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Posts filed under ‘Interesting Engines’

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 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, article

Image credits:,,

Editor’s note: This post is part of an ongoing series examining unique and significant powerplants. Read the other installments here:


Interesting Engines:
The Rolls-Royce Goshawk

January 28, 2013 by Matt

Rolls Royce RR Goshawk

A few years before the development of the world-beating (and war-winning) Merlin in the late ’30s, Rolls-Royce released this turd of a powerplant.

The Goshawk was a 21-liter, 600-hp V12 engine developed to power the fighters bidding for the 1934 British F7/30 specification. As it turned out, all eight of the designs submitted turned out to be completely unsuitable for combat even before they left their respective drawing boards, their immediate obsolescence caused in no small part by the Goshawk’s inherent design flaws. In fairness, the British government’s specification was remarkably backward-thinking and short-sighted in many respects, but the fact that Rolls-Royce powerplant was totally inappropriate for a fighter should have been obvious to any casual observer.

Hawker P.V.3. F7/30 Fighter

Fitted to the Hawker P.V.3. shown above, among others, the engine’s basic design was decent; it was the inclusion of a trendy design feature that doomed its prospects: Evaporative, or steam cooling. Instead of a conventional pressurized water cooling system, where the coolant is kept in a liquid state past its boiling point, the Goshawk was built around the principle that letting the coolant actually boil would absorb more heat by virtue of the energy needed for the state change from liquid to gas. The upshot would be less coolant capacity required, and while the principle was sound, in practice the system suffered from at least two major flaws:

  • Radiator size. The actual amount of coolant making the rounds in the pipes may have been less than that of a conventional setup, but the radiator (in this case, condenser) capacity needed to allow the gas to condense back into a liquid was much greater, posing insurmountable difficulties when it came to integrating them into the airframe with an acceptable amount of drag.
  • Total unsuitability for combat maneuvers. The Goshawk, with its steam cooling system, was intended primarily for fighter aircraft, a type designed with a high level of agility, including negative-g maneuvers and inverted flight. It’s obvious what kind of problem this flight behavior would pose to a cooling system dependent on gas and liquid to occupy specific locations in order to operate properly—the mildest movement would cause the steam and liquid to trade places and completely ruin the effectiveness of the system.

Successful? Hardly. Interesting? Sure. Oftentimes engineers learn as much from what doesn’t work as what does, and viewed from an historical perspective, it’s perhaps fortunate they learned “the hard way” from the Goshawk’s difficulties before the more urgent days of the late ’30s arrived.

Image credits:,

Editor’s note: This post is part of an ongoing series examining unique and significant powerplants. Read the other installments here:


Interesting Engines:
The Mercedes-Ilmor 500I

December 26, 2012 by Matt

Mercedes Ilmor 500I IndyCar Indy 500 1994 Penske PC-23 Engine Motor Pushrod

How far would you go to win one race?

Would you design an engine completely from scratch with the knowledge that it would almost certainly be banned by the next race, expending hundreds of thousands of dollars in development and production costs just to score that lone victory?

Mercedes and Ilmor would—and did. Their 500I 3.4l turbocharged, methanol-fueled V8 was a clean-sheet design constructed with a sole purpose: To exploit a loophole in the 1994 IndyCar rulebook and thus win that year’s Indianapolis 500. It could be argued that the nature of the race in question—the prestige of winning the Indy 500 being up there with the Monaco GP or Le Mans—made the resources committed to the project slightly more worth the investment. Still, the scale and audacity of the endeavor shocked the racing world.

Mercedes Ilmor 500I IndyCar Indy 500 1994 Penske PC-23 Engine Motor Pushrod

Some background: The IndyCar technical regulations for the 1994 season allowed pushrod engines to run higher turbocharger boost pressures, as well as additional displacement, over their multi-valve counterparts as part of a kind of equivalency formula. IndyCar reasoned that some constructors would simply use non-optimized off-the-shelf production-based pushrod engine designs as a less-expensive starting point, and gave teams who chose to do so a leg up on their more affluent competition by allowing them the benefit of a few extra cubic inches and pounds of boost.

Mercedes Ilmor 500I IndyCar Indy 500 1994 Penske PC-23 Engine Motor Pushrod

Prior to the 1991 season, engine manufacturers had indeed been limited, by the rulebook, to production-based engine blocks. After 1991, however, that requirement had been dropped, a development that went largely unnoticed—except by engine maker Ilmor. They figured that a clean-sheet, carefully-designed pushrod engine could take advantage of the regulatory loophole to overcome its inherent design disadvantages compared to a multi-valve engine, and thus trounce the competition for at least one race before the powers-that-be cracked down on the rulebook’s oversight. Ilmor placed their bets on the 1994 Indy 500, and before long Mercedes came on board to help finance and lend technical assistance to the top-secret project.

