Razor's PAC Kit - Turn on point

[zebra78]

Installed my alky kit today without problems. PAC kit from alkycontrol.com, Julio Don.

The install is not complete yet, as I don't actually have the pump, but I completed the electrical side and verified correct operation.

My car is an 87 GN with analog dash. This kit requires a 3 bar map sensor, so I got one with the kit and installed it. Using my multimeter, I traced the wire that connects from the map sensor to the factory tach/boost gauge. Instead of running an additional wire from the MAP sensor connector all the way to the inside of the car, I spliced into this connector.

For future reference, Razor, the wire is the green one in the tach harness.

Now here's the odd thing. And I *THINK* this makes sense, but I'd like to pose the question anyway.

Preset turn on point was listed in the installation guide as 4 PSI. I floored the car with the normal boost level (15), and the kit turned on at around 9 or so according to my aftermarket gauge.

Repeating this excercise, I looked at the factory gauge this time. At 15 pounds or so, the gauge read about 8 psi, and the kit turned on at 4 psi.

I think this is due to the fact that the scaling of the 3 bar MAP signal voltage is different from the factory 2 bar setup. Thus, when at 15 psi, the factory boost gauge reads lower, because the new sensor has more range.

Razor, I think you are setting your turn on point a little high on these kits from the factory. Is this a fair assessment?

[Razor]

Well.. here's the situation, see the 3 bar sensor has a different voltage swing than the two bar. For instance they are both powered by 5 volt source, now the three bar scaling is different. For instance the three bar at zero vacuum is 1.6volts on the green wire. The factory 2 bar is 2.4 volts on the green wire.

What this means is the factory GN boost guage is calibrated for 2.4 volts at zero boost, so you have to get to like 6-7 PSI of boost on the three bar before the factory guage starts to read. If you would like to have the the factory guage to read correctly, then a new plug would be needed for the three bar, and piggy back its 5volts and ground..then use the green wire from the three bar. Most that use this kit will not use the factory LED guages siince its limited to 15 PSI and not accurrate.

Hence why I include an LED to be placed next to your aftermarket boost guage, so as its needle sweeps up past 4 PSI it turns on. Now you dont have to follow anything I decide, this is just done in an effort to make the kit plug-n-play as far as settings are concerned. Just keep in mind the larger the boost swing, the greater the resolution you will have on the system due to the greater voltage swing coming from the MAP sensor.

Example, you want the kit to produce 100 PSI pressure at 20 PSI boost. You can get to this level by turning on the kit at whatever PSI you wish and then recalibrating the "Initial". The higher the turnon point, the greater amount of initial needed to multiply voltage increase per PSI. Turning it on lower produces a gradual rise in pressure.

If you move the turnon point, from factory 4 PSI to lets say 8 PSI, and leave the initial alone, if before you got 100 PSI at 20, now it wont happen until your at 24 PSI. Now turning it on at 8 PSI .. increase the "Initial" you can get your 100 PSI at 20 PSI boost.

Make sense.

This is what makes my controller what it is.

So to recap, putting the 3 bar sensor in place of the factory 2 bar makes the factory LED boost guage useless. It wont hurt the factory LED guage. Sorry. Solution is to run the 3 bar on stand-alone if the factory guage is important to you.

[zebra78]

No, I don't care about the factory gauge at all, I was just worried about the descrepancy between the actual turn on point (~9psi) and the 4 that it was factory (you ) preset to.

I'll tweak it so that it turns on at 4. (According to the aftermarket gauge, of course)

[Razor]

The turnon point knob should point to the 10 o'clock position approx. Also getting your meter, you can probe the center leg on the control and set it to 2.2 volts.

Maybe in the process of burning in the controller we moved the setting for test purposes

Thanks

[turboG]

Mine comes on at about 4#....preset the way Julio had it. Excellent unit...good choice zebra.



Good to see Julio didn't get blown away by Frances...