Microtech + new injectors

[DeMenTia]

G'day all,

I'm about to upgrade my injectors from 550cc Purple RX7 Injectors to 880? MSD injectors.

I dont have the specs for the MSD injectors just yet, but what i want to know is if the microtech needs to be changed at all if the injectors are of a different impedance. I have emailed microtech with no reply as yet (3 days).

Also, this car has been tuned with the 550cc injectors. Should i be able to replace the injectors with the bigger ones and using a AFR meter just change the injector timings to get the right ratios again and NOT have to touch timing ? (its a MTX-8 and i have the program controller).

Thanks for help.

[Madhatr]

I would think the Microtech should have a form of modulation which will allow you to run both high and low impedence injectors. The difference will be in the paramaters you specify when you setup the ECU.

You dont really want to change timings, you want to focus more on pulse widths.

[takai]

However, im pretty sure that the modulation is set from factory. I.e. you need to return it to Microtech in order for the impedence to be changed. This was how it was for the MT8 when i had it.

[Madhatr]

If that is the case and you cant reprogram it, that seriously sucks. Glad i have an MS.

[DeMenTia]

Yeah, the tune on the car is good atm, has a perfectly smooth power curve with no dips or bumps and apart from a few small light cruise issues (less than 5% throttle) its fine. I dont really want to touch the ignition maps. Just wanted to clarifying that a small variation in fuel tuning will not need a ignition change. And on that note, can anyone point me in the direction of a good tuning theory guide or something of similar interest?

[Madhatr]

well you are going to have to change pulse widths because of the larger injectors, so yeah, i would say you are going to have to tweak the maps. But if you want to utilse the larger injectors you are going to have to go through it all again anyway, if you dont want to, what is the point of fitting larger injectors?

[DeMenTia]

1. Because i'm actually swapping my old rail and injectors with a family member to their bigger injectors/rail (long story).

2. The microtech is mapped to 24psi with the injectors going to max duty cycle @ 22+, i know they are running slightly rich, but meh, its good to have some headspace i guess, plus leaves room for a bigger turbo in the near future.

I dont care about the fuel maps, i know i have to adjust them (obviously) i want to know what relationship amount of fuel has with ignition. This will lead on to more question like

can i add more timing, if i can where and how much, and without a dyno should i even bother trying to use more advance to get more power during boost etc as the increase will probably be only small from the point of tuning atm.

*continues searching*

[10sec rx7]

dont have to do anything to the ecu to run larger injectors, you can run 2x 2ohm injectors per channel or 4x 12ohm with out a problem, so you could run 12 injectors with out problems.

use the mixtrim to get the fuel close then fine tune with the approate tuning gear

[CA18escort]

The bottom line is that if you tune the new injectors so that the A/F ratio stays the same then you won't have to change the ignition. You should be able to work out a rough tune just by looking at the increase in size ie 550/880 = 0.625 so for example if at a certain load point the injector was open for 10ms with the 550cc injector then you should be looking at around 6.25ms for the 880cc injector. Having said that this is also dependant on relative flow at a given pressure for each of the injectors and even the spray pattern at a given pulse width. If you were to factor in a safter margin and set the pusle with to 75% of what it was with the 550cc injectors you should have a driveable start point that will get you to the dyno for a final tune.

Paul

[DeMenTia]

Thanks for the reply lads! ...

No doubt i'll be back in this thread asking more q's soon