Optimum shift time in Boxster S
 

Well after a lot of saving finally managed to get myself an early Boxster S a couple of days ago - wow, what a car!!

I noticed in a technical spec somewhere that it develops it's 252BHP at 6250 RPM and having changed from third to fourth at 6250 and pinning the throttle again it seems to drop right back into the power band..

Other cars I've had go faster overall if you take them to the limiter. Do you think it's faster to change around 6250 or to take it to the limiter?

Thoughts anyone?!

For optimum acceleration, most auto makers will design gearing and powerband in their performance vehicles to be shifted at redline. The Boxster is one of these vehicles.

Yes, you should run the car at redline at all times. I am told that the car will last much longer if you keep the pedal to the floor always.

:D

If you can keep the revs between 3 and 4k (blip the throttle) I think you'll find it will perform nicely; however, running it up higher all the time will surely make it feel faster but it cannot be good for the car to be run up to near redline on every shift!

And yes, I know Brucelee was only kidding.

Pretty sure BruceLee wasn't kidding. Although keeping the throttle pinned at all times might certainly be overdoing it, the engine does need to be revved up and down, at least above 4. It clears the valves and simply allows the engine to wear correctly.

What you also need to consider is when is peak TQ? By keeping the motor between those two peaks, you should have the most power.

You also want to not run the car to redline because, unless the HP and TQ curves show otherwise, peak HP and TQ will drop off (relatively) at that point. I know in my stock 911SC, peak hp was somewhere around 5200rpm and fell off quite abit thereafter (redline was 6250), and peak TQ was around 3700 rpm for instance.

You also dont mention what you wish to optimize? I am assuming speed/acceleration as opposed to Fuel Economy ;)

Uh, no, I'm really pretty sure BruceLee was kidding...

I agree with brucelee...I don't think he was kidding. Everyone is so afraid of running their cars hard. Times have changed from the mustang and camaro days, with the RX-7's and the mitsu 3000GTs and the supra's... cars are more high-tech and built to last much longer and take more abuse.

I also thought it was stupid to always push your car, hitting red-line all the time... but after my ex bought her new lexus IS300 a while back i took it to the dealer for an oil change and the mechanic said "make sure you floor it and shift at redline everywhere you go"... at first i thought it was a joke, but then he told me the cars need it and thrive off of it. This must have been around 2004 I think, and he said all the cars (2004's and other later models, 03, 02, etc) were the same way, they will thrive and there is no negative to driving them as hard as you possibly can. He also said that he noticed the elderly crowd who would always say they pamper the cars were the ones bringing the cars in after 3 or 4 years due to engine problems, etc. He said the 20's crowd and the group who has rims, mods, etc only came in to the dealer for oil changes, and scheduled visits. He was the head mechanic also that told me this. Since then friends have told me the same thing about their cars when they buy'em new.

"Times have changed from the mustang and camaro days, with the RX-7's and the mitsu 3000GTs and the supra's... cars are more high-tech and built to last much longer and take more abuse."

Too bad my RX7 didn't make it :( Also, alot of RX7 owners are throwing in LS1's too make more power and reliability.

OK, here's the way it's done. This will probably lead to some useless torque vs power debate that I won't be participating in.

You look at the torque produced at the wheels in every gear for a given vehicle speed. This gives you a set of curves of torque vs vehicle speed. In fact, this will often give you 3-4 gears to choose from at a given speed. You choose the gear that gives you the highest torque at any given speed and you stay there until redline or until the torque curve drops below the torque curve of the next gear. This is part of the process used to define gear ratios and it's also the process you use to decide what shift pattern will give you the best acceleration. In the Boxster, as with just about every other high performance sports car, redline is where you shift in almost every gear.

Here's a spreadsheet showing what I'm talking about. Take off the .txt extension and unzip it.

http://986forum.com/forums/attachment.php?attachmentid=3282

Keeping RPMs between the torque peak and power peak is incorrect and shifting at power peak is incorrect. You ALWAYS have to look at the torque at the wheels if you want to answer this question correctly.

It clears the valves and simply allows the engine to wear correctly.

Not sure what you mean by this. Can you elaborate?

Shift at 6k and you'll be good to go :)

O.K. so is this spreadsheet interactive where I can plug in my wheel size, tires, torque... and it will give me my shift points?

Yup. You put in the data in the yellow fields and it will output the estimated wheel torque curves. Then you choose the gear that shows the most torque at any given speed.

I think the torque curve in the spreadsheet now is for a 911. I don't remember what car I was looking at when I made that sheet.

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.

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.

What was the original question again?

:D

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?

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.

See?? I TOLD you he was kiddin'.

I come from the honda/acura world where we always shift at redline without any consequence. I shift right before 7,200 very often in most gears.

I agree with Bruce Lee for all of the reasons he lists. It's only common sense. Try driving your Boxster by doing all your shifts at 6K + and if you're smarter than a 5th grader you'll quickly understand why it's not practical unless you are racing on a track.

If you want to know, take it to a dragstrip and do timed runs videoing your tach. Real life stuff, not theoretical. I race sailboats and VMGs and performance plots are one thing, but the race course is where it matters. Obviously one can extrapolate values from the Porsche owner's manual and determine intersection points btwn hp and torque and factor in variables like timing and lift off and such, but whatever....

That's too technical. Shift it when it feels good - for me that's just before fuel cut-off (because I dislike the feeling of the engine stuttering due to fuel starvation).

6000, 6500, 7000, whatever, just keep it pegged until it feels good to you, then shift and do it again. That's the "best" time to shift - the point when you're having fun - and the person beside you is smiling too (or keeping her eyes closed).

Sorry if this isn't technical enough. :dance:

Cheers :)

And Frodo and 70Sixer, you guys crack me up. Good on you :D

Cheers :cheers:

I agree. You explained it perfectly. Forget the technical stuff and "use the Force Luke!"

Thanks for backing me up 2000SoCalBoxsterS you're on my good guy list too. You know me by now, if you have a Pcar ...... floor it ....... and drive safe. Can that be done .......... yes! I do that all the time and my family and friends just love it! :D :D

Ciao (and no that doesn't mean anything more than I like that word) :)