LOL, that's the attitude that got you to the moon!

Whereas reaction time is certainly an issue keep in mind that it also takes time for the engine to rev up and destroy itself at high revs. Split seconds perhaps, but then that's what we're talking about here.

 

Ideally you would want a system that didnt allow the clutch to release ONLY if the gear selected and speed would cause an over rev.

You could have a rpm activated clutch release, would make driving interesting if the car put the clutch in at the redline under acceleration. It would really test the algorithm of the stock rev limiter going from full load and throttle then sticking the clutch it. I suppose you could also design it so the protection mode was only triggered in the second or so after a gear change. The trick is also when to re-engage the clutch after activation.

One things these gearboxes really need is a much stronger centering spring. I've only driven mine a handful of laps, but when you are pulling 1-2lateral G's you need to be very careful with a gear lever with almost no centering action. I replaced the alloy shift knob and stripped the stock lever back to almost nothing to reduce the interia of the whole assembly and found the shift much more precise. The sychro action of the boxes is so good that it doesnt baulk if you select the wrong ratio like lesser transmissions.

Chris.

 

i believe a fringe benifit of the CAGS on a corvette 6 speed is that it locks out the lower gear in a mis shift/ mech over-rev. if this is correct then maybe it can be applied to different applications.

i found a lighter knob resisted normal shifts, so i guess it would be less likely to slot wrong gear, but stronger centering spring mod would be valuable, where do i get one

 

I've looked into the stronger centering spring. Its not easy, one option is to beef up the standard spring which is inside the gearbox and not easy to get to.

The other option would be to use two spring loaded plungers either side of the shifter housing so it pushed either side of the bottom of the lever.

Early SAAB 900's 5 speeds pre 1986 had a clever nylon centering affair on the lever above the ball on the shift socket. I may look at knocking one up on the mill if I have some time available.

Chris

 

Considering that I'm an aero-astro engineer, I guess you would have to say that it is!

 

Did you have anything to do with the missing Mars probe?

 

No, I work on the commercial airplanes you fly around in.

 

Well the next time I need to get a commercial airplane to the moon I'll look you up.

Do you have anything useful to add to this thread? Do you know how much force is required to disengage the clutch. Or how long an electronic actuator with sufficient force takes to engage? Or how quickly a mechanically overreved F20C fails?

These things would actually help and would address the point you brought up. As much as I am enjoying the discourse let's keep it on topic.

 

I've thought of the same thing each time I hear of over-rev realated problems. Some ideas that spring to mind are:

1. Know that the selected gear is incorrect for the current road speed before the clutch is engaged (eg. sensor on the shifter), so we just need a simple solenoid to prevent the clutch from engaging.

2. Detect an over-rev condition and fire a solenoid that disengages the clutch. We could assume this is a rare condition, so use a one-shot system such as an airbag Nitrogen generator to power a pneumatic mechanism that will temporarily disengage the clutch.

3. Use a mechanical lock-out. Detect the road speed and move a mechanical lock-out into place to prevent the shifter from being placed in an inappropriate position for that speed.

 

I repeat;

There is NO street going manual Porsche, GT2, GT3, Turbo, WHATEVER, with any kind of factory clutch safety for wheel driven overspeed (missed downshift).

Electronic rev limiter yes- "fused" clutch or something similar-no.

The only way you have protection (barring a malfuction) against overrevs is with the tiptronic. If you select a gear that is too short for the given road speed, it will suspend the command until your road speed drops to an acceptable range-just like any other computer controlled automatic. It is impossible to hit the revlimter with the tip-the tranny justs upshifts when it sees the end of the ROPM limit.

That is not to say that guys racing these cars will retrofit some wizard-of-oz clutch, which may protect their six figure engine from disaster.

I have the factory manual which warns about type 2 overrevs; i.e. wheel driven overspeed. The car's DME (computer) stores both type 1 events (rev limiter) and type 2 overrevs forever.

There is no magic clutch mentioned in the owners or service manual.

Type 2 overrevs have been used as the basis to deny warranty coverage.

I also have the large hole in my check book that admits me to the "club"

Regards
BD