LPG conversion on 5.7 Hemi

[badger]

Hi gang, as promised a write-up on the gas conversion of my Hemi. Don't know / can't suss out picture uploading, all the photos I took are way too large! Anyone help with that?

I spent a lot of time researching the 'net for info on the MDS system as I needed to know how it operated so that I could work out how it would then interract with the gas ecu. I spoke to a lot of people who all said the same thing - "oh, yeah, no issues mate, done loads of them engines in Dodge Rams", but no-one would admit to having done, seen or knew of a 300c that had been converted. Anyway, I took the plunge and bought the system and it then lay in a corner of the workshop until I had time inbetween customers vehicles to install it! I opted for 2 tanks, so that I could maintain enough boot space for the dogs but still achieve over 300 miles between fills.

I also had a look over the engine and discovered that the petrol injector plugs aren't anything like good old Lucas/Bosch, so I'd pre-ordered all the plugs from the good ole U.S. of A. some time ago.

First task - remove wipers and scuttle trim to gain access. I hate trim clips!!! (Yes, I broke one!).
Next, spend quite a while trying to fit vapouriser and ecu in different locations until happy, then manufacture bracketry and paint. Wiper mechanism out for access also.
With the ecu and vapouriser installed, time to start running wiring in. Easiest place was along the top wiper support bar, ty-wrapped to keep well clear of wiper mechanism!

Now time to connect the wiring, gas injectors and pipework to the inlet manifold. Now, I'd normally remove the manifold to drill and tap for the gas nozzles, but as it is plastic (and about 6mm thick!) I elected to use a drill coated in grease, stopping to clear swarf and re-grease just before breaking through, then for threading the tap was coated in grease also. Saved probably 2 to 3 hours doing it that way! At the same time, I installed the gas/manifold pressure sensing unit (dual map sensor) to the underside of the wiper motor steady bracket.

On to the tanks. it's amazing that feeling you get the first time you take a drill or hole cutter to your pride and joy's bodyshell, but it has to be done! 3 holes in the boot floor for the torroidal tank that sits in place of the useless space-saver spare, tank in and bolted up with a reinforcement strap across the underside. Torroidal fitted, it was time to do some careful measuring and make the mounting frame for the cylinder tank then paint it. Tank and frame bolted down, time to make another 2 holes in the boot floor (!) for the pipes. Now, before anyone asks "why not connect the pipes in the boot and save making more holes?", all pipework has to be sealed within ducting that is vented to the outside world, should there ever be a leak for whatever reason, so the individual tanks feed via ducts to the underside of the car where any connections are then made.

Next up, run the copper 8mm feed pipe to the vapouriser at the front, in beside the brake master cylinder. Ever tried to hand-form that stuff? It's hard!! Especially when it has to take a tortuous path up and over the rear subframe, paying special care and attention to its proximity to the rear anti-roll bar. It is then cleated at least every 600mm (LPGA rules), in this case the longest single unsupported run is about 450mm so no probs there. All pipes are cleated with rubber-lined stainless steel clips for safety and longevity. I picked up on the handbrake cable support clamp mounting points, saving the need for more hole drilling. (Phew).

Final pipe connections made at vapouriser (coolant and gas), switch/contents indicator cable fed through bulkhead and switch fitted (after taking a lot of trim out to gain access), scuttle trim and wipers re-fitted, engine cover back on, and it's time to go and fill up with gas! 79.2 ltrs later (£44.25, yippee) and I'm back in the workshop with the laptop hooked up to the gas system. Prime the system and leak check using "snoop detector fluid", all ok.

Now, it's always a moment of extreme trepidation and anxiety with a new conversion as to what's going to happen next... Will the gas ecu read the rpm signals correctly? Will it calibrate properly on an engine with an electronic throttle? (Part of cal. procedure is to hold at steady 3000rpm - try it, it's nigh on impossible!!) Well, I needn't have worried. A few small tweaks and adjustments of ecu settings via the laptop, a bit of mucking around getting a steady 3000rpm, straight through the autocal procedure and then some small final adjustments. Fuel trims checked against previously recorded petrol values, all ok, switch off and tidy away laptop.

Final task was to modify half the liners etc from the boot floor to make them fit around the new tanks (that liner that goes in first, the undertray, is blooming tough stuff to cut!) then invite "she who must be obayed from time to time" to inspect finished article. Start up, wait 20 seconds, blip throttle to 1400rpm and wahey, we're on gas! She even looked impressed...

I haven't actually driven the car any distance as yet (just a couple of miles) but if initial impressions are anything to go by, then the "job's a good 'un". Started up, pulled out of driveway, next time I looked down at contents indicator/changeover switch unit it was already on gas and I never noticed the changeover at all. I'll report my findings re. mpg etc in due course.

[badger]

Oh, forgot to add - 28.5 hours working time! No doubt I could trim a couple of hours off that if I ever have to do another one, and a single tank setup would have simplified matters as well.

[Stefan Tapp]

Nice write up, brings back memories of running a 3.9L V8 Discovery on LPG a few years ago!

Keep us updated!

Stef

[watsonofearnock]

Hi Brian,
Nice write up - and very clear. if you want to resize photographs quickly and easily you could download PIXresizer from Image resizing, do it with PIXresizer
Normally I would use and recommend Photoshop but it ain't worth buying just to resize a few photos. I reckon you will find this very straightforward - if not then ask!!
Cheers John

[UK CHRYSLER 300C]

or photobucket.com,its free and idiot proof(I use it.lol)

[devilmaycare]

Nice write-up badger.

I came across the following item in today's budget statement. Can't pretend to understand it, but maybe you can:

"A.93 The compressed natural gas differential will be maintained until 2010-11 and the
liquefied petroleum gas differential will decrease by 1 pence per litre on each of 1 October
2008, 1 April 2009 and 1 April 2010. (*)"

[UK CHRYSLER 300C]

it means if they cant f@ck you now but they will in a couple of years.I will no doubt be banned from here,but I rarely give a sh1t,cos the truth really does hurt

[UK CHRYSLER 300C]

do they really know how the internal combustion engine works?? no of course they dont,it depends on how many coffers the manufacturers pay the gov,cos the gov know fuk all,all they do is jibe each other and take the p1ss.I would love that job at their rates,hey! I could give up taking life so seriously with that kinda job and probably make some money.No wait,I'd rather earn it properly like my Ol 'man n Ma did

[Murphy The Cat]

Interesting stuff badger.
I feel that you bought your Hemi at the right time. Whilst the running costs on a big petrol car can be scary (or less scary with an LPG conversion), the biggest cost of running a car is depreciation.
I can imagine that in a couple of years time, you will be able to start picking up mint condition, large petrol engined cars for chump change, and then just have the scary fuel consumption and increased VED to worry about.

[propus]

Nice one badger, I look forward to seeing some pictures and hearing how it performs once you have done a few miles in the beast.