CanberraVR-X
08-06-2006, 03:02 PM
The basic Magna 6G74 engine as designed and developed by Mitsubishi Motors Corporation (MMC) is so good, with its racing-style compact 4-valve combustion chambers, central spark plugs and well-shaped ports, that the MMAL engineers knew it must be capable of responding to tuning for higher output. Once the potential gains were determined efforts were undertaken to smooth the design to fit within MMC requirements.
A team, comprising people from Engineering Design, Development Engineering and the Lonsdale Engine Manufacturing Plant, came up with several alternative designs which were subsequently tested during the development phase.
The final iteration has an increased compression ratio (9.4:1 compared with 9.0:1) which was achieved by a reduced piston bowl depth while still maintaining top land height. This ratio was finally settled on, to ensure the car will give optimum performance on ordinary unleaded petrol. Higher ratios could have required the car to run on PULP which was considered undesirable.
An anodised piston crown and top compression ring land were specified to reduce wear and blow-by, while maintaining top end power.
The cylinder head combustion chamber was modified to reduce valve shrouding and improve breathing at small valve openings, thereby making full benefit of the 4-valves per cylinder configuration.
A high lift camshaft profile with 10% additional lift for improved top end performance was fitted. Although other camshafts which produced greater power were tested the deterioration in idle quality and exhaust emissions were considered unacceptable.
Special high lift valve springs, which have a unique cross-section to give increased clearance between coils at the increased lift, and are made from a special nitrided material for improved fatigue strength, are fitted.
The VR-X exhaust system, which was used as the base, was revised with the addition of a large bomb-type muffler to the centre pipe to improve the mid-high rpm exhaust note. After testing three alternative exhaust headers, specially fabricated stainless steel header pipes were added to increase top end power.
The engine ECU has also been remapped to:
increase idle speed in "Drive" from 625 to 680 rpm to maintain idle quality,
increase the speed limiter to complement widely available V-rated tyres (the car is fitted with 270 kph tyres),
revise the spark map for optimal power with the increased compression ratio, and
raise the air flow sensor map limit to accommodate the improved volumetric efficiency at high rpm,
keep emissions within required limits.
A team, comprising people from Engineering Design, Development Engineering and the Lonsdale Engine Manufacturing Plant, came up with several alternative designs which were subsequently tested during the development phase.
The final iteration has an increased compression ratio (9.4:1 compared with 9.0:1) which was achieved by a reduced piston bowl depth while still maintaining top land height. This ratio was finally settled on, to ensure the car will give optimum performance on ordinary unleaded petrol. Higher ratios could have required the car to run on PULP which was considered undesirable.
An anodised piston crown and top compression ring land were specified to reduce wear and blow-by, while maintaining top end power.
The cylinder head combustion chamber was modified to reduce valve shrouding and improve breathing at small valve openings, thereby making full benefit of the 4-valves per cylinder configuration.
A high lift camshaft profile with 10% additional lift for improved top end performance was fitted. Although other camshafts which produced greater power were tested the deterioration in idle quality and exhaust emissions were considered unacceptable.
Special high lift valve springs, which have a unique cross-section to give increased clearance between coils at the increased lift, and are made from a special nitrided material for improved fatigue strength, are fitted.
The VR-X exhaust system, which was used as the base, was revised with the addition of a large bomb-type muffler to the centre pipe to improve the mid-high rpm exhaust note. After testing three alternative exhaust headers, specially fabricated stainless steel header pipes were added to increase top end power.
The engine ECU has also been remapped to:
increase idle speed in "Drive" from 625 to 680 rpm to maintain idle quality,
increase the speed limiter to complement widely available V-rated tyres (the car is fitted with 270 kph tyres),
revise the spark map for optimal power with the increased compression ratio, and
raise the air flow sensor map limit to accommodate the improved volumetric efficiency at high rpm,
keep emissions within required limits.