I only run about 12% water max as I have an intercooler already, so I am not sure what my car would do at 25%. No sign of foulling at those levels on plugs 1 heat range cooler.

I'm looking forward to the water experiments. All the physics say I should be able to get down to 65F at full boost with just water. We'll see...

Btw, you guys with NB Miatas, when calculating the percentage of water you're running, do you correct your calculations for the different fuel system you're running? I mean i.e. 240 cc/min fuel injector flows 240cc/min in NA Miata, but not in NB one

No, I have 550cc injectors and look at my actual logged duty cycle. I have to say a good aftermarket ECU makes projects like this SO much easier!

You have 550 cc injectors but these flow 550cc/min in NA and not in NB. Let me calculate ~ how much they flow in NB car. This has nothing to do with what ECU you're running. The ECU controls how long the injectors are open, and not how much fuel they flow for that time

P.S. Robbi, Julian here btw

550cc/min injectors should be around 650cc/min in a NB Miata

So what is the flow from the stock injectors in an NB?

Brant told me that the flow is 235cc/min and the powercard pushes the injectors as high as 95% capacity during boost.

Hey, Julian!

Strewth! I just checked my shop manual and you're right - the NB runs from 90psi peak to 50psi hold. I was thinking 43 psi all this time.

What numbers are you using?

The shop manual injector test section says from 66-82cc/15s which is 264-328cc/min FWIW. They do not specify the fuel pressure for the test, though, just that the stock pump is used.

I've heard the NB run at 60 psi (and that's what I used) but I've never had one or seen a friends car with fuel pressure gauge installed - so I am just guessing.

The NA Miatas run around 43 psi fuel pressure stock (IIRC 40-46).


So the formula is injector_actual_fuel_flow = sqrt( actual_fuel_pressure / injector_rated_fuel_pressure) * injector_rated_fuel_flow

RC Engineering rate their injectors at 43 psi (probably like most of the other manifacturers)

The NA8 (like mine) has these same size injectors and flows that much what you say. These same injectors flow more in NB because your fuel pressure is not standard. I've never done experiments with NB cars. Just install fuel pressure gauge in yours and then calculate what you get :)