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Old 04-08-2011, 08:14 PM   #1
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raise rev limiter/shift point on 986 Boxster?

Is there any way to do it?

Sorry for being so blunt on my first post, i'm unable to search for it.

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Old 04-09-2011, 04:30 AM   #2
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Why?

The peak power band is from about 4,500 RPM to about 6,500 RPM.

Is your a Tip?
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Old 04-09-2011, 08:17 AM   #3
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I'm turbo. I'm certain my powerband goes over 7,500rpm if it was raised to that level.
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Old 04-09-2011, 08:31 AM   #4
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Quote:
Originally Posted by Flavor 987S
Why?

The peak power band is from about 4,500 RPM to about 6,500 RPM.

Is your a Tip?
Max torque at the road is at redline in every gear.
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Old 04-09-2011, 08:32 AM   #5
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Originally Posted by promo
I'm turbo. I'm certain my powerband goes over 7,500rpm if it was raised to that level.
Must be done thourgh programming the DME (ECU)
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Old 04-09-2011, 09:23 AM   #6
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Originally Posted by blue2000s
Must be done thourgh programming the DME (ECU)
Who can do that for me? Is there a tuning company I should get a hold of?
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Old 04-09-2011, 10:05 AM   #7
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If your car is turbo'd then you have had the dme reprogrammed correct? Then your tuner could have done that for you. Even if that was done you would have had to redo the valve springs and valve train. The limiter is there because that is the design limit of the motor.

Pics please. Interested in seeing the kit. There only a few out there.
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Old 04-09-2011, 10:12 AM   #8
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Quote:
Originally Posted by blue2000s
Max torque at the road is at redline in every gear.
LOL! That's news to Porsche (and me).

Boxster S 3.2L
280 HP
236 lb.-ft. at 4,700-6,000 RPM
Redline is 7,200

993 Twin Turbo 3.6L
400 HP
400 lb. ft. at 3,500-5,500 RPM
Redline is 6,700

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Old 04-09-2011, 11:47 PM   #9
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Quote:
Originally Posted by Flavor 987S
LOL! That's news to Porsche (and me).

Boxster S 3.2L
280 HP
236 lb.-ft. at 4,700-6,000 RPM
Redline is 7,200

993 Twin Turbo 3.6L
400 HP
400 lb. ft. at 3,500-5,500 RPM
Redline is 6,700
I doubt it's news to Porsche, all engineers learn this in school, maybe to you though. Multiply the torque by the gear ratios and wheel diameter. There's always more torque at redline in the lower gear than at the same road speed in the next gear up in a street Porsche.

Last edited by blue2000s; 04-10-2011 at 12:02 AM.
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Old 04-10-2011, 03:32 AM   #10
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Hey blue2000s

I think ur getting engine torque mixed up with gearing. Yes a lower gear will produce more torque, but the engine will be losing it pulling power as the rev rise. So yes u are correct a lower gear at 40kmh will produce more torque than 40kmh at a higher gear, but ur poor engines torque output is in decline after it reaches its peak output.

What u will find is even though the higher rev range may be available, if the engines peak torque is at 5000rpm and peak power at 6000 rpm u won't want to rev past 6500 as the engines pulling ability just won't be there, it would be more beneficial to change to the next gear. Remember a gear box only multiplies the engines torque output, and Porsche spent hours working out the ratios to ensure maximum performance through the gears.

If in this case the turbo has changed where peak power and torque is, then yes the limit might need to be raised, but this could have reliability issues for the engine as it was made to rev to a certain limit.
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Last edited by Tobz; 04-10-2011 at 03:45 AM.
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Old 04-10-2011, 04:42 AM   #11
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Blue2000, just look at the graphs in your Owner's Manual. You'll see it.
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Old 04-10-2011, 07:29 AM   #12
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A high reving, turbo M96...sounds like a recipe for disaster. How many hours do you think that engine will last?
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Old 04-10-2011, 08:25 AM   #13
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Quote:
Originally Posted by Tobz
Hey blue2000s

I think ur getting engine torque mixed up with gearing. Yes a lower gear will produce more torque, but the engine will be losing it pulling power as the rev rise. So yes u are correct a lower gear at 40kmh will produce more torque than 40kmh at a higher gear, but ur poor engines torque output is in decline after it reaches its peak output.

