Volume IX, Issue 2, Page 38


by Dave Koehler

I want to know "is there a basic guideline (math formula) etc..for determining injectiion nozzle size & pump size for any specific engine combo?"  Let's say I have a 477" bbc and a 555" bbc that I want to inject on alky? Is there an easy way to determine a starting point?

Kurt Kappus, Oklahoma City, Oklahoma


I suppose the easy way is to ask whoever you bought the parts from. This recommendation will probably go down the track just fine but will be less than ideal for your combination.  As for an answer to the math, yes, there is some, but it's pretty darned complicated. Even with the math it's a fairly generic result and the final nozzle, jet and high speed choices will still ultimately depend on experience.

When I setup and flow a system I ask for a lot of information on the engine and car, including cylinder head air flow, cam specs, type of racing and so on. Armed with that information I will have a good idea of what your engine can potentially create for torque and HP. From there, it is a matter of choosing a pump, nozzles and main jets that should hit the target Air fuel ratio from launch through different points in the rpm range. Notice that I said "should". Where flowing the system becomes critical is that the nozzles and jets may flow more or less than we need and a change is required to hit the mark. The pump itself is critical as each one has it's own characteristic flow rate as it climbs in rpm against the restriction of the nozzles and main jets. I know this did not solve your problem but it should give you a good idea as to why systems are flowed and are preferred over off the shelf kits.  FWIW, I have an in house Windows program that does what you want. I have been developing a consumer version of it but due to time constraints it will be a while before it is ready for prime time.

Have a safe race,

Dave Koehler

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