6G Celicas Forums

I have a swapped celica gt, with a st205 engine. I'm running 16 psi and for some reason my car tops out at 112 mph? I was wondering how I could get my top speed up. Help?

This post has been edited by Celica_kid_st205: Jun 5, 2013 - 9:46 PM

Japanese cars have a speed limiter of 180 kmh, or 112 mph.

Well, those sold in Japan I should say anyway. Supposedly there's some kind of converter so that it tops out at 180 mph instead of 180 kmh.

Can I take off the speed limiter?

I'd imagine you can. I know on the FD RX7 one of the wires going to the ECU is responsible. You might want to try editing your title to "Help with removing speed limiter" or something to that effect, to try and get someone that's done it already to respond.

HKS Speed limit defencer

why on earth do you need to go over 112MPH?

so he can win!

you can just buy a coffin. you dont need to win one

For mad street credz, obviously.

Let's assume here for a moment he's using it for some form of track based racing. Even if not, I know I wouldn't want my 3S swap to have a lower top speed than the 5S lump I just spent all that work replacing. It's a mental thing for me anyhow. Besides Smaay, would YOU want your cars limited to 112 mph even though you may well never go that fast?

This post has been edited by Box: Jun 6, 2013 - 1:30 PM

Easy way with an FD is just to put a chevy ECU in it.





112 trap in a 1/4 mile isn't very high. Not sure if his car can get there, but just saying.

Standard ST205 finishes it's 1/4 on around 105mph, getting anything more out of it would normally require standalone + tune

Interesting. Never thought my ST would be "faster" than a stock Faff.

someone on another forum board swapped over his import SSii speedo with a UK unrestricted one from a GT (both 3sge engines) and said that removed the restrictions and switched from km to miles....

Not done it myself so couldn't vouch for it.

Take the ecu apart and find the circuit on the circuit-board that controls the speed limiter function. Not a difficult task, an electronics repair person/place may be able to do it just find somebody who is knowledgable in electronics

I would assume this wouldn't work because I dont think there's any feedback from the gauge cluster to the ECU. You can run your car without a gauge cluster connected.

This post has been edited by czwalga: Jun 7, 2013 - 6:56 AM

and then share with everyone else lol

I'm an EE. Doubt that's possible. It's most likely a microcontroller , maybe some are FPGA based not really sure. But either one there's no circuit dedicated towards just the speed limiter. Its logic inside the IC. If you f'd with that it the ecu just wouldnt work.

For example most newer cars can be 'flashed' via OBDII. You're not adding or subtracting circuits you're just adding different logic inside the microcontroller.

So.... Here is how you would do it...

The Speedo is a 3 wire sensor (+, GND, Signal), The signal wire goes to both the instrument cluster and ECU, meaning that they are essentially in parallel. This is good because you can muck with the signal to the ECU while having the Speedo report the correct value


If you throw a cheap and cheerful scope across that signal, you should be able to see if it is analog (0V ~ 0 MPH to 5V ~ 200 MPH) or a square wave / pulse train (basically the frequency of the pulses will change with velocity)

If its a 0V-5V signal (unlikely) you can switch in a little high K resistor divider network to spoof the speed of the car to the ECU - 80% of the actual speed means that you could hit 140 MPH before the limiter kicks in

If its a pulse train (more likely), you would need a little circuit (inc a 555 timer) to do the same thing and report a slower frequency of pulses than what is really being reported. This would be a fun little project and not out of the realm of the first year electrical engineering student.

You could also possibly do one or both of these little hacks with an Audrino and some kind of shield, which would allow you to switch the hack in and out depending on your needs.


Some Risks:

- These cars predate CAN buses and more advanced OBD systems and the controllers probably are not smart enough to validate the speedometer against Wheel Speed Sensors... However, if you car is new enough to have OBD II and/or ABS - you may create signal quality faults to set in the software and the car may enter some kind of limp home - or disable ABS - or some kind of fault recovery / limp in action... Basically if you pulled this stunt in today's car - you would get Christmas lights on the cluster and possibly scaled back performance.

- Speaking of OBD II, If a signal is deemed to affect emissions, the controller must have the ability to detect a short to 12V, Short to GND, or a Open Wire... If you try to just cut the wire, and it has been identified as OBD relevant - you will set a MiL lamp which may spell bad news for you (depending on your state's laws)

This post has been edited by qatar11: Jun 7, 2013 - 4:06 PM