hit the rev limiter!
10-02-2005, 12:32 AM
#1
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hit the rev limiter!
had the shark down for almost 1 FREAKIN' MONTH due to me having a flat tire causing me to pull the intake (posted about this a month ago). Took forever to get my 86.5 only intake gastets in (the ones that cost me my first-born son) as they only made them 1/2 a year...
Anyways, on the first test drive back on the road (and MAN I REALLY LOVE THIS CAR!!!!), I decided to give it a little gas out in the country from a stop light. I flipped my toggle switch (Auto Transmission) while turning on the side farm road (that is my manual kickdown switch) but forgot I had it in 2nd gear. The car goes roaring through first, up to 2nd and to 6500 RPM (I have Autothority chips) with me wondering why it hadn't shifted yet, and then bounce-bounce-bounce-bounce-bounce very quickly at that rpm limit while I finally realized I still had it in 2nd! Huh - rev limiter I say to myself - cool!
Anyways, I'm not one to drive it up to/past the redline normally (I don't baby it though), but for a first time, it was pretty cool and nice to know we have this safety-feature built in and I won't float the valves while forgetting to shift. These cars still amaze me as to how they just keep pulling and pulling when the revs come up. I couldn't imagine what a SC or Turbo would be like! (don't want to start any wars here
). It feels like a new car after not being able to drive it for a month... I couldn't imagine moving back up north when you have to park these things for months on end.
Anyways, on the first test drive back on the road (and MAN I REALLY LOVE THIS CAR!!!!), I decided to give it a little gas out in the country from a stop light. I flipped my toggle switch (Auto Transmission) while turning on the side farm road (that is my manual kickdown switch) but forgot I had it in 2nd gear. The car goes roaring through first, up to 2nd and to 6500 RPM (I have Autothority chips) with me wondering why it hadn't shifted yet, and then bounce-bounce-bounce-bounce-bounce very quickly at that rpm limit while I finally realized I still had it in 2nd! Huh - rev limiter I say to myself - cool!
Anyways, I'm not one to drive it up to/past the redline normally (I don't baby it though), but for a first time, it was pretty cool and nice to know we have this safety-feature built in and I won't float the valves while forgetting to shift. These cars still amaze me as to how they just keep pulling and pulling when the revs come up. I couldn't imagine what a SC or Turbo would be like! (don't want to start any wars here
). It feels like a new car after not being able to drive it for a month... I couldn't imagine moving back up north when you have to park these things for months on end.
10-02-2005, 03:27 AM
#5
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How do you eliminate the rev limiter? It operates (at least in early models) by fuel starvation, which can be sudden death to a supercharged/turbocharged car as it cuts the fuel on and off - cycles of fuel starvation. It is a low $ way to have a rev limiter, but ignition reduction is better.
10-02-2005, 03:37 AM
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Supercharged 928s drive like a big block and turbocharged cars really rely much on rev limiters as the higher the rpms, the harder it pulls (increasing boost until wastegate kicks in.)
I doubt floating the valves is going to happen on an 86 32V. There reportedly is an oiling problem to a couple of the crankshaft main bearings much beyond 6,000 rpm is sustained (this last comment is hearsay from others in this forum.)
Did you also play with it in the corners? It is extremely unlikely that your courage exceeds the corning ability of your 86 1/2.
You probably noticed difficulty having a sense of speed without looking at the speedometer. 928s in their magazine reviews and owners both come to quickly understand that a 928 has basically the same feel at 50 miles per hour and 150 miles per. It is difficult (for the longer ratio models particularly) to tell much difference in movement between 45 and 85 mph.
Yeah, these a great cars. That is why they cost from $150,000 to about $210,000 in today-dollars, depending upon the model year.
Your 86 1/2 is very fast and even faster in the corners.
If you just got it, quickly check (or have checked ) the cam belt tension (if you are new to 928s). If the belt slips, you lose your motor. After that, every 15,000 miles or so, unless you drive it REALLY hard...
Others probably would suggest more often and it would depend probably on belt age/mileage also.
Mark
I doubt floating the valves is going to happen on an 86 32V. There reportedly is an oiling problem to a couple of the crankshaft main bearings much beyond 6,000 rpm is sustained (this last comment is hearsay from others in this forum.)
Did you also play with it in the corners? It is extremely unlikely that your courage exceeds the corning ability of your 86 1/2.
You probably noticed difficulty having a sense of speed without looking at the speedometer. 928s in their magazine reviews and owners both come to quickly understand that a 928 has basically the same feel at 50 miles per hour and 150 miles per. It is difficult (for the longer ratio models particularly) to tell much difference in movement between 45 and 85 mph.
Yeah, these a great cars. That is why they cost from $150,000 to about $210,000 in today-dollars, depending upon the model year.
Your 86 1/2 is very fast and even faster in the corners.
