Interesting Engines:
Saab’s Variable Compression Engine
This engine had real promise.
Killed by Saab’s GM overlords due to budgetary reasons, the Swedish automaker’s variable compression engine, or SVC, had one of the most favorable risk/reward ratios I’ve ever seen. In other words, for the small amount of new, unproved technology used, the potential benefits were phenomenal.
As with most new engine technology, the touted benefits of the SVC included (much) more power from a given displacement, along with substantially increased efficiency. The proof-of-concept engine, shown in the accompanying images, was a supercharged 5-cylinder displacing only 1.6l, yet it delivered a remarkable 225 hp, with 30% less fuel consumption than a conventional engine of similar output.
The secret to the SVC’s capabilities was the movable “Monohead” that allowed the engine’s compression to vary dynamically between 14:1 and 8:1. The engine’s control unit would raise the compression toward the higher setting in low load situations in order to squeeze the most energy from a given amount of fuel. And when higher power was required, the compression was lowered to accommodate the boost delivered by the supercharger and avoid engine-damaging detonation.
The Monohead was hinged on one side, and actuated from the other with a stepless hydraulic crank (shown above). In practice, the system moved the cylinder head alternately closer to and farther away from the top of the pistons at top dead center, decreasing or increasing the “squish” volume, thereby varying the compression ratio.
Simple, robust, effective: The Monohead was really the only innovation introduced by the SVC; everything else—pistons, ignition system, intake and exhaust, supercharger, etc—was proven, off-the-shelf technology. As I mentioned, given the engine’s promise, the amount of R&D required was shockingly low.
So what happened? After being unveiled at the 2000 Geneva Motor Show, Saab’s corporate bosses at General Motors decided the project would consume too much development capital, and pulled the plug. They apparently thought badge engineering Subarus and GMC Envoys as Saabs was a better direction for the brand than potentially groundbreaking new engine technology… Given the Swedish automaker’s demise last year, we’ll never know if the SVC would have secured Saab’s future, but we know for certain that GM’s pathetic and shameful marketing strategy didn’t.
Check out Saab’s promotional video for the engine:
Further reading: SaabNet article, autozine.org article
Image credits: autospeed.com, carenthusiast.com, autocentral.com
Editor’s note: This post is part of an ongoing series examining unique and significant powerplants. Read the other installments here: