displacement

[c32b1 NSX]

sory i dont know but whats the advantage of having a higher displacement? say 2 engines have 200hp 200tq but one is 2.0 and one is 2.2, what does the 2.2 have over the 2.0?

[CBFryman]

200cc...maybe a flatter torque curve/more torque in the lower RPM's....

[public]

And possible more potential.

[c32b1 NSX]

no ones got a straight answer?

[Rufe]

Perhaps you do not understand what they are saying?

Both answers were concise and to the point, and I agree with them.

10% is not much of a difference, however the easiest way to more horsepower is more displacement.

[public]

Bigger is usually better. Semi trucks use bigger motors for a reason. Even with blowers and turbos they need a BIG engine. You can only do so much with a given volume. Otherwise you would see oceanliners with a 1.6 liter with 85 sequencial turbos and a bazillion shot NOS system.

[MagicRat]

Originally Posted by c32b1 NSX

no ones got a straight answer?

In theory, the 2.2 liter engine is able to burn 10% more fuel for about 10% more power at full throttle.

To be as simple as possible, as the engine is made bigger, the power characteristics change. Often, larger engines do not always produce proportionally more power than the smaller ones. But they may produce the same amount of power at a lower engine RPM.

For example, a 1.2 liter 4 cyl motorcycle engine can make 140 hp at 9000 rpm. This is good for a lightweight sporty machine, becuase it likely makes very little power at low revs. The engine must spin fast to make the power.

My 3 liter 4 cyl engine in my boat makes the same 140 hp, but only needs to turn at 4500 rpm. This is good for pulling heavy loads, becuase the engine does not have to spin fast to make the power.

[beef_bourito]

If they have the same power, I'm guessing, the 2L would have better fuel economy but you would be able to get more out of the 2.2L. If you look at cars that exist, with a civic (1.6l i think) and a camaro (350ci) with the civic you'd be lucky to get 30 hp from an exhaust system but the camaro could get from somewhere in the 100-200hp up to 400+ with carb, intake and exhaust.

[SaabJohan]

Originally Posted by MagicRat

In theory, the 2.2 liter engine is able to burn 10% more fuel for about 10% more power at full throttle.

To be as simple as possible, as the engine is made bigger, the power characteristics change. Often, larger engines do not always produce proportionally more power than the smaller ones. But they may produce the same amount of power at a lower engine RPM.

For example, a 1.2 liter 4 cyl motorcycle engine can make 140 hp at 9000 rpm. This is good for a lightweight sporty machine, becuase it likely makes very little power at low revs. The engine must spin fast to make the power.

My 3 liter 4 cyl engine in my boat makes the same 140 hp, but only needs to turn at 4500 rpm. This is good for pulling heavy loads, becuase the engine does not have to spin fast to make the power.

Have you heard about the gearbox?
A nice little invention that makes it possible to change the output speed to whatever speed you want!

When you are pulling loads, accelerate fast or whatever the only thing that counts it the power, if you have power you have torque I can guarantee you that. So if the engine makes 140 hp at 9000 rpm, 4500 rpm or what ever doesn't matter for the performance. The only reason for using the larger engine in the boat is cost reasons. With cars one reason to use low rev. engines is because of driveability, and of course the cost issue.

With gas turbines for example they are always using very high revs, but it's simple to gear them down to the speed that is needed.

It should also be noted that an engine with a given bore area can produce the same amount of power almost independant on displcement (stroke). So, the high revving engines usually use a large bore area but a short stroke, which means that they can produce a lot of power with a small displacement.

[MagicRat]

Originally Posted by SaabJohan

Have you heard about the gearbox?
A nice little invention that makes it possible to change the output speed to whatever speed you want!

When you are pulling loads, accelerate fast or whatever the only thing that counts it the power, if you have power you have torque I can guarantee you that. So if the engine makes 140 hp at 9000 rpm, 4500 rpm or what ever doesn't matter for the performance. The only reason for using the larger engine in the boat is cost reasons. With cars one reason to use low rev. engines is because of driveability, and of course the cost issue.

With gas turbines for example they are always using very high revs, but it's simple to gear them down to the speed that is needed.

It should also be noted that an engine with a given bore area can produce the same amount of power almost independant on displcement (stroke). So, the high revving engines usually use a large bore area but a short stroke, which means that they can produce a lot of power with a small displacement.