If you just got it, quickly check (or have checked ) the cam belt tension (if you are new to 928s). If the belt slips, you lose your motor. After that, every 15,000 miles or so, unless you drive it REALLY hard...
Others probably would suggest more often and it would depend probably on belt age/mileage also.
Mark
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10-02-2005, 05:04 AM
#8
DFWX,
I might be wrong but as I was wandering thru the WSM's the other night there were some confusing Distributor info:
WSM -pg 28-1 & 28-2
Without reference to year but a reference to model 928 and distributor model;
928 602 032 01, or, Bosch# o 237 401 006 with centrifugal advance
and vacuum retard . An additional note refers you to the next page which basically says:
the fuel pump relay is designed to cut fuel at 6300rpm.( Signal from dist? Tach?)
WSM -pg 28-20 Model 928
List's the Distributor as 928 602 032 03, or, Bosch # 0 237 405 010
Centrifugal and vacuum advance and retard. Distributor rotor without rev. limiter.
WSM -pg 28-21
NOTE:
List's Distributor vacuum control range change and is identified with
928 602 032 04 Bosch# 0237 405 020 no mention of limiter.
WSM pg 28-27 Model 928 S
928 602 032 06 Bosch# 0 237 401 018 Distributor rotor without speed govenor.
WSM pg 28-31 MY 928 S 1983 blah blah blah
There are year gaps that may be filled in by engine model M28 - whatever but I haven't cross referenced that yet.
I might be wrong but as I was wandering thru the WSM's the other night there were some confusing Distributor info:
WSM -pg 28-1 & 28-2
Without reference to year but a reference to model 928 and distributor model;
928 602 032 01, or, Bosch# o 237 401 006 with centrifugal advance
and vacuum retard . An additional note refers you to the next page which basically says:
the fuel pump relay is designed to cut fuel at 6300rpm.( Signal from dist? Tach?)
WSM -pg 28-20 Model 928
List's the Distributor as 928 602 032 03, or, Bosch # 0 237 405 010
Centrifugal and vacuum advance and retard. Distributor rotor without rev. limiter.
WSM -pg 28-21
NOTE:
List's Distributor vacuum control range change and is identified with
928 602 032 04 Bosch# 0237 405 020 no mention of limiter.
WSM pg 28-27 Model 928 S
928 602 032 06 Bosch# 0 237 401 018 Distributor rotor without speed govenor.
WSM pg 28-31 MY 928 S 1983 blah blah blah
There are year gaps that may be filled in by engine model M28 - whatever but I haven't cross referenced that yet.
10-02-2005, 05:22 AM
#9
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Thanks for the info... A rev limiter is a good idea in general, but fuel starvation not the way for a boosted motor and, of course, if a person wants higher rpms obviously. From what you wrote, it seems that the rpm sensing is coming from the distributor, but is maybe overall feed into the system's computer and therefore difficult to defeat without knocking other components out (such as
tach, possible dist. advance etc...
I would think the 928 racers would have the answer if they stuck with stock FMU as they would go beyond factory redline - which generally is quite a bit on the conservative side.
Mark
tach, possible dist. advance etc...
I would think the 928 racers would have the answer if they stuck with stock FMU as they would go beyond factory redline - which generally is quite a bit on the conservative side.
Mark
10-02-2005, 06:30 PM
#13
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The 'distributor rev limiter' from Bosch is the rotor with a spring contact inside. At rev-limt, the centrifugal force causes the rotor to 'open', cutting spark. For catalyst cars, cutting spark without cutting fuel is a ticket to a fire, hence the switch to fuel cut-off. I guess I'd look at some combination for the SC or turbo cars, where the rotor opens and the fuel pump cuts off. To do this right, though, the solution might be to configure the ignition power to come from the fuel pump relay, possibly through another relay (?). I haven't looked at those schematics to see how all this would play, but that's certainly the method I'd look to.
Rev-limiting rotors are seldom know to fail, but they can. Cars with dual distributors might see slight differences in speed at which the ignition is killed. Tough on cranks and torque tubes. Moderrn hi-voltage ignition units will often kill a coil if the secondary circuit is open, when voltage exceeds insulation breakdown. If the rotors are your only option, they are better than nothing in a pinch.
Good discussion.
Rev-limiting rotors are seldom know to fail, but they can. Cars with dual distributors might see slight differences in speed at which the ignition is killed. Tough on cranks and torque tubes. Moderrn hi-voltage ignition units will often kill a coil if the secondary circuit is open, when voltage exceeds insulation breakdown. If the rotors are your only option, they are better than nothing in a pinch.
Good discussion.
10-02-2005, 11:36 PM
#14
Nordschleife Master
A couple of note on the distributor rev limiter...at least the one on my '80 Euro
The cut-out function is done by grounding the spark into the shaft.
The RPM is variable using a pliers. Simple and easy.
The cut-out function is done by grounding the spark into the shaft.
The RPM is variable using a pliers. Simple and easy.
