New project

[cal1320]

Here's the basics. 56 chevy truck, 350 sbc, GM crossfire tbi injection (2- 2.5 ohm 65 lb injectors), HEI (7 wire), wide band, high pressure pump in a surge tank, going to use a microsquirt version 3 that has not been purchased yet. I will probably have a lot of questions before I finish this, so let's start with the injectors. Current injectors are 2.5 ohm each. One on each bank of the mS.
Ohms law says 14 volts/2.5ohm injectors=5.6 amps. 5.6amps x 14 volts= 78 watts. Way over the 5 amp maximum. I've read up on using resistors to raise the impedance of the injectors, but no one is really in agreement of by how much. I know they have used the Micro on the TPI successfully. Those injectors are 18.2 ohms each (4 per bank) which is a connected load of 4.55 ohms. These put a load of 3.076 amps (43.064 watts) on the drivers. Should I resistor(2.0 ohm 50watt) my 2.5 ohm injectors to match the 4.55 ohm load of the TPI? Some say to add 8 ohms or so but reduce it if it wont run. I would like to only do this once if possible. I've read the injectors operate more accurately at the lower ohm loads at idle and WOT. Will the Microsquirt live a long and happy life at 3 amps of load on the drivers, or would it be better at a lesser amperage? I know it's long winded for a simple answer, but I would like to know the whys and hows of this too.

[Matt Cramer]

3 amps ought to be OK. From other customers' reports, 3 to 5 ohms of inline resistance tend to work fairly well with TBI injectors. You'll want to make the resistors oversized; 25 to 50 watt power rating would be a good idea as you don't want to run them at their maximum power rating.

[cal1320]

OK. Getting back on track again. Finally. Was getting set to purchase the mS V3 but need to confirm, am I on the right track? Would a Megasquirt 1 or 2 be better suited than the Micro? I know the Micro and MS1 cannot run the IAC motors,and the mS cannot be altered like the MS ecus and thats OK. I dont see the need for the extra future expansion of the MS2 for my application and I like the compactness of the mS. There's not a lot of room under my dash. This is going to be a very basic injection system, nothing fancy. Basic HEI and 2 injectors. So what do yall think? Will the mS leave me wanting more?

[Matt Cramer]

MS2 can driver the stepper IAC and its injector drivers have considerably higher current capacity, which is very useful with TBI injectors. I'd use an MS2 over a MicroSquirt for this application.