How does a rev limiter work?
01-02-2003, 04:42 PM
#1
Drifting
Thread Starter
How does a rev limiter work?
I've been wondering this for a while and thought I'd through it out for discussion.
What limit do most chips have it set at?
Justin
What limit do most chips have it set at?
Justin
01-02-2003, 05:55 PM
#2
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For the 944/951, the DME quits pulsing the injectors, for a certain time period, when the current RPM exceeds the rev limit hard coded in EPROM. If you set the rev limit real low (~ 2000 rpm) Motronic will gently bounce the engine against the limit and you can't rev any higher. At the normal rev limit of 6480 your head will bounce off the steering wheel when you hit the rev limit.
Rev limit for the chips I have seen:
Autothority - 7000 rpm (one at 7040)
Welt/Dinan - 7000 rpm
86-87 944/86-89 951 Stock and most aftermarket chips - 6480 rpm
88 944 - 6640 rpm
Rev limit for the chips I have seen:
Autothority - 7000 rpm (one at 7040)
Welt/Dinan - 7000 rpm
86-87 944/86-89 951 Stock and most aftermarket chips - 6480 rpm
88 944 - 6640 rpm
01-02-2003, 11:07 PM
#3
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[quote]Originally posted by TT:
<strong>For the 944/951, the DME quits pulsing the injectors, for a certain time period, when the current RPM exceeds the rev limit hard coded in EPROM. If you set the rev limit real low (~ 2000 rpm) Motronic will gently bounce the engine against the limit and you can't rev any higher. At the normal rev limit of 6480 your head will bounce off the steering wheel when you hit the rev limit.
Rev limit for the chips I have seen:
Autothority - 7000 rpm (one at 7040)
Welt/Dinan - 7000 rpm
86-87 944/86-89 951 Stock and most aftermarket chips - 6480 rpm
88 944 - 6640 rpm</strong><hr></blockquote>
<img src="graemlins/roflmao.gif" border="0" alt="[hiha]" /> <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />
<strong>For the 944/951, the DME quits pulsing the injectors, for a certain time period, when the current RPM exceeds the rev limit hard coded in EPROM. If you set the rev limit real low (~ 2000 rpm) Motronic will gently bounce the engine against the limit and you can't rev any higher. At the normal rev limit of 6480 your head will bounce off the steering wheel when you hit the rev limit.
Rev limit for the chips I have seen:
Autothority - 7000 rpm (one at 7040)
Welt/Dinan - 7000 rpm
86-87 944/86-89 951 Stock and most aftermarket chips - 6480 rpm
88 944 - 6640 rpm</strong><hr></blockquote>
<img src="graemlins/roflmao.gif" border="0" alt="[hiha]" /> <img src="graemlins/roflmao.gif" border="0" alt="[hiha]" />
01-03-2003, 12:40 AM
#4
Race Director
"At the normal rev limit of 6480 your head will bounce off the steering wheel when you hit the rev limit."
I think that's for the overboost-protection where it cuts the fuel completely! Better have your seatbelt on securely.
But the rev-limit is much softer than that. I've gotten caught up in the heat of a drag-race and can't figure out why I'm not accelerating any more. Then DOH! time to shift.
Could the rev-limit behavior be different amongst the different chips out there?
I think that's for the overboost-protection where it cuts the fuel completely! Better have your seatbelt on securely.
But the rev-limit is much softer than that. I've gotten caught up in the heat of a drag-race and can't figure out why I'm not accelerating any more. Then DOH! time to shift.
Could the rev-limit behavior be different amongst the different chips out there?
01-03-2003, 02:42 AM
#6
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[quote] I think that's for the overboost-protection where it cuts the fuel completely! Better have your seatbelt on securely.
<hr></blockquote>
Motronic uses the same flag and counter value to cut fuel for both overboost and rev limit. When looking over the code at first, I missed the overboost protection since it was modifying the same values as the rev limit code.
Having hit the redline in the 944 and overboost in the 951, I have felt no difference in the effect, its like hitting a wall. I believe that it would be different if you were to hit the rev limit while not under heavy acceleration. Since I replaced the engine in my 86 944 with a 88 944 engine and DME, I have never hit the rev limit at 6640. That little bit extra helps alot.
In my 951, the Dinan chip rev limit is 7000. In 1st and 2nd I can get to that limit easily since the turbo is not really under much load. For 3rd and up anything above 6400 causes my car to hit the overboost limit due to maxing out the stock air flow meter at high rpm. That problem won't remain much longer.
<hr></blockquote>
Motronic uses the same flag and counter value to cut fuel for both overboost and rev limit. When looking over the code at first, I missed the overboost protection since it was modifying the same values as the rev limit code.
Having hit the redline in the 944 and overboost in the 951, I have felt no difference in the effect, its like hitting a wall. I believe that it would be different if you were to hit the rev limit while not under heavy acceleration. Since I replaced the engine in my 86 944 with a 88 944 engine and DME, I have never hit the rev limit at 6640. That little bit extra helps alot.
In my 951, the Dinan chip rev limit is 7000. In 1st and 2nd I can get to that limit easily since the turbo is not really under much load. For 3rd and up anything above 6400 causes my car to hit the overboost limit due to maxing out the stock air flow meter at high rpm. That problem won't remain much longer.
