LPG- V8 Conversion

[Thor]

If you really want to run a Bristol with Chrysler V8 on LPG I would recommend the following :

1) Rebuild the engine with a high compression ratio, this gets back some of the torque and fuel economy otherwise lost. LPG is a very 'high octane' fuel, so it stands a lot more compression, and high compression improves thermodynamic effeciency.

2) Run the gas as a stand-alone injection system, using a wide-band lambda sensor in the exhaust, investing a reasonable time on calibration. The gas injector pipe design can improve combustion considerably (but this is proprietory knowledge, sorry).

3) Use two gas regulators (gas evaporation/pressure regulation) to achieve enough fuel flow capacity.

4) Either learn how to do the switch over to and from petrol manually, or remove the petrol system altogether, keeping the carburettor only as a throttling device (Alternatively buy a 4-barrel replacement throttle body of the fuel injection type.). Don't worry about cold start except in the deepest depths of winter, I can tell you how to deal with this down to about -15°C.

5) Plan long journeys to allow for the need to re-fuel at known LPG outlets.

6) Carefully think through the tank options, such as under-wing tanks, etc. to optimise the car for your personal requirements. If the petrrol system is removed, a good size LPG tank can go where the petrol tank used to be.

"Simples."

Total cost including the engine re-build : about £9,000 + VAT. SO probably not actually worth it in pure economic terms, but delightful when you get that feeling of enjoying all that performance without thinking of all the £s being ejected from your exhaust pipe.

As a complete alternative, I know somwhere which could fit a Land-Rover/Jaguar V6 turbo-charged diesel engine with about 400 lbf.ft and over 200 bhp.

[Kevin H]

As another complete alternative, you could move to Saudi Arabia where petrol costs less than 10p per litre

Seriously, if petrol prices bother you, maybe you shouldn't drive a V8 Bristol ...

[Kevin H]

Originally Posted by Thor

.. but delightful when you get that feeling of enjoying all that performance without thinking of all the £s being ejected from your exhaust pipe.

Until of course the government realises that more people are converting to LPG and so increase the tax on LPG to make up for any revenue they might be losing out on, due to reduction in petrol and diesel consumption.

They're already onto it.

From Deloitte's 2010 budget report;
"From 2011 to 2014, the duty differential for road fuel natural gas will be maintained and that for LPG will be reduced by the equivalent of 1p on a litre of petrol each year."

[lansdownplace]

Thank you to all the contributors. I think that comprehensively covers everything. The range of technical issues which get brought into play are quite mind blowing and I can see why an engine management system is near enough mandatory.

It is always worrying when the only reason for doing something is to take advantage of a tax differential rather than for a good underlying reason.

I was working on the basis that as few Bristols seem to have this conversion it probably meant it wasn't the best idea in the box. It does make sense that the best way to do this would be to start at the setup for the Bleinheim 4, which I know caused much hair pulling and teeth nashing at Bristol Cars whilst they perfected it. As Greg says it works very well in that car.

It seems a classic case of 'If you want to go there, I wouldn't start from here' Perhaps if I were starting from scratch with a car it might work, but as I already have an uprated engine, courtesy of Geoff Marsh which works very well, I will live with the fuel cost.

Perhaps I will get a letter from the PM congratulating me on my outstanding contribution to the exchequer!

Perhaps not.

Paul

[GREG]

Originally Posted by Thor

As a complete alternative, I know somwhere which could fit a Land-Rover/Jaguar V6 turbo-charged diesel engine with about 400 lbf.ft and over 200 bhp.

Tell me more ! cost etc ?

[lansdownplace]

Originally Posted by GREG

Tell me more ! cost etc ?

Could you shoehorn the VW 5l V10 diesel in? That would give you stupendous torque, relative economy and displacement.

[Kevin H]

Originally Posted by lansdownplace

Could you shoehorn the VW 5l V10 diesel in?

You would probably need a bit more room lenghtwise, but you could move the radiator forward like in the attached picture, (and do away with the stupid fan cowling up front).

[Philip]

Originally Posted by lansdownplace

Could you shoehorn the VW 5l V10 diesel in? That would give you stupendous torque, relative economy and displacement.

