Fuel Injection for Beginners (Apr. 20th 2005)

This (left side) is a Mono Jetronic central fuel injection unit from a 90 HP VW Golf/Rabbit III GT (also called Throttle body injector or electronic carb). The unit is stripped to the bare bone. What is left is the throttle body, the butterfly valve with position sender, the injection unit (black dome) and the fuel pressure regulator (below the injector). Throat diameter of the Mono Jetronic is 38 mm. This unit weights 1400 grams. For comparision the Revflow carb on the right weights 840 grams. But there's a weight advantage for the injector because I don't need a carb heat box. The Revflow's throat diameter is only 34 mm. Maybe I'll cannibalize the Revflow for the spring-loaded lever.

Bottom side. At right the socket for the injector, at the botton the position sender with socket.

This original Rabbit airbox fits very nicely, is lightweight and I'd like to keep it. The crankcase vent inlet stud will not be used. The tube flange is 65mm (2.5") in diameter.

Lots of strange and most unnecessary thingies left over.

Time now to order the Megasquirt II controller.

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Thoughts for a (little bit) more modern Engine Management (Apr. 3rd 2005)

What I always disliked were these old-fashioned ignition and carburation systems of most aviation engines. What's wrong about these, you may ask?

• Magneto ignition is a hundert years old of a technology with a hundert years of problems, say: erosion of mechanical points
• Carburation is almost as antique. In order to create a vacuum for sucking in the petrol all carbs have an airflow restriction build in. This restriction compromizes the 'breathing' capability of the engine, thus reducing the theoretically availabe horsepower

There are more shortcomings of this antiquated technologies. This is a reason almost 100% of the latest cars operate on a different technology.

Recently I browsed the Internet for a better solution and after traversing several dead-end roads I stumbled over the Megasquirt homebuild EFI controller. THAT'S IT! An EFI controller fully under MY control! Even the sourcecode is public domain!

So, minor details had to be decided after this enlightening:

• which type of fuel injection to be used
• what ignition to be used

Because I already own a nicely chrome-plated induction manyfold, I decided for a central fuel injection (throttle body injection). This is only a gradual step away from the traditional carburator. After some more Internet research I found a nice unit: the Bosch Mono Jetronic (also known as 'electronic carb'). This injection system was used for the 90 HP Rabbit/Golf III GT. This car is still very popular in Germany, the spareparts are reasonably priced. The HP rating of this car (90) is similar to my Revmaster (80), so is the displacement (1,9L to 2L).

Fortunately the MegasquirtII controller also offers the ability for ignition advancing. Because I don't love points distribution, only a distributor-less ignition will be allowed to trigger my Revmaster. The favorite is the Ford EDIS-4 ignition system. It is a waste-spark (two coils) distributor-less ignition controller. It is compatible to the Megasquirt II.

So after settling the main issues what else left to consider?

• the EFI needs high (better say: moderate) fuel pressure. There are lots of after-market electrical fuel pumps around. I will use two redundant pumps in parallel.
• two separate fuel line routings (one tube to supply the engine, one return line from the pressure regulator to the tank). This should be not a problem either. The fuel pressure regulator is already incorporated into the Mono Jetronic.
• a good fuel filter is mandatory
• a redundant electrical power supply is essential to'limp home'. This could be either a small second battery or good signal condition of the alternator output (if the EFI/Ignition can run on alternator current alone this would be the best solution)

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