Subject: Saving fuel 555
From: Rotary Engine
Date: 7/10/2008, 7:27 AM
To: AAA Put this in the To box


Paul,
A better mass air sensor to use is the unit found in ford V8 trucks
from 97 and up. Many of them in salvage yards. They were for engines of
220 to 260 hp putting them in the flow range we need. Also very light
and reliable. Just don't get one from the supercharged trucks, as they
are 90mm diam. Larry

Thanks for the tip Larry. Are they mechanical like the Mazda or
electronic? The electronic are harder to use as they are tougher to
interface with the 555. The Mazda unit is just a trap door connected to
a pot.

-- 
Paul Lamar ...No rotor no motor.


Paul,
Pin out attached.
Larry

The problem is 5 volts is high airflow and the 555 fed 5 volts would be
narrow pulse. Zero volts would be a wide pulse out of the 555. What you
one must do is come up with a circuit that reverses that and probably
increases it to 12 volts. Using the Mazda simple device you just wire
the pot backwards.

I am not saying it can't be done. Just more trouble.
-- 
Paul Lamar ...No rotor no motor.

I would call such a circuit an op-amp.  Inversion and scaling in one
step.

Bob W.


-- 
N93BD - Rotary Powered BD-4 - http://www.bob-white.com
3.8 Hours Total Time and holding
Cables for your rotary installation - http://roblinstores.com/cables/


Sounds like you are the man for the job Bob. Care to do a schematic and
make a prototype on a plug board?

Here is what the Mazda unit would look like along with the original
Chaparral 2D  ram air box from 1965.

-- 
Paul Lamar ...No rotor no motor.

OK, I'll draw up something 0-5V in, 12-0V out and build a breadboard
circuit.  It may be a few days as I'm trying to finish up a couple of
other projects.

Bob W.

-- 
N93BD - Rotary Powered BD-4 - http://www.bob-white.com
3.8 Hours Total Time and holding
Cables for your rotary installation - http://roblinstores.com/cables/


Great Bob.
Thanks.
------------------------------------------------------------------------

Here are the pin outs and resistance data on the Mazda mechanical
air flow sensor if you want to keep it as simple as possible.
The sensor air flow area is about 5 square inches so it is a bit of a restriction
on a P-port engine with two... 1 7/8 ID runners have 5.52 square inches
total  area. How much that is going to affect the power is hard to say.
I intend to get the prop dyno working with the P-port RX8 engines
so perhaps I will find out.

The resistance varies between 50 and 500 ohms so the 555 pulse width
with a 100 uF cap should be in the right range (1 ms to 50 ms) I am not sure this
is going to work. It would be better if the pot was higher resistance.
I'll have to mock it up on the bench.
----------------------------------------------------------------------------

I am coming around to the hot wire and op amp approach.
I suspect that a 100uF cap may not be practical for drift reasons and temperature
change reasons.

Here is a great little opamp calculator. http://www.bcae1.com/
Scroll down to about the middle of the page.

It will also work with a FreeScale MAP sensor if you don't want to use
a mass airflow sensor.

Here are hot wire sensor pictures from a Ford Escort.
-- 
Paul Lamar ...No rotor no motor.

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