Can tell from the pics you do neat work and have thought things through.
About the nozzles, I did buy directional but
Yes, I nearly said with nozzles where you've mounted them directional ones wouldn't be an advantage. I brought them up in case you looked up some of those other threads on Valvetronics, they have been mentioned on those threads.
I dont understand about fuel pressure differential. If The petrol supply line is at constant 50psi then petrol injection will be little affected by manifold pressure, does the lpg reducer at 15psi have a problem? will pushing the reducer pressure up help to counteract this?
By differential pressure I just mean relative fuel pressure - as you know, petrol pressure is relative to manifold pressure on most vehicles (most having a mechanical pressure regulator linked to manifold vacuum) but like you say the Valvetronic has 50psi relative to atmosphere. So, when in Valvetronic mode, the relative pressure is 50psi because there is no manifold vacuum, but in part Valvetronic mode manifold pressure might be .5 bar (7psi below atmosphere) so relative pressure increases to 57psi at low loads, when the engine isn't running Valvetronic mode (instead uses the conventional throttle) relative petrol pressure might increase to 61psi because the engine will idle with about .3bar manifold pressure (.7 bar / 11psi vacuum) like a conventional throttle controlled engine.
The petrol system knows which mode the engine is running in and has a different map and set of fuel trims for each mode, if it didn't then when petrol differential pressure was at 61psi above manifold then open loop either fueling would be 20% rich or closed loop fueling would see fuel trims go to -20%.
The above is relevant regards how the LPG system is installed and calibrated. Picture the scenarios...
1. On most vehicles the LPG reducer would be connected to engine vacuum to facilitate LPG pressure being kept at a relative constant above manifold pressure, just like petrol pressure is usually kept at a constant relative to manifold pressure by the mechanical petrol pressure regulator which connects to manifold pressure. On most vehicles the LPG system's combined LPG pressure and manifold pressure sensor would be connected to both to allow the LPG ECU to react to fluctuations in relative LPG pressure and adjust LPG injector duration to keep fueling correct (with changing relative LPG pressure, as LPG reducers are not as pressure stable as petrol fuel pressure regulators).. If you connect manifold vacuum to the LPG reducer and the pressure sensor on a Valvetronic, LPG pressure then remains constant relative to manifold pressure (relative to atmosphere the pressure goes up and down with manifold pressure) while petrol pressure remains constant relative to atmosphere at 50psi. So, the LPG ECU sees that relative pressure (LPG versus manifold) remains constant and does not adjust LPG injector pulse duration on account of pressure but the petrol ECU decreases injector pulse duration to account for the increased difference in petrol pressure versus manifold pressure (the 20%). As the LPG ECU works as a slave to the petrol ECU's injector duration signals it responds by decreasing LPG injector pulse time by around 20% depending on the system calibration. Because relative LPG pressure has remained constant above manifold pressure while LPG injector pulse duration might have decreased 20% in copying the petrol injector pulse duration, the fueling can be expected to be lean by 20%...
2. If you don't connect manifold vacuum pipes to the LPG reducer or pressure sensor on a Valvetronic, the LPG pressure will be constant relative to atmosphere, much like petrol fuel pressure. So at first consideration this might seem a complete fix, but... Petrol pressure is 50psi over manifold in Valvetronic mode, rising to 61psi in throttled mode, a difference in the range of 20% which while running on petrol is fully expected and accounted for by the petrol ECU (as said above). LPG pressure might be 1.2bar (18psi) over manifold pressure in Valvetronic mode, rising to 1.9bar (28.5psi) over manifold pressure in throttled none Valvetronic mode. If you calibrated the LPG system in Valvetronic mode, in throttled mode the pressure would become 60% greater without the LPG ECU noting any difference in pressure, so the LPG ECU would not decrease LPG injector duration to account for the higher pressure. So now running on LPG in throttled mode the fueling might be 40% rich because the petrol system only decreases injector duration by 20% while the LPG system sticks in 60% more fuel without realising. The effect is of course due to the higher constant petrol pressure (50psi) compared to constant LPG pressure (18psi) - any change in manifold pressure represents a greater % relative difference in relative pressure for the LPG.
3. If you don't connect manifold reference to the reducer but do connect manifold reference to the pressure sensor, LPG pressure remains constant relative to atmosphere, so pressure changes relatively to manifold pressure and the LPG ECU sees the actual relative pressure. So now in Valvetronic mode the LPG ECU sees the relative 1.2 bar and in throttled mode sees the relative 1.9 bar. In throttled mode it decreases LPG injector pulse duration by 60% to compensate for the higher pressure, plus it decreases LPG injector pulse duration copying the petrol injector pulse duration. Result might be 80% lean.
4. If you don't connect manifold reference to the pressure sensor but do connect to the reducer - LPG pressure stays relative to manifold pressure but the LPG ECU sees LPG pressure relative to atmosphere, so in throttled mode the LPG ECU sees LPG pressure fall to from 1.2 bar to 0.5 bar and increases LPG duration by 60% while decreasing LPG pulse duration by 20% following the petrol pulse duration. Result is 40% rich.
LPG injectors are never totally linear, they take longer to open and close than petrol injectors, some are vastly better than others in this respect. If a nozzle size for a given LPG injector at a given pressure would flow the equivalent amount of fuel (when open constantly) as a petrol injector on a given vehicle, then since injectors pulse, for an LPG injector to flow the same during a pulse as the petrol injector pulse it would need to pulse for as long as the petrol injector plus the time it takes the LPG injector to open minus the time it takes the LPG injector to close. If the LPG injector takes 1ms longer than the petrol injector then for a petrol injector pulse of 3ms the LPG injector needs to pulse for 4ms, for a petrol injector pule of 16ms the LPG injector needs to pulse for 17ms.. a mutliple of 1.33 for 3ms but only 1.06 for 16ms. If we configured the multiplier in calibration to these points and all points between this would be the ideal multiplier map (K line) for this engine.
With a very linear LPG injector, using case 1 we could calibrate the system with a K line that would look similar to the K line of a none Valvetronic engine but could expect to compromise on fuel trims with +10% trim at idle in throttled mode, -10% trims in Valvetronic mode (thus steering away from too excessive extremes of fuel trims that would put the Mil light on by aiming for the average trim of zero).
With less linear injectors we can use injector latency to advantage in case 2. In case 2 with linear injectors we'd expect the system to be rich in throttled mode but when we do the maths it can work out OK, at least for idle... Just doing the maths for fairly linear injectors that take only 1ms to open we can see the effect - multiplier of 1.33 at 3ms petrol duration, LPG injector pulse of 4ms (actually flowing 3ms worth of gas) for correct mixture in Valvetronic mode. With vac pipes disconnected actual pressure is 1.9 bar but ECU still reads 1.2 bar, Petrol injector duration goes from 3ms to 2.4ms so with same 1.33 multiplier the LPG injector pulses for 3.19ms of which it is only flowing gas for 2.19ms, this is 27% less than the 3ms so fuel trims would only be out by 13% (from the ideal injectors 40%). With this setup, the situation improves if we use less linear injectors and improves if injectors become less linear as gas pressure versus manifold pressure increases (can take longer for some injectors to open as pressure difference across them increases)... No wonder in the old days with less linear injectors manufacturer advice was generally to use method 2. But in this case a flatter K line should be used...
Maybe needing to read a bit between the lines but you'll see how choice of injectors, nozzle size, working pressure, piping arrangements, calibration are all very much inter-related and how sometimes, with some piping arrangements, the best spec components are not the best components for the job.