Northeast Street Car Association

Standard relay wiring

With this schematic you can do a number of wiring projects. I had a pic of a trans brake/N2O diagram up here but even I couldn't explain it to people who were confused by the 4 relays wired in series. Here is a simple way to wire up a brake (trans / foot or line lock) and a N20 syatem so that as the brake is released the N20 comes on. This works on BOSCH RELAYS only. I bought some off brand ones at a swap meet 2 years ago and realized that 87 & 87A were wired together internally (bad news for what we are doing but good news for fog lights which is what they made for). Terminal 30 is your 12V input from the N20 toggle arming switch inside the car (2-3 amp max load). 85 is power from the trans brake circuit. 86 is ground. ( 85 and 86 are interchangeable unless you are running a diode between the poles (recommended) in which case the  striped end of the diode needs to face the positive pole). 87 is unused or can activate an indicator lamp showing the armed nitrous system disengaged by the trans brake. 87A is the power out to a full throttle switch/MSD rpm window switch/digi-set box  and on to the actual high amp nitrous relay. So here's how it works in practice: 87A is norrnally closed (normally allows current to pass) so if you are footbraking the car, it works fine without the trans brake and behaves as a regular throttle controlled N20 system (the throttle microswitch is still active). When the trans brake is activated it switches power away from the N2O system. When you let go of the brake, power is now sent to the full throttle microswitch, if that passes power (WOT), the last N2O relay is engaged. As a side note I have seen people wire the microswitch to power the #30 terminal on the BOSCH relay and run the 87A output to the solenoids in an effort to remove a second relay and clean up the wiring. On a small nitrous kit it may work. But remember, a big shot N2O solenoid pulls 20-30 amps to open it, plus the fuel solenoid (3-5 amps). Those little microswitches on the throttle are really neutral safety switches, they are made to carry about 1-2 amps. Install a big ford starter solenoid (cole hersey ones are excellent quality) as the last solenoid relay and leave it alone. Many mysterious N2O problems like surging, backfiring and laying down at mid track can be sourced to lack of electrical power at the solenoid.  Enough juice to activate the system, but not enough to keep it going fully &  piss you off in the process because it will work fine in the garage and in the pits.  I am still amazed at guys who will spend $400-$500 on a dedicated N2O fuel system but will use PEP Boys relays and 18 gauge wiring to power the nitrous solenoids. FYI, I have recently gotten an education as to how a 16v system dramatically increases the amperage draw on all of the car's electrical components. According to dedenbear an electrical accessory on 16v system will draw 1/3 more power to operate  than a 12v system. take that 30 amp N20 solenoid and kick it up to a 40 amp draw with a 16V  system. Something to think about.

Digi-Set boxes

Digi-Set Schematic .pdf

The most popular way to time a nitrous system is with one or more digiset boxes. They are compact, light and function similar in many ways to a standard bosch relay with the added function of controlling when the relay engages. By setting the pin switches, delay can be set from one tenth of a second to over three minutes. FYI, they were originally intended for Heating and AC systems so the time delays are not tailored for motorsports. Most digisets use an 8 pin (octal) base that requires a special base wiring adapter. the schematic page link explains how this relay timer functions. Quarter Max racecars, www.quarter-max.com currently has the lowest price on these units, $60 with the base. These are ideal for activating a second stage of nitrous or as a trans brake delay for low budget bracket racers. They can also be used to retard timing for x seconds after launch. This has become a popular way to hook up high HP radial tire cars. BTW, check the time delay on new units , they are not all 100% perfectly synchronized.

These are double pole, double throw relays, so they have two power inputs and two power outputs with one switch and one ground

Textual schematic: Pole    Description 1       Constant Power in (A) 2       Switch signal common (signal from full throttle sw or trans brake relay out) 3       Main Power Out (A) 4       Disengaged Power Out  (A) Like #87 above 5       Disengaged Power Out (B) 6       Main Power Out (B) 7       Common Ground 8       Constant Power in (B)