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Dynamohum Dynamohum is offline
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Join Date: Jan 2008
Location: Midland Ontario Canada
Posts: 173

Interesting thread, sign me up Iím up to learning more about Motronic and exploring different strategies to control the fuel and timing needs of a low boost turbo conversion.

Thoughts that come to mind,

Defining the target hp attainable within the limitations of the Motronic components and reverse engineering from there for the most cost effective conversion.

Target Hp: this is open for debate, but for a starting point lets say in the range of 350 to about 400 hp max. (From what I have read 400 hp seems to be the limit from stock injectors operating at higher rail pressure) also the restriction of the barn door becomes more of an issue as CFM flow increases. Also there is the Blow through VS Draw through debate, perhaps some interesting feedback will emerge along the way.

Bumping fuel rail pressure using a variable rate regulator is one method that is already proven to work and may very well be the simplest. Off boost the injectors are properly sized can run on the stock fuel maps and on boost the pressure regulator is tuned to supply the extra fuel needed.

Some will say that running larger injectors with stock fuel pressures is better and thatís fine but the downside is that you need the properly tuned chip or programmable system and even then the larger injectors are more difficult to tune for a decent idle. Though perhaps the best method when all sorted, it is by far the most expensive and most complex to install a programmable system.

Supplementation of the fuel system with Water/Methanol injection has the added benefit of reducing charge temp while having the same effect of increasing octane thereby reducing detonation potential.

Another idea that Iíve toyed with mentally anyway is adding 1 or possible 2 extra injectors (depending on size) mounted in a fabricated spacer housing bolted just under the throttle plate. Placing the injection spray in the direct path of the incoming air providing the best atomization and delivery. This in essence is throttle body injection TBI. These injectors would be controlled by the onset of boost by a pressure switch and only operate when needed.
The Motronic injectors are batch fired, alternately left and right bank, so Iím thinking is it possible to additionally fire one more small injector of the same impedance off each bank?

Simple software with the ability to Reprogram the Motronic chip fuel and ignition tables would be great if anyone knows about this and is willing to share.

I will go out on the limb here and say that, it seems as though we can control the additional fuel needs with out changing the fuel tables in the chip. The bigger hurtle is how can we alter or control the ignition timing without altering the timing maps?

What options do we have to retard timing under load (boost)
Thank You for your time, Paul. We do because we can.
87 911 3.2 (Turbo conversion, build in progress, Thermal Barrier Coatings, High Pressure Dry film coatings) Modified heads, boat-tailed case, ARP hardware, OBX Header, 930 clutch disk, G50 Trans
89 5.0 Mustang convertible (For Sale)
Old 01-26-2010, 06:56 PM
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