4 replies to this topic

[gtmdriver]

At the moment I'm running a 1293 A series in basically MG Metro spec apart for a 266 cam and 1.5 roller tip rockers. I'm looking to convert from the HIF44 on an MG Metro manifold to twin injectors.

I want to use a pair of BMW boxer motorcycle throttle bodies as they are pretty much self contained and also include the injector mounts and a throttle position sensor.



I have machining facilities and intend to make a couple of manifold stubs to mount on the cylinder head then connect the throttle bodies using flexible tubing as on the bike.

I have read around this and it seems that there can be a problem with fuel distribution or charge robbing with twin injectors due to the siamesed inlet ports on an A series so here is where I need the help.

Why does this problem occur with injection when it doesn't happen with twin SU carbs, a DCOE Weber/DHLA Dellorto or split Webers?

If I run the injection as continuous rather than pulsed or timed does this overcome the problem?

If I move the injector further from the port does the problem lessen and if so what's the safe minimum distance?

Does the problem occur with any power output?

Is it worse with different cams?

As you can see this is a serious enquiry and any help will be gratefully accepted.

[Dan]

Moved to the injection section.

[elvisthepizzaman]

First off, the charge robbing occurs on both single carb and twin carb setups. It happens regardless of the injection setup. Rover got close to optimum with their mpi setup but it still has charge robbing.

All those twin choke and large carbs just overfuel both inner and outer cylinders to avoid the problems of the siamese fueling. The whole point of injection is to optimize the fueling for max economy and by doing so it becomes very important...

Doing a throttle body injection with continuous injection is just like having a carb there but you get to regulate the fuel injected instead of the mystery of the SU needle selection. It works well but you need to make sure that you have an oxygen sensor mounted on your inner exhaust port to watch the mixture as the inner cylinders go lean before the outer ones do.

Megasquirt has lots of code for doing what you want, you will need all the hardware to do it: tooth ring, pickup sensor, etc... Many people have the fueling and ignition maps to get you started but as usual for all tuning it needs to be taken some place to do a rolling road for optimum power and econ.

[Sprocket]

The subject of port injecting a five port head, is complex, as is trying to implement it. There is much to read about it, and most of it can be found on www.tubominis.co.uk forum, where, there is a lot of research and development going into this problem using Megasquirt.

At the current time, there is only one programable ECU on the market that can tune a port injection five port head and that is CANEMS

Moving the injectors away from the port is a solution, but how far is considered ideal, is unknown untill some one tries it. There are successful instalations using the Jenvey throttle bodies, so I dont thin there is much of a problem in what you are looking to do, just keep the injectors as far away from the inlet valves as possible

[elvisthepizzaman]

you could measure from the head to the jet assembly for a twin carb setup and make that your distance to your injectors.