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Dimensioning fuel system for use with nitrous

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Hello dear All,

I'm currently trying to figure out what size my complete fuel system has to have (pump and injectors basically). The thing is that I'm going to have a NX kit aiming for 75-100 hp extra.

The engine in question is a fully stock F20C (europe, not JDM), inside the corresponding S2000 (MY2001), so my first question is if the pump will be able to keep up, due to I will be running a wet system first, but due to I'm going to upgrade ecu to an Elite1500 soon, I would like also to be able to calculate the requirements for a dry kit installation, to make the conversion later on (maybe).

So, tuning an engine with nitrous requires an approach similar to a boosted one, so AFR is clear, a 1st approach to be safe could be 0.82 lambda, BUT, on a boosted engine you know how many extra psi will be producing, therefore, you can know how much O2 is going into the engine, or taking it easy, you go to Injectors Dynamics website, use the Flow calculator, "et voila", there it is.

But how to do the calculation on nitrous?

If we keep the formula provided in the Webinar 142 for injector flow, I have a way to start the calculation from the injector point of view, so:

(Flywheel Power (hp) x BSFC) / (# Injectors * Max D.C.) = Injector Size (lb/h)

(350*0.45) / (4*0.75) = 52.5 lb/hr which approaches to 550cc. That would lead me to pick a set of 600cc injectors for my car (rounding up again), like the Deatschwerks 21U-02-0600-4.

*BSFC aprox, taking into account that a F20C is almost efficient as a K20A, which is rated around 0,3

So if I move on towards fuel pump, my pump would require to push more than 2400cc/min which equals 144L/h, which equals to 173L/h after applying a 20% safety factor on top.

So considering Battery Voltage stable and Alternator in proper condition, providing solid 13.5V or above, the numbers calculated here should describe the requirements of my application in a safe manner, isn't it?

Any feedback will be appreciated and I thank you in advance,

Joan

With a dry nitrous system the injectors and pump obviously need to be able to support the additional O2 provided through the nitrous system. I work on a fairly conservative approach of needing 1 litre of fuel per minute for every 200 hp you want to make. So for a 100 hp shot you're going to need approx 0.5 l/min. This covers the fuel pump flow requirement and if you divide that by 4 then you know you need injectors that are 125 cc/min larger to cope with the fuel supply when running nitrous. Please understand that these are 'rule of thumb' values and in most cases will be slightly overkill but always better to have a little more fuel rather than a little less.