SDS users wanting to run Nitrous, I have an idea.

[Guest 73TPIZ]

An idea came to me the other day and i'd like to share with you guys and get some feedback.

 

As all you SDS users know, there is the +50% (rich) to -50% (lean) knob that is used to get the tuning right and then forgotten about. If you unplug the unit, the controller defaults to 0% no matter where it was when plugged in.

 

If you were to run a nitrous dry shot on the car, you could have a switch to close the circuit from the preset rich/lean knob to the controller. You'd have to determine how much richer for say a 100 shot via a wideband or dyno session, but easily doable.

 

I talked to one of the guys at racetech and he says the controller is just a potentiometer and the computer read the ohms of resistance when plugged in. When unplugged (no resistance), it defaults to zero. He said he sees no reason my idea wouldn't work. You could take a relatively easy to hook up dry shot and it would work as good or better than a more complicated wet system with its extra plumbing, extra injector,EIC, and such. Set the dial at 30% richer or whatever and when you hit the 100 shot, the circuit closes from the knob to the computer, and walla, instant compensation.

 

You could even take it one step further. Determine how much richer needed for a 50 shot and how much for a 100 shot. Convert those settings to ohms, and obtain resistors to match those two settings. You could then wire that to a 2-step system or 2 independent systems where switch 1 activated the 50 shot and closed the circuit through resistor A (17% richer) and switch 2 would activate the 100 shot and closed the circuit through resistor B (34% richer). If your car makes 300 hp on motor, looks like maybe ~33% richer on a 100 shot would be close (don't know if it's linear, that's what the dyno testing is for).

 

What do you guys think?

[drzed]

I think you might be on to something!

 

I was thinking of maybe using a 50 shot to help spool the turbo but was not interested in plumbing a wet system due to the complexity.

 

I can't see any reason why it wouldn't work.

[TheNeedForZ]

Excellent idea, I do not use SDS now but I've read your post closely. I think it should work but that depend on how stable the "switch on" circuit is. If the switch is not debounced, it might do something funny to the ECU when it is turned on. I would also design my circuit to make sure the NOS cannot be turned on unless the enrichment circuit is on, ie both on, both off, but never one on one off.

 

Is the NOS switch powered by electricity too? How many volts?

[240hoke]

I would be concerned about how fast the switch reacts. Ive been tuning my SDS with my LM1 the last couple days so I can test it out today. Flip it rich during a pull and see how fast it richens up. If in fact it richens quick enough then you could tie the resister and the solinoid into the same circuit and run them both with a WOT switch.

 

Cool I dea for sure, Ive been wanting to go nitrous, this would defiitly be a more affordable way.

[TheNeedForZ]

That's why I did ask "how many volts does the NOS switch(solenoid) use?"

 

It seems very tempting and simple to wire the NOS switch inside the enrichment control circuit. However thing can be more complicated than that. Here's what I would find out :

 

What is the operating voltage of the solenoid?

How much resistance is in that solenoid?

 

If the answer is "about 4.5 volts, nearly zero ohms" then you can wire the NOS solenoid with the control knob in series(not parallel).

 

If the answer is anything other than that, you have to separate the circuit. Because the rich/lean knob is probably not a potentiometer it is a variable resistor. The analog-digital converter is the real potentiometer. The computer sends out a steady 5 volt, you turn the knob(variable resistor) to control the resistance to change voltage output, the analog-digital converter translate the output voltage to digital values, then the computer does things(enrich/lean out) based on the digital value. The voltage inside the rich/lean control wire is probably 4.5 to 5 volts. If the operating voltage of the solenoid is 12 volts it will not be properly powered. If the solenoid has much resistance to it, it will offset the reading of the analog-digital converter, ie, the knob is turned to 30% rich, but the computer reads something else. If the resistance is high in the solenoid the computer might even default back to 0%.

[Guest 73TPIZ]

The guy at Racetech called it a pot but i imagine it does similar to what you describe. I should pull the Z from under the tarp and check it out with my mutimeter.

 

If I ever try it, i'd probably want to run it separate from the NOS system, but then my luck the NOS would work and the enrichment wouldn't. The good news is, it'd only fail once. Bad news is you'd be ordering new pistons the next day!!

 

Austin,

did you get to experiment with it this weekend? I'd bet the enrichment is pretty instantaneous but i'd like to hear what you found out.

