It is true that there is no best system.
Not any system will do on a BMW V8. These engines make 286bhp. You need a system with a reducer capable of flowing that much LPG otherwise you're going to either be running lean at the top end of the power range or using petrol at the top end of the power range. To make for a neat job, you want injectors that will fit under the plastic engine cover. Ideally, the injectors shouldn't fit with the plunger shafts mounted horizontally, as this can make the injectors wear out quicker.
There are good and bad performing parts, and then there are reliable and unreliable parts.
There are combinations of components that complement each other better than other combinations on specific applications.
Then there is what will physically fit on the vehicle - either for the amount of space available full stop, or bearing in mind you want to keep the install looking neat and tidy / like factory fitted.
I consider all of the above when choosing components to make a system to install on a vehicle.
Let's look at a thought process when considering parts for a 4.4 RangeRover, and I'll just mention / consider a few components to keep it simple....
There is plenty of room under the bonnet on a 4.4 Range Rover to fit the reducer, ECU, injectors and everything else - But to make for a neat install you want injectors that will fit under the plastic engine cover of the BMW engine. This rules out all the 'down draught' type injectors. I like OMVL Superlight injectors for many applications because they perform very well (if not the best) and are extremely reliable. Incidentally, these are side draught not down draught. On the 4.4 Rangerover they just fit under the plastic engine cover if the sound deadening material is removed from it. Or, MagicJet injectors perform even better than the superlights and fit easily under the engine cover, but I've seen a couple of coil failures on these injectors and, although I like their performance, I think the wires that connect them to the loom look like they might easily break off. I have fitted many different reducers on 4.4 RR's, mostly OMVL Dream reducers and MagicJet reducers, but also KME, Bigas, Prins to name just a few. I don't fit many OMVL reducers these days as the temp sensors don't seem as reliable on them as they used to be and they're not great on pressure stability, but they are good at high flow rates. The MJet reducers don't flow quite as well as the OMVL and don't respond to demand as fast, but they are more pressure stable. One downside to the MJ reducer is that the pressure limit is 1.5 bar. If we fit the MJ reducer along with MJ injectors, no problem with getting the gas into the engine even with only 1.5 bar as the MJ injectors flow exceptionally well.. No problem except for a possible low pressure blip due to the not so great response to demand from the reducer. Now we're into ECU's - which ECU? With most LPG components including those mentioned above, we might expect a short and slight low pressure blip if the driver suddenly slammed his foot down on the throttle... it's not like most people drive like that often, but as installers we've got to make the system drive on LPG just like it does on petrol in all circumstances. If we fit an AEB system we're not fitting a truly sequential system, as AEB only measure the petrol injector durations from number 1 and number 5 cylinders and each LPG injector gets the same injection pulse time. In contrsast, there are many none-AEB systems that are truly sequential. If we fit an AEB system we have the advantage of being able to dial in a petrol addition to cover the low pressure blip, which is not possible with other systems. Not being truly sequential, the AEB ECU might suffer slight hesitation due to not being able to respond to quickly changing individual cylinder injection durations at low rpms with a quickly adjusting throttle position, but this could be dialled out in a crude fashion by using the 'enrichment in acceleration' slider. This slider isn't necessary on truly sequential systems however, as they do measure each injector's duration individually. The AEB ECU has facility, due to the 'petrol addition' capability, of correcting any issues with getting gas into the engine under demanding circumstances but the none AEB ECU, though more technically correct, has not. The AEB ECU offers very good calibration prospects for both load and rpm, whereas the none AEB offers very good load calibration but cruder RPM calibration. However, on most applications, rpm calibration is not very important.
Just a note, but the BMW 4.4 engine, fitted in the RangeRover, runs with a different ECU than the same engine fitted in the X5. The X5 takes longer to calibrate properly, whereas the RangeRover is quick to do a good job of calibration. With the X5, fuel trims seem to change even though you're seeing the same petrol injector durations but the RangeRover is a more conventional vehicle to calibrate.
So, turning the question around for a moment, armed with all the above information, which combination of components out of those i've just mentioned would you fit? There is no easy or best answer, and we have fitted all combinations of the above, and all run better than most other systems you'd pay more for fitted elsewhere. All components are amongst the best in their field. Any shortfalls mentioned are me being hypercritcal and detecting slight areas which could be improved upon whilst using a connected compouter. The driver wouldn't be aware of any difference when driving on petrol or LPG. On RangeRovers we don't just fit the components mentioned above, we've fitted many other components to make up many different systems too. There are dozens and dozens of L322 RangeRovers out there that we've converted and all run on LPG just like they do on petrol. Any company that says they 'fit the best system' are talking from bias, and where does that bias come from...? It comes from the fact that they only fit a limited range of systems, and they only fit the standard components that come in those systems.
The Jag engines convert fine too, and have converted many supercharged RangeRovers with the Jag engine. The Jag engines, though, do need valve lube systems, petrol returns, injector impedance matching units. Have converted supercharged RangeRovers and not used a petrol addition, courtesy of the two reducers capable of flowing enough gas for 800bhp between them and the excellent performing injectors we fitted.
It is worth noting that AEB is the manufcaturer who makes ECUs for OMVL, Bigas, Zavoli, Romano, etc etc.
If you have a preference in components that you'd like installing, we will likely be able to fit a system comprised of those components. We may offer advice where components complement each other for your vehicle and will, of course, offer advice anyway if we think you want it! In most cases when the customer chooses their own components it doesn't affect our price. Some components do affect price. By default we choose components that perform very well, are very reliable and are suited to the application. This is a much better approach than the 'one size fits all' mentality that people get elsewhere.
Simon in Yorkshire