Injectors

The standard injectors of a 1.6 are 205cc, which makes you can turn up boost to about 9.5psi.  If you want more boost, you can use the 230cc injectors of the 1.8.  With those injectors, boost can be turned up to about 11psi.  If you want even higher boost, you can use injectors up to 250cc max in the '90-'93 1.6 and up to 270cc for the 1.8.  If you use too big injectors, you'll get a rough idle.  This is because at a certain point, the injectors get so big that the ECU cannot handle them anymore.  You can work around this problem by tightening the spring of the AFM (Air Fuel Meter).  A few clicks should do the trick.  You could also adjust the air bypass screw of the AFM,  I didn't try it myself though since, at the moment anyway, I'm pretty pleased with the 250cc's.  On the picture you can see the 3 types of injectors, the brown ones are 230cc, the blue ones 205cc and the black ones are RC Engineering 250cc's.  Although these look very different, they do fit the fuel rail.  Does anybody know which injectors the Euro 1.6 from '94-on uses?  If so, please send me a mail (but don't forget to remove the 'nospam' bit)!  
For more info about AFM's, take a look at Randy Stocker's site.

The 1.8 injectors are an identical fit to the 1.6 injectors, there's no need to modify anything.  The total swap shouldn't take more than 30 mins (if you don't drop anything at least ).  Before removing the injectors, it's best to prime the fuel system.  Start the engine and remove the yellow connector under the steering wheel column (fuel pump relay).  After a few seconds, the engine will stall.  Remove the ignition key and refit the connector.  Now disconnect one of the fuel rails on the chassis, next to the charcoal canister (I disconnected the fuel gauge, it's more easy to get too).  Keep a rag handy, there will be some fuel spillage.
To get an easy access to the fuel rail, remove the air valve on the throttle body (4 8mm bolts).  It's advisable to use a new O-ring afterwards.  Remove the 12mm bolt on either side of the fuel rail.  Now you can gently pull it backwards, and you should have just enough room to pull out the injectors.  Keep an eye on the black plastic spacers under the fuel rail.  Don't drop these when pulling back the fuel rail.  Murphy says they'll fall somewhere you can't find them anymore.  In my case, one of them fell in between the starter and the block ... took me over an hour to find it. 

When fitting new injectors, it's advisable to renew the O-rings on top.  Out of safety precautions, I also renewed the bottom ones (see pic).  These usually stay in the block when pulling out the injectors, but they're easy to remove.  When the new O-rings are fitted, you can gently push the injectors back in place.  On the top picture in this page, you can see that the RC Engineering injectors have a much wider groove on top than the originals.  I just used 2 O-rings on top of each other.  This probably isn't the way to do it, but what can I say, it works.  Haven't had a leak yet, so it'll be OK I guess.

If you want to use bigger injectors then the 1.8's, you'll have to use aftermarket units, but this also means you must change the connectors too.  In my case, I'm using 250cc injectors of RC Engineering.  These use the same connectors as the old 323 1.6i and 323 turbo (and probably a few other models).  These should be easy to find used.  Just cut of the entire wiring loom, not just the connectors (this only cosseted me 10€).  I have no idea of 323 1.6i injector size, but I suspect them to be about the same size as ours, so they're of no use.  The turbo (GTX) uses 300cc's, so these are useless too, since they're too big for the ECU.    

Since the injectors of the '90 - '93 1.6 (not so on the 1.8 and the later 1.6 models) are wired in pairs, there's only 3 wires to control all 4 injectors.  Instead of cutting of all the connectors (8 wires), I decided to put the new wiring loom in parallel with the old one.  I soldered it onto the existing wires, just in front of the 6-pin connector at the back of the block.  From this connector, there's 3 wires going to the injectors.  A white/red one for common earth (my tech sheet says so, although I measured 12V on them ... never mind, it works), a yellow/black one for injectors 1 and 3 and a yellow one for injectors 2 and 4.  At first, I had left the existing wiring loom in place.  Since this was a bit of a silly sight (see pic), I decided to start over again.  I cut off both the new and the old wiring loom (cut that one off behind the connector of course)  and soldered the new one back on instead.  Much better look and only 3 wires to cut/reconnect.  This is the final result. 

