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A Simple Example​
Everything explained thus far can be illustrated with an example. My 1982 Chevy Caprice has a three speed automatic transmission, with 2.52:1, 1.52:1, and 1.00:1 gear ratios. The rear axle gear ratio is 2.41:1, and the tire diameter is 27 inches. At 80mph, the wheels are turning at approximately 1000RPM, so I can choose to be in either second or third gear at that speed without over revving the engine. The engine has 170hp at 3700RPM, and 270ft-lb at 2400RPM. Using the horsepower formula, we can see that at 3700RPM, I have 245ft-lb of torque, and at 2400RPM, I have 123hp.
Below is a diagram that demonstrates the effects of changing from 3rd gear to 2nd at 80mph in my Chevy Caprice.



The force at the wheels went up when the engine's power went up, even though the torque at the engine went down.



It can clearly be seen that the decision to drop a gear had a positive effect on the car's ability to accelerate. Even though I had less flywheel torque to play with, the increase in power allowed me to get more force onto the pavement by trading engine speed for torque using second gear in my transmission. The wheel RPM did not change because I'm still doing 80mph. With the wheel speed held constant and the power increased, the wheel torque must therefore increase too. The added torque at the wheels means that I will now have a better acceleration force when I floor it.

-This applies only IF you haven't went beyond the mechanical limits of the previous gear. Ie you can't downshift from 6th to 1st at 80mph becuase your engine would be way above redline!

-This shows why the Si is able to be such a quick little car IF you play within the gear ranges. And explains why a high torque engine is easy and less demanding to drive just mash on the pedal. Where as the Si could require 2 or more downshifted gears. Nothing wrong with either one - personal choice.
 

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Comparing Two Cars​

I think at this point, it is clear that the car's acceleration ability is related to its engine's power output. Now, let's compare two different cars with two very different engines. ( I apolgize for the racial slur of the below ) Also not that great of an example since Honda makes good engines that have flat torque bands. But it does show why a nice flat thick torque band is great.


Both vehicles will have the same curb weight, and peak horsepower figures. They will also have the same transmission, tire radius, and so on. In fact, the only difference between the two cars will be the engines. One car will be equipped with a 500hp turbocharged 4 cylinder engine, and the other will have a 500hp big-block V8. The 4 cylinder will be named Ricer, and the V8 will be named Redneck. The 4 cylinder is able to rev to 9000RPM and produce a fair bit of torque, while the V8 can rev to only 6000RPM, but produce a ton of torque. To keep the math very simple, the Redneck's engine idles at 600RPM, and the Ricer's idles at 900RPM.
Below are plots of the two fictitious engine's torque and horsepower curves.



Figure 1: Torque versus RPM for Redneck and Ricer. These are unrealistic curves which have been exaggerated to help illustrate certain concepts.

Figure 2: Horsepower versus RPM for Redneck and Ricer. This is calculated from the torque at each RPM.



Both engines produce a peak of 500hp, just like I promised. The V8 produces 500hp at 5000RPM, and 573tq at 4250RPM, while the I4 produces 500hp at 8000RPM, and 337tq at 7500RPM.
RicerRedneckDifferenceRev Range900 - 9000RPM600 - 6000RPM50% more for RicerPeak Torque337tq573tq70% more for RedneckPeak Power500hp500hpEqualBecause the V8 was revving lower, it needed to produce more torque than the I4 to reach the same peak power figure. Conversely, the I4 needed to rev higher than the V8 to produce the same power, because it offers up less torque.
The Power Band

A very important aspect of an engine's output is its power band. The power band is the rev range where the engine is producing an arbitrary percentage of its peak power figure. I will use 80%, which is 400hp or more on our two 500hp engines.

Figure 3: Power band comparison of both motors. Note that the Redneck's average power production (area under the curve) is higher, and that the peak power is the same, at 500hp.


