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Interesting Engines:
Saab’s Variable Compression Engine

March 13, 2013 by Matt

Saab Variable Compression Engine Motor SVC

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.

Saab Variable Compression Engine Motor SVC

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.

Saab Variable Compression Engine Motor SVC

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 overloads 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:

Filed under: Interesting Engines, Saab, Technical

3 Comments

  1. Yves Petit says:

    I had always wondered what had happened to this SAAB engine. I would be very very surprised if your marketing/cost explanation is the real reason for GM’s scrapping of this engine.

    Knowing that a 30% fuel economy was at hand with a quite simple engine configuration, I’m convinced that the oil guys did not like the prospect of less fuel consumption and thereby reduced profits. They killed GM’s EV-1, did’nt they? Nothing will stop these planet destructors!

  2. Matt says:

    Agree with the last comment, SAAB shoulda kept quiet about the fuel savings til the last moment and plugged it purely on it power an torque for its displacement.
    Lol them oil barons eh, shouldn’t we all be driving water powered cars by now.

  3. Thomas Bennett says:

    I read about the Variable Compression Ratio Engine various mechanisms and thought of another solution probably not as efficient but it is something in between.

    Take a standard design four cylinder engine with two cylinders at 8:1 ratio and two at 14:1 ratio. When operating at full power, the cylinders with 8:1 ratio will produce the full power with the turbocharger at its maximum, high performance, and at slow speed the two 14:1 cylinders will operate reducing consumption and have low emissions, high efficiency.

    In between speeds, it is a matter of producing the required power with the optimum consumption and emissions controlling the air intake and fuel ratio into the four cylinders. In this way avoiding the mechanical complexity the VCR Engine has.

    Thank you very much.
    Thomas Bennett
    Buenos Aires
    Argentina

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