What u will find is even though the higher rev range may be available, if the engines peak torque is at 5000rpm and peak power at 6000 rpm u won't want to rev past 6500 as the engines pulling ability just won't be there, it would be more beneficial to change to the next gear. Remember a gear box only multiplies the engines torque output, and Porsche spent hours working out the ratios to ensure maximum performance through the gears.

If in this case the turbo has changed where peak power and torque is, then yes the limit might need to be raised, but this could have reliability issues for the engine as it was made to rev to a certain limit.
Torque follows a curve, but it's multiplied by the gear ratio. As long as the gear ratio is low enough, the torque at the lower gear will exceed the torque at the next gear up. As long as it's making more torque in the lower gear, that's where you get the best acceleration. Just about every sports car will be geared to take advantage of the entire rev range. See attached for the 986S.
Attached Images
 

Last edited by blue2000s; 04-10-2011 at 09:00 AM.
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Old 04-10-2011, 08:26 AM   #14
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Quote:
Originally Posted by Flavor 987S
Blue2000, just look at the graphs in your Owner's Manual. You'll see it.
The plot that I made above came from the data in the owners manual.
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Old 04-10-2011, 08:47 AM   #15
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Turbo M96 engines can be real powerhouses when the engine is stripped and prepped for forced induction. I have yet to have anyone pull the trigger on one of these engines that is ultimately prepped and coupled to an application specific, top of the line turbo system.

Otherwise, you have a grenade with the pin pulled. Instead of "forced induction" its more like "forced failure".
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Old 04-10-2011, 09:22 AM   #16
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Quote:
Originally Posted by Jake Raby
Turbo M96 engines can be real powerhouses when the engine is stripped and prepped for forced induction. I have yet to have anyone pull the trigger on one of these engines that is ultimately prepped and coupled to an application specific, top of the line turbo system.

Otherwise, you have a grenade with the pin pulled. Instead of "forced induction" its more like "forced failure".
Jake, what kind of power would your turbo setup produce and how much would it cost as a fully installed system?
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Old 04-12-2011, 05:04 PM   #17
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Blue2000s, I don't think that this is going to work out as you expect...

As you can see from your plot of Wheel Torque vs Road Speed, 4th gear torque peaks and is going down as the engine reaches the max rpm. It happens to reach max rpm just as it is about to cross below the 5th gear curve. If you extend the redline (increase the max rpm), all you're going to do is extend the 4th gear curve below the 5th gear curve. Which says that you should have shifted.

And in fact, you really should have shifted when the rear wheel torque peaked instead of riding out the decline as it is more beneficial to be on the increasing side of the torque curve than on the decreasing side.

Look at it this way, a CVT transmission does not simply run the engine at max rpm, instead it runs the engine up through the maximum torque.
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Old 04-12-2011, 05:31 PM   #18
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Originally Posted by thstone
Blue2000s, I don't think that this is going to work out as you expect...

As you can see from your plot of Wheel Torque vs Road Speed, 4th gear torque peaks and is going down as the engine reaches the max rpm. It happens to reach max rpm just as it is about to cross below the 5th gear curve. If you extend the redline (increase the max rpm), all you're going to do is extend the 4th gear curve below the 5th gear curve. Which says that you should have shifted.

And in fact, you really should have shifted when the rear wheel torque peaked instead of riding out the decline as it is more beneficial to be on the increasing side of the torque curve than on the decreasing side.

Look at it this way, a CVT transmission does not simply run the engine at max rpm, instead it runs the engine up through the maximum torque.
You stay in the gear that gives you the most torque. Whether it's on the increasing or decreasing side of the slope doesn't matter. If you shift out of a gear to the next and drop in wheel torque more than you would have by staying in gear, you loose acceleration. No way around it.

For max acceleration, a CVT keeps the engine around peak torque and alters the gear ratio to match road speed, which is the way to keep the most torque to the wheels.

You're right about 4th gear in that at redline, it's just crossing 5th gear torque. There's a slight benefit to shifting before redline in 4th. I doubt anyone could hit that exactly right. If the OP just increased redline without altering the engine torque curve, there would be no acceleration benefit in the higher gears, but there would still be benefit in the lower gears. If you alter the torque curve, everything could change.


Last edited by blue2000s; 04-12-2011 at 06:00 PM.
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