I just updated the simple and cheap 555 EFI system
  on the web site. We hope to test it this coming year
  on a RX8 P-port engine I have installed on Milo's
  test stand.

  http://www.rotaryeng.net/simple-cheap-555.html

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BTW the apex seal oil hole pressure taps give a much more
uniform manifold pressure readings so the 555 system should
work pretty well. An unintended favorably confluence of
technologies :)

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I woke up this morning with another idea for the 555 EFI system.
One needs to enrich an engine for starting and how I was
going to do that was festering in my subconscious.

All one needs to do is open the throttle, set the leaning knob
to full rich and hit the starter button. With this system the
mixture ratio is directly proportional to the pressure of the
air mass getting in the engine. When the air pressure in the
engine is atmospheric which happens at WOT the mixture is full rich.

With my O-470 I must prime the engine and just crack the throttle
because the carb venturi injects only as much fuel as the air
flowing into the engine. Basically it is a mass air flow sensor
and this system is a manifold pressure system.

This system could wind up being cheaper than the $500 2 barrel Holley
500 CFM carb.

Dirt simple.  If this is not clear ask me questions.

Paul Lamar


Paul,
Are you going to use a temp sensor with your 555 system. That is what the
OEM's use for start enrichment.
An idea for cheap ABS sensors; get to be friends with a local Dodge dealer.
When we replace wheel bearings now, the new one comes with the pick up and
wire. Some require 12V power to operate and are sensitve to polarity. Some are
still like the older ones. Just a thought.

Dale Davies

I had not planed on using a temp sensor but with clever design
in might be incorporated into the leaning circuit.

The older sensors I think have magnet in them and a coil of wire.
They are a self contained voltage generator. All they need
is a chunk of ferrous metal passing by. Polarity is of no
significance. The Mazda RX8 crank angle sensor is of the
same type. The trick to figuring out which is which is
the magnetism you may notice when ferrous metal comes close.

Paul Lamar