It worked. Mated to Penske’s all-conquering PC-23 chassis, the 500I’s extra 650cc and 2.5 psi of boost (as allowed by the regs) netted it an extra 150-200 horsepower compared to its multi-valve rivals, and Al Unser Jr won the race going away. Some sources quote a remarkable figure of over 1,000 hp over the duration of the 500-mile race. And naturally, caught with their pants down, as it were, the regulators banned the engine almost as soon as the checkered flag waved at Indy. Still—it’s to Ilmor’s and Mercedes’ credit that they had the creativity to consider an “inferior” engine design in light of the racing series’ rules, and the commitment to follow through with it, with spectacular results.

For a more in-depth look at the engine and the racing politics that surrounded it, check out this 8W article.

Editor’s note: This post is part of an ongoing series examining unique and significant powerplants. Read the other installments here:


Interesting Engines: The Napier Nomad

October 29, 2012 by Matt

Napier Nomad 1 Aero Engine Motor

The Napier Nomad is unquestionably an incredibly complex piece of engineering. Whether it qualifies as brilliant or completely overwrought is more arguable.

Fresh off the success of the Sabre, most notably the powerplant for the V1 buzz bomb killer Hawker Tempest, Napier embarked on another ambitious engine development program, one that eventually led to the Nomad. First tested in 1949, the Nomad was Napier’s attempt to leverage their piston engine mastery and introduce a fuel-efficient alternative to the then-new jet engine technology.

Napier Nomad 1 Diesel 2-Stroke Aero Engine Motor Schematic Diagram Operation Drawing

At least with respect to the company’s goals of creating an economical engine, the Nomad succeeded. To this day, it remains one of the most efficient piston engines ever made when examined from the standpoint of specific fuel consumption, or fuel consumed per unit of power produced. That said, such economy came at a price: An almost Rube Goldberg-like level of complexity. At its core, the Nomad was a 41-liter, valveless, 2-stroke, horizontally-opposed 12-cylinder diesel engine. Around this, Napier added an array of combustion chambers, valves, couplings, clutches, turbines and compressors designed to capture every last bit of exhaust energy in service of turning the twin contra-rotating propellers bolted to the nose of the engine.

Napier Nomad 1 Diesel 2-Stroke Aero Engine Motor Schematic Diagram Operation Drawing

When it worked, it worked: Mounted in the nose of an Avro Shackleton testbed aircraft, the Nomad produced 3,000 hp with exceptionally low fuel consumption for its day. It’s a tribute to Napier’s expertise and persistence that they managed to get all its parts working harmoniously for 1,000 hours of testing.

Unfortunately, the Nomad, like other incredibly sophisticated piston engines of the day, was simply overtaken by progress—new jet engine technology promised much higher speeds with an exponentially lower level of engine complexity, and as for fuel consumption, it was farther down on most customers’ lists of priorities; the lean days of the early ’70s were still over 20 years away. The Nomad found no takers, and fell into obscurity.

Editor’s note: This post is part of an ongoing series examining unique and significant powerplants. Read the other installments here:


Interesting Engines: Mazda’s R26B

October 6, 2012 by Matt

Mazda R26B 4 Four Rotor Engine Motor Le Mans Win 787B

Mazda’s 4-rotor, 2.6l, 700-hp R26B is the only engine by a Japanese manufacturer to win the 24 Hours of Le Mans race outright. In doing so, Mazda scored an achievement that has always eluded such pillars of the Japanese racing scene as Nissan, Toyota and Honda.

The year was 1991, and Mazda had something to prove. Perennially stung by criticism of their signature Wankel engine as an unreliable gas guzzler, the automaker had long sanctioned factory entries into endurance racing series across the globe. And though Mazda had achieved a remarkable amount of success through the years in that form of racing, Le Mans stood as the unconquered peak, the title that would perhaps finally demonstrate, to the racing world at least, that the rotary engine deserved to taken seriously from a competition standpoint.

