Advanced Technology

230HP Boxer 6 Engine

By: Jacob Nowicki

Question...what does the Porsche 911 and a Subaru SVX have in common ? You might think this is a trick question...it is not. The SVX and a 911 share the flat six cylinder "boxer" engine. This engine is a rare design among cars. The benefits of such a design are significant. First the engine is shorter than a "V" or an inline configuration. This lowers the center of gravity of the car improving the handling. Also the pistons run in opposing directions minimizing the vibration of the engine without the need of special engine mounts. Thats all great...I've read all that in brochures, but how did they do that?

Starting from the inside out....First there is a two piece aluminum engine block. The two halves each contain 3 cylinders. Each cylinder is cast with the block from molten alloy to ensure maximum rigidity. The cylinder walls themselves are also cast in place but are iron for strength. This is an actual improvement over the seperate cylinder "jug" design used in Porsches. Since this a flat layout the engine can be assembled around the crankshaft. First the crankshaft is rested in the main bearing saddles. Then the each halve is mated with its rods. Then the assembled halves sandwich the crankshaft. The crankshaft itself is a beefy one. A forged steel unit supported by seven main bearings looks like it has planned many visits to the 7000 rpm redline. The cylinders themselves are impressive. You have the now common place double overhead cam (DOHC) and 4 valves per cylinder but unlike other cars you have automatic hydraulic lash adjusters. This mechanism saves you the trouble of adjusting your valves. To meet the performance requirements and the low emissions of California and Japan the cylinders employ a pentroof combustion chamber. Althought the compression ratio is high at 10 to 1. The piston tops have four reliefs embedded into them to prevent a coming together of valves and pistons.

Although the advances pioneered by the SVX and the Porsche 911 carrera are now being adopted by other performance cars it makes you wonder what else the SVX has under the hood that others still only have on the drawing boards.

Suspension

By: Richard Silva

The Subaru SVX went throught a few different ideas and revisions before the svx team of chassis and suspension engineers finally came to a common agreement. During the development of the svx suspension the current trend was towards double wishbone suspension. Double wishbone suspension has its advantages. Primarily in keeping the tires perpendicular to the road. Even when the chassis is being tossed in and out of turns.

Yoshimitsu Kobayashi of the SVX chassis design team was not pleased with some of the drawbacks that also came with a double wishbone arrangement. Double wishbone produces more friction because of the many links and pivots in its structural design. The SVX chassis and suspension team knew that they wanted a car that had a smooth ride quality to compliment it's excellent traction. The Mac Pherson strut design would provide less friction which in the end would ensure the desired level of quality.

Now that the problem of ride smoothness had been addressed cornering was the next issue. Where as the double wishbone suspension that had been voted out would have solved this problem of cornerning. The SVX team knew going into the MacStrut project that unibody front chassis flex would be the Mac Pherson strut's worse obstacle to overcome to ensure superb handling. To ensure a higher performance on handling and cornering on a MacStrut design it requires a much more rigid chassis in order to return good handling. SVX engineers decided to mount the suspension members to the steel subframes at the front and rear of the SVX. Each bolted to the body through four floating rubber cushions. Besides helping stiffen the car, the front subframes would support the weight of the engine while the rear subframe would support the rear final drive unit (i.e. the rear axle and the differential).

With the problem of stiffness being resolved another decision had to be made. How to keep this rigid design from transmitting tire vibrations to the driver and passenger. To avoid this the team decided to use liquid silicone bushings as the lower A-frames bushing and in two engine mounts.

Now that the MacPherson strut system had been incorporated to work with the SVX the rest of handling was left up to the springs, struts and anti-roll bars and passive rear steering. During cornering the lateral forces that are created are purposely used to distort the bushing of the rear suspension twin parallel arms, causing the outer wheel to turn in (toe-in) and the inside wheel to turn out (toe-out) slightly, hence passive rear steering. Every SVX produced has passive rear wheel steering. Active rear wheel steering relies on the same lateral forces but is assited by a rear hydraulic steering rack to turn of the wheels. Both active and passive rear wheel steering are designed to help prevent high spirited drivers from losing the back end in long high speed lateral turns. In race prepped cars rear steering is almost always disabled do to the already high skill of the driver.

The SVX team of engineers made countless decisions when building and designing the SVX. Many of their decisions where molded by their quest for the perfect luxury sport coupe. Double wishbone suspension was voted most likely not to have a smooth ride so the MacPherson strut design was utilized, but it relied on a stiff and rigid chassis which would certainly go against the ideology of the SVX. So finally the stiffness issue was resolved through the use of a well designed bushing system.

Goes to show that the SVX team of engineers always had the occupants of the vehicle in mind even down to the silicon filled rubber bushings. Just something to think about or as the SVX engineers hoped not think about as you drive to work.

The above articles reprinted by permision from the SVX Journal