 

NeedforZ,

I imagine Radio Shack or the like would sell resistors in many strengths, wouldn't they. Shouldn't i be able to turn the knob and see the voltage drop/measure resistance and then buy a resistor to match it, unplug the knob, jumper the resistor across the leads from the computer, and see it switch to XX% leaner or richer. What you think?

[Guest 73TPIZ]

The computer sends out a steady 5 volt, you turn the knob(variable resistor) to control the resistance to change voltage output, the analog-digital converter translate the output voltage to digital values, then the computer does things(enrich/lean out) based on the digital value. The voltage inside the rich/lean control wire is probably 4.5 to 5 volts. If the operating voltage of the solenoid is 12 volts it will not be properly powered. If the solenoid has much resistance to it, it will offset the reading of the analog-digital converter, ie, the knob is turned to 30% rich, but the computer reads something else. If the resistance is high in the solenoid the computer might even default back to 0%.

 

NeedforZ,

How much juice would a small relay pull on its trigger side? I wonder if 4-5 volts would trigger it and not throw off the computer much. That way the relay would send a full 12 volts to the NOS system and you could be a little more sure that the enrichment system was on, along with the NOS. If the relays current draw was consistent, you could just adjust the enrichment resistor from "Radio Shack" accordingly. For example, you need the 5 volts to go to 2 volts for the computer to give 30% richer. The piggybacked relay to the NOS alone drops the voltage to 4 volts, so you would obtain a resistor to drop it another 2 volts.

 

This is all hypothetical until i or someone does some experimenting.......

[TheNeedForZ]

I imagine Radio Shack or the like would sell resistors in many strengths, wouldn't they. Shouldn't i be able to turn the knob and see the voltage drop/measure resistance and then buy a resistor to match it, unplug the knob, jumper the resistor across the leads from the computer, and see it switch to XX% leaner or richer. What you think?

 

That depends on the value of resistance you want to duplicate. Most resistors come in large, whole numbers :1,5,25,100,etc. If you really want precisely 2.6 ohm then it becomes difficult to create. I would find out how much resistance is when the knob is at 30%, then find out the resistance in the NOS relay, then make up the difference with RadioShack resistors. i.e. 30%rich = 40 ohms, NOS relay = 11 ohms, then you need to make up 29 ohms with Radioshack resistors. This idea you have is a good idea because the knob is eliminated. You can't knock the adjustment out accidentally. But I don't trust relays because they are coils, when you turn on and off the circuit the magnetic field builds/collapses and cause the voltage in the circuit to change. In the worst case scenario it might fry the computer.(the 50000v spark discharge created in inductive discharge ignition is the result of building/collapsing magnetic field in coils)

 

If the relays current draw was consistent, you could just adjust the enrichment resistor from "Radio Shack" accordingly. For example, you need the 5 volts to go to 2 volts for the computer to give 30% richer. The piggybacked relay to the NOS alone drops the voltage to 4 volts, so you would obtain a resistor to drop it another 2 volts

 

That depends on how meaning is assigned to the voltage values

If you need 1v for 30%rich and the relay make 5v step down to 3v, you can make 3v drop to 1v by adding resistors. If you need full 5 volt for 30% rich and the relay has taken it down to 3 volts....you can't add voltage.

 

You can seperate the enrichment circuit and NOS circuit into completely isolated circuits but use a double-pole-single-throw switch to turn on both at the same time(and pray the NOS is turned on WITH enrichment)

 

OR you can put a solid state relay(photocoupler or transistor type of thing) in the enrichment circuit to control the NOS solenoid circuit. This setup GUARANTEES the NOS will not be turned on unless the enrichment circuit is on first. If you suddently unplug the enrichment knob during a spray the NOS will go dead immediately.

[TheNeedForZ]

73TPIZ,

 

I searched on wikipedia and yes pot=potentiometer=variable resistor. So the Racetech guy and I were referring to the same thing. We just called it by diff names and I thought pot and variable resistor are different things.

http://en.wikipedia.org/wiki/Potentiometer

 

The pot has three leads that allows it to function as a voltage divider. If you have the control knob with you, check how many leads are used. If it only uses two leads then it probably functions as we discussed. If it uses all three leads then it gets tricky.