MSefi.com read only forum (Jan.15,2018)

Hey,
I'm planning on putting a TBI system on my suzuki samurai engine, which is currently using a carburettor, and so has a very small plenum volume (if any really). What problems is this going to cause with a TBI bolted straight on? I have seen photos of engines set up like this but can't see it working well.....? I'm thinking I'm going to have to add some volume in there somehow, correct?

Putting a TBI on a carbed manifold usually works out OK. About the worst that may happen is that the fuel distribution is rarely ideal, and it may be a bit rough on a cold start until you get good fuel vaporization. Putting a TBI on something with a port injection sized plenum probably would not work out very well actually,

hedgeboar,

I have done this, it works fine. Both TBI and carbs require 'wet-flow' manifolds.

The plenum has two main effects - it smooths the manifold vacuum spikes from the valves opening and closing, and it smooths the air flow through the throttle so the net air flow is greater. However, a smaller plenum with a larger throttle sees the larger vacuum spikes and uses these to meter fuel more efficiently. In the case of TBI with a small plenum, you don't need a large vacuum spike to draw fuel from the venturi like a carb. But you might need to use a 'damper' on the MAP sensor line to get a consistent signal, as described here: http://www.megamanual.com/v22manual/mtune.htm#trouble

Port injection doesn't generally use a wet flow manifold in a OEM application, so as Matt says a TBI on a port injection ('dry flow') manifold wouldn't be a good idea.

Lance.

OK cheers that's good to know. How many injections per ignition are/were you using lance? Would I be correct in assuming that it would be best to maximise this while keeping the pulse width at idle at an acceptable level?

hedgeboar,

I can't recall how many squirts I used (this car has been gone for at least a couple of years - it was my beta MicroSquirt test vehicle), but I do remember experimenting with both the number of squirts and the injection start to get it to run the best (this took less than an hour). I suspect I ended up at 4 squirts/alternating.

Lance.