A speed de-restrictor

FloydV

Donating Member
Registered
No this ain't a TRE.

I stole this from SH.org:

Speedlimiter on 2002 models
When your only problem is the speedlimiter in the 6th gear, the easiest way to bypass it is by using a zener diode wired with the cathode to the pink wire and the anode to ground. You will need a voltage of 4.3volts and 250 mw should work fine. It will leave all gears up to sixth alone. As soon as the bike goes into sixth the diode will clamp the voltage to 4.3 volts so the ecm sees fifth gear selected so no speed limiter.

The part about 4.3 volts at 250 mw is confusing me.  Where does the 4.3 volts come from?

It seems like this mod could be done close to the pink/blue/black connector and you wouldn't have to pull the GPS.  Is he saying get a zener diode that passes 4.3 volts @250 mw to ground? I know some of you guys with electronics knowledge can elaborate on what he is saying. Do you think this would work?



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FAVahalik - A zener diode acts as a voltage regulation device. Normally used in power supply circuitry, it maintains a constant voltage drop across itself. I'm not familar enough with the Busa's circuitry to know how it would effect the Busa's top end. But I tell ya... I'm beginning to think there's very few out there that know what Suzuki did to create the 186 restriction. It would be fun to the zener to a test on a Dyno though.
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"The part about 4.3 volts at 250 mw is confusing me.  Where does the 4.3 volts come from?"

I just realized I didn't answer your question.  Assuming the circuit in which the zener is placed has a voltage "higher" than the rating of the zener diode, the zener will drop and maintain the voltage in that circuit to 4.3 volts regardless of what the input voltage changes to (again, assuming the voltage in the circuit remains higher than 4.3 volts).  The 250ma is the current rating of the zener.

To find out whether the zener actually eliminates the restriction, I'd need a complete technical explanation of what the original restrictor circuit does.  I wonder if the Service Manual goes into that depth of technical explanation?  
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FJ, here is the whole post. Perhaps this will explain what the author is doing. I think this is the secret to the "send me your GPS " method of de-restricting only. If you read through, you will see the voltages listed. The zener diode is affecting the 6th gear voltage, I think. I put an arrow to the part that seems significant (can't seem to get the bold to work). Anyway see what you can make of it, please. My interpretation is that you would buy a 4.3 volt zener diode (rated at 250 mw), connect it from the pink wire to ground, and the bike would now see gears 5 and 6 as the same without any effect on the timing, etc.

What is a TRE
From the gearbox there's a signal going to the ECU to let it know in what gear you are. The way it is done is very simple. Just a multiswitch in the gearbox with a set of resistors. Depending of the gear there is a resistor selected, what will give a geardepending voltage on the output to the ECU.
For the technicians here are the geardepending resistorvalues and the voltage-output to the ECU (between the pink and black wire):

Voltage Resistance to ground Gear
1.8V 560 Ohms 1st
2.26V 830 Ohms 2nd
2.99V 1.5k Ohms 3rd
3.68V 2.7k Ohms 4th
4.38V 6.8k Ohms 5th <-----voltage author is seeking?
4.70V 15k Ohms 6th
5.08V open on pink wire, connected through the blue wire for neutral light Neutral

The TRE , what is a simple resistor what is replacing the gearswitch-depending resistors will let your bike think that it's always in the same gear, normally the 4th, 5th or 6th gear. The result is (for most bikes, not for all) that the bike will run better in lower gears and the speedrestriction in 6th gear is gone.

You can buy them as plug-in system in a shop (G-Pack, Timing Retard Eliminator, etc..), but when you do it yourself you will save about $70, so for me it was easy to choose.
I started with a homemade TRE and removed it after a few months. But, after all the modifications I did, I installed the TRE again, just to get rid of the retarded timing. After the homemade TRE and the intelligent TRE I finally bought the ATRE, just because it is a good looking box and it is easy to switch between different gearsettings.

The simple TRE-modification
There's a wire coming from the Gear Position Sensor (GPS) in the Gearbox what will tell the ECM what gear you're using. You'll find a white connector just before the flat part in the main wiring under the tank at the left side of the bike with three wires in it. Take the pink wire out at the side that's going to the back of the bike, solder the first site of the 6k8 resistor on it and the other site of the 6k8 resistor to the black wire on the connector. You have to leave the black wire in, so I soldered an extra wire to the black one to have an extra groundwire. Ok, when you are finished with soldering you have to seal the resistor and solderings so that they would not get wet. You have to find a right place to put it. I used tire-wraps to keep the resistor on his place (see picture)

I put the resistor in some black heatshrink and used tire-wraps to keep it on his place

After you installed the TRE you can put the airbox on his place (don't forget the hoses and the connectors), tank down and have a ride. When you feel more stumble in the lower rpms range I think it is better to remove the TRE and stay stock. When the drivability is better then before, leave it in.

