Extra injectors for boosted NA motor.

[mullett]

What's a cheap, effective way to supply fuel to a supercharged NA motor? I was thinking along the lines of a hobbs switch mounted to 2 extra injectors, one at say, 5psi, one at 8, to dump extra fuel. Any better ideas?

RM.

[thechuckster]

i think an after market computer would be a more sensible thing to do than this very ghetto approach.

[slide86]

fit larger injectors!
what engine we talking bout? adding injectors before the throttle body and such can be done, but its probably more effective and safe to upgrade the injectors and fuel pump.

Or, get an adjustable pressure regulator. But this is just a minor upgrade, there is only so much pressure a fuel pump can supply....

[mullett]

Absolutely, this is a ghetto approach, that's the idea Aftermarket managment is out of the question, the aim is to supercharge it for under $800. This is more of a 'let's see what we can do to a cheap motor' than anything major. For reference, it's an LE18 motor out of an N13 pulsar, MAP fuel injection.

RM.

[RWDboy]

Depends whether you max out the flow of the stock injectors or not?

If it's a closed loop computer (EGO sensored), then no matter how much you play with injector sizes and fuel pressure then it will always try and tend towards the stock air:fuel ratios regardless.

[slide86]

'let's see what we can do to a cheap motor'

Blow it up and set it on fire me thinks

[mullett]

Yeah, the main problem is that it isn't a boosted motor, so it will have no idea how much extra air is going in, and will never get enough fuel. It needs some sort of auxillary standalone system for a couple of injectors...

RM.

[RWDboy]

It's MAP sensored ... so it DOES have an idea how much air is going in (p.v. the MAP sensor is wide enough band). It won't be able to enrich the fuel mixture to deal with the extra *heat* generated by the supercharger, but it will be able to get the air:fuel ratio's close to normal (probably tuned for somewhere in the realm of 11.0:1 to 12.0:1 when on W.O.T. and stiochiometric for all closed loop applications)

[mullett]

So you're saying that if I get a widerband MAP sensor, the standard ECU will deal with the boost?

RM

[RWDboy]

Not likely that the ECU would be compatible .... again, you may not even need a wider-band sensor depending how much boost you run and what the factory map sensor is like.

[mullett]

Yeah, so we're kinda back to square one eh? I think a couple of extra injectors should do well, because the SC will give a really linear amount of air. Might google some info about setting this up...

RM.

[RWDboy]

Google some info about the map sensor of your car first - don't waste time looking up injector bollocks yet!

[YelloRolla]

look for the archaic "microfueller". this is a systems designed to control additonal injector(s). Have fun - a programmable system (even a real cheap one) is a better approach.

[thechuckster]

It's MAP sensored ... so it DOES have an idea how much air is going in (p.v. the MAP sensor is wide enough band). It won't be able to enrich the fuel mixture to deal with the extra *heat* generated by the supercharger, but it will be able to get the air:fuel ratio's close to normal (probably tuned for somewhere in the realm of 11.0:1 to 12.0:1 when on W.O.T. and stiochiometric for all closed loop applications)

-the ECU map wont cover boost situations, the ECU might be smart enough to extrapolate from the 'edge' of it's map but the result wont be fantastic

-as others have noted, the MAP sensor may not be boost sensitive or capable - and given that most boost sensors have a 0-5 volt range of output, changing to a boost-capable map sensor would be a retrograde step as your ECU is coded to suit the stock MAP sensor

-if you have an intercooler, the heat from the SC is a moot issue. Anyway, if you shift the air-intake sensor to after the SC, it might then compensate. Air-temp compensation will only have a limited affect anyway.

-closed loop is only going to trigger during cruise and warm idle - neither of which will be generating any significant boost (if any).

-timing is going to be a serious issue - without boost-retarding the timing, the engine will grenade from the excessive advance when a boost.

You could get the ECU from an early-model nissan pulsar turbo? that knows what boost is. You'd also need it's dizzi.

But a 2nd-hand programable ECU and proper injection will bypass most of these problems in one step.

[RWDboy]

Yeah - basically, if the map sensor doesn't cover a wide enough range (as the chuckster is saying) then yeah you will have to look at the other options that he has stated. Looks like he's got a bit more idea what tech was floating around back then than I do !