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post #1 of 5 (permalink) Old 04-14-03, 07:49 AM Thread Starter
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De-speed limiter, adjustable pedals and other theoretical dodgy mods

As a result of my short attention span, I've been toying with a couple of dodgy ideas for a while. They're not a big deal but they're cheap and I have a lot of time. Hopefully Easter will give me a chance to try a few of them out:

1. Dodgy De-speed limiter
Using a binary counter IC (I used a MC14020BCP), connect clk to vss signal and bit 1 (wtf, no bit 0) to the ECU. Also make sure Vdd = 12V and Vcc and reset is grounded. Have done this and verified it works. What it does is it counts up in binary every time the VSS signal goes from low -> high.
Taking bit 1 quarters the frequency of the VSS and hence the speed the ECU thinks ur going. The speedo takes the speed directly off the VSS so it's unaffected, but u can't just cut the VSS wire at the ECU because it limits u to ~3500rpm if u go WOT when the vehicle speed is 0. I've only tried this on a manual, but I assume it'll work on an auto if u reset the computer and let it relearn the shift points. Anyone brave enough to try?

2. Adjustable pedals
I find the brake and accelerator pedals are a bit too different in height. So what I'm gonna do is move the brake booster back a couple of mm's by adding shims between the brake booster and the firewall in the engine bay side. I think the bit the accelerator pedal pivots on can be removed and shimmed as well, but I'm not sure. Might be able to get the butterfly open a few more degrees if I shimmed it too. : ) Anyone tried this? How much is this going to endanger my life?

3. Coil per cylinder
This is purely theoretical and I have no intention of trying it this Easter at least. Basically, the coils on an EF & AU 6pot fire 2 cylinders at a time. The idea is that the cylinder under compression get more energy because there is more air in the spark plug gap and hence less resistance, but some energy will be wasted sparking the other pot. So what I'd do if I had a spare EF coil-pack (if u don't then it's not cheap) is to split the ECU signal to fire the coil up to the other coil and hook 1 lead per coil. U'd get a tiny bit more spark, which will lead to bugger all RWHP and MPG gain (by my logic anyway). Anyone care to estimate how much?

4. Increase compression
Basically rip out the old gasket, get a shop to make up a thinner copper 1, bung it in. Takes hours, but shouldn't cost much. I believe JMM already does this with 1 of their wilder DEV kits but anyone got any idea how much this is worth by itsef? How much compression would I get? I run PULP all the time anyways and the EF's got knock sensors. Should make some HP and MPG as well... Would a copper gasket be better or worse than the already dodgy Ford ones? This mod I'm keen to try too.

Also, I've got a spare BTR EF open diff carrier. Anyone know how to lock it? Do you weld it? Is it possible to weld it without opening it up? Damn LSD, I reckon it's only got another year or 2 left in it and I'm hoping to replace it with a locked 1...

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post #2 of 5 (permalink) Old 04-14-03, 02:56 PM
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Interested in the Dodgy De-speed limiter. Can you elaborate on what exactly this will do?

AU XR lookalike wagon
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post #3 of 5 (permalink) Old 04-14-03, 08:38 PM Thread Starter
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Basically the IC is hooked up so it gives 1 pulse every 4 pulses it gets so it quarters the speed signal frequency and the ECU thinks the car is going 1/4 the speed it really is (ie. 200km/h -> 50km/h), hence u got a speed limiter of around 700km/h. If u can get an IC which u can get bit 0, it will only half the speed signal frequency, which I guess will b better.

No biggie for a manual cause I'd imagine the fuel mappings at 200km/h r roughly the same as at 50 anyway, but on an auto the ECU also does gear changes. I'd imagine the ECU can relearn the shift points because they can use the same ECU on different diffs and this is kinda like having a 12:1 diff.
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post #4 of 5 (permalink) Old 04-14-03, 09:10 PM
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Hmm . . . I'd be really careful with the pedal changes . . . if you were really desperate to change things, I'd try to make the accelerator match the brake, and leave the brake alone . . . if your accel falls off ( as long as it doesn't fall under the brake ), your a lot better than if your brake falls off Even accidental WOT isn't as bad as no brakes, at least you can turn it off. . .

Otherwise, perhaps a more interesting suggested application for your speed limiter mod, would be to use it to make a shift light. If you link it to the tacho instead ( i think it uses a similar electronic system to the speedo ), and get it to trigger another circuit ( i.e. a led or something ), at a certain frequency . . . . Could be a *lot* more subtle than alot of the ricers... was thinking of doing this one myself, but haven't quite got there yet . . .
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post #5 of 5 (permalink) Old 04-14-03, 10:14 PM Thread Starter
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Yeah, pretty worried about the nuts working loose and brake booster just falling right through and me gettin no brakes. Is there a standard regarding the length of thread u should leave at the end of a bolt?

Interesting u should mention the shift light. U'd have to use another IC, which usually need RC circuits attached them to run the timing, so u need a pcb. I've seen a tachometer IC in the Farnell catalog (I'll find u the # later) when I was looking into the de-speed limiter, and if I remember right, it shows u how to hook it up to do an overspeed warning in the spec sheet. Costs ~$15 I think.

I've been toying around with a pic microcontroller which u can program with a computer. Originally I was using that as a de-speed limiter, but now that I've got the IC in there, I've been thinking of using the pic as a shift light controller. Prolly make it like the 1 they got on the HSV GTS, as u near redline, the light will come on to tell u to get ur hand on the shifter and a buzzer will go off when its time to shift.

Traction sux.
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