The VAG V10 and V12 diesels are very heavy, I doubt there's much aftermarket knowledge to sort the engine and gearbox electronics for swaps, and I suspect he'd prefer to stick a Land Rover/Ford 4.4 TDV8/ZF8HP in there.

In terms of cost vs performance vs economy, I think there's a strong argument for just putting an LS into one.

[GREG]

I have been running a Merc 320 CDI Estate for quite a few years as my work horse - Turned out to be the best all round car I have ever owned and nowhere near the most expensive - never broke down or missed a beat. ( touch wood )

I would love the 320 CDI engine and box in a 411 if someone could suss out how to keep the electronics happy ! I guess you would have to move the whole loom over and then get a boffin to turn a pile of stuff off on the dreaded ECU. Anything can be done with time and money :-)

Some of the Taxi customers at my Merc dealer are over a million miles on the original engine and it's plenty powerful for me. I have even heard a few have thrown some cheap rape seed oil in over Summer

But then the purist in me is fighting to keep everything standard. I guess it would need a 411 to come up with a dead engine at a very cheap price to make it all happen -- little chance :-(

[Thor]

Well, this is where I have to be careful because it is my own compmnay which can do this thing. So the following is by way of engineering explanation, not promotion.

Firstly, talking generally about using diesels inplace of petrols. At present we have a range of conversions for Land Rover Defenders, including 4.2 Supercharged Petrol V8 (460 bhp, 570 Nm), 4.4 Normal Petrol V8 (320 bhp, 422 Nm), and 2.7 Twin-Trubo Diesel (240 bhp, 530 Nm). It is torque which breaks transmissions (together with very bumpy roads/paths), so for the 4.2 SC and the 2.7 TD, we uprate the propshafts, diffs and halfshafts. We have often been asked to fit the 4.4 litre Land Rover TDV8 engine but there is no way it can be worth it becasue the transmission and chassis just can't deal with 800 Nm. Similarly, the 460bhp of the 4.2 SC is rather challenging, but at least it doesn't break anything, by itself.

The point I'd like to make is that when retro fitting an engine to an older car, it is the torque figures one must look out for, so in turbo-diesel terms one tends to end up with a smaller capacity engine, for obvious reasons. As I understand it the 411 engines made about 450 Nm (335 lbf.ft), and we can easily exceed 500 Nm from the 2.7 V6 diesel, so it is more than enough. The 240 bhp is also plenty to get a Bristol to cruise at well over 100 mph, if not as fast as with the 6.3 litre Chrysler engine. The main difficulty is persuading a hydraulically controlled gearbox to changeup before the diesel rev-limiter comes in.

As has been implied, these modern diesel engines tend to be tied in with loads of electronics and the electronics of the auto gearbox. We buy in an aftermarket, stand-alone ECU to run then engine and we similarly have our own controller for a 4-speed ZF gearbox. Trying to modify the original ECUs for these engines and gearboxes is virtually impossible unless you have full cooperation from the manufacturer, and Bosch, and ZF, which aint gonna happen.

For the Bristol, the most practical solution would probably be the V6 diesel with the 4-speed ZF (it has a lock-up TC), and keep or sell the old engine and box together.

Also, because of all the electronic and wiring loom costs, these conversions are no longer cheap and cheerful. We use new engines, but even with second-hand units I doubt you would get much change from £10,000.

[lansdownplace]

I saw a reasonably new defender 90 in Trafalgar Sq yesterday with a pretty rorty V8 and ventilated disks. If it hadn't been for the wider wheels and alloys you wouldn't have know it wasn't standard. Awesomely quick pickup, great in traffic. I wanted one! (I was trying to work out if the mud was hand painted on though)

As the V8 engines are reasonably cheap to replace there isn't such a good case for switching engines. Unlike the 401/403 cars...... there are quite a few which have lost their engines and would make great sleepers

[Kevin H]

Originally Posted by Thor

Well, this is where I have to be careful because it is my own compmnay which can do this thing. So the following is by way of engineering explanation, not promotion.

Given the amount of advice you given us over the years (particularly on the old BEEF mail list), I have no problems with you mentioning your business, especially when it's relevant to the discussion.

Kevin