The x-axis may seem unusual. Because the Redneck's engine revs from 600RPM to 6000RPM, while the Ricer's engine revs from 900RPM to 9000RPM, the power production cannot be compared directly with revs. The Ricer has a 50% greater rev range than the Redneck, so the Redneck's graph has to (or "gets to") be stretched by 50%. Showing the x-axis as a fraction of each engine's rev range helps to equal the comparison.
If this seems confusing, there is a separate page on comparing power curves which explains why the rev ranges can't be compared directly.
We will see later on that Figure 3 is a more accurate comparison of the two engines ability to accelerate a car than Figure 2.

Notice that while both engines have the same peak power figures, the Redneck's engine has a much wider 80% power band. This situation is a considerable advantage for the Redneck. Between the two cars, the one with the made-up V8 is going to be faster than the one with the made-up I4, because the V8 has a higher average power level throughout its rev range.
An exotic sportscar, such as a Lamborghini Murcielago, will have such a wide power band that it can accelerate very hard from almost any RPM. This means that it can do things like go from 0-60mph in one gear. This is why exotics have such impressive performance.



Force on the Road​
Let's now look at how much force the Redneck and Ricer are putting to the road, which as we talked about earlier, is the force which accelerates the car. For simplicity, both drivers will race by rolling from 20mph, flooring it, and then shifting at their redlines in each gear. Top speed will be considered redline in top gear, because we are ignoring aerodynamic drag.
We'll start off by giving both of them a good old TH350 3-speed automatic transmission, and a 3.73:1 final drive (axle) ratio.
Drivetrain Layout




TH350 and 3.73 Axle Gears


Figure 4: Rear wheel force versus vehicle speed for Redneck and Ricer when using a TH350 transmission and 3.73 axle ratio. The steep vertical drops are the gear changes at redline. Gear changes take place instantaneously for simplification.

Notice that the Redneck has a considerable advantage over the Ricer in first gear, but then not so much in second or third gear. This is because when he shifts into 2nd gear, the transmission doesn't bring him back to idle, but to approximately 3600RPM instead. The Ricer's engine also stays in reasonably high revs after the first gear change, and we saw in Figure 2 that he has plenty of power at high revs. Also note that the Redneck had to shift into second before the Ricer, so his ability to accelerate between 60-65 and 100-115mph is about the same as the Ricer's.
Now, let's move into modern day by giving them both a Tremec T56 6-Speed close-ratio manual transmission.



Drivetrain Layout

Tremec T56 6-Speed and 3.73 Axle Gears





Figure 5: Rear wheel force versus vehicle speed for Redneck and Ricer when using a Tremec T56 transmission and 3.73 axle ratio. Note that the close ratio transmission has reduced the drops in power at each gear change for both motors, especially for the Redneck's.

At certain speeds, the Ricer has caught up slightly. The close-ratio 6-speed transmission helps keep his engine revving near his power peak, and that has helped narrow the gap. The small dips on the Ricer's graph show the effects of having a narrow power band.
The Ricer's acceleration in first gear is still very poor, but the Ricer has a trick up his sleeve. He is going to install a set of 5.67:1 gears in his axle without the Redneck knowing.


Drivetrain Layout

Tremec T56 6-Speed



3.73 Axle Gears for Redneck

5.67 Axle Gears for Ricer


Figure 6: Rear wheel force versus vehicle speed when using a Tremec T56 transmission and 3.73 axle ratio for the Redneck, and 5.67 for the Ricer. Note that both cars shift gears at about the same vehicle speeds as each other now.

The Ricer has pretty much completely caught up now, especially at speeds above 40mph. With those gears he put in, he has traded his higher revs for higher torque to the wheels. Now, for certain vehicle speeds, he can accelerate alongside the Redneck. (if he is in the correct gear)

The Redneck would also see benefit from putting in different axle gears. However, this "arms race" cannot go on for long, because as the wheel torque is increased, speed is traded away. It would be very embarrassing for the drivers if they crossed the finish line sitting at redline in 6th gear, not accelerating. The Ricer can use a lot more gear because of his extra revs. Conversely, the Redneck doesn't need them because he has so much flywheel torque that he doesn't need to multiply it as much. There is not a significant benefit to either driver in this regard.


