LPG on a air cooled engine(Porsche 911S) 1

[rdd48856]

I was asked about this and I found 3 problems:
1)How to make the vaporizer work(there's no heat water)
2)Where to place the LPG tank(the engine is at the back and is forbiden to install it at the front)
3)How to stop gasoline injection, because it is mechanical(Bosch K-Jetronic)
(you can see it here

http://www.auto-solve.com/mech_inj.htm)

1)I'm thinking in using exhaust to heat water to make vaporizer work
2)May be under the seat
3)The big one. How can I stop gasoline injection without damaging the mechanical pump. I can't just stop fuel pump or the mechanical pump will run dry...may be cutting fuel supply just before the injectors.

Suggestions welcomed

Thank you...

 

[franzh]

Eventually someone will point to me, so here goes:
Do not use exhaust heat to vaporize the LPG, even with water as the medium, the heat is not controllable. You should consider a type of electrically heated unit with thermal limits on temp and pressure.
European LPG cylinder manufacturers offer torodial LPG tanks that fit in the spare tire location, you will need to carry a can of "fix-a-flat".
There is no mechanical fuel pump, not sure what you are trying to describe. Just open the power lead on the electric fuel pump.
Your largest hurdle will be finding a fuel system which will work on your 911, with dual carbs etc.
Franz

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[magnograil]

Do you need the petrol system for starting? The K-Jetronic system is mechanical in regulation. There is no mechanical pump. The disc in the intake cone controls how much fuel is continuously injected. If you do not want to turn off the electric pump, you can add solenoid to route the fuel back to the tank, bypassing the mechanical control unit entirely. The check valves in the injectors will keep the fuel in the control unit.
If you need the cold start injector then just plug the running injector line and the control unit's pressure regulator will return excess (in this case all) fuel back to the tank.
You should be able to add your LPG injector to the existing air box or possibly replace the petrol injector with a LPG one.
Your heater system will need one way valves to keep heated LPG from feeding back into the tank causing over pressure and to keep air from entering from the delivery end that might cause an explosion.
There is no room under the rear seats. They sit directly on the body sheetmetal.
How do you intend to regulate the LPG injection? One possibility is the MegaSquirt DIY EFI. This is a pulsed system set up for petrol but probably can be adapted.
Franz - the spare on a 911 is in the front boot so that location for the tank is unacceptable (sic). The K-Jet has a single large air box covering all the intakes. Otherwise he will have to go back to the '72/'73 mechanical injection to get separate intake throttle bodies and add separate injectors.

 

[rdd48856]

Thank you both for your answers…
I will be using a continuous flow gaseous injection LPG system, based on two steeper-motors for flow control and a distributor. The steeper-motors are controlled by an ECU, with inputs such as revs, engine temperature, MAP(it has to be added one sensor), lambda sensor(one will be added), etc. You can see it here:

http://www.tartariniauto.it/productlist.php?cat=2&sub=2.It

is a proven system. The only two things new are need for a source for heat water and mechanical injection.
Heating systems for vaporizers on air-cooled cars based on exhaust heat are well proven too, but on VW Beatles and Citroen 2cv. You can see it here:

http://www.cats-citroen.net/citroen_atypes/lpg.html.But

for a 180 HP engine it's not so easy. So I'm thinking in using a three position controlled by-pass to maintain temperature on the water circuit. Regarding injection-pump, there are pistons moved by the engine and a belt(you can see it here

http://www.classicmotorsports.net/projects/porschepix/911injectionpumpspring.jpg)

and mechanics call it an injection-pump. I don't know if these pistons raise fuel pressure or just regulate it, but I think it's wise to keep fuel inside this "pump". The idea of bypassing the mechanical control unit entirely is a good one, but are you sure it will not run dry, Magnograil? I don't have problems with the cold start injector, the engine will always start on gasoline…

 

[rdd48856]

The correct links:

http://www.tartariniauto.it/productlist.php?cat=2&sub=2

http://www.cats-citroen.net/citroen_atypes/lpg.html

 

[magnograil]

That is the mechanical injection pump used on the '72/'73 and not the Jetronic. The pistons are driven by a cam from the input shaft and the ports are controlled by a centrifugal bob-weight with a pointer on a space cam. The bob-weight moves the pointer axially along the cam for RPM input and the throttle moves the pointer radially around the space cam giving a mechanical "map" of the injection. An electric fuel pump feeds the mechanical pump and recirculates the excess back to the tank.
I doubt this pump will work with LPG. I thought you were using the Jetronic continuous injection system.
Are you sure your stepper motors will have enough bandwith to keep up with the inputs?

 

[rdd48856]

Fist the owner told me the injection was a K-Jetronic, than he told me about that mechanical pump. Any way my problem still is how to stop the pump from injecting gasoline without damaging it. LPG will be injected through a completely different injection system and it will handle the 180hp of the engine. Thank you again…

 

[magnograil]

Now you have more of a problem. Is the car a '72/'73? I think the '71 2.2L still had carburators. I am not sure if it was '74 or '75 when they changed to K-Jetronic. You say 180 HP which indicates a '72S. I believe the '73 was rated at 190 HP. '74 were less even though 2.7L.
Regardless, modifying that pump to not inject fuel without putting a clutch on the drive pulley would be a problem. It has an oil feed/return but also uses the fuel to lubricate the pump pistons. As far as I recall, they cannot be adjusted to zero fuel output. You have six pumps and injectors so valves to divert the fuel back to the tank would be expensive and a plumbing nightmare. You could fit the K system or use an electronic FI off a Saab 900 that uses an air mass flow meter. Not perfect but it is only for starting, right? Otherwise look into the MegaSquirt DIY EFI system.
The '72/'73 has a central airbox/filter with velocity stacks over each cylinder. Are you going to have an injector over each stack? Injecting from the center of the airbox will be injecting before the air filter (unless you remove it). You may not get a good fuel distribution either.