Re: [OMC-Boats] Fuel Injection

On Wed, 16 Dec 2009, Lee K. Shuster \(lks\) wrote:
> I think you made a good choice. You should be able to "dial-in" a Rochester
> 2G-series fairly accurately with a little care and understanding:
> http://www.oldcarmanualproject.com/manuals/Carbs/Rochester/2-Jet/1964Manual/pages/64Rochester2Gmanual_0002_jpg.htm
> Moving to just about any type of fuel injection (TBI or MPFI) system on an
> old boat would be financial folly, IMHO. 1) You would spend more than the
> boat is worth, 2) It would no longer be original and 3) the "improvements" in
> turn-key reliability, serviceability, performance and fuel econonmy would be
> barely noticeable.
> Not only would you potentially be looking at major changes to electrical
> wiring, fuel delivery, distrubutor, possibly intake and exhaust manifolding,
> and ECM programming, but to what means? Most likely you'd run the ECM in
> "open-loop" mode, without an O2 sensor, which negates the ability to have the
> ECM adjust Air/Fuel ratios based on 02 feedback.
> I've given this subject a lot of thought for my own boat, as there are many
> alternatives out there for my small block Chevy V8. I've decided that the
> stock marine Rochester carb is pretty hard to beat, when it's properly dialed
> in.

I'd agree with Lee here. Having implemented electronic fuel injection on a
variety of engines that didn't originally have it (mainly motorcycle
engines used in snowmobiles applications), I would say it's not worth it,
*unless* you are doing it for curiosity and entertainment.

These engines generally aren't run over a wide range of conditions
(temperature, altitude (excluding Lee)) and don't have exhaust
aftertreatment (catalytic converters) that is sensitive to precise mixture
control Carburetors can work very well for steady-state applications,
especially when you care more about performance than emissions or fuel
consumption.

I've never adjusted the fueling on my engine, but I would guess it is tuned
to run 5-10% rich - an air/fuel ratio that leads to maximum power output
and lower exhaust-gas temperatures. This is a range where small variations
in fueling don't really make a huge difference in any aspect of
performance.

The reason fuel injection systems exist is primarily because modern
emissions controls system require that the air-fuel ratio be maintained
within 1% or less of stoichometric over a wide range of operating
conditions. Three-way catalytic converters used in gasoline engines
require that the air-to-fuel ratio rapidly switches from lean to rich
around this range - if it were to stay slightly lean or slightly rich for
any length of time, emissions might be 10 times higher, and you might end
up burning valves if it were to be a bit too lean on a high-performance
engine. When engines are run "a little rich", there's a lot more tolerance
for errors.

Electronic engine control systems also have advantages for easy starting
and warm-up, but I've never had problems with that on my engine - even at
below-freezing temperatures it usually starts within a few seconds of
cranking, will idle right away with the throttle slightly advanced, and is
ready to idle with the throttle fully closed within a minute or so.

Another advantage to electronic control systems is that "tune-ups" might no
longer be required - the systems (with O2 feedback) are self-tuning and
adapt for variations in fuel and other factors. However, the amount of
time you'd put into the initial setup of the system and tweaking it
(because you can!) would be far more than the time you'd spend on decades
of tune-ups.

It really wouldn't be hugely complicated to do (add an crank encoder on the
flywheel or distributor, drill ports in the intake runners for injectors,
cobble together a fuel rail, mount up some coil drivers, add a TPS and MAP
sensor, and come up with timing and volumetric efficiency map for various
RPM and throttle positions), but the but benefits would be fairly small.

I'm guessing you'd get perhaps a 5-10% improvement in fuel consumption over
a well-tuned carbureted engine, significant improvements in emissions (100x
or more, though you'd never know without hooking it up to an emissions
bench), a lower idle during warm-up, and improved starting (probably on the
first or second revolution).

Really, I'd love to add forced induction, electronic throttle control,
electronically-controlled shifting, and closed-loop fueling control based
on feedback from a wide-band O2 sensor, but what's the point? I'd also
like to get out on the lake and enjoy my boat, regardless of whether it is
working as well as it good be! Carbs really are awesome, as long as having
fueling within 5% or so is "close enough" and you don't mind having to
adjust them once in a while. Feel free to add fuel injection if you are so
inclined (and definitely tell us about it - I think it'd be awesome), but
it's definitely not necessary!

Ethan
Received on Wednesday, 16 December 2009