If we fitted both cars with a Continuously Variable Transmission (CVT) that had an infinite ratio spread, which can hold both engines at their horsepower peaks, the acceleration of both cars would be identical at any vehicle speed.


Low-Speed Acceleration​

Even after changing the rear axle gears, the Ricer's (but the 8thgen k20 and R18 have a nice fat torque band) car still could not match the Redneck's acceleration from a slow roll up to about 35-40mph. This shows that the benefits of a having a very wide power band are most significant in first gear, and is therefore an important part of tuning an engine for drag racing, where the cars start from rest.
That low-RPM "hole" can be reduced with a few tricks:
With a manual transmission, the car could be launched by revving the engine way up and then easing off the clutch pedal quickly.
With an automatic, a torque converter with a high stall speed could be installed, which allows the engine to be revved up without moving the car too much while holding the brakes on. A good explanation of torque converters and stall speed is beyond the scope of this article. Think of a high stall converter as behaving like a slippy clutch at low revs, and a fully engaged clutch at high revs.


Shift Points​

When the Ricer and Redneck were racing, they were shifting gears at their engine's redlines. In many real-life cases, shifting gears earlier may be advantageous for acceleration. An engine with a power curve that begins to "fall off" at very high RPM should be shifted earlier, if doing so would help yield more power. Gear shift points should always be chosen in such a way that the engine is putting out the highest average power to the wheels. (key phrase is Too the wheels not the flywheel)


Driveability​

Driveability is a subjective term used to describe the ability to "access" an engine's power. A naturally-aspirated engine (or any engine) with a wide power band will have very good driveability. (provided the wide powerband is also large enough to get the work done) Putting the pedal to the floor at any speed in any gear should yield reasonable acceleration. On the other hand, a car with a narrow power band would not be considered as "driveable". Passing cars while cruising on the highway often requires dropping a gear to bring the engine's revs up to access the power. This is one of the reasons that luxury cars often come with large, naturally-aspirated or supercharged engines, while small, turbocharged engines are not as common and often found in more "focused" sportscars where outstanding driveability is not expected or required.
Engines are sometimes described as being "torquey". This is slang for having "good driveability" or "a wide power band". "Streetability" is also somewhat synonymous.


High Torque Engines versus High Revving Engines​

Torque is somewhat related to the displacement of the engine. Larger displacement engines are likely to be much bigger and heavier, making them unsuitable for certain types of vehicles. This is why many small race cars have engines with small displacement, high-revving, and sometimes equipped with forced induction to produce high horsepower. Also, race cars are often given limits on displacement, which means their only chance at producing a lot of power is to rev very high or use boost. A large engine may be able to produce power more reliably than a smaller one, but not necessarily. There are plenty of big, gutless engines that don't last.
Heavy vehicles are almost always equipped with large displacement engines because they require more low-RPM power to accelerate from rest (and very low speeds). As the weight of a vehicle goes up, the acceleration from rest becomes increasingly significant. A 650hp V12 from a Ferrari Enzo could in fact tow a loaded semi at high speeds, but it's unlikely that it would have enough power at very low RPM to get the semi moving in the first place. On the other hand, a huge diesel engine can produce all kinds of power at low RPM to help get the vehicle rolling.


Conclusion​

:coffee:Shaft power is the product of shaft speed and torque, and the speed and torque can be altered proportionally using gears. If we want to apply a lot of torque to a shaft that is rotating, a lot of power is needed. The more power the better. However, the power must be accessible from all vehicle speeds, which can only be accomplished by producing a lot of torque throughout the rev range, or by having a transmission with many gears. It is this fact that has spawned phrases like "Torque is King", or "Horsepower sells cars, but torque wins races", which can be misleading. Torque on its own isn't useful in accelerating a vehicle, because it is not at rest; it is moving. Therefore, power is what matters. Cars are often described by their power-to-weight ratio, not their torque-to-weight ratio.
The vehicle with the largest average acceleration is the one that has the largest average force going to the pavement through a wide range of speeds.
" Peak power sells cars. High average power wins races. "
A vehicle's peak torque and horsepower figures can only give a general idea of performance. The best way to make a good comparison between two vehicles is to go racing! (or do all of the math formulas above - not as FUN)



Ive been writing an application in my free time that simulates car performance based on specs such as: Weight, coeFficient of drag, gear ratios, and dyno graphs.

