I didntk now which forum to post but I was wondering exactly what makes the torque. Youll see engines with like 350hp and 375tq and youll see engines with 375hp and 350tq etc..... I was just wondering exactly what causes and how you would produce torque?

 

Horsepower = (Torque X RPM)/5252

Basically, engines just produce their peak torque at different RPM's.


Throw some #'s in that equation and it should solve your problems

 

so each engine has a peak torque ? like an engine has a max torque? i guess what im getting at is why, like what decides the max torque the engine can reach? and i noticed like when it comes to cams ill see hp #'s higher than torque #'s, and when I start looking at like FI Ill normally see torque higher if it was originally higher to start out with. Lik ex: if my engine stock had 300hp and 325tq after a cam ill notice higher hp like 375hp and 360tq, but with FI maybe I would see 360hp and 375 tq

 

So your asking why a FI engine produces more torque than a carbuerated engine or at least seems to?

 

i think hes asking what makes the tq, and what determines how much and where.

 

I think hes talking about Forced Induction, not Fuel Injection.

 

I'd be curious to know too. I'm running a vortech kit with all the info and mods in my signature and ended up with more HP then torque... I'm looking at ways to increase me torque up a bit....

 

An engine is basically an air pump, and the point at which the cylinders get filled the most with air and fuel is the point at which it produces peak torque.

You will hear people talk about Volumetric Efficiency, basically it means how much air is going into the engine compared to the displacement. If your cylinder fills exactly the same and has the ideal fuel mixture and burn your torque will be constant for any RPM. (i.e. a completely flat torque curve)

Therefore if your engine does not run over 5252rpm, you will always have more torqe than HP

If your engine operates along the flat torque curve above 5252 rpm, your HP will always be higher than Torque.

Thats all based on the equation listed above. If you want to go over to Metric with kW and Nm the #'s are different

Keep in mind that HP is POWER and Torque is Force.. you can have Torque at 0 RPM but you wont have any Power.

 

we need a better shot of your hood, looks cool.

 

so would that explain why for the most part civic and most of your smaller engine or engines with less cylinders like 4's and 6's usually have higher peak hp #'s than tq#'s because they for the most part are reaching their peaks over 5252rpms?

 

as a generalized statement don't bigger engines have more torque?...like mod for mod.

also is it true that you get the best gas mileage at peak torque rpm?

 

airflow=torque

 

The more mass of moving parts you have the more torque you create.

That is why your general statement would be correct for the most part.

 

Not nessecarily, Its the stroke that creates torque... a longer stroke means a larger moment arm is placed on the crankshaft given equal force of combustion.

If the effective pressure in the cylinder is constant which means equal force, a longer stroke will create more torque. Think of it like putting a pipe on the end of a wrench. You can only apply a set amount of force, but if you extend the length you can have more torque!

 

then how come on a civic( or other 4cyl's) dont they have longer strokes? how come they dont make the 4 cyl engines and what not have more tq?

 

Displacement = Bore area x stroke

If the imports increased stroke they would therefore increase displacement and that would hurt fuel economy.

Besides the downside to more stroke is higher piston speed, so for the same RPM your pistion is actually moving faster on a longer stroke engine.

Look at Formula 1, if they have 700+hp but its at nearly 20,000 rpm they dont have much torque.

The good thing about torque is that it can be multiplied and divided through gears. if you have a 2:1 gear ratio, it will transfer half the torque but at 2x the speed but will still have the same POWER.

So for low torque, high rpm engines, they have large gear ratios essentially Multiplying torque.

If you have a 350hp @ 5000rpm and 350hp @ 1000 rpm, and your transmission is 'geared correctly', they would produce the same acceleration force at the wheel at a given speed.

However, the same cannot be said for Torque. If you have 350lb-ft @5000 RPM, it will always be better than 350lb-ft at @1000rpm. because if your driving at the same speed, the 5000rpm motor needs to be "geared down" more and basically MULTIPLYING torque through the gears.

 

Part of this has to do with bore and stroke.

Take the HP and TQ equestion above. Now think about it realistically. If the stroke is increased, then the pistons have to move that much further to complete a cycle. A tiny civic 4-banger has an extremely short stroke, so they can rev very high (get much higher RPM's) do to basic physics which therefore yields greater HP/Liter. So the HP/Liter has to do with how small the engine is, that is why tiny crotch rocket engines can have over 200 hp/liter stock. So the clueless ricers who brag about it don't know a damn thing about engines.

