Homespun LPG on a supercharged car???

[5318008]

Hello folks.

I was wondering what it would take to rig up LPG on a 1275 A series engine with a suck through supercharger on it. The blower is geared for 12PSI max residual pressure. The car is to be LPG only and will be optimised as such.

I know my webers, SU's, FI but not LPG.

I'm sure PH will have the answers, as it used to in the old days

[GreenV8S]

Dual fuel conversions seem quite popular but I thought LPG only was not. Are there any practical issues that crop up if you try to use LPG full time?

[5318008]

Off the top of my head, most engine designs will run about another 5 units on top of their CR before detonation. You can run LPG in a 15:1 engine (tow start)... or lots of boost. What you loose in calorific value, you get back in raised CR. Duel fuel is a compromise which is why LPG is not as good as petrol, however, if the engine is optimised, it's a different story.....

Saves a lot on funny heads/dished pistons for FI though

[stevieturbo]

5318008 said:

Off the top of my head, most engine designs will run about another 5 units on top of their CR before detonation. You can run LPG in a 15:1 engine (tow start)... or lots of boost. What you loose in calorific value, you get back in raised CR. Duel fuel is a compromise which is why LPG is not as good as petrol, however, if the engine is optimised, it's a different story.....

Saves a lot on funny heads/dished pistons for FI though

Why does this question sound a little familiar :S


Anyway.....15:1 sounds very high.....too high, but not having used LPG before, perhaps it can.

Also, dont forget, and its mentioned elsewhere. Suck through and LPG....thats a big volume of gas sitting somewhere, just ready to be ignited by a wrong spark. OK in a standard, n/a engine, where little ever goes wrong.
I'd be very careful in a boosted engine.


If at all possible, id consider a gas injection system, assuming there arent the same A-series problems associated with petrol injection.

[5318008]

I thought about this, it is starting to get complicated though. Ideally, simple is the name of the game, this is a temporary engine rather than a well thought out one. I would consider doing a large bodge and seeing what sort of huge BOV's I can get. Perhaps one which could discharge into a pipe. Getting the required flow would be a problem. I would like to steer away from burst plates as much as possible as the orientation of the blower makes them difficult to site and difficult to replace. I would assume the higher octane of the fuel makes it less likely to flash off.

It would be likely to go off a treat when it did though.

I'll ask my engineer mate about big BOV's. I assume the danger of flashback with a suck through petrol is the same for suck through gas.

[Howitzer]

My friends 4.0 litre Range Rover with a new inlet manifold and LPG injectors running from a new ECU was unable to start on LPG.

Also, of the vapouriser kits i've seen, 2 out of the 3 blew the bonnets off of Range rovers, both classics.

Personally I wouldn't bother for practical reasons, for project reasons it sounds like a good challenge but results would be very hard i'd imagine.

Dave!

[ssray]

the reason you dont start on lpg is that most kits are not setup for the kind of choke or fuel enrichment upon startup,it can be done but its easier to start on petrol and change when warm.
small startup tank?
ray

[chuntington101]

worth noting that LPG runs at about 106 octane i think!!!

Chris.

[5318008]

ssray said:

the reason you dont start on lpg is that most kits are not setup for the kind of choke or fuel enrichment upon startup,it can be done but its easier to start on petrol and change when warm.
small startup tank?
ray

It would have to be avgas as my whole point of using it will be that I can run a blower on a standard compression engine.

[350Matt]

It would start Ok on regular 98 leaded petrol with no det issues as long as you didn't put your foot down whilst still on petrol, bear in mind det is caused by excessive cylinder pressures. throttle shut = no air = low cylinder pressure

Matt

[Mr2Mike]

ssray said:

the reason you dont start on lpg is that most kits are not setup for the kind of choke or fuel enrichment upon startup,it can be done but its easier to start on petrol and change when warm.
small startup tank?
ray

I thought it was more down to the fact that unless you have a system that injects the LPG in liquid form, the vaporiser has to be hot before the system will start working?

Out of interest would you even need much enrichment with vapour injection, it surely won't condense on manifold and port walls like petrol does?