Its still a work in progress, it dosnt take into account some factors like shift time and tire traction, but it has proven to be pretty accurate at 0-60 times etc. (I am still working on the Coefficient of drag portion, that has more of an impact at higher speeds)

Anyways recently Ive used it to generate a graph of Wheel torque Vs Velocity to prove a point to a friend with a V6 Mustang.

Despite the mustangs much higher flywheel torque the Si manages to put down close numbers to the wheel due to its higher redline and gear ratios. The civics lighter weight (smaller aluminum engine) gives it an advantage over the mustang.

Its still close enough to be a drivers race though.

Wheel Torque Vs Velocity


Velocity Vs Time
 

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Example-An engine that produces 300 pound-feet of torque at 4,000 rpm produces 228 horsepower at 4,000 rpm. This is based on the formula that horsepower is equal to torque multiplied by engine speed and that sum divided by 5,252. The constant, 5,252, is used to convert the rpm for torque and horsepower into rpm's.

then how come all cars dont have the exact same hp to tq ratio? my car has 290 tq and 205 hp, yet the si has 139 and 197.. seems that "constant" is not a constant at all.. btw im a noob to this stuff
 

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Example-An engine that produces 300 pound-feet of torque at 4,000 rpm produces 228 horsepower at 4,000 rpm. This is based on the formula that horsepower is equal to torque multiplied by engine speed and that sum divided by 5,252. The constant, 5,252, is used to convert the rpm for torque and horsepower into rpm's.

then how come all cars dont have the exact same hp to tq ratio? my car has 290 tq and 205 hp, yet the si has 139 and 197.. seems that "constant" is not a constant at all.. btw im a noob to this stuff
thats not what its saying. its saying that the torque @ 5252 will equal the power @ 5252 no matter what teh car is. its not a constant per se, but the definition of horsepower and a unit conversion. it makes no mention of whether peak HP and peak Tq happen at 5252.

another problem is this. it makes zero sense to talk about torque without talking about RPM.

the reason your ratio of tq:hp is less, is because of two reasons.

the main reason is that the peak power is achieved at a higher RPM.
if the peak power of one car comes at 4k, and for another comes at 8k, the peak torque SHOULD be around half in the car that revs to 8k. (but the torque @ peak HP will be EXACLTLY half)

the second reason (and the reason its not exactly half) is that peak torque and peak hp dont always happen at the same RPM.
 

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how come some cars can have more tq than hp, some more hp than tq, and some about even? who says the civic si couldnt be like 200 hp and 180 tq?
the torque curve and the redline say so. at peak HP the Civic Si makes about 130lb-ft of torque @ 7800RPM. if we increase this by 40, now we plug in the formula. 7800RPMx170Lb-Ft/5252=260HP.

the only way around this is to change this is to change the redline, the torque curve, or both.

for the car to rev up to 8200 and only make 200HP, torque NEAR redline cant be much more than about 140lb-ft. you have to understand that HP comes from RPM AND TQ. you cant just up one and expect nothing else to change.
 

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Discussion Starter #31
how come some cars can have more tq than hp, some more hp than tq, and some about even? who says the civic si couldnt be like 200 hp and 180 tq?
Science says. Look at the cars that have 200hp/tq or more out of 4 cylinders.

Sentra 2.5 liter, 6.5 redline
GTi, 2.0 Turbo, 6.5 redline
MS3, 2.3 turbo, 6.5 redline
STi, 2.5 bigger turbo, 7 redline(bigger than the tiny MS3 and GTi turbos)
EVO, 2.0 bigger turbo, 7 redline(bigger than the tiny MS3 and GTi turbos)
Solstice GXP/Sky redline, 2.0 slightly bigger turbo, 6.5 redline

And in a league of their own...

