Performance - Torque vs Horsepower

[2ndgenz28]

Build for Torque and HP will follow.

[wylde1]

This debate has and will rage on to the end of time, or until we stop using engines.

but long story short, there is no best engine at EVERYTHING. Each does their own thing, and gearing is the ultimate equalizer. Comparing racing engines to every day DD or even drag racing engines is apples to oranges. They share similar parts, but are hardly the same and built for two different purposes.

Formula 1 cars are the pinnacle of automotive achievement in performance. If they were left un-limited it would be absolutely rediculous what they could do. And for the record they are beginning to cap RPM's because they're running out of things to regulate to keep the cars to a (somewhat) safe speed. It's more for driver safety than anything. I believe the cap is at 18,000 rpm this year, they sound like they're stalling at 6,000.

The key to a good engine IMO is average power output. Power (HP) is just energy, and the more energy you can put to the ground the better. Energy is a byproduct of Torque (force) You NEED one to make the other. So naturally, in a DD because it's impractical to spin your engine to 18,000 rpm the engines are designed for TQ to create more average power over the rev range. An F1 car hardly ever needs to stretch all the way through it's rev range since they can change gear boxes from race to race to different ratios etc etc. so it makes sense for them to build something that can have little power down low and make more power at a rediculous RPM (they're only designed to last about 4-5 hours anyway).

So you see how this debate has no answer... because it ENTIRELY depends on the situation that the engine is being used in. But I guess you could say as a rule of thumb - the best engine gives you the most average power for the practical rpm in the context of which it is going to be used. Beyond that, you can pick and choose componets for one or the other and make a million combinations to end up in the same spot.

[wylde1]

Originally Posted by 2ndgenz28

Build for Torque and HP will follow.

yes... in a street motor.


large displacements are condusive to making tq, but harder to spin fast

HP = TQ*RPM/5252

if you, for the sake of argument, say street/strip engines can only rev 0-7000. More tq = better for the situational constraints

say a racing engine can rev 0-10,000 .... TQ will help, but you'll make more average power if you can spin it faster.

I know these are oversimplifications... the reality is MUCH more complicated than this and relies on too many factors to list here. I'm just trying to make the point that this isn't a black and white issue across the board.

[bigearl]

However you can get a much higher return on investment in HP. The problem with torque is it's pretty specific to how much fuel you burn. You can burn fuel slightly more efficiently at any given displacement, but torque is limited.

To burn more fuel requires bigger pistons, bigger valves, etc. which are heavier and can't be moved as quickly. As these components get bigger and are asked to be spun faster, they fail faster (Dragsters have time to rebuild measured in seconds). You get more torque (instant twist) to develop the best launch.

On a normally aspirated F1 car, they have achieved 5x more hp then torque. As you add torque, which means adding displacement, which means reducing rpms. If you want to add displacement, an F1 guy will want to add cylinders to reduce the inertia of each piston. HP is the measure of work over time and is more about your ability to cut through the air.

That's all extremely meaningful in 19,000 rpm race cars, and maybe somewhat so on a crotch-rocket. HP is really esoteric in real world driving. You can definitely feel HP when you accelerate, but it's not that instant whump in the back.

For my mortal-ass, I prefer torque because I want to feel the engine power when I put my foot to the floor. It doesn't matter to me if my engine has enough power to keep pushing through the wind past 150.

[wylde1]

Originally Posted by DGthe3

If you have the choice of either getting 20 hp more because of torque, or because of rpms, one or the other (not both!), you'd be stupid to take the revs. Why? Well, if its only at the top end you have to go through your entire opperating range before you get to use it. Meanwhile, the other guy gets more power almost the entire time. As you're waiting for your extra power, the other guy is pulling ahead.

Sorry for the triple post guys but I got too excited and started responding before I read the whole thread (mods please merge if this annoys you)

Here's a neat thought that this part of the quote brought to mind. Making power because of TQ OR RPM is becoming less and less mutually exclusive. With advances in materials and other technologies engines are starting to be able to have the ability to have large displacements (TQ) AND be able to spin to the moon (HP). Our LS3's are a good example. but take Lexus' LFA motor, granted it's not the tq monster the LS3 is, but it's materials and build quality allow it to change RPM's extremely rapidly. It can go from 0-9000rpm in 0.6s making it's peak power, no matter where it makes it in the range almost instantaneously reachable (via the right gear selection) And eventually that type of technology could trickle down to your average engine. (generations from now of course)

all very interesting no matter how you look at it.

[wylde1]

[QUOTE=bigearl;2310052]However you can get a much higher return on investment in HP. The problem with torque is it's pretty specific to how much fuel you burn. You can burn fuel slightly more efficiently at any given displacement, but torque is limited.

To burn more fuel requires bigger pistons, bigger valves, etc. which are heavier and can't be moved as quickly. As these components get bigger and are asked to be spun faster, they fail faster (Dragsters have time to rebuild measured in seconds). You get more torque (instant twist) to develop the best launch.

On a normally aspirated F1 car, they have achieved 5x more hp then torque. As you add torque, which means adding displacement, which means reducing rpms. If you want to add displacement, an F1 guy will want to add cylinders to reduce the inertia of each piston. HP is the measure of work over time and is more about your ability to cut through the air.

That's all extremely meaningful in 19,000 rpm race cars, and maybe somewhat so on a crotch-rocket. HP is really esoteric in real world driving. You can definitely feel HP when you accelerate, but it's not that instant whump in the back.

For my mortal-ass, I prefer torque because I want to feel the engine power when I put my foot to the floor. It doesn't matter to me if my engine has enough power to keep pushing through the wind past 150.[/QUOTE]




very well said. It entirely depends on what you're using it for. We're now in an era where rotating assemblies in big displacement motors (5-6L) are light enough we can spin them pretty quick. so we're seeing the nice nearly 1 to 1 rise in HP and TQ which is great for average power.

/end multiple posting rampage haha

[LostInMoscow]

Thanks guys! There's a lot to ponder here!

[LOWDOWN]

Originally Posted by wylde1

HP = TQ*RPM/5252

If you ALWAYS drive at 5252 rpm, it's a moot point...BOTH numbers are the same.

[matt55]

Originally Posted by 8cd03gro

HP in the usable rpm range is the most important for total performance, but not necessarily the most enjoyable for driving if you sacrifice too much low end torque and thus low end horsepower.

[zero]

Originally Posted by chain777

If you want to feel fast, you want low end torque. If you want to go fast, you want max horsepower.

yeah true it`s like a V6 grand am will feel more powerful than a honda S2000 off the line due to higher torque and would prob beat it in the first 30 feet then the high strung hp of the S2000 would destroy it