Bigger injector with FMU

[Belette]

Does bigger injector like Prelude 325cc ones need resistor box with FMU ?

Can I reduce static pressure little bit with prelude injector and go with lower ratio FMU ? if yes, which one ? 6:1 ? 8:1 ? i want to reduce overall fuel pressure, fuel will last longer and injector too ... :)

thanx a lot

:)

[kyosoeg6]

your best bet would be to remove the fmu all together. they boil gas which means u will be more prone to detnoation. if u really need more fuel you can always go with 450 dsm injectors

[S Q A D]

scrap that p.o.s manual FMU :) then again, im biased against those things ... :-D

[Belette]

It's not the way that I want to know :( I want to know if someone had experiences or know setup with FMU and bigger injectors, if yes how about FMU ratio with some 280 to 325 cc ones and if I need resistor box anyways with FMU (NO AFC or SMC or anyt hing like that). I'm little bit tight on cash to buy eletronical parts this summer...

thanx

[TurboEF9]

OK, let me sort this out a bit..

As far as the injector type, you probably won't need a resistor box if you're using newer injectors. The size doesn't dictate whether or not you need the box, the type does; Peak and Hold vs Saturated.

As far as larger injectors and an FMU... you're going to kill your drivability. Think of it this way: Your ECU thinks it's going to have 240cc injectors. The fuel tables were written in such a manner that the injector pulse widths give the proper amount of fuel when using those 240cc injectors. If you slap 325cc injectors in, you'll be flowing 26% more fuel per pulse! Then, on top of that, during boost your fuel flow will start to increase exponentially, running you horribly rich unless you have the air flow to compensate, which, I don't think could be accomplished well enough on a small enough for a D series to spool, practically speaking.

[hatched]

the fmu is too work with the stock injectors. if you want to upgrade your fuel set up then change the injector size get a boost hondata computer set up and then you will be good after a bit of tuning.

[eg8]

obviously I think money is an issue here. I know hondata is good, but we cant just tell people to get that before exploring other options. How about this, Ive been learning ALOT, so a missing link and 440's on a stock fuel system running 7 psi? will that be just as good as running a 12:1 fmu? (in terms of flow rate, I know it be MUCH better in terms of life becuase the system is running at stock pressure)

[BseriesKllR]

why not go with uberdata?

[eg8]

I was actually considering that, but I dont want to take my ecu apart and get eproms and eprom burner when I can goto a junkyard and grab larger injectors for cheap. I mean, both will work, I guess its just what you want to do with it.

[Belette]

I read this:

'The FMU is great because it allows the car to run normally on a small injector, but can also increase the rail pressure under boost which, in turn, forces more fuel through the same size orifice. The fuel that the FMU adds has a direct relationship to the boost pressure. The proportionality is usually stated in a ratio, for example 12:1. This means that the FMU will add 12psi of fuel for every psi of boost. (For example, 10psi of boost will add 120psi of fuel pressure.) When all is said and done, this could net a total of about 140psi of fuel pressure which is often too much for a little injector to handle. It is also the reason most people opt for a combination of larger injector and lower ratio of FMU. This is an ideal setup because it allows the same quantity of fuel but at a lower pressure which is more constant for tuning and less fatiguing on the injectors.'


It's sure ! But If for exemple, I set FPR -10 lower static pressure with 325 equal about stock 240 cc ones ? If i put smaller ratio like 6:1 or 8:1 FMU, Can I reach good idle, no lean condition or too rich, but lower gaz pressure at fuel rail & fuel pump ?

ex:
like static pressure at 30, + (6 x 1 ratio FMU) x 6 psi of boost, we are going 30+36= 66 psi with ~300cc injectors ? Does it sound goods ? or something like that ?


thanx a lot

[oscarmayer]

FYI the stock honda ecu cna handle up to a 310 injector. the ecu can automatically adust for fueling. he could run a fmu at like a 6:1 and 310 prelude injectors and he shoudl get an afc to tuen it in properly. not running somethign to adjsut the upper levels of the fueling dueing boosting is totally asking for a blown motor. for anythign udner 10 psi i recommend a afc and 310 injectors. I ran 10psi and 222 wheel power on 270 cc rc injectors before i switched to my hondata. I ran a 8:1 fmu as well.

[Belette]

You ran only FMU with 8:1 with 270 injectors ? Good I'll try to find set of them...

I will not boost at 10psi, but 6psi.

I didn't know that ecu adjust little bit bigger injector !


thanx

[TurboEF9]

I didn't know that ecu adjust little bit bigger injector !


That is because it can't.

Oscarmayer, again, is giving incorrect information.


The ECU will make minor adjustments to fuel (even in closed loop, only minor adjustments based on some lousy O2 *AND* the fuel tables), a 26% flow rate differential is not a "minor" adjustment. The ECU will adjust based on ECT (using hte cold start routine), IAT (very minimal changes ~.25 milliseconds duration), and MAP signal. MAP signal.. interesting, where does it get the adjustments for that? OH YA! The fuel tables!! ..and if the fuel tables are tuned for a 240cc injector, you're going to run entirely too rich. Plain and simple. Then on top of that, stick that FMU in there.

Yes, rich is better than lean, but a fireball from your exhaust is not the healthiest thing for your car.