im using old school technology so not concerned with efi lpg sytems etc.

Am using the convertor to 2 su mixers into the su carb(acting as a throllte body) and into the engine, so its a basic and underperforming system by modern standards anyway.

It supplies way to much gass for an a15 setup and would be perfect on a mild L series.
Spoke to my installer and he says keep compression around 10:1 or 11:1 max for longevitys sake and we will get the a/f spot on. will still out perfom the current set up which is mostly all top end performance anyway

Quote:
dont know about this info...
what do they mean by excessively high, 17:1 or more? LPG has octane rating over 100 ron, and the only way to have a lpg motor that isnt gutless is with high comp.

and how does a "bigger" cam raise the compression, too much overlap actually allows compression to escape,especially under boost.

also not sold about the simple mixer/converters and 'jets in carb" being that effective for tuning and control, ok for towtrucks and taxis, but the problems of jetting and boosting with carbs in the radically different requirements for on and off boost are compounded with lpg since "fuel pressure" relies so much on the pressure from the tank, they just cant keep up with hi performance flow needs, I would be also talking to some other lpg performance specialists who are using new style of computer controlled mixer/converter on efi engines for real hp on lpg. like 3-400kw xr6t's running on lpg.

and i value my life so if i spend any more im sure my wife and kids will kill me, one way or another on my shhh conversion

you only live once

funds do not permit the ka head. also have a choice of L series heads for cheap/free. just the way i like it

You have to go the ka24e head!!!!
KA24e 12v 34mm inlets 40mm exhaust




Just look at the exhaust valve differences and the position of the sparkplug with the 2 inlet valves, perfect combustion.

If you go the polyquad head mod (1 larger inlet valve size) you will have a monster Polytripple for very little input.





David Vizards Polyquad technique

should have gone here from the start:

here


The following is a brief and nonspecific guide to engine building for the use of LPG/NGV as a primary fuel. Most of the following is aimed at V8 engines but the theories relate to 4 & 6 cylinder engines as well.

Compression ratios
Excessively high compression ratios only lead to detonation problems and optimum ignition timings will never be realised. Compression ratios are directly related to cam choice. I.E. the "bigger" the cam the higher the compression. Concave pistons work well in an engine which is designed to work in combination with a particular cylinder head combustion chamber shape. Compression ratios are also directly related to boost pressure(turbocharged and supercharged engines)and cam choice.

Camshaft
Extended exhaust duration (split timed / dual pattern) camshafts are recommended for LPG (square timed work well in some performance 4 & 6 cylinders) . Voodoo cams supplied by GasResearch have been tested and proven. Custom camshafts are available.

Heads
Seat inserts and bronze guides are always an advantage (whether using petrol or gas) as are large valves and porting for high rev applications. Well designed extractors assist exhaust scavenging.

Inlet manifolds
We recommend the use of single plane (open plenum) V8 manifolds as LPG vapour takes up to 30% more area in the manifold than petrol which is still in a liquid state. For high revving V8's the GasResearch Tornado manifold is advised. Some V8's use after market dual plane manifolds, with reasonable results, by lowering and knife edging the centre divider. Two or four barrel manifolds should be used in 4 or 6 cylinder applications. Fuel injection manifolds generally work extremely well with gaseous fuels. They have been designed to flow large volumes of air which provides good cylinder filling with gas.

EGR systems
These can be used provided they are in good condition. Exhaust crossovers in the inlet manifold should be blocked when possible. Cool air induction is an advantage on LPG for maximising cylinder filling and therefore power.

Ignition
Electronic ignitions are a big advantage when running on LPG. We also recommend the use of low resistance wire wound leads (as supplied by ICE Ignitions). The vacuum advance mechanism, unless modified, should be deleted. As an example a good mechanical ignition curve that was 10

yes but low comp and large ports on a L20... not ideal for compression on L16.

hmm you would think the L20b gas head was designed for gas, no?

When i go L16, i have a quandry over which head to use.

As its ging to be straight Lpg, i need to keep compression up to get the most power from it... heres the dilema.

Do i use an a87 head (L18 or l 20 gas head)with nice compression and bigger valves/ports as it works well with petrol, more fuel in, burn it and more gas out= more power.

Gas works differnet though, likes a leaner stoich mix. so my reasoning and research is, do i use an L16 small port head to keep comprsion nice but smaller valves and ports that will not flow as much fuel but keep gas velocity higher, making better use of the leaner requirements of LPG?