Using NB8B injectors (purple) in the NB8A..

[slowpoke]

Has anyone with an otherwise standard NB8A (engine)replaced the original (brown) injectors with the slightly larger injectors from the NB8B? And if 'Yes', what was the result, please?

[Okibi]

I've considered doing it if I ever ecu the NB8A, can someone confirm the difference? (I seem to remember they had 10% more flow)

[timk]

Yeah I have. The car will run OK on the stock computer, just a bit rich. Have you got something to lean them out?

[Rotary]

I've considered doing it if I ever ecu the NB8A, can someone confirm the difference? (I seem to remember they had 10% more flow)

The injectors from my NB8A and the NB8A ones I got from Paul(93_Clubman)
Are Denso #195500-3310
They flow 256cc according to witchhunter.com



The 10% your thinking of Dave is from the miata list which appears here from time to time which says

99-00 Mazda Miata 240cc - Thin Red Body #195500-4430 (maybe US Spec)

The 4430’s flow 225cc according to witchhunter



Overall if the NB8B injectors are indeed 265cc, then it will be 3.5% larger and will richen the mixture by approx 0.4 A/F ratio

The richening will only occur when running in open loop mode(no feedback) mostly when heavy throttling or when warming up.

Otherwise in closed loop(O2 sensor feedback) the ECU can compensate for pretty much any condition, you can use 100cc larger injectors and it will adapt precisely, you could run 80% E85(A/F 9.8 )- 20% ULP(A/F 14.7) and it will adapt precisely

Won’t adapt in open loop though so any changes must be considered according to the application.

[Okibi]

Thanks Rotary, as usual your advice is valuable and appreciated.

I'll try and get a photo of the NB8B injectors I have in the shed somewhere.

[Okibi]

4 boxes of MX-5 parts later ..

[93_Clubman]

Has anyone with an otherwise standard NB8A (engine) replaced the original (brown) injectors with the slightly larger injectors from the NB8B? And if 'Yes', what was the result, please?

SP, manga_blue has commented a couple of times on swapping the injectors in his NA8 for these NB8B injectors. In the NA8 he found "they make a difference, especially to low speed tractability" & "smoother & stronger low down". Manga_blue also commented "they have a better spray pattern, they're slightly richer but they do give a much smoother response low down".
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The injectors from my NB8A and the NB8A ones I got from 93_Clubman are Denso #195500-3310 - they flow 256cc according to witchhunter.com

Rotary, I got those injectors from a locally delivered vehicle on the West Coast of Canada.

[slowpoke]

Thank you everyone for your very helpful feedback. I had felt a bit concerned that the 'economy aspect' might suffer too much, but from your positive comments I now feel confident that such a swap-over will be worth the money.
Thank you 93Clubman for alerting me to this upgrade, and for steering me towards a good source of the purple injectors..
Cheers from slowpoke

[slowpoke]

Thank you everyone for your very helpful feedback. I had felt a bit concerned that the 'economy aspect' might suffer too much, but from your positive comments I now feel confident that such a swap-over will be worth the money.
Thank you 93Clubman for alerting me to this upgrade, and for steering me towards a good source of the purple injectors..
Cheers from slowpoke

[93_Clubman]

no probs SP - obviously it would have been nice to get feedback specific to the nb8a, but i think the na8 feedback kindly provided by manga_blue is a useful guide.

btw, the source still has a few sets of injectors if anyone needs them.

[Rotary]

Compared to the NA8 older style injectors the NB8B injectors have an Finer spray with better atomization of the fuel, This can improve efficiency and emissions ever so slightly.

The NB8A is exactly the same type of injector as the NB8B so there is nothing to gain in this area, and by nature larger injectors have less precise control of fuel metering
e.g.

a 250cc injector operating at 10% duty will flow approx 25cc, at 11% duty it will flow 27.5cc a step of 2.5cc
A 500cc injector operating at 5% duty will flow approx 25cc, at 6% duty it will flow 30cc a step of 5cc
So now for each 1% step the injector will be half as precise at giving us the exact fuel we need, leading to inefficiencies

The NB8B injector is only slightly larger so in practice will make little difference, but the point is, it won’t be better.

Not sure why your thinking of changing them but if the current ones aren’t running right then it can’t hurt replacing them otherwise there won’t be any gains

Hope this helps.

[project.r.racing]

no probs SP - obviously it would have been nice to get feedback specific to the nb8a, but i think the na8 feedback kindly provided by manga_blue is a useful guide.

btw, the source still has a few sets of injectors if anyone needs them.

details?

[93_Clubman]

Many thanks Rotary - I guess the improvements felt have been due to the older less efficient type of injector on the NA being replaced by a the new & more efficient NB injector. Still for $60 posted it's cheaper for some than cleaning their old ones.

btw, the source still has a few sets of injectors if anyone needs them.

details?

pm'd

[Okibi]

..Overall if the NB8B injectors are indeed 265cc, then it will be 3.5% larger and will richen the mixture by approx 0.4 A/F ratio

The richening will only occur when running in open loop mode(no feedback) mostly when heavy throttling or when warming up.

Otherwise in closed loop(O2 sensor feedback) the ECU can compensate for pretty much any condition, you can use 100cc larger injectors and it will adapt precisely, you could run 80% E85(A/F 9.8 )- 20% ULP(A/F 14.7) and it will adapt precisely

Won’t adapt in open loop though so any changes must be considered according to the application...

So to try and outline the differences between the tiny differences in NB injectors.

Please correct me if i'm wrong.

When in closed loop mode, a 195500-33-10 is running at 50% duty the ECU would compensate and run a 195500-4060 at 48.3% duty.

When in closed loop mode, a 195500-33-10 is running at 70% duty the ECU would compensate and run a 195500-4060 at 67.6% duty.

When in closed loop mode, a 195500-33-10 is running at 100% duty the ECU would compensate and run a 195500-4060 at 96.6% duty.

An injector will create a more efficient spray pattern the closer it runs to 100% duty.

At WOT (wide open throttle) the ECU goes into "open loop mode" and runs off a fuel map.

The in open loop mode the fuel map doesn't take into consideration readings from the O2 sensor and the 195500-4060 injectors will flow 3.5% more fuel than the 195500-33-10.

I seem to recall that the MX-5 also goes into open loop mode above 4k rpm, can anyone confirm?

[manga_blue]

I seem to recall that the MX-5 also goes into open loop mode above 4k rpm, can anyone confirm?

This is from an NA8. You seem about right for that model at least.

California Fuel Map.jpg