Another thing is the gearing. You can take the exact same engine and make more HP than Torque or more Torque than HP simply by changing the gearing.

 

Nope, power is power. Output is the same no matter what the gearing is.

 

Ok, here you go. Torque is created by pressure on top of the piston. This pressure is created by the expansion of the burning of the air fuel mixture. The piston moves downward and the connecting rod pushes on the crankshaft. The crankshaft then takes this motion and transmits it to the trans. The trans has different gears in it which multiply the torque. this torque is output to the rear end where it gets multiplied again. It then goes through the axle to the tire which takes multiplication away. The end result is the tire turns.

What a longer stroke does is two things, it multiplies the force created by the piston and it also increases piston displacement which increases its speed. This makes the air column fill the cylinder sooner in the RPM band.

You can also gain more torque by increasing piston diameter. Because you still have the same pressure on top of the piston, now you are taking advantage of more of it so it pushes the piston down faster. The downside to this is there is no multiplication.

The other way to increase torque is to increase air trapped in the chamber. This increases the air/fuel mass on the piston so there is more expansion which creates more pressure. This is how forced induction works.

You can also chemically supercharge an engine by the fuel. This is how Nitrous and any fuel that contains oxygen works. If the fuel used has oxygen, it can burn with less air in the chamber. This means there can be more fuel for more pressure. Fuel expands more than air, therefore you have more pressure.

As far as gearing a car goes, your engine still only makes x amount of torque and horsepower. Gearing cannot change the hp of the engine, it will however multiply the torque created. For instance, if your engine creates 400 lbft of torque, and you have a 2:1 final drive, your engine will "feel like" it has 800lbft of torque. If you change the gearing and you now have a 3:1 final drive, your car feels like it has 1200lbft of torque.
Gearing is the #1 way to make a car faster, well besides giggle gas. And if you were only interested in the 1/4 mile, you would gear your car such that in the highest gear you woul be 200rpm past the horsepower peak of the engine when crossing the finish line.

But this would pe totally impractical on the street, as you would need around a 5:1 final drive to achieve something like this. Also, the other problem you run into with gearing is over powering the tires. Remember, a tire can only handle so muchpower, and, if you go and increase the torque there is a great chance that you are not going to hook the car up so it will actually be slower.

I hope this helps.

 

A few possibilities for confusion in the above posts. To recap:

To create torque, you need combustion pressure. Engine designers have a term for average combustion pressure: Brake Mean Effective Pressure (BMEP). What mostly determines BMEP is how much fuel and air you can burn per 4-stroke cycle. For normally aspirated motors, this is heavily tied to displacement - more cubes = more torque capacity. Through careful combination of intake tuning, exhaust tuning, and cam timing, you can make an engine ingest air/fuel very efficiently over a particular RPM range - that will be the range of max torque. FI motors have fewer restrictions on intake design, since they don't have to maintain fuel in suspension, and so optimally designed FI motors will often have somewhat higher max torque for a given displacement, due to better intake tuning.

The other factor that impacts combustion pressure is compression ratio: burn the same amount of air/fuel in a smaller space, you get more combustion pressure, hence more torque. Compression ratio, obviously, is limited by detonation for a given octane fuel.

Horsepower, as noted above, is a function of both torque and RPM - make the same torque at a higher RPM, you make more HP. To make the same torque at a higher RPM, you need to ingest more air and move more exhaust in a given period of time, hence the popularity of 3 to 5 valve setups in smaller high performing motors.

Forced induction is the only way to radically increase the torque capacity of an engine for a given displacement. The engine's cylinder filling capacity doesn't change much, but the cylinders are being filled with a denser fuel/air mixture, and hence you get higher average combustion pressures.

One quick note regarding torque production: it is a myth that small bore/long stroke motors make more torque. For a given displacement, the max torque capacity does not change with different bore/stroke ratios. With a large bore, the combustion pressure pushes on a larger piston area, creating more force, which acts on a smaller crank arm. With smaller bore, the combustion pressure acts on a smaller piston area, creating less force, which acts on a longer crank arm. The tradeoffs between piston area and crank arm leverage exactly cancel each other out. Now, different bore/stroke ratios are often different in other areas - rod ratio, valve area, valve shrouding, combustion chamber shape, etc, and these have their own effects, but in general cubes is cubes, no matter how you get 'em.