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 Post subject: BMW E38 750il Conversion
PostPosted: Tue Mar 01, 2016 12:56 pm 
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Hi all,
I am on the brink of buying a BMW 750 and intend on lpg'ing it.
I have previously converted an RX8 and a BMW 540.
Has anybody on here converted one and what kit did you use?
I know I have to have 2 6 cylinder kits so was looking at LPGTECH having had good results on the Mazda along with Hana Injectors.
Has anyone got a recommendation for a 350-400hp reducer which is compact as space could be a bit limited?
Thanks
Julian


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PostPosted: Tue Mar 01, 2016 4:05 pm 
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750's are only about 300bhp anyway aren't they?

Plenty different reducers will run to 300hp, most that will do much more hp are physically larger units - you'd probably be better off fitting 2 small reducers rather than try to shoehorn 1 large reducer in. Depending on the year of your 750 this could make for a more technically correct install anyway - some 750's use separate throttle bodies for each bank of cylinders, so it's possible each manifold can be at a slightly different MAP's (reducer absolute output pressure depends on map reference). 2 Reducers could only make a small difference but a difference none the less. With 2 reducers you'd have the choice of a very large range of 200bhp reducers, some of which are very small...

Your best bet will be to keep your options open at this stage - Look around the tight engine bay for possible mounting locations while considering different makes.. Of course, it helps to have different makes on the shelf to offer into considered locations, not something the occasional installer will be able to do..

My LPG'd 750's had reducers at the front where the air filters are, aftermarket cone filters were fitted by the original install who'd fitted the old Etagas system. When I updated the install I fitted new reducers in the same location but wouldn't fit reducers there on a new install.

Simon

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PostPosted: Thu Mar 03, 2016 9:42 am 
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Thanks for the reply Simon,
Yes 750's are about 320 hp and I was thinking of one compact reducer up by the firewall on the drivers side as these is a bit of space there but will have a good look at 2 smaller ones in a different location.
Do you have any recommendations for 200hp compact types?
Yes this one runs two separate management systems for each bank so this may be a better solution anyway.
Thanks
Julian


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PostPosted: Thu Mar 03, 2016 11:13 am 
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What year / body is it? 1st gen 750 had 3 ECU's drivers side bulkhead, one to run each side of the engine, the other syncs them with command throttles etc, throttle body and separate manifold on each bank - both banks will generally pull a very similar manifold pressure but there will be the odd moment when pressure is slightly different (returning to idle etc).. Each bank also has it's own petrol pump, fuel pressure regulator, map sensor, dizzy, etc.. like running 2 separate engines. So 2 reducers and 2 ECU's would have a slight fuelling accuracy advantage but it is possible to get good results using any combination of 1 or 2 reducer(s), 1 or 2 ECU(s).

A wide range of reducers are both compact and capable of flowing gas for more than 200hp.. As said above, if it was here I'd offer up a few types to possible mounting locations before deciding which type to use and where to fit.. pipe connection points and angles can be just as limiting as reducer size. One type of reducer that is often handy for tight spaces is MagicJet, a small and handy cylinder design, it doesn't have a solenoid built in (no sticky out coil), the gas outlet can be moved around the diameter, water connections are interchangeable between straight or 90degree (and 90 degree can be rotated) simply by unscrewing one type and screwing in the other, mounting bracket simply clamps around the cylinder shape of the unit so can be rotated around the circumference and slid up and down it. If you're going to fit 2 reducers and I had to suggest a type without looking I'd suggest this type - smaller types are available but don't offer the same install flexibilities.

Simon

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PostPosted: Thu Mar 03, 2016 9:16 pm 
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Hi Simon,
Thanks for the info.
I was looking at KME reducers as they look very small but what you say about the Magic jets make sense.
I suppose I could use one solenoid tee'd off into two reducers.
What are the Magic Jet injectors like? As good as Hanas?
Yes this car has 2 Engine modules controlled by a main one.
Thanks again
Julian


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PostPosted: Fri Mar 04, 2016 9:20 pm 
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Wouldn't say KME reducers are particularly small really..

Yes you could use one solenoid. More on this point - If you go the fully separate system route including using 2xECU's then unless ECUs are a type which has discrete tank solenoid and reducer solenoid outputs, then whenever one ECU connects power to the tank solenoid both reducers will be flowing gas. Not usually a problem, but would be a problem if one side of the gas system developed a severe leak i.e. pipe blow off - Under such conditions a system would usually switch back to petrol (turning the gas off), interpreting the condition as run out of gas. There are ways around this using diodes and (ideally) relay(s).

