Using RX7 550cc injectors in a DSM It has been discovered that the 550 cc injectors from 2nd generation RX7 Turbo II cars can drop right into Eagle Talons and provide a good upgrade over the stock 450’s. The pintle ends on the RX7 injectors are a little fatter than the stock 450s, so they are a little harder to press into the grommets at the engine but the tops fit Perfectly into the 1G Talon fuel rail. The over all length of the RX7 unit is longer than the stock Talon 450’s. The Talon units look stubbier and fatter than the RX7s, but they fit perfect, aside from a little bit tighter fit at the engine. The fuel rail bolts right down and doesn’t require any extra spacers or washers due to the seemingly taller RX7 units. Just keep the stock plastic spacers on the bolts and you are in business.
Electrically speaking, these were High impedance injectors. Mazda switched Injector impedances midway through the generation. When in the junkyard, just pull up the air box behind the pass side headlight and look for a resister pack. If there is one, the RX7 is equipped w/ low impedance units, which are plug and play for the Talon. If there is NOT a resistor pack, then they are high impedance, like the ones I used. They are called "Purple top" injectors in our RX7 club, because the plastic tops are Purple, but can fade to a pink due to aging and heat.
Apparently there were two different generations of Denso High impendence 550 cc injectors found in RX7’s. I had to pull 2 pairs off two different Turbo II's. One pair has oval connectors, and the other has square connectors. If you want to use the oval ones, you can cut the plug off the RX7 and splice that in place of your stock DSM connector, OR modify your stock connector to plug into the RX7 injectors. If you get the square connectors, they will fit perfectly, provided you either shave the notch off the front of the receptacle, or cut a groove into the Talon connector. The Talon and RX7 injectors both have notches, which are keyed to their respective connectors, but are obviously in the wrong position to provide easy connectivity. The Oval injectors are more work to use the stock connectors. We had to trim the outer part of the DSM connector off, and leave the center plug intact, that will plug directly into the RX7 oval top injector, but won’t stay on as tightly as normal. Ill probably use a Zip tie to lock it down in place.
Impedances are important. Talon ECU’s actually want high impedance injectors but they use low impedance injectors and supplement this with a little rectangular Resistor pack mounted on the firewall near the battery. That resistor pack contains 4 10-ohm resistors, which increase the stock injector impedance from 3-4 ohms to 13-14 ohms...the same impedance as my Turbo II 550's. There are 4 black wires going to this pack and one central white wire. All you have to do is remove the pack, and splice all 4 black wires to the 1 white wire, and effectively bypass the resistor pack. If I had forgotten to take that pack out, my RX7 injectors would effectively had 23-24 ohms of Impedance. I’m not sure how that would affect the car, and I don’t want to find out so remember to remove the resistor pack if using the high resistance RX7 injectors and leave it alone if using the low impedance ones.
RX7 550s are pretty easy to come by, more so than the 680/720's found on the 1st Gen RX7's (the 84-85 GSL-SE’s). They had 2 injectors on their "new" fuel injection unit. The 2nd Gen RX7's switched to a set of four injectors. The Non turbo cars use 4x 450cc, and the Turbo II cars use 4x 550cc which are the ones you want. Most of the time, you’ll see RX7 owners selling only two of their 550’s. This is because they are selling their secondary injectors (operate above 3800 rpm) and going to install larger ones, like 650, 720’s. The ones from the 84-85 gsl-se's are 720's.They also drop right in (tight on the bottom) and they are low impedance so there is no modification to the resistor pack required. Finding out if your RX7 injectors are high or low impedance is simple. Just hook an Ohmmeter up to the two poles on it.
The following is a list of RX7 models and the injectors typically found in them. (Either color of 1370’s is the best for use in a DSM but at least some of the purples will need your resistor pack removed. The 2020’s will work with plug modification and resistor pack removal)
- 1984-1985 GSL-SE (195500-0900 primary 460cc/min ORANGE TOP) (secondary 680cc/min)
- 1986-1987.5 NA - (195500-1350) RED TOP 460cc/min, low-impedance, square plug, side tab
- 1986-1987.5 turbo (195500-1370) TAN TOP peak/hold 550cc/min, low-impedance, square plug, side tab <--- you want these
- 1987.5-1988 turbo - (195500-1370) PURPLE TOP saturating 550cc/min, high-impedance, square plug, side tab <--- or these
- 1987.5-1988 NA – (195500-1350) ?PURPLE TOP? peak/hold 460cc/min, high-impedance, square plug, side tab
- 1989-1991 NA - 460cc/min, high-impedance, oval plug, center tab
- 1989-1991 NA (195500-2020) PURPLE TOP - saturating 550cc/min, high-impedance, oval plug, center tab <--- or these
- 1993+ injectors are of no use to DSM's as they switched to side feed
*Update, Oct 2005* I've been using the 195500-2020 oval plug injectors for over a year and a half now. No complaints. Modifying the plug to fit the square DSM clips was easy. All I did was carve the notches off each injector so they were a smooth oval, they fit on snugly and shouldn't fall off even without the clips or "staples" holding them on. The resistor mod is very simple too, just make sure you solder it well.
Some tips on the install: 1) clean well or powerwash under the rail before you remove it, there may be crud and debris under there that you don't want falling into your head. 2) there are black plastic spacers between the rail and head, a bit of crazy glue or somthing to prevent them falling off might save you some swearing. ;)
Tools needed: 10mm and 12mm sockets, 1/4" driver with long extension, also 10mm wrench, flat screwdriver to pry off rail end lines, 15mm to remove PCV, and wire cutter/stripper, soldering iron and electrical tape if you need to mod the resistor pack. Oh and beer of course (2-beer job) domestic will do. :P
Whole process should only take 30 min if you're prepared.
Make sure your new injectors have new o-rings don't count on the existing ones being re-usable they never should be.
This information originally provided by flubyux2 of
www.DSMTalk.com November 19th 2002. Information amended and additional info on injector part numbers and specs added by Jeremy Clarke
www.BC.DSM.org November 2003. Not all information has been verified and this is not a complete list of all RX-7 injectors. To be used only as general guide, all replacements or conversions to be done at your own risk.
