TongMan

I was checking out comparisons of the Civic Si, Acura RSX, Toyota XRS, and the Scion tC. THe specs shows that the tC has the most torque out of all the other three models. Can someone explain why having more torque is a good thing or a bad thing? I googled it and went to howstuffworks.com and I couldn't understand it. Also, how different is it from Horsepower?

TheQuietThings

torque is a measure of twisting force. this is why the tC chirps off the line.

However, horsepower is determined by torque at a certain RPM. The tC has lots of power off the line, but once the RPM's get up there, it doesnt seem as fast anymore.

TongMan

So, the tC will win from the startline but lose speed during the middle?

TheQuietThings

It wont lose speed, but it wont be accelerating as fast as a higher revving motor that is making more HP once the race gets going.

Yes, the tC should be able a car with less torque off the line, assuming the tC makes more torque first

scholarbb

The way I understand it torque is the true measure of engine power.
Horsepower is Torque X RPM.(Engine power times another variable)
This is why torque gains and loses generally reflect in horsepower gains/loses.
This is also why dyno HP and TQ always cross at 5252 RPMs because it is where they reach the 1:1 ratio.
Here's a good example:



Notice that an 8 torque gain at 3500 rpm only results in about 4hp.
But a 9 torque gain@6000 results in 11hp.
This is because rpms are now having a greater effect on the horsepower sum.
This is how honda makes a lot of horsepower with a low torque motor. Very high RPM's times the torque.
This is also why crotch rockets and race cars rev so high-to make the most possible power from available torque.

For a tc I prefer parts that increase torque from 3000 RPMs to redline.
Parts that show large increases in the high rpms will make your car faster when you rev the crap out of it.
But if you don't rev that high you won't get the power gains.
This is why some people complain about performance parts causing power loses.
The car actually has less power at the RPMs they use.
Because of this it is most beneficial to pick parts that increase torque at the rpms you use the most.

senseiturtle

Very much correct.

Torque is actual "twisting force," and horsepower can be thought of as "how well the torque is applied to acceleration."

The horsepower figure is more important for all-out racing. It implies how much torque there is up top, as well as alludes to how well the car takes advantage of gearing. For a balanced racer, you want as much of both as possible.

I did a long HP vs. TQ thread, if you want to search for it.

peteyd

sensie is the man on this one...ill search for it and if i find it ill post it but thats was a bit ago.

scholarbb

Sorry guys. Changed my original post. Felt that it needed improved.

engifineer

There has been a long standing debate (that really isnt a debate) of which is more important.. and niether is. The reason I say that is because one is a product of the other.

Horsepower is work over time. It tells of how the tq an engine produces is used to create power. So tq and rpm and how they are related on the power curve determine the power number. There is the constant 5252 in the equation which is why the two lines intersect there on a dyno.

To give you an idea of how tq is related to the overall performance. Look at a honda with lower tq than the tC. It may have great hp, but it will lie at a different point on the powerband, which is why you see honda motors spinning high rpms.

If you had more tq throughout the entire band.. you would wind hands down to an engine with less tq throughout the band. But keep in mind that hp and tq numbers are given at peak, not an average over the band, which is why those numbers can be misleading. Just because a car has a ton of tq or hp at peak means nothing if it has a very sharp curve. A car with less peak power, yet, a much flatter curve could still outperform it.

But, a simple definition of what tq is given as an example. If you place a 1ft wrench on a bolt and apply 1 lb of force perpendicular to the wrench, you have created 1 ft lb of tq. So think of the same on you crank. The combustion pressure (pressing down on the piston) is pushing down on the rod, which is applying pressure to the crank journal, which is offset from the centerline of the crank. That amount of force coupled with that distance of offset produces tq. So at that given rpm you can determine hp from hp = tq*rpm/5252 as shown above on the graph.

Try not to get caught up in comparing the two. Think of it as a system in which each part creates the whole. Proper combustion and exhaust flow work to maximize the downforce on the piston over the largest possible band for the application. This down force is applied to the crank offset to produce tq. This tq at a given rpm produces X amount of hp. This hp is applied through gearing to get it to the ground and has to overcome the loss in the drivetrain. The power delivered to the ground is working against friction due to the weight of the car, the size and make up of the wheels and tires as well as wind resistance.

So change any one of those variables and everything changes. Sorry, a little bit more than a definition of tq, but helps to relate it to everything else.

hahaitzskippy

^^^
true its not a debate so dont make it one

KEEP IT SIMPLE AND PEOPLE

TQ is the force taht gets teh car moving because its the force that spins the wheels and other moving parts outside of the engine itself.

HP is a measurment of the combination of the ignition of the amount of FUEL and AIR mixture in the cylinder when compressed and burned.

TimmyT

^^^^
What these guys said.

TheQuietThings

and before this turns into a debate... LOCKED!