I used to think a pressure sensor driven EFI system required an air temperature input and a computer to work. That ruled out the pressure sensor in my feeble mind for a simple and cheap 555 system. I thought I needed a MAF sensor. Then I found out that mass air flow sensors are not linear. Then I thought well I would use a cheap computer to linearize the mass air flow sensor.

I have since changed my mind. All one need do to start the engine is set the leaning knob commensurate with the out side air temperature. Cold day set it richer. That simplified the system greatly and we can use an ordinary 555 system as a manifold pressure sensor puts out a linear signal unlike a mass air flow sensor. TLC555 are linear devices. PW hence fuel injected is directly proportional to sensor voltage.  I now agree with Tracy Crook almost.

The benefit is a much cheaper system with no need to buy a $80 or $100 mass air flow sensor and install it on the plenum. If it is not there it weighs nothing and is absolutely reliable. The other benefit is pressure sensors cost less than $10 each so we can use two.... one for each rotor. A little redundancy for back up use.

Since the manifold pressure is linear we don't need the super 555 microcomputer chip and a $1 analog TCL555 will work just fine as is.

I have got to get something working soon. As I will have some engines to test soon.


Paul Lamar