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fuel injection
Written by revconprince on 12/2/2010 at 02:12 pm

More tid-bits. One of the more difficult problems with FI is getting the engine
to idle. The reason is that when the on time for the injector is really short,
it does not fire reliably. Most FI units have a fuel regulator that is vacuum
operated. This reduces the pressure at high vacuum so there is less flow to the
injector and the computer can use a longer pulse width. This means you need 2
vacuum ports, one for the MAP sensor and one for the regulator. GM sold their
ECM to several foreign car manufacturers. This means you may be able to find a
single barrel throttle valve that is much smaller than what is used in a V8 and
will be much more conducive to installing on a bike. I think even Honda used a
GM ECM in the early days. Most after market FI systems are based on the GM ECM.
I know you were considering MegaSquirt which I think uses GM compatible sensors.

One other thing to think about is how you are going to accomplish tuning. Riding
around on a bike with a laptop strapped to the tank may not work out so well.
I've seen several homemade Dyno set ups. Some spin a very heavy wheel and use
the inertia of the wheel to provide load. It is something to look at and see
what others have done and begin thinking through some ideas of what can be
easily rigged up.

Dave

--- In ipcrc@yahoogroups.com, "revconprince" <daveinet@...> wrote:
>
> Yes, the block idea may be the easiest and least destructive. I always lean
towards recoverable mods. Aim the injector right at the valve. The reason is,
that is the hottest point. When the fuel hits the hot surface, it will turn to
vapor, thus mixing with the air better.
>
> Glad to see an engine under that plastic. I wasn't sure.
>
> There are 2 types of injectors. The standard ones and the new pico injectors.
The pico injectors are much more precise, but they also pull less current. If
you go with the pico's, you will need to ad a load resistor, so the ECM is
happy. Current draw for 8 picos is the same as 2 standard injectors. The ECM
measures the current draw, so you have to keep it happy, otherwise it will go
into limp mode.
> Dave
>
> --- In ipcrc@yahoogroups.com, "douglasvanb" <douglas.vanbossuyt@> wrote:
> >
> > Hi Dave,
> >
> > Here are some photos of the engine with the carbs removed
http://www.douglasvanbossuyt.com/2009/12/16/mystery-oil-update/ (ignore the
text. I solved the oil leak by replacing the seal around the shifter). Yes,
there is an engine under all that plastic. Although I suspect on some bikes
it's electric. Otherwise you'd expect the bike to make noise!
> >
> > It looks like *maybe* there is a point that could be drilled out just below
where the carb insulators attach. Don't think I want to do that though as
that'd be a hard hole to fix if I screwed it up :-) Also it would require
removal of the engine which I don't want to do just yet...
> >
> > I think I will go with the injector-in-aluminum block idea. It seems the
most straight-forward and reversible if I someday want to go back to carbs. Do
you have any advice on how I should orient the injectors? At a 90 degree angle
with the intake? At 30 degree angle in an attempt to squirt the fuel more
toward the valves? Directly over top of the valves and have the tube running up
to the throttle bodies take a jog over to the side to accommodated that?
> >
> > Cheers,
> >
> > Douglas
> >
> > --- In ipcrc@yahoogroups.com, "revconprince" <daveinet@> wrote:
> > >
> > > I'm not sure if there is a flange that one could weld an injector bung to.
You know, I've never seen the engine on my PC800. I can only assume it has one,
I mean it makes noise when I push the start button. Is a similar flange used in
newer bikes? If you could find some stock aluminum block, you make a thick
spacer between the flange and the engine. Then just drill out a place for the
injector.
> > > Dave
> > >
> > > --- In ipcrc@yahoogroups.com, "douglasvanb" <douglas.vanbossuyt@> wrote:
> > > >
> > > > Hi Dave,
> > > >
> > > > I'm glad someone on the IPCRC has struggled through FI on an engine
before. Moral and technical support are obviously needed :-)
> > > >
> > > > Without drilling into the engine, would placing the injectors directly
above the valves (basically where the throttle bodies on our bikes are) be close