You won't need to be overly concerned about injector performance on this car.. Why ask the 2 types specifically? MJ injectors are quicker to open and close than Hanas, even on a demanding install it is unusual to approach the limits, they will outperform Hana. Hana response isn't as quick but they are predictable / accurate nevertheless and may outlast MJ's.

Simon

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PostPosted: Sun Mar 06, 2016 9:56 am 
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Thanks for the response Simon.
I guess I am hung up on injector speed after converting my RX8 so a high performing injector isn't required in this application due to it's low output per cylinder?
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Julian


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PostPosted: Sun Mar 06, 2016 8:54 pm 
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Had another thought and wondered if this is possible due to lack of under bonnet space.
Could I use one 6 cylinder controller and an emulator for the other 6 cylinders and then wire up the injectors in pairs in parallel in sequence of firing order?
I'm still looking at 2 reducers but may just go for one 350 hp Magic jet as I don't want to use cone filters in place of the airboxes to gain me space for 2 reducers.


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PostPosted: Sun Mar 06, 2016 9:07 pm 
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Fast opening isn't the same as high flowing, some high flowing injectors are slow to open.
Fast injectors are well suited to installs where petrol injector minimum pulse duration is low, such as on the RX8 (min pulse durations well below 2ms) and/or where pulse frequency is high (usually high rpm on a 4 stroke - RX8 has Wankel engine).. but how did you know you needed fast injectors for the RX8? :lol: There are certainly better injectors than Hana for Wankel engines, for which would prefer MJs.

The Beemer V12 injection system conforms pretty much to old skool Bosch standards, idles with 3ms+ duration. For the Beemer aim for reliability, design lending itself to neat install, ability to run at low temps, to a lesser extent fuelling accuracy. You don't need very fast injectors, just don't go for slow like Master injectors!

Simon

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PostPosted: Sun Mar 06, 2016 9:13 pm 
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ZiggyB wrote:
Had another thought and wondered if this is possible due to lack of under bonnet space.
Could I use one 6 cylinder controller and an emulator for the other 6 cylinders and then wire up the injectors in pairs in parallel in sequence of firing order?

Yes but not quite in sequence of firing order, as firing order will have a pot firing on one bank followed by a pot on the other bank. You need to keep each bank's fuel dosage separate, so, rather in sequence of firing order on each individual bank of cylinders.

Have a read here http://www.lpgforum.co.uk/viewtopic.php?f=33&t=14022

Simon

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PostPosted: Mon Mar 07, 2016 10:02 am 
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Hi Simon,
Thanks for the reply.
I have decided to go for a single controller with another emulator (Stag2-E6), Valtek 3 ohm injectors (as I plan to run these in parallel so effectively 1.5 ohm) and a single Magic Jet 3 Compact reducer.
Thanks again for you help
Cheers
Julian


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PostPosted: Mon Mar 07, 2016 11:27 am 
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OK Julian,

Single MJ may flow enough gas for the engine at full throttle high rpm, they are supposedly rated at 350bhp using 2 outputs and 250bhp using 1 output. In practice there isn't much difference in peak flow between using 1 output and 2 outputs and in both cases the standard MJ's may struggle to flow enough for 300bhp.

Using 1 ECU you'll need to set switchover to switch all cylinders over to LPG at once and set emulators to turn off petrol injectors immediately (if adjustable).

Find out firing order and wire emulators to every other cylinder (in firing order) per bank..

Though I wouldn't expect any problem, the Valteks will be electrically driven differently to using only 1 injector per channel and selecting Valtek in software. Injector selection effects current peak and hold levels and durations.

Simon

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PostPosted: Tue Mar 08, 2016 1:33 pm 
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Hi Simon,
Thanks for all your help and sorry to be a pain but can you check what I have below for the correct configuration of the injectors and Emulators?
LPG Injector order is for ECU controller connections and E is for the corresponding Emulator connection.

Rear
Cylinder Firing LPG Injector Cylinder Firing LPG Injector
Layout Order Order Layout Order Order

6 (7) (E) 12 (8) (E)
5 (3) (E) 11 (4) (E)
4 (11) (E) 10 (12) (E)
3 (5) (3) 9 (6) (4)
2 (9) (5) 8 (10) (6)
1 (1) (1) 7 (2) (2)

Front

Ignition firing order is 1-7-5-11-3-9-6-12-2-8-4-10.

Thanks again
Julian


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PostPosted: Mon Mar 14, 2016 5:37 pm 
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Your diagram doesn't show how the LPG injectors would be wired in pairs...

Here's a diagram that does... Cylinder number / (Actual or Emulator connection), Cylinder number / (Actual or Emulator connection).

