Modifying Volkswagen engines is not new; indeed most of what we do now is a progression from what was happening in the '50s.

For Volkswagen, speed was never a consideration above normal traffic and cruising. The Beetle was built to transport its occupants from A to B reliably and efficiently. For many years Volkswagen felt it unnecessary to increase the power of the flat four.

Naturally some people can't help themselves. Even Porsche continued to tinker with the design. There were many backyard devised techniques and modifications, some more reliable and effective than others. There were many, many VW engines cooked in the early days of VW modification, as indeed today, from failed attempts at squeezing more out of the little air cooled engine.

There were 3 methods available for getting more power from the VW engine:
* improving the carburetion
* supercharging
* increasing the combustion size of the engine

Improving the carburetion and supercharging were the most popular as they didn't involve completely tearing down and rebuilding your engine. You could of course, use all three methods for a truly massive increase in power.

Improving Carburetion

The most simple and common option. A simple bolt on job using two or more carbs, the only difficult part is balancing the carbs. The stock VW engine used a single carburettor to supply all four cylinders thru a single inlet manifold. Supplying the air/fuel mix to four cylinders can restrict power and when coupled with the tendency of air/fuel vapour to freeze when the air is cold and when moving through the four bends between the carburettor and the inlet valves on the heads the potential of the engine is greatly reduced.

Using a carburettor on each side of the engine reduces the distance that the air/fuel vapour has to travel and reduces the amount of bend that it has to travel through. Dual carburetion also increases the amount of vapour available to each side of the engine. This alone could theoretically increase the power of the 34hp engine to about 44hp.

Supercharging

Another bolt on option, the most common of these was the Judson supercharger.

Natural aspiration relies on the air/fuel vapour being sucked into the combustion chamber by a vacuum created by the piston, as it moves away from the head on its downward stroke. This method fills around 80% of each cylinder.

A supercharger is basically a pump driven by engine rotation which forces the air/fuel mix into each cylinder until it is 100% full. More fuel equals more power. Superchargers could boast a 20hp rise in power out of a 34hp engine to 54hp at 4000rpm, increasing the power output close to that of a 1600cc.

When a supercharger can increase the induction to over 100% it makes the engine act as if it has a much larger capacity. As the engine is then able to burn more fuel, it will produce more horsepower - with a significant increase in torque at lower rpm.

Increasing the combustion size of the engine

The standard engine uses a 64mm crank; this means that that pistons will move by 64mm from top to bottom (swept volume). Increasing the stroke to 69.5mm gives a swept volume of 1293cc. More space to put petrol and air vapour.

Oettinger (Okrasa) and Denzel pioneered the naturally aspirated approach with stroker cranks, dual port cylinder heads and twin carburettors, while others such as Shorrock and Judson went with supercharging.

Throughout this series we will look at the kits produced by these four.

Okrasa

There are many people who do not know what an Okrasa motor actually is. Even people who have been around Volkswagens for years.

Gerhard Oettinger founded Oettinger Kraftfahrtechnische Spezial Anstalt in 1951. They specialised in performance parts for the VW engine. They later began producing body kits and suspension parts. Many Oettinger specialty parts found their way into later factory VW engines and cars. Some of the VW based coachbuilders such as Dannenhauer & Stauss and Rometsch were using Okrasa engines to give their cars a sportier performance.

The Okrasa kit beefed up the engine with dual carbs, special cylinder heads and pistons. The Okrasa engine was the racecar engine for its day. The Okrasa engine could get a VW as fast as 87 mph, compared to 76mph. The acceleration from 0-60 improved by three seconds. Horsepower on a stock VW is at 36HP at 3700rpm, while the Okrasa was 46HP at 4500rpm.

There were two Okrasa kits available, the TS-1200 and the TS-1300/30.

The TS-1200 used a pair of Okrasa high compression twin-port cylinder heads with twin port manifolds, dual Solex 32PBIC carbs as used on early Porsches, carb linkages, balance pipes etc. Optional extras included a Fram oil filter, which could be mounted on the fan housing and Okrasa's own oil cooler - coiled copper tubing behind the fan housing. The new heads offered a compression ratio boost from 6.6 to 7.5:1.

The TSV-1300/30 Kit was much more complete, it came with the same parts as the TS-1200 but also included a 69.5mm chrome-moly crank which gave a capacity of 1295cc. The crank was also '8 doweled' to the flywheel. Clearancing was required with the stroker crank.

In 1956 EMPI started importing the Okrasa kits into the US and advertised them as increasing the HP from 36 to around 48 with "No sign of overheating reported, even in desert"

In 1960 the "40hp" engine was introduced. With it came a new, longer crankcase. Okrasa followed suit with "40hp" versions of their parts, but by that time, others such as Gene Berg were beginning to make their mark and they ceased development of new products for this engine

"Of all the various engine conversions available to the Volkswagen owner in the 1950s, the Okrasa TSV-1300 was probably the best engineered." - Keith Seume

Denzel

Wolfgang Denzel was an engineer and motorcycle and sports car racer who turned his hand to making cars primarily from VW mechanical components. As production increased he used progressively fewer VW parts. Most major mechanical components of his engines (except for the two-piece VW crankcase) were made by or for Denzel, including cylinder heads, intake manifolds, pushrods, rocker arms, pistons and cylinders, con rods, and crankshafts.

