and I am saying.

He said that my program DOES use horsepowe becaues if I use a plot of torque vs RPm then that is horsepower.

I am saying no, I am using a plot or torque and RPM. NO where in my program do I mulitply the two numbers and divide by 5252. That's how you calculate HP.

I was proving a point in my first post that I only used torque in the physics calculations.

He (in a way) makes it sound like you can measure horsepower directly and from that back out RPM and Torque. I didn't want anyone thinking that is the case.

no flames.. I just didn't want to confuse anyone.

:lol:

Here is how my program loop works:

1) Find speed of car
2) Use speed information along with tire and gears to find RPM
3) Look up on my RPM table and pull off the torque value
4) Use that torque value to accelerate the car to a new speed
5) see 1


[Modified by Red94Vette, 2:29 PM 6/6/2002]

 

Red94Vette,

You used HP in all your equations not tq. What if the car with 300 foot pounds was in a lower gear. Who says they both have to shift at the same rpm? Who says they are even capable of the same rpm? You just assumed that.

What if the engine in car a has 300 ft pounds Tq at a maximum engine speed of 7500 rpm and the engine in car b has 400 ft pounds at a maximum engine spped of 5000 rpm? Remember each car has the same trans but doesn't have to be in the same gear.

Horsepower is what matters. The only case where tq will win is where both cars are in the same gear at the same speed and at which one has more tq than the other which in turn means that it also has more hp at that speed.

Show me an instance where a car with a 225 hp engine with 575 ft pounds of tq will beat an engine with 375 hp and 550 ft pounds of tq. Remeber this first engine has 25 more foot pounds of tq so it should be faster right? Maybe at one speed or way down lower in the same gear it might be for a fraction of a second but then what about higher in the rpm band? See we have a choice as to what gear we pull the car down to when we're accelerating or racing. Higher hp equals higher RWTQ when geared right or when you have the ability to keep it in the lower gear longer as we obviously do with a higher hp engine because if we didn'y have the rpm we wouldn't have the higher hp in the first place would we?

 

...and I thought I was going to have a boring afternoon :lol: :lol: