Yeah, please don't. Seems the last time you tried that, we found your claimed (fixed hp) loss remained within 1% with over 100hp engine difference.

And now with quite a few 2010 ZR1 dyno results out there, we are still seeing that loss percentage remain quite consistent.
On the dyno, the 350hp C5 nets about 300rwhp - loses about 50hp (14% loss).
The 638hp ZR1 seems to be averaging 540-550rwhp on the rollers - loses nearly 100hp (but still a 14% loss).

Loss percentage with nearly double the input power continues to remain within 1%. Amazing if not predictable.

Good thing you didn't bring that topic back up.

 

That's true, if we're just talking about rear wheel torque.

In the F1 engine versus semi engine analogy, the F1 engine produces lower torque, but higher rear wheel torque, because the high rpm potential of the engine allows use of a lower gear ratio, and more torque multiplication between the engine and the wheels.
Any time one can move the operating range of the engine up without too great a reduction in torque, this advantage comes into play.

What really moves the car is rear wheel torque at a given speed (allowing for differences in tire diameter) which translates to force at the tire contact patch. Engine torque bears only a very sloppy relationship to this. Horsepower bears a very direct relationship to this.

Engine torque alone kinda sorta doesn't give much information about how well an engine will move a car, except that knowing where the torque peak is will allow knowing at what rpm the acceleration will be highest if you were to stay in one gear. So it really doesn't say much unless you include the rpm where it's produced. Once you do that, you're really talking about horsepower.

 

btw, you're right... and what I said above is true only if you have a constant gear ratio... mechanical gear reduction multiplies torque - so the key is that when you include gear reduction, you'll get the most torque at the wheels and hence accelleration at peak horsepower...

 

cool - and thanks. we were posting at the same time but you made it clearer

 

Here's an example:

You have one engine making 600 torque at 3000 rpm. This goes through a 3:1 gear reduction, producing 1800 rear wheel torque.

Another engine makes 200 torque at 9000 rpm. This goes through a 9:1 gear reduction to produce the same rear wheel speed, and produces identical 1800 rear wheel torque.

Both engines happen to produce identical horsepower, which is 343, so horsepower correlates very well with the motive potential of the engine, while torque alone does not.

That said, I understand what people mean when they talk about a "torque" engine, which would be one that produces good horsepower at lower rpms.

 

The guys on this forum are not the first & certainly not the last to try to straighten out the confusion & myths about "Torque vs. HP". Many of you are struggling in trying to explain & put all in perspective in just a few sentences. Not an easy task.

Fortunately there are a few articles on the topic. I'm a physics/engineering/car-guy so I gave a quick read to a few, discarded the ones with their own obvious biases & obvious errors...... & I came up with 4 worth a read.

You certainly don't have to read them all, & you will get bored if you duplicate all the math, but give a quick read. You may find some bits that just click & make clear some of the underlying concepts & facts needed to deal with this discussion.

http://www.mustangsandmore.com/ubb/D...orqueVsHP.html
His 1st paragraph alone is helpful in restating how the "torque vs. HP" question really should be asked

http://www.vettenet.org/torquehp.html
The benefit of making max torque at high RPM

http://www.largiader.com/articles/torque.html/

http://www.epi-eng.com/piston_engine...and_torque.htm

Mike

...... Read more.. Argue better & more easily.....

 

I'm really confused. If I have a 2000 vert with just bb exhaust and wanted to go quicker than a 2010 comaro or ford(at the strip) Just by changing gears would not change my 0-60 times. This is because I am not increasing hp? I was to understand that different length header move the torque up or down. So to make me faster with a stock motor this can't be done? Sorry for not being a gear head.

 

Yes, changing the gears has the potential to reduce 0-60 times, if you have the traction, and if it doesn't require an additional shift.

Dropping the rear end ratio will increase torque to the rear wheels in first gear. It will do it in the other gears too, but it starts to be a wash, because you will need to shift to a higher gear at a lower mph, and each time you shift, the torque to the wheels drops. So rear wheel torque versus time, and rear wheel torque versus mph can average out to be about the same, once you're out of first gear.

