Rob, thing is if you run a reducer for each bank, due to there only being one gas pressure sensor (one LPG ECU, one sensor), if each reducer outputs a slightly different pressure (which they will), one bank ends up with more fuelling than the other (the one with the pressure sensor attached should be the one that keeps correct mixture) - something you might just about get away with for closed loop operation(?) with very closely matched pressure but will lead to inconsistent mixture between banks at the top end, could get mixture right one day only for the next day the unmonitored reducer's pressure to have drifted.
If you fit a combination of 2 reducers that far exceed 500bhp capability (say 2 x 350bhp), in parallel, then there won't be a problem, especially not if they're not the most pressure stable. If you fit one reducer that is good for 500bhp flow then there won't be a problem, but if you fit 2 reducers each rated at 250bhp you might struggle to get them to conjunctively flow enough for 500bhp, especially if they're very pressure stable. Although since you already have one reducer I suppose (like you've said) you might as well try fitting it in conjunction with one new one before buying 2 new ones
Tomorrow I have a modified Mustang coming in (just had different cam fitted which has changed firing order, owner's had the car a few years but recently decided he wanted it to sound like a 60's hotrod), shaker hood and a few more goodies were already fitted. I've done a lot of work for this owner on various vehicles and previously sorted this Mustang's LPG system (before the recent mods) and removed engine bay LPG bits before the car went to a mustang specialists for the cam change... When I first saw this car I told the owner that really it should have a petrol fuel return and a lube system fitted as part of the LPG install but these weren't fitted and due to lack of fuel return the petrol ECU sees petrol pressure rise, so decreases petrol injector pulse duration to compensate for the high petrol pressure reading, turns on the MIL, goes open loop and since the LPG system works as a slave to the petrol system makes the LPG system open loop and difficult to calibrate or get consistent fuelling from. Options on ways forward were to ideally fit a lube system and a fuel return, or I could get decent results by setting the LPG system to pulse petrol injectors for 1ms (petrol addition) whenever the engine was running on LPG, which would also negate the need for a lube. He chose the latter option, so there is still no lube or fuel return fitted and the LPG system is set to provide a constant petrol addition of 1ms. Due to the petrol addition I had to fit smaller nozzles in the LPG injectors to prevent LPG injectors pulsing below minimum rated pulse duration (or they wouldn't meter LPG properly at idle, over-run and low engine loads, since 1ms of petrol pulse time equates to about 40% of fuelling under these conditions, so would otherwise decrease LPG injector pulse duration by 40% if LPG injectors were totally linear, which would push them well below duration at which they could work properly). Since then the reducer has developed a slightly leaky diaphragm so is leaking LPG through it's vacuum connection to the manifold, and the car is up around 75bhp on previous power levels due to the cam and other mods, pushing power to around 400bhp. Usually with such an old LPG system, when the reducer goes wrong I might offer the choice of reducer repair or a new reducer but this reducer is an old spec OMVL Dream reducer and while old spec Dream reducers are probably good for 400bhp, new spec Dream reducers will flow nothing like as well as the old reducer, so in this case to avoid having to change lots of piping to fit a different spec reducer altogether (not a new Dream reducer) I advised repairing the old reducer. Hopefully the old Dream reducer will flow enough gas for the engine with it's new cam by itself, but if it doesn't there is no guarantee that most other reasonably priced reducers would manage that sort of power level either, so in that case I would fit a second reducer in parallel with the Dream reducer and set the Dream reducer at a higher pressure than the second reducer... because Dream reducers are not very pressure stable the Dream will do most of the work until the driver really gives it some and even then the second reducer won't see a very sudden need to provide a massive flow of gas, second reducer might just see a fairly quick need to flow maybe 50bhp worth of gas. The thing is, due to having already employed the LPG ECUs petrol addition capability in order to provide the 1ms pulse to prevent petrol pressure rising to a peak and holding, which as said above would totally mess up fuelling on LPG, I cannot use that facility to add petrol addition to make up for any shortfall in flow of the LPG reducer(s), so it is either fit a fuel return and a lube system, which he prefers not to do, or fit reducer(s) that will flow enough gas for the engine.
First time I saw and sorted this car it was silver, now it's yellow. A mustang specialist who races mustangs did the cam change etc (same specialist apparently also has a few Nascars, one is an 'days of thunder' model, another newer model currently doesn't have an engine and he is looking to pay £40K for an engine)... My customer is having a roll cage fitted next (not by me), back seat removed, another LPG tank to be fitted in it's place (by me), after I've sorted the LPG fuelling. Other work I've done for him is converting his little fleet of SRT8 6.1 hemi engine'd vehicles, and having me sort his brother's car LPG system out was his Xmas present to his brother the other year.
Good idea with the dynamic take off, how effective are they (terms of increased manifold relative fuel pressure at high air flow)? I suppose one thing we could draw from that is confirmation that the old LPG installer advice to fit outlet nozzles in manifolds at similar angles to each other is correct.
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