I don't want to speculate or spread misinformation but my understanding is that since you have 1 MAP sensor to read the manifold pressure values for 3 throttles the ECU reading the info/reporting the info must know which cylinder is inducting at that time to assign that MAP value to that cylinder.
It must do this by reference point such as the crank position sensor.
I also assume triumph have the ecu set to take the MAP value for each throttle when it's corresponding cylinder is at a certain point in the induction stroke e.g. Bottom dead centre or there abouts.
It might be when peak vacuum is achieved by an inducting cylinder.
This is known by crankshaft position in degrees and there are 360 degrees between CPS blips and cylinders in a triple are 120 degrees apart.
Anyway let's say you are just idling, at say 850rpm - that means there are many induction events happening per second.
This means that the ECU has a fraction of a second to take the presumably optimum or peak pressure in the manifold for each cylinder
If that timing is put off then the engine won't run optimally. Too low a vacuum reading and (taking fueling for example) too much fuel will be injected, too high a vacuum reading and not enough fuel will be injected.
That's the way the fueling table works at low throttle positions.
See a low vacuum makes the ecu think the throttle is wide open so in such a case you'd need lot more fuel so it fires in more making you run rich and maybe bog and die.
Anyway if you picture a tube it has a certain volume of air in it. This volume needs to be sucked out by the engine vacuum in a fraction of a second in order so that the vacuum pressure in the manifold it equal to the vacuum pressure at the MAP sensor itself.
If you have a longer pipe, then it takes longer for the pressure to equalise in it, and as we established the timing has to he perfect of when the optimum pressure is achieved at the MAP, therefore the MAP might not read the peak vacuum, it will read prematurely.
Premature reading will be a lower vacuum than should be there and that means too much fuel.
Conversely too short a pipe and the optimum pressure condition reaches the MAP too early and is then on the decline by the time the ECU notes the MAP value.
You can map the fueling to compensate I. E. If your tubes are longer then you can take out fuel to compensate for the lower vacuum.
But that's only if your 3 tubes are the same length (and diameter.. this affects volume).
If your tubes are different lengths then you'll need to map by cylinder which would be a nightmare
Either way this is just messing when there is no reason not to use same length and diameter tubing.
Basically inequal length (or different length to OEM) vacuum hosing affects quality of MAP readings and upsets fuelling and ignition.
Anyway that's my understanding I could be talking shi'ite
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