Re: [alfa] Re: Downsides of bigger injectors?

[James Montebello <jamesm@xxxxxxxxxxxx>]

In a properly working fully closed loop system, there wouldn't be really
any downside until you went with injectors so big that idle mixture
couldn't be controlled adequately.  The closed-loop part of the system
would simply adjust the injector pulses down to compensate.

However, very few EFI systems are fully closed loop all the time.
Most switch to an open loop mode at larger throttle openings for two
reasons: the O2 sensor has a response rate that's too slow to keep
up with an engine accelerating a full speed, and the required mixture
for good performance at WOT is typically richer than an O2 sensor can
accurately read even if it could keep up.  So, the ECU, since it "knows"
how big the stock injectors are, simply falls back to a fixed internal
map based on the size of the stock injectors.  Obviously, if you put
in larger injectors, this will richen the mixture at large throttle
openings, which *may* be a good thing, but could easily be too rich,
reducing power, increasing fuel consumption and increasing emissions.

The flip side of your question: what is the upside to larger injectors?
The answer would be: nothing, unless you're doing something else to
increase fuel demand, like porting, hotter cams, etc.

jamesm

On Fri, 28 Nov 2003, Sonny wrote:

> What would the downsides of switching to bigger injectors be? Decreased low rpm torque? Increased fuel consumption? Also, in an injected engine isn't it air flow, rather than fuel supply that limits performance?
> Sonny
> '91 164 S
> Baltimore
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