Rev Limiter Question
Burning Brakes
Joined: Feb 2010
Posts: 1,143
Likes: 29
From: Apex, North Carolina
Is it true that the rev limiter will not kick in if you skip a gear? Say, from first to third? Not that I'm in the habit of doing that. It seems I read that in the 993 E. Companion.
Rennlist Member
Joined: May 2002
Posts: 23,303
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From: Baltimore, MD
I would be amazed if this were true and can see no practical reason for the factory to program this for the limiter.
Banned
Joined: May 2008
Posts: 7,299
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From: Arlington Heights, IL
Burning Brakes
Joined: Feb 2010
Posts: 1,143
Likes: 29
From: Apex, North Carolina
From Adrian Streathers 993 Book, page 190 :
"RPM Limiter
The DME(ECU) software has a built-in limiter to protect the engine against over-revving. This protection only works when shifting gears up or down in a known pattern. The rpm limiting system does not protect over-revving when a gear is missed.
Example: shifting from 4th gear to 1st gear and forgetting to go via 3rd and 2nd gears."
Perhaps he is mistaken? I agree that it does not make any sense.
"RPM Limiter
The DME(ECU) software has a built-in limiter to protect the engine against over-revving. This protection only works when shifting gears up or down in a known pattern. The rpm limiting system does not protect over-revving when a gear is missed.
Example: shifting from 4th gear to 1st gear and forgetting to go via 3rd and 2nd gears."
Perhaps he is mistaken? I agree that it does not make any sense.
RL Technical Advisor
Joined: May 2001
Posts: 11,870
Likes: 75
From: Portland Oregon
The DME(ECU) software has a built-in limiter to protect the engine against over-revving. This protection only works when shifting gears up or down in a known pattern. The rpm limiting system does not protect over-revving when a gear is missed.
Example: shifting from 4th gear to 1st gear and forgetting to go via 3rd and 2nd gears."
Perhaps he is mistaken? I agree that it does not make any sense.
Example: shifting from 4th gear to 1st gear and forgetting to go via 3rd and 2nd gears."
Perhaps he is mistaken? I agree that it does not make any sense.
The rev limiter doesn't function when the car's speed and weight force the revs too high when there is no load. This can occur when too low a gear for the current speed is selected during a downshift and the engine's revs are forced too high after the clutch is released.
Skipping gears under load such as when upshifting preserves the rev limiter function and it works just fine.
Banned
Joined: May 2008
Posts: 7,299
Likes: 19
From: Arlington Heights, IL
From Adrian Streathers 993 Book, page 190 :
"RPM Limiter
The DME(ECU) software has a built-in limiter to protect the engine against over-revving. This protection only works when shifting gears up or down in a known pattern. The rpm limiting system does not protect over-revving when a gear is missed.
Example: shifting from 4th gear to 1st gear and forgetting to go via 3rd and 2nd gears."
Perhaps he is mistaken? I agree that it does not make any sense.
"RPM Limiter
The DME(ECU) software has a built-in limiter to protect the engine against over-revving. This protection only works when shifting gears up or down in a known pattern. The rpm limiting system does not protect over-revving when a gear is missed.
Example: shifting from 4th gear to 1st gear and forgetting to go via 3rd and 2nd gears."
Perhaps he is mistaken? I agree that it does not make any sense.
Instructor
Joined: Feb 2003
Posts: 193
Likes: 1
From: Woodinville WA
During acceleration it is pretty common (with a straight cut/sequential transmission) to apply firm pressure on the shifter and when the engine loses power as it hits the limiter, the pressure on the gears is reduced and the transmission will shift. This works well on a bike.
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Race Car
Joined: Mar 2006
Posts: 4,515
Likes: 245
From: Montreal, QC
During acceleration it is pretty common (with a straight cut/sequential transmission) to apply firm pressure on the shifter and when the engine loses power as it hits the limiter, the pressure on the gears is reduced and the transmission will shift. This works well on a bike.
Best,
Matt
Rennlist Member
Joined: May 2002
Posts: 23,303
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From: Baltimore, MD
During acceleration it is pretty common (with a straight cut/sequential transmission) to apply firm pressure on the shifter and when the engine loses power as it hits the limiter, the pressure on the gears is reduced and the transmission will shift. This works well on a bike.
Nordschleife Master
Joined: Jul 2007
Posts: 5,613
Likes: 52
From: DFW, TX
It's not really "technique" but more along the lines of mechanics.
You cannot easily pull the transmission out of gear w/o using the clutch if the gears are under load (i.e. accelerating or decelerating) but you can easily pull it out of gear w/o the clutch during that transition moment between accel and decel (or vice-versa).
You don't really have to be driving the car hard to try this theory out either.
Next time you're in your car (or any manual car if you prefer not to try it in your Porsche), just start driving, get up to maybe 2nd gear in the 15-20mph range. As you're accelerating in 2nd, start applying light pressure on the shifter as if you're going to go from 2nd to 3rd. As you apply pressure to the shifter, lift off the throttle, the shifter should pull out of 2nd easily, and as the revs drop and you continue to hold pressure on the shifter to get it into the 3rd gate, the shifter should fall into the 3rd gear gate when the revs fall in line w/ the relative speed at which 3rd gear would be at the speed the car is traveling.
Obviously, you don't want to make it a habit of going around shifting sans clutch, but it is possible.
I assume most of you have not raced at autocross w/ hyper competitive drivers? Those guys will shamelessly ride the hell out of their limiters every single weekend if it happen to be the fastest way through a section of the course.
You cannot easily pull the transmission out of gear w/o using the clutch if the gears are under load (i.e. accelerating or decelerating) but you can easily pull it out of gear w/o the clutch during that transition moment between accel and decel (or vice-versa).
You don't really have to be driving the car hard to try this theory out either.
Next time you're in your car (or any manual car if you prefer not to try it in your Porsche), just start driving, get up to maybe 2nd gear in the 15-20mph range. As you're accelerating in 2nd, start applying light pressure on the shifter as if you're going to go from 2nd to 3rd. As you apply pressure to the shifter, lift off the throttle, the shifter should pull out of 2nd easily, and as the revs drop and you continue to hold pressure on the shifter to get it into the 3rd gate, the shifter should fall into the 3rd gear gate when the revs fall in line w/ the relative speed at which 3rd gear would be at the speed the car is traveling.
Obviously, you don't want to make it a habit of going around shifting sans clutch, but it is possible.
I assume most of you have not raced at autocross w/ hyper competitive drivers? Those guys will shamelessly ride the hell out of their limiters every single weekend if it happen to be the fastest way through a section of the course.
