Bosch k-jet with throttle bodies conversion.

I could go efi, I bought a box of bit's years ago to convert the car, but I just never have.

The engine in question is a mercedes M104, which I have allready messed about with. I have a theory that the existing throttle body is too small for a 3.6 engine, so need a bigger one, or a set of itb's.

I quite like the thought of keeping the k-jet system, just to see what gains can be had (if any).

I like the the idea of a tappered plenum chamber.

Cool idea but it needs a little more working through. The trouble is the metering head in the k-jet system measures air-flow rather than engine load (which is what vacuum is used as a measurement of.) You could do it with the MAP sensor idea, but you'd have to take into account engine speed and use a load vs. RPM map to determine how much fuel is needed, at which point you're pic-axe controller is basically becoming an ECU.



carat 3.6 amg - You may well find that you have the same problem with the EFI system you have if it's a standard production car one. Most use a MAF sensor to measure the volume of air entering the engine in order to calculate the correct fueling, this is just the electronic equivalent of the metering head in a k-jet system, and will come with all the same issues. To run ITB's you'll need a system that runs off MAP or throttle position based rather than air-flow, and it'll need to be able to be re-mapped (or piggy-backed) to correct the fueling enough.

If you're right about the throttle body being a significant restriction at the moment then you should get some decent gains by just up-sizing it still as a single throttle, and with a lot less work.

If you do decide you want ITB's, then I fear the easiest option would probably be to use most of the EFI bits you have, but with a standalone aftermarket ECU. (Switching the MAF for a MAP/TPS.)

Thought I'd better post an update on this.

This is the mercedes inlet manifold after I cut most of it off.


And these are the throttles from a triumph motorbike.


Which line up very well with the inlet manifold.


Then I got hold of a second set of triumph throttles and did this mock up.


I've also got hold of the metering unit from a v8 s-class, which is a fair bit larger than the original.

and if my research holds true - you simply block off the two unwanted fuel feeds from the v8 metering unit. I'm assuming you've seen that bloke who adjusted the fuelling with a "wedge"screwed to the side?

Basic theory being, as the flap has its airflow restricted by the lump of aluminium on the side, it has to move further, to get the same airflow. If the fuelling is too much,simply trim it down until you're at a more suitable AFR

Kinda like filing an SU needle... but it's bigger, and a hollow cone,rather than a needle! Lol

found a pic of it, from within my "archives"

but screwing on a small adjustable section, is more practical for the home mechanic, than making entire cones lol

I also recall stories of manufacturers using different cones for racing at different altitudes, when differing A/F ratios where desired

there's "easy"... and then there's "because I can"

My thoughts exactly. ;D

I could go efi, but I just think a tuned k-jet setup would be cooler. I can always convert to efi later on.

Now running a turbo on k-jet is something I'd find a noble effort; hell go really old school and run a suck-through turbo on a carb. My workshop buddy wants to find that holy grail of Pinto items, a Janspeed turbo kit. But I digress. Going back to the topic at hand, what about using the metering head with just one big throttle body? It would surely have the advantage of better airflow. Also, what injectors would you use:

Continuous Injection System' (CIS)-type?



or the solenoid type?



I'm guessing the CIS type, as they don't (necessarily) need any type of ECU to run them, unless you really want to use components from a KE-Jet system, which is a Pandora's Box you don't want to open.