 

Cant we just throw power out the window and just talk in terms of torque?

In a mechanical motor you can have torque without power, but no power without torque, and isn't power just a way to explain how much work a certain measurment of torque at x rpms can perform?

Don't dynos measure the torque and calculate power based on that torque?

For instance you can come up with an arbitrary torque number at a certain rpm range and assign it a power figure:

Say a semi motor makes 1000 lb/ft at 2000rpms. To calculate its ability to do work at that point you multiply torque by RPMs and divide by 5250 and get 380.95hp.

You can do that for any measurment of torque at a specified RPM and come up with the power figure, so the power is dependent on the amount of torque and where it is in the rpm range. So I can understand where the guys like to talk torque because if you know where the torque is then you can identify the power.

 

Cool idea. I'm not sure where you'll buy torque to fill the tank though.

Peter

 

Yes, you gave torque and rpm so the number means something.

Yes again, if you specify the torque and the rpm then you know what you have. If you just say, "I want more torque" the it's an incomplete statement. Would you be willing to accept a 2000 ft-lbs torque peak at 500rpm if you had to give up ever bit of the torque (and power) you have above 1000rpm? You said you wanted torque....

Peter

 

Sure, but at some point people will wonder why all the low torque cars are running the fastest.

 

True, but isn't the same true when you hear guys saying, "I want more power" You need to know where they want the power and what the use will be b/f you can make decisions on how to build the motor

 

I want a high Kilowatt (Kw) engine.

 

Then you're doing it wrong.

 

I like that rpm/5250 multiplier effect. It shows how torque at a higher rpm is better than torque at a lower rpm assuming you build the car to make use of it.

I never talked about the rpm part of the formula much but the same applies to the rpm and the HP. There is a direct relationship between rpm and HP too. If the torque remains the same then the HP increases by the same percentage as the rpm increases.

If you think about it even further, the HP will increase with rpm as long as the torque doesn't decrease more. So, even if the torque curve is dropping at the higher rpm's, you still want to operate the motor at those higher rpm's because the HP is higher.

Peter

 

Yes, when you specify I want this torque in this rpm range then you are basically asking for the same thing as this power level in this rpm range.

One point I was trying to make is that you can't just want torque, you have to say where you want the torque. You can just want more HP because HP measures how quickly the car will accelerate. when you say you want. The other point is that saying something like "I want torque" or "I'll give up HP for torque any day" is nonsense.

Power is power regardless of rpm. 100hp at the crank translates to (100hp - drivetrain losses) at the ground. It doesn't matter what rpm the engine created the HP, it goes directly to moving the vehicle.

Saying "I want more torque" without giving the rpm detail is nonsense, because you might be giving up power and you might accelerate slower.

Saying "I'll give up HP for torque any day" is also complete nonsense. If you increase the torque at some rpm then you also increased the HP at that rpm.

Saying something like "I'd give up a little peak HP to increase my torque in the 1500-3500rpm range" is fine. The requirement for more torque and the rpm where it's desired is given. Once you say "I want more torque in the 1500rpm to 3500rpm range" you have also basically said you want more HP in that range too. "I gave up peak HP to gain lower end HP".

I also know that when some people post "I'd give up HP for torque" any day that they mean giving up peak HP for lower end torque and that many of the people reading that statement also understand what they meant. But, some of the people reading this thread probably don't understand the HP and torque relationship. So, just throwing out "buzz" phrases does an injustice to those readers. If you want to be an "expert" that shares their opinion then at least try to make it educational and not something that can confuse or leave others still lost on the whole concept. I'm trying, but I really have no idea if I'm having any sucess.

Lets try not to pull the specifications needed for building an engine into this discussion.

Peter

 

Some day wanting one or not might not count.

Peter

 

By this do you mean torque and horsepower relationships b/t different bore and stroke combinations? Such as what would be the advantages of an oversquare motor vs an undersquare motor? Should these details be left out to avoid any further confusion?

P.S. It was fun playing devil's advocate for a while which I think gave you a chance to better explain your views, or at least repeat them again which will help people who are interested in this topic to further understand it.

 

Of course they should.

Peter