would LPG be good for my car?

Ralphh85 · Post by **Ralphh85** » Mon Jan 05, 2009 1:59 pm

im almost at the end of a fast road V8 car for daily use. once done im gonna build up another engine, should i build a mainly LPG engine?

if so i guess i can use a higher compression ratio, would this mean i couldnt use petrol? or would i just need to use the optimax higher ron petrol?

also wheres the best place to buy tanks and kits from?

how does LPG get in to the engine, guessing since its not through the fuel rail it must have its own injector(s)?

what are the down sides to LPG? other than extra weight? does it ware the engine worse?

Ralph

Quagmire · Post by **Quagmire** » Mon Jan 05, 2009 3:27 pm

ChrisJC and Bodger seem to be the LPG people on here, so i'm sure they can correct me later on anything i may say that is actually rubbish...

Yes you can use a higher compression ratio, the higher the better for LPG but to run on standard 95 unleaded i think the max you want is 10.5:1 or possibly 11:1 at a push. You are correct in saying that you could use super unleaded or an additive to boost octane for when running on petrol to compensate for the higher comp ratio and help prevent pinking.

As for how it gets into the engine you need to check out single point or mulit point injection and see what you want to go with. I use the most basic single point injection on mine, where the lpg gas is sucked into the engine via a mixer ring inserted in the air intake after the air filter. More sophisicated kits can do more funky injection stuff, but i know zilch about these so can't comment.

Downsides to LPG are generally:

-Having to store it somewhere (usually the boot) and so losing loadspace
-Finding places to buy it, although mosty BP and Shell garages near me seem to sell it now, especially the larger ones.
- Slight drop in performance.

Pros of using LPG are

-Better for engine as it burns cleaner, oil stays in better condition. In that respect you could say it will prevent engine wear. This is generally good except i believe for when you have an engine with new rings that need running in.
-More green
-Half the price
-Smells better than petrol fumes!
-Mine runs slightly quieter on LPG i think, though not by much.

Places to check out are

http://www.drivelpg.co.uk/faq.php

http://www.tinleytech.co.uk/ (suppliers of kits- read their info on types of systems)

ChrisJC · Post by **ChrisJC** » Mon Jan 05, 2009 4:11 pm

There are two types:
- 'Mixer' type, equivalent to a carburettor. Both of mine are of this type. Basically liquid LPG comes from the tank into a vapouriser to turn it into a gas. It then passes to a venturi (the mixer) on the air intake tract, and then into the cylinders. The vapouriser delivers more or less LPG depending on the draw from the mixer.
- 'Injector' type, equivalent to fuel injection. Still has a vapouriser, but the fuel is delivered through injectors into the inlet manifold. Needs an ECU.

Mixer is very simple, however it's crude. The mixer is a restriction in the inlet system, which saps power. The mixture is an approximation of what is needed (much like a carb!)

Injector type is much better, but much more expensive.

I run 10.5:1 in my van on LPG, runs great.

MPG worse on LPG, so the savings aren't as great as you might hope for!

Most systems are designed to start on petrol, then switch over, but I configured the one on my Landie to run on LPG from cold. Seems fine.

The other issue I have run across is that running on LPG only means that there isn't a 'petrol wash' on the inlet valves. Twice now I have removed the valves to find the backs of the valves covered in a black gunge, which I presume has come through the breather system. Occasional running on petrol should cure it though.

The vapouriser needs to be plumbed into the heater piping.

Chris.

Ralphh85 · Post by **Ralphh85** » Mon Jan 05, 2009 5:12 pm

cool thanks for the info, i will see how much it is but i think i would go with the injection type, i want to fit an after market ecu anyway so guessing if i get an ecu which can have multiple maps then i could switch between LPG and petrol on it.

whats needed to run it from cold? i know theres a chap on another forum with a 1800 k series engine which runs fine from cold, and also fork lifts obviously run from cold.

guessing some need to be hot because of the vaporiser?

Ralph

Post by **Rossco** » Mon Jan 05, 2009 6:40 pm

If you run at 12:1 you'll see no drop in performance, however that does preclude running on petrol.

Ralphh85 · Post by **Ralphh85** » Mon Jan 05, 2009 10:33 pm

presumably 12:1 would also give better economy to? would it work on the higher octane optimax?

Ralph

ChrisJC · Post by **ChrisJC** » Tue Jan 06, 2009 8:16 am

Nothing special is needed to run from cold. I think some people are concerned that if the coolant isn't hot enough, then the vapouriser will freeze over, but I've never had that happen.

I'm not aware of a single ECU that does both petrol & LPG, however that doesn't mean that one doesn't exist.....

Chris.

Ralphh85 · Post by **Ralphh85** » Tue Jan 06, 2009 9:35 am

ChrisJC wrote:Nothing special is needed to run from cold. I think some people are concerned that if the coolant isn't hot enough, then the vapouriser will freeze over, but I've never had that happen.

I'm not aware of a single ECU that does both petrol & LPG, however that doesn't mean that one doesn't exist.....

Chris.

emerald's K3 has 3 maps which are on a dash switch, chap on another forum has this running on his K series engine.

if using this is the way forward then guess its best to get the ecu running on petrol and then fit the LPG later. only trouble is emerald is miles away from me.

Ralph

ChrisJC · Post by **ChrisJC** » Tue Jan 06, 2009 10:10 am

It's not so much the maps, it's persuading the ECU to turn off 8 injectors and start using a different eight.

Unless it can control 16, and you just blank out the appropriate 8 in each map...?

Chris.

Ralphh85 · Post by **Ralphh85** » Tue Jan 06, 2009 10:16 am

since its just a normal 2/3 way switch you could just run a relay setup to switch injectors, il ask how this other chap did it, either way must be possible.

Ralph

edit, enless you just make it turn off the fuel pump an on the LPG?? and have it firing all injectors all the time?

bodger · Post by **bodger** » Tue Jan 06, 2009 10:52 am

Ralphh85 wrote:cool thanks for the info, i will see how much it is but i think i would go with the injection type, i want to fit an after market ecu anyway so guessing if i get an ecu which can have multiple maps then i could switch between LPG and petrol on it.

whats needed to run it from cold? i know theres a chap on another forum with a 1800 k series engine which runs fine from cold, and also fork lifts obviously run from cold.

guessing some need to be hot because of the vaporiser?

Ralph

what sort of injection do you have at the moment ralph ?
on mine i just switch of the ECU and and fuel pump ( don't forget that bit , if you happen to run out of petrol the pump still runs and will burn out )
keep it simple just stick a mixer on the intake

Post by **Rossco** » Tue Jan 06, 2009 11:05 am

I've got a set of injector emulators you could have for £40. That waythe ECU is fooled into thinking the injectors are still firing and that gets around any lean issue when switching back to petrol.

Ralphh85 · Post by **Ralphh85** » Tue Jan 06, 2009 2:05 pm

i have range rover flapper EFI setup.

the way the other chap did it was to run the LPG setup which watches your petrol injection then injects the LPG as it thinks relevant, as he switched to LPG he also changed the fuel/ignition map on the ecu so that the LPG ecu read the new signal and did the correct thing if you get what i mean.

i want to get rid of the flappy air flow meter anyway an get a map sensor so that will need an after market ecu anyway.

Ralph

Post by **Rossco** » Tue Jan 06, 2009 3:53 pm

Just get rid of all the electronics and go 100% LPG

I did that for 3 years with a supercharged 3.8 and it never let me down.