| Reading Spark Plugs - for signs of how your system is operating
Start with the lowest power level nitrous jet and corresponding fuel metering jet. Make a full throttle pass at the drag strip and read the plugs. Not enough nitrous / too much fuel results in a sooty, black plug coloration. This coloration means that the fuel mixture is too rich. Too much nitrous will exhibit high heat in the form of a bluish or rainbow-like coloring on the plug's metal surfaces. This means you're engine is about to, or is, detonating. If this is observed, ensure the proper spark plugs are installed, reduce nitrous / increase fuel delivery, and ensure the proper grade of fuel is being used. When you check the spark plugs, check EVERY plug. Don't just spot check the easiest plug you can access. Due to the wide possibility of air / fuel mixture variations, you need to check every single plug for signs of detonation or other problems. If your plugs indicate too much fuel, trim the fuel delivery down by installing a smaller metering jet. If you are too lean / not enough fuel, you need to install a larger metering jet to increase fuel delivery.
As said before, check every spark plug, not just the easiest plug to get to. No two cylinders ever run exactly alike. Nitrous has the unique characteristic of cleaning the spark plugs very well and leave them looking like you just installed them. If there are any signs of detonation such as tiny silver or black specks deposited on the porcelain, reduce the nitrous jet size. If the ground strap of the spark plug exhibits a bluish-rainbow coloring, reduce the nitrous jet size. If the ground straps shows signs of melting, reduce the nitrous jet size and change to a spark plug with a shorter and thicker ground strap.
A burned electrode on a sparkplug is a clear sign of detonation. Another sign of detonation comes in the form of black dots and a greenish tint on the plugs. A "clean" plug will show slight brownish coloration and the electrode will be in perfect condition.
When tuning the nitrous, always tune for the leanest cylinder.
Spark plugs & nitrous performance
Quite often, a factory type wide-gap projected nose plug will produce a detonation condition after a few seconds of nitrous use. The detonation is not due to the heat range, it occurs because the ground strap of the spark plug becomes a glow plug instead of a spark plug. The ground strap is too long to dissipate the extra heat produced by a nitrous accelerated burn. The correct solution is to replace the plugs with units that have shorter ground straps. By doing this, you will shorten the heat path from the ground strap to the plug base.
If you only change the heat range of the spark plug to a colder heat range, you may very well still have the misfire problem. Since the length of the ground strap is the cause of the misfire, a colder spark plug may have the same length of ground strap as the hotter plug you replaced it with.
Importance of using a system purge - Nitrous purge kits
A nitrous purge kit clears the delivery lines of unwanted air and vapor and guarantees immediate power from your nitrous system.
After opening the bottle on a nitrous system, the liquid nitrous flows through the line and up to the solenoid. More often than not, there will be air in the line, especially when you change bottles. The purpose of a purge is to allow pure nitrous to fill the line right up to the solenoid, filling the hoses with nitrous rather than air. To do this, another solenoid is used, but rather than shooting the nitrous into the motor, it's usually shot up over the hood, or out of the grill so you can purge until it creates a nice fog. It also looks real cool :) Of course, no fuel is used during a purge. In addition, if bottle pressure has built up beyond the recommended pressure you can vent the line to return pressure to normal.
It's recommended that you purge the system and close the bottle when you finish a run.
Limits of your engine`s internal components
Nitrous oxide has great power-making potential, but the "shot" or horsepower level you decided to use must be tailored to the capabilities of your engine. In addition to basic tuning procedures, it`s important to know the limit of your engine`s internal components. The nitrous user must understand that as power levels rise, the strain on the internal parts increases. As you increase the level of nitrous, you must also increase the strength of the engine parts. While stock rods and pistons will work with a 125-175 shot, a 250 shot normally requires stronger rod and main cap bolts, forged pistons, a stronger crankshaft, and aftermarket connecting rods.
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