Februari 2001

I bought a Link ECU so I had to replace the 250's with bigger injectors.  Normally you want some 440cc's, but I found a set of used 450cc DSM's.  Just like the 250's, they are a bit shorter than the stock injectors.  I never realized it before, but since they are shorter, there is a risk that they don't protrude far enough into the head, making them spray against the sides of the opening.  

Here's  (left to right) the 250cc, stock and 450cc's.  You can clearly see that the body's are all the same length, but the tip on the stock injector is a few mm longer.   I wanted to get the 450's to sit as deep into the block as the originals, so I decided not to reuse the stock (thick) bottom seal you can see in the right picture.  Instead I used a much thinner O-ring.  This way, the injectors stick into the engine as for as the originals.  Of course, they're too short now and won't fit in the fuel rail.  To compensate for that, I just removed the plastic spacer under the fuel rail and replaced it by a plastic washer of about 2mm thick.  That way, the fuel rail lowers by a few mm, causing the injectors to sit tight enough.  I don't know if it's absolutely necessary to do this, since the car always ran fine with the 250's and the stock washers, but I guess it's much better this way.

The O-rings I used are 3/32" thick, 3/8" ID and 9/16" OD, I paid about $0.40 each in the local auto parts shop.  Just to have a better idea of their size, the small O-rings in the picture are the stock ones used on the top of the injector.  

Since the 450cc's have a lower resistance then the stock injectors, you need to insert a 4.7ohm/25Watt resistor in series with each injector.  Since the 1.6 fires its injectors in pairs, it's much more easy to connect the resistors directly at the ECU.  That way there's only 2 wires to cut instead of 4.  Of course, by connecting them at the ECU, you need to place 2 resistors in parallel per wire (thus 2.35 ohm total, yes you read it right, 2.35 ohm total).

Update

I found that the 1989-1992 RX-7 is a good source for injectors. 
The normally aspirated RX-7 uses 460 cc's which have the correct impedance (14 ohm) and the correct connector. The part number is 195500-2010, and it says Denso on the other side of it.

If you're looking for 550 cc's, then you need those of the 1989-1992 RX-7 Turbo II.  Again, they are the correct impedance and the correct connector.  The part number is 195500-2020, and it says Denso on the other side of it.

Both injectors are plug and play. 
Pre '89 TII's had 550's too BTW, but they where Low Imp and the connector was different from the Miata's.  This means that you can use them allright, but you have to use 4.7 ohm / 25 Watt balast resistors in series with each injector and fit a different connector on the wiring loom.  I'm told most GM connectors are the right fit (haven't verified this).

86-87.5 Non-Turbo, low imp, 440cc, Square connector
87-87.5 Turbo, low imp, 550cc, Square connector
87.5-88 Non-Turbo, high imp, 440cc, square connector
87.5-88 Turbo, high imp, 550cc, square connector
The last build for the low impedance injectors was Vin#7601 built in June 87
There was no 86 Turbo
89-91 Non-Turbo, high imp, 440cc, oval connector
89-91 Turbo, high imp, 550cc, oval connector
 

If you're looking for cheap 250cc injectors, than the Toyota Corolla is a good source.  The 4A-GE engine uses these and they fit fine.  They are 13.8 ohms, 250cc and the tops are green.  On one side they have 23250-16110 imprinted on them and on the other 9F27 is imprinted.
 

A few other Toyota injectors that are a direct fit:
- 87-89 1.6 DOHC: 213cc beige top
- 89-91 B2200: 224cc
- 89.5-92 Supra: 305cc light green top,
- 89.5-92 Supra Turbo: 430cc black top
- 89-91 B2600: 326cc

The Ford Probe uses 305cc injectors which are also totally plug and play, same connector, size and ohm.

Another option, if your having a hard time finding 1.8 injectors or want to spend less, is to use Eclipse injectors (they are 235cc). Find a G1 ('90-93) NA auto. The injectors have silver bodies with a salmon color plastic top. The connector is different. Either get the Eclipse or GM connectors and replace the originals.
L-R Stock 205cc, Eclipse 370cc (turbo auto), Eclipse 450cc (turbo stock), RX7 460cc

home