I’ve been looking at the Falcon for conversion to LPG, a no brainer really as the backs easier to modify to hold a 80ltr tank than a Locost would be, plus it does tend to blast through the petrol too. It’s also going to be my daily driver so needs to be economical. There’s heaps of LPG filling stations around here so I want to ditch the heavy petrol tank and the carb.

I was thinking of using the downdraft manifold with a couple of bike throttle bodies and a gas mixer underneath like this (don't ask what the springs for...I have no idea) –



The whole system is self regulating using a closed loop lambda setup So do I need anything more complex than the throttle bodys. I was going to use a very thin gasket (maybe try and get a material that conducts heat well) between the gas mixer and the manifold so the heat of the engine (it’s also heated by the coolant) I’d assume that doing that would remove the need for initial running on petrol to stop it freezing up??

would I be better keeping the throttle section of the carb and simply replacing the top with a plate and a couple of trumpets?



[Edited on 2/9/09 by Mr Whippy]

The the vapouriser/reducer that needs heat to turn the liquified gas into vapour the big problem will come mid winter your area gets some pretty hard winter weather.

If you are using a weber manifold keep the weber and use a very small petrol tank to supply the carb.
You can also pre-heat the engine using an electric sump pre-heater or electric coolant pre-heater.
Sump heater pads can be bought quite cheaply from the USA in 12v, 110v or 220/230 volts at various wattages.

The only reasonably priced coolant pre-heater I have seen recently is a german made device called the Hot Frog which sells around 85 pounds.

Could I use hot air from around the exhaust manifold to preheat the air in the winter as is normally fitted to the carb cars? I could keep the whole petrol system but am very limited to room under the bonnet and that mixer look like it adds a hell of a lot of height

without the petrol you wont have a cold start option as there will be no heat from the exhaust until it runs...

The mixer systems are a bit crap to be honest, they give the worst power loss and the greatest chance of back fires causing damage since the manifold is full of gas. The multi-point systems that use a gas distributor to supply one gas feed per inlet port are much better.

It also seems a lot of effort to fit bike carbs if they are simply going to be used as throttle bodies. Why not just stick with the original downdraught carb?

Agreed can't start without petrol first as gas will not vapourise

[Edited on 2/9/09 by big-vee-twin]

quote:

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Originally posted by big-vee-twin
Agreed can't start without petrol first as gas will not vapourise

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Forklifts and other low power operation generally use tanks/bottles that the gas comes out from the top as gas.
ISTR the limmit for this type of system is about 40hp or less.

For higher power engines the gas comes out the tank at the bottom as a liquid the the liquid LPG is supplied to the vapouriser in the engine compartment where it is heated then to the mixer or gas injectors as a vapour.

quote:

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Originally posted by big-vee-twin
Agreed can't start without petrol first as gas will not vapourise

[Edited on 2/9/09 by big-vee-twin]

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thanks plenty to think about there

I'd like to keep it as simple as possible tbh and if I could get away without a petrol system I'd like to do that. Its very easy for me to supply warm dry air to the inlet even if I used a cable operated butterfly valve for drawing warm air into the engine in the winter.

I'll have a look at the inlet manifold and see it I can get some of the height machined off so I won't run out of clearance under the bonnet if I kept a full carb

[Edited on 2/9/09 by Mr Whippy]