The intelligent TRE
On one of the Hayabusa boards there's also an intelligent TRE published by one of the members (see schematic) . Because the intelligent TRE only changes the first three gears, the ram-air compensation in 5th and 6th gear is still available.
You have to connect the pink wire coming from the front of the bike to the IN connection of the schema, the pink wire part going to the backsite of the bike must be connected to the OUT connection of the schema.
The most people are using the simple modification with a resistor, but when you have an electronic background you can make the intelligent TRE.

Schematic of Intelligent TRE

The ATRE
Another possibility for the people who want to play with the settings for different gears or for the people without electronic background is to buy the ATRE.
The ATRE is a box with the same features as the intelligent TRE, but with the extra feature that you can choose what settings you want to use for what gears. More info about the ATRE you can find on the website of SJL products (motorcycleradar.com). For their link see my linkpage.

this is the ATRE box complete with cables

Speedlimiter on 2002 models
When your only problem is the speedlimiter in the 6th gear, the easiest way to bypass it is by using a zener diode wired with the cathode to the pink wire and the anode to ground. You will need a voltage of 4.3volts and 250 mw should work fine. It will leave all gears up to sixth alone. As soon as the bike goes into sixth the diode will clamp the voltage to 4.3 volts so the ecm sees fifth gear selected so no speed limiter.



<!--EDIT|FAVahalik
Reason for Edit: None given...|1129339638 -->
 
this is why I just made my mod, swap it out and be done. I can swap one in less than an hour. most shops will charge about an hour. or wait till you need a clutch (quite frequently on most busas) and do it then
 
FAVahalik - Sounds like JC has already worked through these issues.  From what I've read he definitely knows what he's talking about.

Just being technically curious, please point me to the where you found this information so I can take a look at the schematics.  I'm curious to see what these different resistances are doing to the ECU and how those changes effect the rest of the circuitry.  It's always helped me if I get the big-picture to really see what's happening with all the circuitry.  Engineers just can't leave well enough alone sometimes!  
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this is why I just made my mod, swap it out and be done. I can swap one in less than an hour. most shops will charge about an hour. or wait till you need a clutch (quite frequently on most busas) and do it then
That's my plan. When I decide it's time for a speed run, I'll let someone pull out the GPS, swap with you, and let them put it back in. I'm way too lazy to do all the work. I used to, but I've gotten old and have a little more money than when I was young.

I was mainly interested in how zener diodes worked, and what the author was doing. I wanted to see if my interpretation was right. And maybe some of the other members might want to do their own work.

Glad to see that you are still in business.
 
FAVahalik - Sounds like JC has already worked through these issues. From what I've read he definitely knows what he's talking about.

Just being technically curious, please point me to the where you found this information so I can take a look at the schematics. I'm curious to see what these different resistances are doing to the ECU and how those changes effect the rest of the circuitry. It's always helped me if I get the big-picture to really see what's happening with all the circuitry. Engineers just can't leave well enough alone sometimes!
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Fastsjonny

Click on motorbikes, then GSX1300R modifications, then TRE.

It looks to me that the zener diode from pink to ground senses the voltage trying to rise to 4.7 volts to indicate 6th and clamps it at 4.3 the voltage for 5th. This would leave the lower voltages free to change in gears 1 through 5, so the maps would stay the same. It's only when it tries to rise above 4.3 that the diode kicks in.

Sounds slick. One cheap diode from one wire to ground and you keep your stock maps.

Am I close?
 
Off the above topic--sort of. I finally pulled out Ivan's Smart TRE and put it on after sitting in a box forever. The bike's reaction?
Smoooother. I thought it was OK before, kind of cammy running, but now it purrs! The idle speed stayed the same, but now it's like someone put a stray spark plug wire back on. And it pulls harder in the lower gears.

I'm going to leave it on for a while. If it doesn't foul plugs or cause some, as yet undiscovered, side effect, I'm willing to give up a couple of hp.

Gotta try it a while to be sure, but it's plug and play-snaps in and out. Pleasant surprise.

Still interested in the Zener diode idea.
 
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