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
Paul,
I have not gotten deep into the megasquirt code as yet but I can tell you
it is not C, but assembly lanuage which quite frankly is a relief.
Megasquirt recently came out with the latest hardware version,
Microsquirt in a small 2.6" by 3.5 seal AMP enclousure. MAP sensor is
remote. Unit sells for under $500 completely assembled with surface
mounted components.
Without going into detail, Megasquirt allows you to roll your own and
change any parameter in the MegaTune.set-up software. The code is open
and freely available and many people have tweaked it to suit their
applications.
http://www.megamanual.com/MS%20FAQ.htm
Megatune with any PC becomes a free dyno software, a feature that pays
for the board in my opinion.
I am still machining parts on my slide throttles (one per port) but it
will have a TPS built-in and the abilitity to be motorized if desired.
Both the TPS and oxygen sensor are not really needed. They are there to
help in idle, cold start-up, and acelleration events and can be disabled
manually or via software settings depending on the users wishes. I will
probably disable the O2 sensor at the 50% power level and go to manual
leaning. The O2 will then be used to monitor the A/F levels.
Megasquirt system can be configured to be a simple as Tracy's or as
sophisticated as the higher priced ECU units. I am not 100% sure at
this moment but it appears the user can control WHEN the sensors are
polled. Obviously at 7500 rpm there is not enough time to take more
than one reading per intake event even though the computer can perform
24000 calculations during that time. The tach trigger signal is the
reference from whence all sensors are sampled. When that signal is
generated can be altered of via hardware or software set-ups.
I am using E-85 and as a back-up auto gas. NO 100LL. Meg. Sq. allows
for use of a flex fuel sensor that tweaks the fuel map table depending
on what percentage of ethanol it sees in the fuel.
Sensor cost is about $300.
For aluminum prep. the directions on the DEVCON box said the metal had
to be clean, free of oil and surface roughened to a 3-5 mil profile.
They advise cleaning, (I've used a caustic soda base solution before)
sand blasting or sanding with 8-40 mesh grit, and then another cleaning
to remove sanding grit. I would then clean with alcohol or something to
neutralize the caustic soda.
Naturally no touching the metal with un-gloved hands and leaving oily
finger prints. While the metal is still bright and warm apply the epoxy.
DEVCON, like any epoxy needs accurate proportions, mixing and surface
prep. It says on the carton for maximum strength to oven cure at 200F
for 4 hours after room curing for 2 1/2 hours.
Doug in Japan
Early version of the MegaSquirt hard ware were assembly language and I commend
you for using it because you have close control over exact timing. That is one
thing you cannot say about C compilers. I did not know you knew how to program
in assembly language. I am very impressed. All the latest hardware versions
however uses C.
The problem, as far as epoxy adhesion is concerned, is aluminum oxidation which
happens immediately. Back in 1965 when we were building epoxy bonded race car
chassis we anodized the aluminum first as epoxy sticks better to anodized
aluminum. Nothing to do with cleaning. I have been there and done that several
times the hard way. The prep kit is called a conversion coating. It is a pain in
the butt but absolutely necessary and it is why I invented the welded in SS
p-port. Makes two 1/2 inch wide test strips of aluminum and bond them together
with a 1/2 inch over lap. Try to bend the bond area and you will see what I mean.
Paul Lamar
Paul,
Don't be impressed yet. My software days were far and few and I am not
wired to think that way:)
Yes the later versions M.S. versions were done in C+ but either boards, I
believe, will work with either software version except for supporting
some of the latest features that I don't want to use anyway. In the
worst case I can get a few of Michiwa's 16 yr olds at highschool to
help me out.
Hmm aluminum etching is a no brainer. What the heck is a conversion
coating? I thought it might be a neutralizer. Sounds like I am wrong.
Perhaps a chemical reaction with the aluminum to create a coating onto
which the epoxy could stick to? ?
.."The newer versions of theMegaSquirt code are fully backwards
compatible with the firmware and otherMegaSquirt specific software
programs. All releases of the embedded software and tuning software are
compatible in both directions. V1 (version 1.01) embedded works with the
latest MegaTune and the old MegaTune releases work with V2 and V3
embedded code (but without access to newer features like priming pulse,
flyback board, and Wide Band O2 support).
The hardware for both v1.01, v2.2, and V3 main boards looks the same to
the CPU, so either code will work on either board.
Unless you have a specific reason to do otherwise, use V3.000 embedded
code (right click and 'Save as') and the latest version of MegaTune,
as they are the most robust. See theCommunication sectionof the FAQ for
details on how to upgrade the firmware.
There are a number of other 'unofficial' versions of the code are out
there for your MegaSquirt. See Colin Gebhart's guide for compatibility
and files.
Here are main versions of code:
Standard code (versions 1.01, 2.00, and 2.98/3.000): Gives 0.1ms
resolution. These were installed on the first [version 1.01] and second
[version 2.00] group buy units.
Dual Table [DT] code: Guy Hill's code allows 2 tables to be programmed.
Each can be alpha-n or speed-density. Perfect for staging with different
sized injectors. Click the link for more information about the Dual
Table code.
High Resolution [HR] code: Gives 0.005ms resolution, but you lose peak
and hold injector current control so you will need a ballast resistor to
run low impedance injectors.
There are a number of other specialized versions of embedded code for
MegaSquirt. See Colin Gebhart's guide for compatibility and files.
Assembly Language Files
There are a number of files that are used to program your MegaSquirt.
Unless you want to edit and recompile the source code, you can upgrade to
any version of the code by uploading the corresponding .s19 file. If you
want to edit the code, you need a number of files:"
Doug in Japan
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