The ultimate incarnation of a long series of endurance-focused rotaries, the R26B built on the foundation laid by its 4-rotor predecessor the 13J-M, itself a variation of the 3-rotor 20B, and added a number of refinements. At its core, the R26B was a basic non-turbocharged rotary engine, but with racing-derived features like intake ports on the periphery of the rotor housings instead of on the side plates (as in all production Mazda rotaries), an arrangement that produced a great deal of overlap between the intake and exhaust “stroke” of the rotor but which allowed for much greater airflow potential at high rpm, where racing engines live.

Mazda R26B 4 Four Rotor Engine Motor Le Mans Win 787B Diagram Schematic Drawing Cross Section Cutaway

Also, the R26B was fitted with steplessly variable intake runners, able to optimize intake length and thus airflow seamlessly for any engine state, as well as 3 spark plugs per rotor instead of the usual 2, promoting more uniform burn of the fuel-air mixture. The engine was capable of cranking out 900 hp at upwards of 10,000 rpm, but was detuned to “only” 700 at 9,000 rpm to in the interests of durability.

Mazda R26B 4 Four Rotor Engine Motor Le Mans Win 787B Cutaway Drawing

And it worked. Fitted to a durable, proven 787B prototype chassis and driven by the trio of Johnny Herbert, Volker Weidler and Bertrand Gachot, the R26B vindicated Mazda’s efforts once and for all at Le Mans in 1991. Perhaps sweetest of all were the primary reasons for the win: Not power, where it was outclassed by the Jaguars and Mercedes running that year, but fuel economy and durability, two attributes which allowed the R26B-powered 787B to keeping lapping the circuit longer and shrug off failures that sidelined other teams. It’s an amazing engine, and Mazda is rightly proud of their success.

To see 1991 Le Mans winner Johnny Herbert driving his race-winning 787B just last year, click here. It’s a spine-tingling clip.

Editor’s note: This post is part of an ongoing series examining unique and significant powerplants. Read the other installments here:


Interesting Engines:
The Pratt & Whitney R-4360

August 20, 2012 by Matt

Pratt & Whitney R-4360 Wasp Major on stand

I’ll admit it. I’m an engine junkie. Despite not being an engineer by degree or trade, I’m fascinated by the myriad methods pioneers have devised to produce motive power for vehicles. So then, this post will kick off a new series aimed at discussing engines I find particularly interesting.

Let’s go for the gold in the first post: The Pratt & Whitney R-4360 Wasp Major, the largest mass-produced aircraft piston engine ever made. A 28-cylinder, 71-liter, air-cooled radial monster, the ultimate incarnation—the “51VDT”—could deliver a staggering 4,300 hp. Even the first versions of the R-4360 could crank out north of 2,500 hp. Initially “just” supercharged, the final evolution of the Wasp Major incorporated a turbocharger as well.

Pratt & Whitney R-4360 Wasp Major case assembly crankcase pistons

As illustrated above by a view of the engine’s crankcase, the four rows of seven cylinders were offset radially to allow cooling air to reach the rear rows; even so, there were teething problems getting temps under control in the rearmost cylinders. The mixture powering each piston was ignited by two spark plugs per cylinder, meaning a full 56-plug change was a full-day job for a mechanic. Fuel injection was in its infancy during the R-4360’s gestation, so a pressure carburetor (with a concept similar to single-point injection) metered fuel to the engine.

Applications? The Wasp Major powered some of the largest and most potent aircraft of its time, including six for the Convair B-36 Peacemaker, and four for both the Boeing B-50 Superfortress and Northrop’s pioneering B-35 flying wing. More recently, the R-4360 has found success in pylon-based air racing, the re-engined Hawker Sea Fury Dreadnought clinching gold in the Unlimited class at the Reno Air Races in 1983 and 1986.

Perhaps one of the most amazing aspects of the Wasp Major arises not from the engine itself, but from the turboprops and jet engines that replaced it. Consider, for example, that eight R-4360s were necessary to lift Howard Hughes’ admittedly gargantuan Spruce Goose just 70 feet off the water for a mile. And nowadays, a jetliner of roughly the same size and gross weight like the Boeing 777-300 is accelerated to speeds and altitudes unheard of during the Wasp Major’s heyday with just two General Electric GE90 turbofans. It says a lot for the quantum leap in efficiency and reliability that the 777’s engines are arguably less complex than the R-4360 even as they develop an order of magnitude more power. We’ve made amazing technological progress in the past 60 years, but that doesn’t dampen a bit of the Wasp Major’s fascination.

Editor’s note: This post is part of an ongoing series examining unique and significant powerplants. Read the other installments here: