Using NB8B injectors (purple) in the NB8A..

[Rotary]

I haven’t analyzed our engine using data loggers to see when and where exactly its going from closed loop to open loop.

In general the transition is when there is a heavy Load/Throttle condition.

So the designer will decide where the best transition will be for each purpose, so it may occur at WOT or it may occur before but usually when heavy throttling.

The transition will usually use the TPS(Throttle Position) or MAP(we don’t have) Sensors, and the designer can also use other parameters to set where the transition will occur RPM, Air flow etc

On warm up it also operates in open loop

The Math is all correct except at 70% duty the ECU will likely be in Open loop mode and maybe even at 50% duty

[timk]

Do you know roughly how much power these injectors can support?

Do you know what the Aussie NB8A fuel pressure runs at?

[Rotary]

I haven’t tested it so can’t give an exact figure, Manual states 39-45psi as it would for many other Mazda models

There are plenty of injector power rating calculators on the net, but they all rely on one thing, Brake Specific Fuel Consumption(BSFC)
http://www.rceng.com/technical.aspx (Bottom of Page)

BSFC represents the power produced from using a certain amount of fuel, this will vary across the RPM range and also vary by load/Throttle (usualy shown by graph), The BSFC graph for different engines will be different.
For working out Injector size we need to know the engines BSFC at max power and WOT

Sometimes SAE Papers may contain a good graph on BSFC which can be useful, although various modifications will change it

Anybody have SAE Papers on the BP engine/s?
Often some very interesting and useful info found in these.

Anyway using the value of 0.5 for BSFC(for N/A) should be sufficient in over engineering the required size of injector

[slowpoke]

Thank you Rotary, you've answered my question.
When I learnt that new slightly larger throated injectors from the NB8B were available relatively cheaply it had seemed like a great opportunity for a perfomance enhancement at little cost..
But as the original (brown) injectors are still operating faultlessly I'll heed your most helpful advice. Thank you again. Cheers from slowpoke.

[Rotary]

Glad to help, I’m a big fan of bang for your buck mods, leaves more cash to spend on the important things in life, like track time

[slowpoke]

Tho' the original brown injectors in my NB8A seemed to be operating without fault I 'bit the bullet' and had them replaced with a set of (light purple) injectors from the NB8B series in the hope of achieving improved response at lower revs. In my view, the resulting improvement is absolutely marvellous!
My '5', a '99 model, has covered 43000km and the engine is completely standard other than having a Loc Stewart C.A.I. and a free-flow exhaust system. But now, with these newer type of injectors fitted, the engine definitely feels as if it possesses a new 'edge'. It now has a 'lift'and a new 'smoothness' that simply was not there when the brown injectors were in place.
On a level road, needing only the slightest pressure on the accelerator, the response at 1500 RPM in 4th gear has improved significantly....!

[93_Clubman]

Good to hear you had a win SP! Sounds like your 5 is a pleasure to drive!

[Hellmun]

I cleaned the injectors in my old camira and got the same effect.... He redirected the spray pattern so all 4 were synched and then cleared them and the car was significantly smoother. I wouldn't discount that as the reason rather than NB8B's just having better injectors.

[manga_blue]

I cleaned the injectors in my old camira and got the same effect.... He redirected the spray pattern so all 4 were synched and then cleared them and the car was significantly smoother. I wouldn't discount that as the reason rather than NB8B's just having better injectors.

The point is, Mark, that you can buy and install almost new NB8B injectors from the ebay guy in Melbourne for less cost and less hassle than cleaning the old ones.