AFR with NOS

Hi Andre

the target lambda varies depending on how much nitrous oxide is to be use.

do i need take some consideratin to the stoichiometric air/fuel ratio should be adjusted accordingly to avoid a lean condition

since air flow is directly proportional to power how can i calculated target afr base upon what porcent of power come from air versus nitro oxide .

on 4 cylinder engine what will be the rpm to begin the addition of nitrous oxide at WOT without exeding the mechanical limits of the engine.

I tend to treat nitrous a lot like tuning a turbo or supercharged engine. To a point the more boost or nitrous you're using, the more fuel you end up wanting to add to control combustion temperature but obviously we just don't keep adding fuel indefinitely as the boost/nitrous increases. Generally a good starting AFR for a nitrous engine running a large shot of nitrous would be around 0.78 lambda. If you're adding perhaps 50-75 hp via a nitrous shot then you could potentially tune for a slightly leaner target lambda in the range 0.80-0.82. You can then test from there to establish what your particular engine wants to see as far as AFR goes.

The point where you activate the nitrous will depend on the size of your nitrous shot as well as the engine design. For example what is safe on a built engine with aftermarket rods could quite likely destroy a stock engine. I generally don't allow the nitrous to activate below about 3000 rpm but you do need to consider the points I've just mentioned. Since the nitrous flow is constant and the intake event takes longer at low rpm, you end up with a larger amount of nitrous in the cylinder compared to high rpm.