Saab, your sarcasm is completely unjustified. You seem to have missed the point of my post which was deliberatly made to be as simple as possible, since the thread starter is obvoiusly a beginner in things automotive.

So for my boat, IT HAS NO GEARBOX. One gear direct drive, like every other boat out there. Boats must have a propellor pitch and size and the final drive ratio matched to the torque curve.

To say that the only reason the larger engine is used is for cost is an astonishingly ignorant statement for you Saab, as it excludes a variety of performance and manufacutring issues.

[Rufe]

Originally Posted by SaabJohan

... So if the engine makes 140 hp at 9000 rpm, 4500 rpm or what ever doesn't matter for the performance. ...

I have to disagree.
If the peak torque output was tuned for 9000 rpm, the engine is only making 81.5 ft.lbs of torque, the torque output for the same HP at 4500 rpms is 163.5 ft.lbs. Which engine would you run in a truck? which engine would you run in a lightweight Honda? Big difference here in power delivery.

With more displacement, you can tune the engine for a wider powerband, or more power overall.

With more displacement, you can have a less stressed engine, it will operate at lower rpms, it will last longer, and may actually get better mileage.

A car company can also add displacement to an existing design, as a cheaper alternative to designing a new engine when more power is needed. (classic hotrod trick)

And don't throw high tech engineering in for one engine, and not the other, as an arguement for smaller displacement.

[MagicRat]

Originally Posted by Rufe

I have to disagree.
If the peak torque output was tuned for 9000 rpm, the engine is only making 81.5 ft.lbs of torque, the torque output for the same HP at 4500 rpms is 163.5 ft.lbs. Which engine would you run in a truck? which engine would you run in a lightweight Honda? Big difference here in power delivery.

With more displacement, you can tune the engine for a wider powerband, or more power overall.

With more displacement, you can have a less stressed engine, it will operate at lower rpms, it will last longer, and may actually get better mileage.

A car company can also add displacement to an existing design, as a cheaper alternative to designing a new engine when more power is needed. (classic hotrod trick)

And don't throw high tech engineering in for one engine, and not the other, as an arguement for smaller displacement.

Good points.

[958Rocky]

Uh the gearbox multiplies torques which means you have enough power to tow and accelerate.

A truck could be powered by an S2000 motor, it would be a horrible to drive but it would work just as well as a truck powered by a 5 + liter 240 hp motor

[CBFryman]

Originally Posted by MagicRat

Saab, your sarcasm is completely unjustified. You seem to have missed the point of my post which was deliberatly made to be as simple as possible, since the thread starter is obvoiusly a beginner in things automotive.

So for my boat, IT HAS NO GEARBOX. One gear direct drive, like every other boat out there. Boats must have a propellor pitch and size and the final drive ratio matched to the torque curve.

To say that the only reason the larger engine is used is for cost is an astonishingly ignorant statement for you Saab, as it excludes a variety of performance and manufacutring issues.

well actually there is a wakeboard/wakesurf boat that has a 2 speed V-drive....one to stay on plane at a low rate of speed and hold that speed for long distances (for wakesurfing) and one to bring the boat up to a higher speed (for wakeboarding) i dont remember what company made it...maybe Tige'...or Momba....i know it wasn't master craft or air nautique.... but anyway yes, you did have a good point...

[Alastor187]

Originally Posted by Rufe

I have to disagree.
If the peak torque output was tuned for 9000 rpm, the engine is only making 81.5 ft.lbs of torque, the torque output for the same HP at 4500 rpms is 163.5 ft.lbs. Which engine would you run in a truck? which engine would you run in a lightweight Honda? Big difference here in power delivery.

This is where SaabJohan’s comment about the gearbox comes in to play. By using a transmission to multiply the torque similar performance can be achieved for both engines. Assume the 4500 rpm engine uses a 1:1 gear ratio to drive the wheels. Then at a road speed corresponding to a wheel speed of 4500 rpms the drive wheels will generate 163.4 lb-ft of torque (w/ 24" tire OD). If a 2:1 gear ratio is used with the 9000 rpm engine the same road speed is generated (9000 rpm / 2), the same torque is generated (81.7 lb-ft * 2), and even the same power.

Originally Posted by Rufe

With more displacement, you can tune the engine for a wider powerband, or more power overall.

You can do that with any engine regardless of displacement.

Originally Posted by Rufe

And don't throw high tech engineering in for one engine, and not the other, as an arguement for smaller displacement.

Very good point, that is often done in arguments about displacement.