MicroSquirt.com read only forum (Jan.15,2018)

Hello everyone,
Recently I picked up a pair of 1600cc secondary injectors for our RX7. Now we're getting ready to crank the car up again and I realised that these injectors arn't "normal". I used my multi-tester across the terminals last night and they read 5.8 and 5.9ohms. I tested the primary injectors again, just to make sure, and they are 14.1 and 14.0ohms (standard RX7 550cc high impedence injectors).

Can I run the car without a resistor pack on these 1600's? I'm going to write down the part # when I get back to the garage tonight, but this is really confusing me right now.

I can swap the primaries to low-impedence if I have to, but I really need to know by tomorrow as we're tuning the car on Sunday.

Michael

Michael,

The 6 Ohm secondary injectors should probably have resistors. Even if you put low impedance injectors in the primaries, they will have to have the same PWM requirements, which seems unlikely.

So resistors on the secondaries seem the way to go. You don't seend much - the current will only be 14/6.0 = 2.33 Amps. Generally 2 Amps is copnsidered the upper limit. If the secondaries see limited duty cycles and limited 'on times' (i.e. their pulse width is low, and they are only on occassionally for a dozen or so seconds at a time), then you may wish to risk it.

If you do want to use resistor the safe3st method, I think), then suppose you used 2.2 Ohms, this would reduce the current flow to 14.0/(2.2+6.0) = 1.71 Amps (-27%), and the Watts rating of the resistors would have to be: P = I²*R = 1.71²*2.2 = 6.4W, 10 Watts is the next size up (Digi-Key 2.2W-10-ND, for example).

Lance.

Not sure this will help but it would be fast and cheap. I just measured the resistance on a resistor pack from an early Honda injector pack and they are exactly 6ohm's. Wouldn't this be about perfect?

Todd

Thanks for the help guys! I went back through everything and actually just went pack to our parts room here at work. We have over 100 5ohm 25w resistors left over from a previous production run which the part # has been discontinued. I'm going to go ahead and order a set of 2.2ohm resistors also Lance, and might put those in, don't really want to limit the big injectors any more than needed.