6 (3E) 12 (6E)
5 (1E) 11 (4E)
4 (2E) 10 (5E)
3 (3A) 09 (6A)
2 (2A) 08 (5A)
1 (1A) 07 (4A)


Where Actual connect petrol injector wiring to same numbered LPG channel, same numbered LPG injector output drives the LPG injector on that cylinder, just as with a normal install.

Where Emulated connect emulation instead of wiring petrol injector wiring to LPG ECU (no wiring connects directly between the petrol injectors and LPG ECU on these cylinders) and wire LPG injector on these cylinders in parallel with bracketed number LPG ECU injector output.

E.g's:
1 (1A) is cylinder number 1 - The petrol injector wiring for cylinder 1 runs to LPG ECU channel 1 and LPG injector 1 feeds this cylinder.
5 (1E) is cylinder number 5, which is on the same bank of cylinders as cylinder 1 - The petrol injector wiring for cylinder 5 runs to an emulator, the LPG injector on this cylinder is wired in parallel with LPG injector 1 (the LPG injector mentioned above), i.e. LPG injectors 1A and 1E are wired in parallel.

Note how LPG ECU channels 1-3, LPG injectors 1A-3A AND doubled up LPG injectors on channels 1-3 (1E-3E) are all on one bank/side of the engine, channels 4 to 6 apply similarly to the other bank - this is critical as each side of the engine has it's own fuel trims (in fact own petrol ECU on this vehicle), it avoids a dollop of LPG appropriate for one cylinder bank being fed to a cylinder on the other cylinder bank and avoids cylinders on the same bank receiving different fuelling.

It doesn't matter that 2A fires after 3A - on a normal install on a straight 6 engine we'd just connect LPG channels 1 to 6 according to cylinder numbers not firing order (1 at the front 6 at the back).

Wired in parallel injectors means half of the cylinders must receive their dosage of LPG in advance of when the petrol system would dose them with petrol. With quickly increasing engine load, particularly at low rpm, the petrol ECU might normally give the following cylinder to fire more fuel than the current / previous cylinders... LPG injectors wired in parallel on same bank according to firing order prevents as much as possible the loss of this fuelling strategy and means fuelling will be more correct during changing accelerator position. It also means LPG isn't sitting in the inlet ports any longer than the minimum time possible when using wired in parallel injectors, not a problem in any case with your engine but would be on others. Cure one point here and you cure the other by default.

Don't forget to order 6x LPG injector connectors! Few quid there, along with the few quid for the emulator wouldn't be too far off the price of another ECU, a couple of diodes and a relay. Calibration of a system with 2 ECU's, 1 for each bank of engine cylinders, is almost as simple as with 1 ECU - Would calibrate one half of the engine while other half is still running on petrol then save the map, upload to the other ECU and confirm all is correct. Particularly for this install the uploaded map would be more likely to be correct for both cylinder banks if you calibrated in Basic mode rather than in Tech mode.

Simon

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PostPosted: Mon Mar 14, 2016 9:12 pm 
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Hi Simon,
Thanks for the reply.
I managed to download a wiring diagram for a BMW 850 today as I couldn't find one freely available for the 750.
The injectors are batched in triples as follows 1, 3 and 5; 2, 4 and 6; 7, 9 and 11; 8, 10 and 12
Each set uses the common triggering earth from the PCM so it's effectively running off four signals for injection.
I agree with what you have stated but due to the firing order should this be changed to this:

6 (2E) 12 (5E)
5 (1E) 11 (4E)
4 (3E) 10 (6E)
3 (2A) 09 (5A)
2 (3A) 08 (6A)
1 (1A) 07 (4A)

These pairs now follow the firing order of the engine.
I have ordered six two pin LPG injector connectors with tails and an emulator and this has come out at about £20 odd quid.
Out of interest what would I need the relay and diode for if I had another Ecu? Is this for fooling it into thinking it's opening the solenoids?
I don't suppose you've got a tank have you?
Cheers
Julian


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PostPosted: Mon Mar 14, 2016 9:44 pm 
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Forgot to say I had another look and measure up tonight and the MJ reducer should go in the void between the headlight and airbox and the ECU and emulator will fit in the enclosure where the brake fluid reservoir is.
I can also feed the switch wiring and the diagnostic connector through from here as a fuse box feeds another in a flip down enclosure by the drivers right knee so I can mount the switch to this.
The heater pipes are also easily accessible on this car which is a bonus so easy to tee into it for the hot water supply for the MJ.
All the front end should be relatively straight forward.


