Down side to bigger injectors?

[d-mag]

As the title states, is there a downside to running bigger injectors?
I'm thinking of taking the injectors up a few sizes as currently mine are running at about 95% duty cycle.
I currently run GTX Familiar injectors on a Turboed BP, along with a RRFPR.

According to the table below, if I want 550cc plug and play I need RX-7 injectors which I've been warned off by a couple of people due to the Rotary spray pattern, but if there is someone with expierence with these or something similar, I'd love to hear from you.



Cheers.

[mx52nv]

What would you like to know?

In all seriousness, the 550cc injectors are great for performance but not for idling due to the spray pattern. I was not worried about idle as I wanted to make sure the motor was never starved of fuel. Great for my twice a month dríven old girl. However, if it is going into your daily driver, there are other options. I seem to recall some Sard WRX ones that Hi Octane sold that would drop into the SE fuel rail. Not sure what flow rate (540/650/800cc) they were and memory also fails me as to their OD. I also think FM and RC sell drop in ones and of course so would Bosch. All of these are not cheap though.

Cold start has never been an issue based entirely on injectors. Just give your tuner time and he/she may spend a few days getting it right but you will never regret it.

Local rotary hero Lee Sanders (EZY9S ) gave the RX7 injectors to me during my build back in 1999. Back then, there were much less aftermarket options than there are now. I still hear of these RX7 injectors exchanging hands for less than $200 a set (would require proper servicing).

Les
*edited several times as I was sloppy and did not check my post as per normal for errors *

[Fatty]

only downside i'm aware of is that its a lot more difficult to get a smooth idle, and maybe cold start(?) with large injectors

[d-mag]

Thanks James and thanks Les, as usual, your scope of knowledge knows no bounds.

[93_Clubman]

here's the list 16bit recently posted - it's got some more options. btw, fuel economy can also suffer with bigger injectors, but i doubt that's a consideration

Complete list of Miata plug and play replacement injectors (“F” connector):

Year Make/Model Engine Size/Color Part #
87-88 Toyota MR2 4AGE NA 213cc – Beige Top #23250-16080
89-91 B2220 Truck 224cc - Yellow Top? #23250-74040?
99-00 Mazda Miata 240cc - Thin Red Body #195500-4430
Toyota 4AGE 250cc – Green Top
Toyota 4AGE 250cc – Violet Top
94-97 Mazda Miata 254cc - Tan Top #195500-2180
01-05 Mazda Miata NA & TURBO 265cc - Thin Lt. Prple #195500-4060
Toyota 3SGE 295cc – Green Top
89-92 Toyota Supra 7MGE NA 305cc – Light Green Top #23250-70080
93-95 Toyota Supra 3.0L 312cc - Maroon Top #23250-46030
Toyota 3SGE 315cc – Pink Top
90-92 MX6/626/Probe Turbo 326cc - Gray Top #195500-2150
89-91 B2600 Truck 326cc - Gray Top #195500-2150
Mazda 323 GTX TURBO 360cc - Black Top #195500-2130
Celica/MR2 3SGE NA 370cc - Green Top #23250-74160
Mazda RX8 420cc - Yellow Body #195500-4450
Subaru WRX 425cc - Lt. Blue Body #3920
89-92 Toyota Supra 7MGE TURBO 430cc – Black Top
89-92 Mazda RX-7 NA 440cc - Blue Top #195500-5740
89-91 RX-7 NA 460cc - Red Top #195500-2010
Subaru STi 540cc - Thin Pink Body #3910
89-91 RX-7 TURBO 550cc - purple top #195500-2020

[Juffa]

I am also of the understanding that putting in a higher flow fuel pump, (or piggy back pump) will give you more fuel, using the same injectors...ie at a higher pressure the injectors need to be open for less and therefore a lower duty cycle for same fuel flow...or greater fuel flow at same cycle??? or am I just talking poo

J

ps what numbers are you running. I have 330cc injectors that never see that kind of duty cycle?

Ps if you do go with RX-7 550cc injectores be careful as the same part number applies to both low and high Ohm injectors. The colour is slightly different, the best way to tell is with a digital meter.

J

[Fatty]

good point juffa. it may be best just to upgrade to a walbro pump.

[d-mag]

Thanks for the tip about the RX 7 injectors, I had no idea there were 2 sorts.
I'm running a Walbro and a FPR already, I can't get anymore out of these injectors.
Numbers Juffa? Power output I'm assuming? 178 rwkw.

[Juffa]

Thanks for the tip about the RX 7 injectors, I had no idea there were 2 sorts.
I'm running a Walbro and a FPR already, I can't get anymore out of these injectors.
Numbers Juffa? Power output I'm assuming? 178 rwkw.

178 rwkw...yes I can see why you are running 90+% cycle

As for the different 550cc injectors...don't ask how I found out

J

[Juffa]

good point juffa. it may be best just to upgrade to a walbro pump.

I have my moments.

J

[SuperMazdaKart]

Familia GTR/GT-Ae orange top injectors from their BP-D engine are also 550cc though officially under-rated at 440cc I think. Injector cleaning services & flow measuring has revealed they're 550cc. But good luck trying to find these ones, only came in 2300 Familia GTRs & 300 Familia GT-Ae's, the homologation specials.

[wazman]

I was just about to do a "what injectors" search and i saw this thread.....

I want to turbo my NB8a ......its stock atm.....but the turbo package will be exhaust,cooler, f/pump, ecu, injectors...

So what injectors do i need to see 180- 200 @the wheels ?? Will the wrx injectors do the trick ??

[d-mag]

I'd like to give the STi injectors a go too Waz, but price and availability are a bit of a turn off.
You can pick up the RX7 550cc injectors for about $250.

[rob323]

If you can use early RX7 injectors, then Mitsubishi vr4 (450cc), Evo 1-3 (510cc) and Evo 4-9 (560cc) injectors will probably also fit. I can measure some up if someone has some mazda injectors to compare them to.

Cheers,
Rob.

[Sean]

A few points to consider/ think about:

*A bigger fuel pump wont make a great deal of difference, the fuel pressure reg will is meant to make sure of that, although if you get enough pressure the reg wont keep up... Either way, it's a far less than ideal way to do things.

* I wouldn't bother with second hand injectors. It's hard to know what you're getting, and by the time you pay for a proper clean and re-pintle, you'll only be a few dollars short of a decent new set. If you must have second hand, the familar GTX are good and can be had for $100 a set. As Rob said, EVO injectors fit the rails, but need new plugs (an easy solder job).

*You will likely need a good fuel pump f you want to run double digit boost, walbro GSS342 is a cheap easy and effective solution and can supply enoug fuel (assuming you have changed injectors) for over 200rwkw, just remeber they are loud! Search for Gary's thread on quieting them down...

*The problems people are talking about at idle come form two things, first the spray pattern on the RX7 injectors is more of a dribble pattern than a spray pattern, think of it kind of like an open hose line, vs a hose line with your thumb over the end and you'll be getting the idea, the spray is more important to our engines than the turbo rotary, but as Les said, you can get it pretty close even with those injectors. The ability to tune them is the biggest thing, if your ecu is fairly low resolution you might the find that stepping the injector open time up just one setting makes a massive difference. If you are happy with a hunt at indle or a sligtly increased idle speed, you wont have problems.


HTH Sean