[ojis]

Originally Posted by NarutoRamen

it's just nor right to call a grocery getter a High-revving car. know what I mean?

What about BMW M5 touring?

[NarutoRamen]

Originally Posted by ojis

What about BMW M5 touring?

V10 engine isn't really a grocery getter car now is it?

I wasn't talking about cars in general btw...I was referring to my honda because hondas and toyotas are usually called grocery getters in the US.

[chonkoa]

Originally Posted by martinbo

Ooo vedjo01

I don't think that by increasing piston speeds you will necessarily lose torque; torque is a product of displacement and not piston speed. Increasing piston speed will produce more power since this is a product of either:

- Stroke length
- RPM

Torque by itself is not RPM dependent, however engine torque is because of the cycle speed.


Engine Torque=P*A*R*Z
P= effective piston Pressure
A= Piston cross sectional area
Z= Number of pistons/Cylinders
R= Radius arm of the piston.

Because we are dealing with a dynamic state, the effective piston pressure is engine speed dependent.
The effective pressure is dependent on the volume of fuel+air mixture:heavier fuel will give more pressure, so will more air in the cylinder
The effective piston pressure is maximum at zero speed and exponentially decay with increasing engine speed. This decay is due to not having enough time for air to fill combustion chamber(turbo engines addresses this problem)

So then, why does torque increase at then decrease? The reason for this are the following:.

1. At zero speed, only half of the cylinders are generating torque, and since this is a cycle, you have to average for the entire cycle.
2. As you increase the speed, more cylinders/unit time contributes to the engine torque, however the torque generated per cylinder decreases exponentially
3. There reaches a speed where the torque generated per cylinder/stroke is so low that the overall engine torque starts to decrease.

[martinbo]

Aw gee, you know how long I've been waiting for that post! Hey chonkoa - good work dude! Nice and concise explanation that makes perfect sense.

Now that's the kind of posting we need in the tech talk forum...

By radius arm of the piston I gather this refers to the stroke length?

[Imhotep Evil]

Originally Posted by chonkoa

Torque by itself is not RPM dependent, however engine torque is because of the cycle speed.


Engine Torque=P*A*R*Z
P= effective piston Pressure
A= Piston cross sectional area
Z= Number of pistons/Cylinders
R= Radius arm of the piston.

Because we are dealing with a dynamic state, the effective piston pressure is engine speed dependent.
The effective pressure is dependent on the volume of fuel+air mixture:heavier fuel will give more pressure, so will more air in the cylinder
The effective piston pressure is maximum at zero speed and exponentially decay with increasing engine speed. This decay is due to not having enough time for air to fill combustion chamber(turbo engines addresses this problem)

So then, why does torque increase at then decrease? The reason for this are the following:.

1. At zero speed, only half of the cylinders are generating torque, and since this is a cycle, you have to average for the entire cycle.
2. As you increase the speed, more cylinders/unit time contributes to the engine torque, however the torque generated per cylinder decreases exponentially
3. There reaches a speed where the torque generated per cylinder/stroke is so low that the overall engine torque starts to decrease.

Thanks.

So there actually is a way to keep up (some) torque as the rpms/speed goes up. In the old F1 V10s they had variable intake systems, variable exhaust systems and variable valve control systems, and (still have) control over air-fuel mixture. Constant adjustments to this from the steering wheel buttons/switches meant a better torque curve.

[Just_me]

the new Skyline is getting Turbo and redline at 7600 rpm. Pretty high for a Turbo car.

[NarutoRamen]

Originally Posted by Just_me

the new Skyline is getting Turbo and redline at 7600 rpm. Pretty high for a Turbo car.

The japanese have always had Hi-revving Turbo cars. I don't know how, but they always manage.

[martinbo]

Originally Posted by NarutoRamen

The japanese have always had Hi-revving Turbo cars. I don't know how, but they always manage.

I've heard of JDM STI Spec C's running to 7500 rpm. That's very high for a turbo'd mill.

[NarutoRamen]

Originally Posted by martinbo

I've heard of JDM STI Spec C's running to 7500 rpm. That's very high for a turbo'd mill.

hmm, I'll have to look into that. My favourite is the (GC8) Impreza STI Type-R...just love that thing. Didn't that also have a pretty high redline?

[speed_kills]

I think it is 7250 for the Impreza. I remember seeing in the net a Evo revving to 8000, on the redline of course...