t2d2

iTrader: (8)

If you're like me and wish the SC felt a bit more connected to the road, with less of that floaty luxury feel, this might just be the best and easiest mod you can do to the car!

http://www.supraforums.com/forum/sho...1#post13201905

I can't take credit for the solution, just connecting some old dots and sharing probably the least known performance improvement for the platform.

I did this mod on the SC300 today and will do likewise on the SC400 when I get another potentiometer of the right resistance.

TXMAG

iTrader: (1)

Neat find. I love platform specific forums for information like that!

tsmith1315

The article says that the only input to the steering ECU is vehicle speed. Any idea where this input comes from or what type of signal it is? I'd feel better manipulating that signal (into the PWM controller) than varying the output voltage/current.

-Tim

t2d2

iTrader: (8)

^ You probably saw sixpack's objection in the SupraForums thread after I posted here. All I can say is, who knows... It appears he's got a MKIII, so maybe we're looking at two different systems?

I haven't tested it a ton, but it's rock solid with no sign of hunting, which seems to invalidate the theoretical objection. Only time will tell. Unless something fails, I'm super happy with the easiest mod ever for a massive improve in road feel.

tsmith1315

Yeah, I did read the SupraForum thread, as well as the SoarerWorld thread. While Sixpack's comments are valid, I was more interested in zedhex's information on the other thread.

If this is a pulse width modulated output driven by a single input, it's fairly simple. The input (vehicle speed) is most likely represented by a voltage or current which varies with speed. This is a very low current signal. The output is a fixed frequency square-ish wave of varying width supplying sufficiently high current to switch a solenoid. Given the choice, I will always fool around with a low current signal first.

Since the PWM output is not DC, the solenoid's impedance will vary with the waveform driving it. As a result, the amount of voltage the potentiometer "takes" from the solenoid will vary in inverse proportion. I don't that would make the system "hunt", but instead would produce a logarithmic change instead of a linear change. No big deal, possibly even desirable, as long as the solenoid is OK operating with that series resistance, which time will tell.

Thanks for bringing the info over to this forum, I'm interested and just happen to have my dash apart at the moment!

BTW, high wattage, low-resistance range potentiometers are commonly found in loudspeakers as a level control.

-Tim

t2d2

iTrader: (8)

You're getting well beyond my element. If you think you've got an angle on modifying the input instead of the output, I'm by no means trying to discourage you. More solutions can only be a good thing, whether or not they're all equally sound.

Okay, I sent back to the SW thread and was reminded that sixpack's comments were well in line with the theoretical stuff from zedhex in post #2, so my wording was too strong previously. I guess the best way to phrase my counter-objection would be, do we know that: a) the valve is problematic in between the fully open and fully closed states, and b) reducing the voltage only to the solenoid will burn it out?

The PS valve description sounds a lot like how the IACV functions, fwiw.

I'm skeptical that it's anything but linear (maybe the solenoid has some means of adjusting for the input??), based on the butt test while fiddling with the potentiometer, but measuring the effect is obviously difficult.

I actually have a SC head unit dissected and was looking at the 5 EQ ***** to see if they had potential for this project. I couldn't determine their specs from any of the markings, though.

I found a few options on ebay and added them to my watch list. Some have gone out of stock since I started this thread, so I suspect a few other SC owners are giving it a try.

tsmith1315

Absolutely not.

If I understand it correctly- (a) at low speeds, the stock system is already operating the solenoid between fully open and fully closed. This is exactly how varying the pulse width adjusts the steering weight. (b) The PWM system effectively reduces the voltage by changing the output signal to narrow "spikes" which, when averaged over time, equate to a lower voltage. This whole system is just a fancy way of accurately changing the solenoid voltage in relation to vehicle speed.

I must disclaim that I am operating on assumptions at this point. Sixpack's argument is based entirely on the pulse train operating at a frequency low enough that the solenoid fully opens and closes in between pulses in the stock system. And with a valve opening/closing that quickly, how much fluid would pass? I don't think that's the case, as it would require a very fast solenoid/valve. Even operating a few times per second (slow for PWM) would be fast for a solenoid, and shorter spike-like pulses would be impossible for it to track. It just wouldn't translate into any consistent fluid flow unless the pulse frequency was on the order of seconds. At that slow of a rate, a PWM system wouldn't make sense to me. (I would also think the pulses would be felt in steering)

I think that the PWM system is operating at a typical high frequency- producing electrical pulses much, much faster than what the solenoid can follow directly. In essence, the solenoid is chasing the PWM output, so it simply follows the average voltage of these pulses and indeed is happily keeping the valve in between the fully open and fully states unless vehicle speed is at one extreme or the other.

If those assumptions hold, then just be sure your potentiometer can handle the solenoid current, I wouldn't expect any other problems. It's cool you have a spare car to experiment with!

I think what sixpack meant by "not consistent" is non-linear/logarithmic. Our human senses tend to perceive in a logarithmic manner anyway, and if the assist change remains smooth from low-high speed, then it doesn't matter.


Those are going to be high resistance, low current pots. Probably in the range of 10k-100k ohms, they won't have a wattage rating. They would probably have potential (no pun intended) to vary the input signal, however.
I should clarify, the speaker level pots I mentioned are usually called L-pads and consist of a couple of variable resistors in combination. Only one set of taps will have the variable resistance you're looking for.

-Tim

93sc400nm

Awesome: would love to have more of a drivers feel

t2d2

iTrader: (8)

Nothing new to report (including anything intelligent to Tim's comments ), other than it's been 2+ months now and the mod continues to work great. If it leads to problems, it's not immediate...

I should also add, the car I tried this out on is ~500 lb lighter than stock and more in need of a heavier steering feel. It was way too light at full assistance.