Optimum shift time in Boxster S

[blue2000s]

Originally Posted by 2000SoCalBoxsterS

I will take my Boxster owners manual and look up the gear ratios and take the power and torque numbers from there and in put them. Why can't I adjust the size on your spread sheet? And I'd like to make the lines on the graph thicker so I can read them better.

It's locked so you can only edit the fields that I designated.

[2000SoCalBoxsterS]

O.K. I plugged in my variables. Shift ratios same as on your sheet. I have 18" wheels with 265/35 tires on the rear. My owners manual only shows my torque in NM at rpms. They look like this:

Enter Engine Speed, RPM Enter the engine torque, ft-lb
1500 240
2000 258
2500 265
3000 280
3500 285
4000 300
4500 302
5000 302
5500 300
6000 290
6500 265
7000 240

But the Drive Torque Chart output doesn't look right? The Wheel Torque Lb-ft scale is in thousands? Showing me that for example at 25 mph I am at 3500 Ft-Lbs? How am I supposed to read this? Use this info?

The stats on my Boxster from Porsche say I have 250 HP / 225 Ft-Lbs at 6250 rpm
Seems to me based on the graphs in my manual that 4,000 to 5,000 is the peak power band.

What am I missing here? I'm not being critical I just don't understand and I want to learn this stuff.

[blue2000s]

Originally Posted by 2000SoCalBoxsterS

O.K. I plugged in my variables. Shift ratios same as on your sheet. I have 18" wheels with 265/35 tires on the rear. My owners manual only shows my torque in NM at rpms. They look like this:

Enter Engine Speed, RPM Enter the engine torque, ft-lb
1500 240
2000 258
2500 265
3000 280
3500 285
4000 300
4500 302
5000 302
5500 300
6000 290
6500 265
7000 240

But the Drive Torque Chart output doesn't look right? The Wheel Torque Lb-ft scale is in thousands? Showing me that for example at 25 mph I am at 3500 Ft-Lbs? How am I supposed to read this? Use this info?

The stats on my Boxster from Porsche say I have 250 HP / 225 Ft-Lbs at 6250 rpm
Seems to me based on the graphs in my manual that 4,000 to 5,000 is the peak power band.

What am I missing here? I'm not being critical I just don't understand and I want to learn this stuff.

It doesn't look like the torque you've got in the columns is correct. You need to have the torque in ft-lb. So it should be 225 at around 6000 rpm and less everywhere else.

Wheel torque in the 2000-3000s in 1st gear is correct. It takes alot of torque to get the car moving quickly.

Then all the plot is telling you is which gear is putting down the most torque for any given vehicle speed (at wide open throttle). If there is a cross-over point from say the 3rd and 4th gear ratios, that's where you'd shift for max acceleration. If they never cross, then you want to shift at redline because you will be making more torque than you would in the higher gear.

Try different torque curves or gear ratios and see what happens to the plot. For example, if a torque curve peaks early and drops off quickly, like a diesel engine would, but your ratios are still tall, you'll see there's alot of crossing of the lines. This would indicate that you want to shift before redline in those gears for the best acceleration.

[Brucelee]

What was the original question again?

[choddy]

I'm a new owner of a 99 Boxster. I have been wondering what is the correct way to drive this car. Is it true that I should shift gears on the red-line...always? Or...at 6K? Help.

[Brucelee]

Originally Posted by choddy

I'm a new owner of a 99 Boxster. I have been wondering what is the correct way to drive this car. Is it true that I should shift gears on the red-line...always? Or...at 6K? Help.

Taking this question at face value, I find it a tad absurd.

Are you suggesting that for on street driving you would shift at 6K RPM in every shift at all times? Or, are you suggesting that if you were tracking the car, that you would drive this way for the fastest lap times?

I don't know any practicable way you could always shift at 6K on the street unless you live in the remote areas of Wyoming.

Nor, would you want to. This way of driving would ensure that you:

Receive speeding tickets

Be involved in accidents

Likely go to jail

Get about 10 MPG

Replace tires every 6K miles

Need new brakes, clutches, every 20K miles

Replace the engine in about 2 yrs. or less

Make sense?

[Adam]

On top of that you shouldn't ever rev a cold engine that high. Keeping it below 4k rpm is a good idea until the engine is up to temp.