Paul,
This week I will sand blast a housing, and fill the outside depression
around the oil
injection location with DEVCON Aluminum epoxy.
Thursday afternoon has become my access day for Michiwa's school
machine workshop and I will be boring the housings and making the
aluminum inserts then.
Pictured below are two types of injector cylinder housings, both with
upper and lower 0-rings. The design on the left has a M-20 thread on
the top part though it isn't shown, and although it takes up less real
estate I have decided to go with Lynn Hannover's design suggestion.
Why? O-rings tend to deform or fold when they are twisted several
revolutions while being pushed axially as well.
I'll pressure test the housings with some glycol/water mix in the cavity
to confirm it works.
FYI the injector interface to the inner liner hole is drilled and V
shaped from the backside to allow the injector tip to insert with about
0.5mm clearance of the apex seal path.
Since I am supercharging the
engine and wish to stick with MAP and
MegagSquirt ECU, the question remains where to put the sensor or
fitting?
Two choices. The present oil injection hole, or in the back plate on the
slide throttle?
I am concerned that the oil injection hole may accumulate fuel in it
during certain engine events, so I am leaning towards the slide throttle
location now.
Cheers
Doug in Japan
Don't forget to prepare the aluminum with an etching solution.
Question: when does megasquirt sample the manifold pressure
and is the short sample representative of the air going in the engine
throughout
the RPM/tuning range? Have you studied the C source code to find out?
What are you going to use for a throttle position sensor?
The O2 sensor will fail if you use 100LL.
How important is the O2 sensor to proper operation?
Paul Lamar
I'm considering something similar and have three questions:
1. Is it not practical to use the standard Mazda 13B injectors through
the oil hole?
2. Is this the Megasquirt shcematic?
3. Could you point me to the Megasquirt code? I did a quick search and
probably gave up too soon.
Thanks,
Philip
It has been tried many times.
Here is the fundamental problem. The pressure builds up in the intake
chamber once the intake port closes reducing the flow of fuel.
At high RPM there is too little time to get all the fuel in there before
the port closes. This can be delt with by upping the fuel pressure. Nobody is
doing this now except Doug. I await his results.
Another problem is atomizing the fuel. Diesel injection is good evidence of this
as diesel injection pressure is now up to 20,000 psi. The longer the fuel is in
contact with the air the more time it has to evaporate and mix throughly with
the air. Several people have noticed an improvement in BSFC and this is one
reason race engines inject the fuel into the intake bell. Mazda among them on
the Lemans engine. However Mazda needed quick throttle response so they moved
the injectors closer to the rotor housing. Others, Mistral among them ,don't
think this is the case. So you take your pick.
Paul Lamar
--
Phillip
What Paul says is true. The standard Mazda injectors are to slow and
flow to little to inject the required fuel into the intake chamber
before the port closes. However I believe this changed with the
creation of the Deka IV pencil injectors. They are fast and flow
enough. I calculated at my targeted horsepower levels above 6,000,
I'll need a fuel pressure of at least 55psi and two in each housing
that can flow about 75lbs/hour.
My choosen injector position is 12mm below the oil injection hole with
the two side by side and positioned to be uncovered a few rotor degrees
after the intake port opens fully. The injectors will only have to push
against deck pressure, as the injection event is finished before the
intake port closes. This is the theory. No practical data yet.
MegaSquirt has reams of info once you hit their main menu and scroll down.
Doug in Japan
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