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PostPosted: Wed Mar 16, 2016 10:40 am 
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With injectors wired in triples and there being 12 cylinders that's 4 injector outputs from the petrol ECU, so if there were a 4 cylinder LPG ECU that could properly drive 3 LPG injectors per channel it would be ideal to use with emulation on the other 8 cylinders for this engine... The Valteks are 3ohm injectors so tripled would be 1ohm. Though LPGTech may have an option to run near 1ohm injectors it's doubtful it would drive the Valteks properly even with 1ohm selected and it's probable selecting 2 or 3 ohm injectors would damage the ECU. You bought the 6 cylinder version, which can work on 4 cylinder installs but would stick to doubling injectors (using all 6 channels) rather than tripling injectors. Anyway, you probably only have 6 cylinders worth of emulation.

LPGTech, like most LPG ECU's these days is truly sequential - it waits until it receives a petrol injection pulse on each channel before pulsing the LPG injector on the output of that channel... So on most engines firing order is irrelevant as long as the wiring/channel to the LPG injector matches the wiring/channel from the petrol injector, i.e. output to each cylinder matches the input from each cylinder.. So as far as the LPG ECU is concerned it wouldn't matter if channels run 1 to 6 from front to back of engine or 6 to 1. The following diagram will give exactly the same results as your diagram (I just copied and pasted from your diagram and swapped relevant numbers)..

6 (3E) 12 (6E)
5 (1E) 11 (4E)
4 (2E) 10 (5E)
3 (3A) 09 (6A)
2 (2A) 08 (5A)
1 (1A) 07 (4A)

Because of the above, if you wire to petrol injectors as per my diagram or your diagram and then wish to change to the other diagram, you would only have to swap LPG injector plugs on the rear 3 cylinders on each cylinder bank! The emulation won't need changing.

Remember to set 'switchover mode' to 'at once' in software.

You wouldn't need a relay or diodes with just another ECU but would need them if you ran 2x ECU's, 2x Reducers (without gas pressure balance pipe between the outlets) and only one tank. The tank solenoid is wired in parallel with the reducer solenoid... So power to the tank (from one reducer, from one ECU), would otherwise turn on the solenoid on the other reducer (reducer to tank to reducer). A diode between each reducer and a relay (that powers the tank) would allow each reducer solenoid to turn on the tank solenoids while not turning on the other reducer solenoid... One ECU may switch back to petrol due to low pressure, perhaps due to a severe leak.. You wouldn't want the other system (discrete system without a balance pipe between reducer outlets) to keep solenoids on the system with severe leak turned on.

Simon

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PostPosted: Wed Mar 16, 2016 12:19 pm 
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Simon,
Thanks for your invaluable help.
Have you got a tank (680 x 270)?
Cheers
Julian


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PostPosted: Fri Mar 18, 2016 8:57 am 
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ZiggyB wrote:
Simon,
Thanks for your invaluable help.
Have you got a tank (680 x 270)?
Cheers
Julian
Nope sorry
I don't think it practical for installers to stock tanks.. There are so many sizes etc available that to stock a concise range of tanks to suit all vehicles would mean holding a great many (big warehouse full of) tanks and not just from one tank manufacturer but from many tank manufacturers... 'Done in a day' installers need to stock tanks, otherwise they could not convert a vehicle in a day (they would need to wait until the next day when tank arrived to fit it much like I do). In very many cases, done in a day installers compromise on tank to allow them to get the job done in a day because they couldn't stock a concise enough range of tanks (don't have money for stock or a tank warehouse) to keep the exact tank that is the ideal fit for the vehicle they are converting. In many cases it is better to very accurately measure each vehicle up to find what dimensions will fit, and then find which manufacturer produces the tank that will hold the most gas for those dimensions, and then order that tank and have it arrive the next day... Each manufacturer produces tanks of hundreds of different dimensions, done in a day installers typically stock 7 different dimensions, done in a day installers typically fit compromise 'best fit out of what we've got' tanks... Some of us fit the best fit tank, not out of what we've got, but the best fit/capacity tank full stop. I use a range of suppliers / stockists to achieve that - they all have big warehouses full of tanks.

Simon

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PostPosted: Sat Apr 09, 2016 12:04 pm 
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I have finally finished my conversion and can confirm it is running well.
It is lumpy on changeover but a bit of tweaking should iron this out.
The map also needs a bit of a tweak at higher injector durations but this is not a problem as I don't need to rev this thing or give large throttle inputs to make good progress.
Will sort this out tomorrow on the way to Henley for rugby as the eldest boy can do the tweaking required on route.
Thanks for all your help Simon, the old dear really even is more gorgeous now at 55p a litre!


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