Civic Si/RSX-S, 2.0, 8k redline, no tq, 200hp
S2000, 2.0/2.2 240hp, 8k/9k, redline no tq

In a engine you are pretty much going to get hp/tq pretty equally unless you up the revs thus sacrificing tq down low. The way to up the HP, and keep the tq is to go force induction especially if you plan on raising the redline.

N/A with a high rev limiter will not have tq.

Look at Ferrari's, Hondas, F1 cars etc.
 

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the torque curve and the redline say so. at peak HP the Civic Si makes about 130lb-ft of torque @ 7800RPM. if we increase this by 40, now we plug in the formula. 7800RPMx170Lb-Ft/5252=260HP.

the only way around this is to change this is to change the redline, the torque curve, or both.

for the car to rev up to 8200 and only make 200HP, torque NEAR redline cant be much more than about 140lb-ft. you have to understand that HP comes from RPM AND TQ. you cant just up one and expect nothing else to change.
im not sure what the torque curve looks like, but the peak torque should be at least 500 rpms lower than the peak hp i would think.. yes i just learned tq and rpm = hp, thus meaning hp is a a measure of overall capability, just like watts is volts x amps, but im still a noob to cars, and the hp vs tq seems to stump me..

i found a really awsome article on how torque is more important than hp, and i emailed the guy and asked him a few questions, and this is what i got back.. "im sure your not stupid, but you look very ignorant typing how you do, blah blah blah" and he gave me a 1 sentence answer ending with "..it appears you already knew this, but chose to ignore it" or something like that.. long story short, i welcomed him to the 21st century, the internet, speed typing, and guess that he was at least 40 years old, probably more like 50, and he emails me back saying hes 65.. what an *******..

Science says. Look at the cars that have 200hp/tq or more out of 4 cylinders.

Sentra 2.5 liter, 6.5 redline
GTi, 2.0 Turbo, 6.5 redline
MS3, 2.3 turbo, 6.5 redline
STi, 2.5 bigger turbo, 7 redline(bigger than the tiny MS3 and GTi turbos)
EVO, 2.0 bigger turbo, 7 redline(bigger than the tiny MS3 and GTi turbos)
Solstice GXP/Sky redline, 2.0 slightly bigger turbo, 6.5 redline

And in a league of their own...

Civic Si/RSX-S, 2.0, 8k redline, no tq, 200hp
S2000, 2.0/2.2 240hp, 8k/9k, redline no tq

In a engine you are pretty much going to get hp/tq pretty equally unless you up the revs thus sacrificing tq down low. The way to up the HP, and keep the tq is to go force induction especially if you plan on raising the redline.

N/A with a high rev limiter will not have tq.

Look at Ferrari's, Hondas, F1 cars etc.
some of the cars you listed have under 200 tq.. but ya, i guess it gets quite complex when you talk about torque and hp curves, and what causes them? let me just ask this, can gear ratios change torque/hp curves? im guessing no, they can only change the amount of torque (but not hp).. if torque is sacrificed with high rpms, then what are you gaining when the rpms go up? torque and rpms determine hp, but if you take torque away and add more rpms, arent you basically doing nothing or very little? also, if torque is sacrificed at high rpms, then why dont we have torque at like 4000 rpms? btw i noticed my current car which has an insane amount of torque, has a 5300 redline (1997 mercury cougar xr7 @ 290 tq)..
 