Denzel built 1100 cc, 1300 cc and 1500 cc engines. Two of each size were built, an entry level and an increased HP model. In 1953 the low power "Seriensuper" model was 1281cc with 52 HP, the Super International was a 1290cc 64hp unit. He also produced a complete kit to convert a VW engine to a highly modified unit with Denzel mechanical components including crankshaft, rods, pistons, cylinders, heads and manifolds.

The components were of much better quality and more expensive than Okrasa. In 1958 EMPI began importing Austrian Denzel products because Denzel machined their parts from aluminium alloy making them the 'Swiss watch' of performance parts. Like the Okrasa heads they were dual port, however they were expensive and today are highly prized by collectors.

Since 1880 the Judson Family have been involved in engineering. From farming machinery through to electronics for the defence and automotive industries. The Judson Supercharger was a spin-off from a small interest in producing custom made racing superchargers. Production superchargers were developed in the late '40s starting with a sliding vane supercharger for the famous Ford Flathead V8. In 1956 a version was produced for the VW. The popularity of the supercharger required a new factory to fill the demand. Judson made two versions of the supercharger for the Volkswagen. The first for the 30/36hp engine and another for the 34/40hp.

Volkswagen designed the flat four with restricted breathing that limited power but produced a low stressed, long lasting engine. The supercharger compresses the air/fuel mix from the carburettor with series of sliding vanes located on an eccentric hub. As the hub rotates the vanes are thrown outwards and seal the supercharger, pressurising the vapour and forcing it into the intake manifold overcoming the restricted breathing of the normally aspirated engine.

The sliding vane supercharger used by Judson provides boost only produced when it's needed. The vanes are closed and producing boosting only when the throttle is open. At cruising speed the manifold pressure is near normal despite the fact that the vanes are still rotating. This reduces wear, fuel consumption and heat.

A pair of drive belts run off a special crankshaft pulley to drive the Judson supercharger. The original generator drive can still be used. The blower is mounted on top of the standard inlet manifold, with the original Solex carburettor then fitted to the inlet side of the supercharger. Part of the Judson set-up is a lubrication bottle. It supplies a feed of oil to lubricate the vanes of the supercharger and is burnt with the fuel mixture in the combustion chambers. The oil also acts as an upper cylinder lubricant.

The Judson Supercharger doesn't over stress the engine; it increases the torque without increasing the revs, creating power where it's of most use. This makes for a more efficient and better-lubricated engine.

Fitting the Judson kit is simple. A few hours and everyday tools. The engine requires no disassembly or removal. The supercharger, oil bottle and drive pulley are bolted on, the carburettor jetting changed (jets were supplied with the kit) and the fitting of a stiffer fuel pump spring.

The Judson's only drawbacks were increased mechanical noise at low rpm, higher temperatures and slightly increased fuel consumption. The oil container also required refilling every 1000 miles.

The Judson Supercharger is now much sought after and expensive.

"There have been many ways to improve the power output of the early Volkswagen engine, one of the most popular being the Judson Supercharger" - Keith Seume

Shorrock

Shorrock had been supercharging all types of engines on cars, planes and boats since 1937. The Shorrock VW supercharger appeared around 1960 after designs by Arnott and Judson. Shorrock adapted its C75B blower to the VW, which had been used since 1955 in Austins, Fords and Morrises, creating the Shorrock C75 BV. Designed for engines up to 1300cc it could provide 750 cm3 per revolution.

In contrast to other supercharging solutions for Volkswagens the Shorrock used rubber hoses between the intake manifold and the head ports. This made the unit very versatile as the manifold could easily be extended in length to suit all VW engines with differing distances between the cylinder head ports. The blower was bolted to the fuel pump studs, which then required the use of an electronic fuel pump. A side draft carburettor was also required with this kit. The body of the unit was also made from much lighter aluminium rather than steel.

The famous EMPI Inch Pincher (EMPI had a commercial alliance with Shorrock for the VW blower) used the Shorrock Supercharger on the 220 HP drag bug. Using a 1:1 pulley ratio and stable to at least 8,000rpm the Shorrock proved itself and still has never been equalled by a vane style supercharger.

The Shorrock Supercharger could well have been the greatest kit for the Volkswagen. The detail in its finishing and the quietness of its operation along with its strength and quality were beat only by price and the skilful marketing of the Judson Supercharger. The Shorrock company suffered a serious cash flow crisis after a disastrous internationalisation, the emergence and adoption of turbo-charging and the abandonment of supercharging by its main clients (MG, Austin, Rover) killing off forever the Shorrock Supercharger for VWs.