Tuning with Nitrous
A nitrous engine is 99% a normal engine in the sense that when you don’t use the nitrous, the engine behaves like any other engine. So tuning a nitrous engine is just like tuning a non-nitrous engine. Almost. Because the 1% of the time, where you actually use the nitrous system, does place different demands on the engine.
There are two things you need to consider. First of all the engine has to be tuned like any other, and then there is one change you have to do. Secondly the nitrous itself has to be tuned properly.
The engine
The one thing that you have to change is to give 2-4 degrees later timing, less advance. This is not because nitrous introduce an added risk of detonation like when talking blower/turbo, it’s simply because the addition of nitrous speeds up the combustion process so less advance is needed. The really ambitious tuner will therefore use the normal setting for daily driving, and then retard the ignition when using nitrous. You can buy a small box with a knob where you can delay ignition timing so you can change this without opening the hood, and some nitrous systems have it incorporated so it’s done automatically when you use the nitrous.
You also need different spark plugs, 1-2 heat ranges colder. This is needed because of the higher pressures/temperatures in the combustion chamber when injecting more fuel/nitrous.
The nitrous
Also here the fuel/nitrous mixture is critical. Simply put, too much nitrous without added fuel will melt your pistons. Too much fuel will dampen performance. Most modern nitrous kits have preinstalled pressure regulators etc., so it should be taken care off. But for those wanting to understand and tune, this is how. Start by installing the kit. Secondly install a fuel pressure gauge you can see while driving. It has to be installed outside the cabin because fuel under pressure is not something you want in there with you. The cowl area is a good choice. Test before using the nitrous whether the pump can supply the needed pressure according to nitrous kit instructions. If not, fix this before moving on. If the pressure is OK, test run the system. No need to do a measured run, just hit the pedal, open for the nitrous and feel the power for 3-4 seconds. Then shut off engine immediately, and stop car. Be aware that stopping the engine can make the car hard to steer and if done incorrectly lock the steering wheel. Now pull a spark plug (the plug that’s 1-2 heat ranges colder, see previous paragraph and section Spark plug reading. This is especially important with a nitrous engine, because the melt down resulting from too lean a mixture will happen a lot faster than with a nitrous engine. If the plugs look OK and you felt power, then the system is probably working as it should. If the plugs are too light, you need to richen (more fuel) the system. If plugs are OK but you weren’t really impressed with the extra power (if it works you’ll definitely feel it) you can try leaning the mixture. Some nitrous systems are very adjustable with jets, some are not, the nitrous/fuel ratio is fixed. For those systems you can tune by adjusting the fuel pressure. Lower fuel pressure means leaner mixture, higher fuel pressure means richer mixture.
Tuning nitrous is fun because the effect is huge. We remember our first nitrous system, fully adjustable, and we definitely started cautiously, much too rich mixture. And when we hit that nitrous button we weren’t impressed. It took us a few days building up the courage to go leaner, one step at a time and reading the spark plug every time. But when we finally hit the right ratio, boy oh boy, it was like adding a second engine. We won a lot of races that year.
One warning, when the system is tuned correctly, fuel pressure is the key. Your fuel pump must be able to produce enough fuel for your carburetor and the nitrous system at 6000 rpm. Even if the gas tank is almost empty. The cautious tuner installs a totally separate fuel line and fuel pump, with a pick up at the rear of the tank. Regardless, you must keep half an eye on the fuel pressure gauge when using the nitrous, if the pressure drops your engine is a few seconds from meltdown…