[Diy_efi] CX 500 EFI?

[Adam Wade]

--- Ernest Buckler <ebuckler at icehouse.net> wrote:

> Tanks a BUNCH for clearing this up for me, had not
> really compared the details (obviously [:oj)

Most of the details between the bikes were never of
interest to most folks; the NA models are basic
transport on a budget, and the turbos were high-tech
sportbike marvels of the day.  With so little
crossover, not many CARED about what the differences
might be.

For reference, the frame of the turbo bikes seems to
be very close to that used on the Silverwing models,
if not completely identical.  They have the same
wheelbase if memory serves, longer than a "naked" NA
CX500, and they were both available only in monoshock
format (all the nake NA CX500s had twin shocks).  It
should in theory be possible to build a CX500T or
CX650T on a Silverwing frame without any major mods,
and I think you could manage to keep the lockable,
detachable hard bags from the Silverwing as well.  A
modern sport tourer, circa 1982!  Something I'll be
thinking about when I have time and money for another
project, especially of a CX500T swingarm and real
wheel plus a CX650 front end (suspension, wheel,
brakes) and a CX650 motor and electronics fall into my
lap...  ;)  Finding a basketcase Silverwing shouldn't
be a problem, although I'm not sure what to do for a
fairing (the Silverwing got that God-awful Goldwing
Vetter copy that sucks so much I'd rather ride a naken
bike on a long trip than be behind that fairing!).

> Will be talking with you more about better EFI 
> possibilities for these 80 degree V-twins??? 
> Megasquirt?  Any reason it wouldn't work?

You could make the MS to work for the 500; I am not
certain whether you could make the "& spark" version
to fire both plugs at the right time, but have not
really explored the possibility.  The MS is a
batch-fire system, although the newer units can handle
bank-fire for two "banks"; since the turbos only have
two cylinders, you should be able to set up what
amounts to a crank angle delay for the second "bank",
and just use a single injector on each "bank" output. 
I'd have to look into it a bit further to know for
certain what it could and could not do easily, or
perhaps someone will step in and clarify a bit for me.

I wouldn't really recommend batch-fire (all injectors
fired at once, probably once per crank revolution), as
I believe some form of sequential injection would
result in notably improved throttle response, and
probably a bit of improvement in fuel economy as well,
espoecially for a street-operated bike that sees a
significant amount of low-speed and stop-and-go
operation.  It should be reasonably easy to set up for
decent performance, especially if you let the
transistorized spark hardware of the stock CX500T keep
on in its duties of handling spark; with a turbo bike
like the CX500T, you can get fairly involved into
building a useful 2D or 3D ignition map, and often it
will take significant trial-and error unless you have
access to a dyno and a variable wastegate so you can
test for a given engine load, engine speed, AND boost
pressure as a 3D matrix.  And errors in spark timing
can be very hard on the turbo, or even hole a piston
quite easily.  You can make a conservative spark map
and run with it, although I wouldn't consider that
optimal, and it would almost certainly not be as good
as the stock spark implementation, on the 500 or the
650.

Two areas that open up with the use of the Donegan
hardware, once fully developed, is EGT feedback
(altering spark and fuel parameters based on exhaust
gas temps, good for insuring long life of the turbo as
well as detecting certain fuel, spark and engine
problems before you require a whole new engine), and
ion sensing feedback for spark timing and as a good
"window" into the combustion process for tuning
purposes.  If they can be implemented with a
user-friendly tuning approach and for not too terribly
much money, they would stand as major advantages of
such a system over pretty much anything else in the
hobbyist market today, and would rank high in (and
often beat some members of!) the hierarchy of
commercial aftermarket systems available today.

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