1.8 HKS Kit - Best injector size.
 

Sorry if this has been covered somewhere else but I couldn't find it, read the FAQ's really interesting thanks, but seemed to be just for the 1.6.

I have a 99 NB 1.8 with an HKS T25 kit, FCON Mini, piggy back and an I/C. Currently running 5PSI.

I would like to increase the boost to around 8PSI (just for a little bit more go :bigtu: ). To do this I would obviously have to use bigger injectors. My questions are???

What size should injector do I need to go to?

Can the factory ECU and/Or the Fcon cope with a bigger injector?

Is it true that because the stock ECU will run rich it will kill my O2 sensor?

What fuel pressure does the NB 1.8 run (no reason really just wondered)?


Thanks

Gazza

'99 will run at 60psi. The 99-00 (red) flow 238cc at 43.5 psi and about 280cc at 60 psi.

If that is correct, (sorry hard to get solid answers on flow rates for miata.) then that's large enough for around 190BHP, most likely closer to 5psi.

The 01-05 (purple)(incl. MSM) flow 264cc at 43.5 psi and about 310cc at 60 psi and the 94-97 (tan) flow 268cc at 43.5 psi and about 315cc at 60 psi.

Those would allow for around 210BHP, around 180rwhp. With the F-con I'm sure you could alter the curves enough to see good AFRs at 8psi. The ECU shouldn't have any trouble idling them.

IIRC the JRPC/Voodoo on NB's was good for 8psi w/ stock injectors [T25].

You could add an O2 Clamp, and WBO2 and see where you're at. [ or take a trip to the Dyno ]

A 255lph pump and 94-97 tan top or 01+ purple top injectors will get you where you want to go. Have fun at an easy 190-200 rwhp.

I have the Voodoo box and stock injectors. I run at 7 psi daily because i don't want to risk 8 untill i have my WBO2 installed so i know where i'm running. Supposedly it will work perfect up to 8 though with the stock injectors, no other upgrades. It's simple, came with my car, but for just about the same price you could go Megasquirt and use any injector you wanted.

Yeah I hear ya, I ran the JRPC for 1.5 years @ 8psi on my T25, it was kinda lean over 6500RPM.

Hey Thanks Guys. I just had a look and indeed they are the red one's. I must put a pressure gauge on a see what kind of fuel pressure it runs at.

But two more questions please.

What is an O2 clamp, is it something you buy? I was told that they don't work on an NB because they run closed loop until 4000rpm.

How do you change the fuel pressure on an NB as they don't have a fuel return?

FYI about the year, most of the MX5's here in New Zealand are imported as used cars from Japan, so mine is really a 98 in Jpan but a 99 in the States (not sure about the UK). My turbo was put on in Japan and the IC added here.

Thanks again. Gazza

Sorry just checking if my picture added OK.:)

What is an O2 clamp, is it something you buy? I was told that they don't work on an NB because they run closed loop until 4000rpm.

The O2 clamp is exactly for that. To trick the stock ecu into thinking it's still in CL mode, by sending the 'correct' V to the ECU when under boost. Otherwise if say your under 4K RPM's and boosting, your ECU will try and lean out the mixture.

Hi poison, slydit here..
the o2 clamp can be used on the NB's...theres just no gaurantee that it wont throw a check engine light depending on how you set it.You may find that with the Jap spec ecu youll be ok as they run less strict emmission controls than U.S spec cars.
Olderguy sells them on this forum.

If you want a mild upgrade in injectors im pretty sure the Nissan RB20DET injectors from the R32 GTST are around 270cc at 43psi so will be in the 320cc range and the Mazda 330cc injectors will be up around 370cc at 60psi.