Perry9394

iTrader: (2)

hi guys, i wanna get the extreme fuel sustem from RX7store, that comes with a secondary fuel rail 2 bosch 1600cc injectors and inline resistors, and if i have a PFC, do i still needa wire up the inline resistor? and would it be better to replace the 550cc primary with the 850cc factory secondary, so the primary and the secondary flow are closer? and is it easier to tune with closer flow rate?

Jason

iTrader: (5)

There are some that say you dont need the resistor and others say you do. We provide them with the kit. You can run 550 or 850cc primary injectors. The car will run fine either way and doesnt make much difference in terms of tuning.

Dudemaaanownsanrx7

iTrader: (23)

if you have a datalogit it will make tuning alot easier. some people have trouble tuning the idle with the 850 primaries. Negative lag is generally required to get a good lean idle.

I would go with the resistors to be on the safe side. ($150 to get the pfc repaired and who knows how much downtime)Resistors do slow the reaction time of them slightly but is really not an issue, your fuel maps will just have a little bump in them where the secondaries first kick in.

The general idea is that the injector drivers on the PFC can only handle a max of 2 amps. The way to figure correct resistor size is measure the resistance of the injectors. most the bosch injectors i have seen are 5.1 ohms. you divide that by the voltage the injectors see. (anywhere from about 12 - 14 volts). so 14 / 5.1= 2.7 amps. a bit too high. So we need more resistance. add a 3 ohm resistor to that and we have 3ohm + 5.1ohm= 8.1 ohm 14/ 8.1= 1.7 amps. less then 2amps.

some people add 10ohm resistors and on 5.1 ohm resistors is too safe and could make them obnoxiously sluggish.

The best solution though more costly is to use an injector driver such as the one from FJO. It allows the injectors to be used in the manor they were designed. Peak and hold. If i wasnt on a strict budget with this car i would go this route, but for us cost effective guys resistors is cheap insurance and works just fine.

Perry9394

iTrader: (2)

thank jason, and Dudemaaanownsanrx7 for the detail write-up, i do have a datalogic and i did some search on this site, seeing ppl have problem with idle when using 850cc as primaries, i wonder would it be a better idea to have 550cc for primaries for easier tuning? and does it matter if the flow rate of the primaries and secondaries are too different? like 550cc vs 1600cc, and when do the secondaries kick in, do the 550 work at the same time when the 1600cc kick in? at last, what is negative lag? i cant find it in the datalogic setttings.