enough to the engine to allow for a length of tube between the injector manifold
and the throttle bodies?
> > > >
> > > > Cheers!
> > > >
> > > > Douglas
> > > >
> > > > --- In ipcrc@yahoogroups.com, "revconprince" <daveinet@> wrote:
> > > > >
> > > > > "Wet intake" is a term that means the air is mixed with the fuel. Wet
intakes are limited in length, because the fuel will fall out of the air at low
RPMs and puddle in the bottom of the intake. You can not build a long wet
intake, or it won't run below 3K RPM. The air velocity is too low to keep the
air and gas mixed for any kind of distance. Racers do it anyway, because they
don't care if the engine won't idle.
> > > > >
> > > > > So, for a street engine, the carb or TBI must be fairly close to the
cylinder. You can put the resonant tube between the TBI and the air cleaner, but
the throttle plate tends to screw up the resonance. It still works to some
extent, but not very well. I've seen experiments with tall velocity stacks on
independent carbs, but it does not work as well as long uninterrupted tubes and
a common chamber.
> > > > >
> > > > > So that is the beauty of port injection. You can optimize the intake
tubes for air flow and not have to worry about keeping the air and gas mixed,
because the injector is right near the cylinder. One of the tricks is to use
different length tubes. This reduces the peak, as only one cylinder peaks at a
time, but will broaden the peak, because you now have to smaller peaks, rather
than one big one. This makes the engine more street friendly.
> > > > > Dave
> > > > >
> > > > > BTW: 2.5 years ago, I had no idea about any of this. When I did my
multi-port Edelbrock EFI project on my 502, I did a ton of reading, some after
the fact, trying to get it to run right. Engine technology has gotten a lot more
sophisticated since the advent of FI. It took a while to take hold, because the
first FI units where exclusively for emissions. No one was bothering to study
performance. One of the first real projects for performance was the Northstar
project. There is a great artical written by one of the engineers on the
project. It explains a lot of things that us lay people never understood.
> > > > >
> > > > >
> > > > > --- In ipcrc@yahoogroups.com, "douglasvanb" <douglas.vanbossuyt@>
wrote:
> > > > > >
> > > > > > Thanks for the article!
> > > > > >
> > > > > > It all makes sense up until the final closing note at the end of the
article. Why would independent throttle bodies negate the resonance effect? If
anything, I would think that would help matters as each cylinder would have it's
own resonance wave hitting the valve at the right time.
> > > > > >
> > > > > > Also that brings up an interesting though. Is there a reason to
have two throttle bodies rather than just one large one on our PC engines?
> > > > > >
> > > > > > Cheers,
> > > > > >
> > > > > > Douglas
> > > > > >
> > > > > > --- In ipcrc@yahoogroups.com, "revconprince" <daveinet@> wrote:
> > > > > > >
> > > > > > >
http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=466
> > > > > > >
> > > > > > > Longer intake runners get tricky on a throttle body. Reason is,
you have to keep the velocity up at low RPMs to keep the fuel mixed in the air.
Dry intake runners are little easier with port FI is simpler.
> > > > > > >
> > > > > > > --- In ipcrc@yahoogroups.com, "douglasvanb" <douglas.vanbossuyt@>
wrote:
> > > > > > >
> > > > > > > >
> > > > > > > > Putting loops in the intake pipes between the throttle bodies
and the cylinders seems like it could cause interesting problems with slowing
down the air flow and delaminarizing it (straight-ish pipes like those found in
cars would tend to make the airflow become more laminar, assuming a uniform-ish
flow). Would it have the same effect if I increased the diameter of those tubes
for part of the way but kept them as straight as possible? Theoretically, I
think it would but that also might create strange harmonics with the shock waves
as the propagate back and forth through that non-uniform-diameter volume. Does
anyone have some suggested-reading links on this topic? I'm not too familiar
with the nitty gritty of using shock waves to pressurize cylinders.
> > > > > > >
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> >
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