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

["Jeff Greenfield" <alfaguy@xxxxxxxxxx>]

My understanding is that the stock L-jet as used on Milanos, and GTV-6's,
tends to run a little lean at WOT at high(er) revs.

So, one solution would be to simply fit a slightly larger injector, so when
the system goes open loop you have some more fuel.

However, the problem is not inadequate flow from the injectors, it is the
internal mapping of the ECU.

I recently built a 2.5 V6, ported & polished, hot cams, CSC headers, high
flow exhaust with 2 high flow cats, etc.

In order to get it all to work well, I replaced the AFM with a mass air
sensor. This uses a programmable (via a windoze PC) piggy back computer.
I've spent a lot of time tuning this car in the past few weeks to get the
fuel curve dialed in properly. This is done using a wide band Air Fuel Ratio
Meter.

I can assure you, that the stock injectors are plenty large enough to supply
more than enough fuel to make the engine run too rich at high revs and WOT.

So, it all comes down to what's been done to the engine in question, and
what you are trying to accomplish.

To coin a phrase  ... Enjoy yours :-)

Jeff

-----Original Message-----
From: owner-alfa@domain.elided [mailto:owner-alfa@domain.elided] On Behalf Of
James Montebello
Sent: Saturday, November 29, 2003 11:05 AM
To: Sonny
Cc: alfa@domain.elided
Subject: Re: [alfa] Re: Downsides of bigger injectors?

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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