GasResearch engine preparation guide
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.
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.
Extended exhaust duration (split timed / dual pattern) camshafts are recommended for LPG (square timed work well in some performance 4 & 6 cylinders) .
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.
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.
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.
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° at idle to 30° at 3000 RPM for petrol would be from 14° at idle to 28° all in by 2800 RPM. (depending on the cam profile) Individual curves should be plotted whilst dyno testing.
Not a problem on gas. Use running in oil for the twenty minutes required to run in your cam. Change this oil whilst hot to regular oil and load the engine on a dynamometer whilst tuning the gas
system to perfection. If you do not tune and load your engine in its infancy the bores and rings will glaze.
Four valve LPG cylinders flow well for high performance engines. Some multi valve tanks may not supply sufficient LPG to make reasonable horsepower. We highly recommend the use of APA Industries LPG cylinders.
Large flow (5/16 - 3/8) service lines and high flow filter lock-offs are essential as supply must meet demand. Twin tank, twin line set-ups for the likes of twin turbo V8's are recommended.
Are of a simple or complex type and must be matched to suit your metering system and horsepower requirements. GasResearch fuel metering systems use simple converters and air/fuel ratios are controlled and adjusted via jets and metering rods in the carburettor.Simple and effective.
If you require more specific information on your particular project contact us using the form below. please include all relevant information to assist us in our recommendations.