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Discussion Starter #33
some of the cars you listed have under 200 tq.. but ya, i guess it gets quite complex when you talk about torque and hp curves, and what causes them? let me just ask this, can gear ratios change torque/hp curves? im guessing no, they can only change the amount of torque (but not hp).. if torque is sacrificed with high rpms, then what are you gaining when the rpms go up? torque and rpms determine hp, but if you take torque away and add more rpms, arent you basically doing nothing or very little? also, if torque is sacrificed at high rpms, then why dont we have torque at like 4000 rpms? btw i noticed my current car which has an insane amount of torque, has a 5300 redline (1997 mercury cougar xr7 @ 290 tq)..
Only the Si and it still basically has 200hp. Gears multiply tq (and hp in a way). Say you had 200 tq and first gear was 3:1 (remember using basic numbers) than in first gear you would have 600tq, and since TQxRPM= HP, your HP would also multiply... Now to dyno sheets.

Here is a pretty much stock Si dyno sheet from XSR civic.
ImageShack - Hosting :: dynoqx6.jpg
Here is a pretty much stock MS3 dyno sheet.

Corvette

S2000 dynosheet

You can easily see how TQ affects HP with RPMs. And you can see how TQ is found in the low rpm's of the dyno and how HP takes over in the high RPMs. Where are you at when you race at the track? High rpms, so why is low tq so important in a drag race, because you are simply sprinting. A good launch is pretty much gold when it comes to 1/4 mile and 1/8 mile racing.
 

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im not sure what the torque curve looks like, but the peak torque should be at least 500 rpms lower than the peak hp i would think.. yes i just learned tq and rpm = hp, thus meaning hp is a a measure of overall capability, just like watts is volts x amps, but im still a noob to cars, and the hp vs tq seems to stump me..
ideally, peak torque should come at 1RPM, and should not drop off at any RPM. but thats not how gas engines work. when an engine gets to peak torque it will drop off. to minimize the amount of drop off, peak torque SHOULD come at redline dont you think? remember that horsepower is made from torque and revs. so for max HP from a set amount of torque, you need that torque to come in the high revs.

the thing is, that even though 'peak torque' comes at ~6500 in our cars and peak horsepower comes at 7800, from 6200 to 7800, the torque BARLEY drops a couple lb-ft. very good.

so unless you were gonna go from 180lb-ft at 6000RPM and then suffer a massive drop in torque and go down to 130lb-ft at 8000RPM, no, your just NOT gonna get an 8k redline and 200tq and 200hp.

not to mention, that would be a bad thing, because torque is what moves a car. you dont want torque to be dropping off.

i found a really awsome article on how torque is more important than hp, and i emailed the guy and asked him a few questions, and this is what i got back.. "im sure your not stupid, but you look very ignorant typing how you do, blah blah blah" and he gave me a 1 sentence answer ending with "..it appears you already knew this, but chose to ignore it" or something like that.. long story short, i welcomed him to the 21st century, the internet, speed typing, and guess that he was at least 40 years old, probably more like 50, and he emails me back saying hes 65.. what an *******..
that really awesome article, is wrong. i dont mean to be agist, but since the guy is 65, he's probably grown up around muscle cars and has a bias against foreign cars and small displacement.

something to understand is that 200lb-ft of torque isnt enough to move a car. but 5000RPM is WAY WAY WAY too much RPM than whats needed to the wheels. what gearing does is transfer RPM to Torque. The amount of potential torque and RPM at the wheels is based on horsepower. what torque and what RPM the engine made is meaningless

see this pic which was up in an earlier post:


what that guy doesnt understand is that "torqeless cars" have more revs for the gearbox to work with.

whats more important than peak torque is the shape of the torque curve. the shape of the torque curve tells us how close we are to peak torque. we want our cars to be close to peak torque all the time, ESPECIALLY in the high revs.
 

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first off, id like to thank everybody for explaining..

but isnt hp a measurement of torque and rpms? meaning you have to either have lots of torque or high rpms to make a car fast.. i dont understand where these curves on dynos come from tho, are they from the engine or from switching gears? like what makes a torque or hp curve..

im going to go read several articles on tq/hp/rpm and get more educated, then i will be back
 

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first off, id like to thank everybody for explaining..

but isnt hp a measurement of torque and rpms? meaning you have to either have lots of torque or high rpms to make a car fast.. i dont understand where these curves on dynos come from tho, are they from the engine or from switching gears? like what makes a torque or hp curve..

im going to go read several articles on tq/hp/rpm and get more educated, then i will be back
cars dont make equal torque at any RPM. they make a certain torque at a certain RPM. the measure of torque along the RPM range is the torque curve. when we say a car has 300lb-ft @4000RPM, that only refers to the peak torque and what RPM peak torque happens at. for all we know, torque could be only 200lb-ft at 5000RPM. staying close to peak torque throughout the rev range is ideal and is whats called a "flat torque curve"
 

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first off, id like to thank everybody for explaining..

but isnt hp a measurement of torque and rpms? meaning you have to either have lots of torque or high rpms to make a car fast.. i dont understand where these curves on dynos come from tho, are they from the engine or from switching gears? like what makes a torque or hp curve..

im going to go read several articles on tq/hp/rpm and get more educated, then i will be back
The torque curve comes because the engine makes varying amounts of power at different RPMs. There is a certain RPM where the engine will make the peak amount of torque. This curve and the point of peak torque depends on the design of the intake, exhaust, cylinders, pistons, valves, cams, etc., etc. By changing any of these things you change the torque curve.

This is why v-tec works so well. If the car simply made more power with the higher profile cams they would simply put high profile cams in and call it a day. However, at low RPMs a lower profile cam makes more torque. Once the engine gets to the point that torque starts to drop off because the RPM is above the peak for that cam profile the v-tec engages the higher profile cam and esentially changes the torque curve to keep the engine making torque.
 

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Only the Si and it still basically has 200hp. Gears multiply tq (and hp in a way). Say you had 200 tq and first gear was 3:1 (remember using basic numbers) than in first gear you would have 600tq, and since TQxRPM= HP, your HP would also multiply... Now to dyno sheets.
HP would actually stay the same. You are multiplying the torque by 3x, but you are dividing the RPM by 3. Horsepower would stay the same.

200 torque x 6,000 RPM = approx. 228 HP

Now first gear ratio of 3:1

600 torque x 2,000 RPM = approx. 228 HP. It is the exact same horsepower.

If you wanted to get technical you could point out that since there is a slight torque loss from friction the torque would be slightly less than 600 and there would be a slight HP loss.
 

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cars dont make equal torque at any RPM. they make a certain torque at a certain RPM. the measure of torque along the RPM range is the torque curve. when we say a car has 300lb-ft @4000RPM, that only refers to the peak torque and what RPM peak torque happens at. for all we know, torque could be only 200lb-ft at 5000RPM. staying close to peak torque throughout the rev range is ideal and is whats called a "flat torque curve"
yes, i already knew this, this was not what i was asking.. the below quote answers my question

The torque curve comes because the engine makes varying amounts of power at different RPMs. There is a certain RPM where the engine will make the peak amount of torque. This curve and the point of peak torque depends on the design of the intake, exhaust, cylinders, pistons, valves, cams, etc., etc. By changing any of these things you change the torque curve.

This is why v-tec works so well. If the car simply made more power with the higher profile cams they would simply put high profile cams in and call it a day. However, at low RPMs a lower profile cam makes more torque. Once the engine gets to the point that torque starts to drop off because the RPM is above the peak for that cam profile the v-tec engages the higher profile cam and esentially changes the torque curve to keep the engine making torque.
yay
 

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first off, id like to thank everybody for explaining..

but isnt hp a measurement of torque and rpms? meaning you have to either have lots of torque or high rpms to make a car fast.. i dont understand where these curves on dynos come from tho, are they from the engine or from switching gears? like what makes a torque or hp curve..

im going to go read several articles on tq/hp/rpm and get more educated, then i will be back
Also two stage intake manifold or now modern german cars have mulistage intake manifolds. And some sportbikes and fancy euro cars have multistage mufflers. They can be controlled by the ECU to alter torque of the engine. The r18 has a two stage intake manifold that allows for a flatter higher rpm torque range. I would guess then next gen Si will have at least a 2 stage or multistage intake manifold.
 
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