Zbrojovka Z 6V

The Zbrojovka Z 6V is a racing car that was produced from 1927 to 1929 by the company Zbrojovka Brno. It was the first Czechoslovak car equipped with a supercharger. The new Z 6V was nicknamed "the Inferno" for its stunning roar and plumes of smoke from its supercharged two-stroke engine.

History
After the victory of the Brno-based Zbrojovka Z 18 Sport in II. year of the race at the Pradědský circuit near Karlova Studánky on June 19, 1927 (class up to 1100 cm3) started by a graduate of the Brno Technical University, Eng. František Mackrle (constructor in Zbrojovce since 1924, since 1928 as construction manager) to work on a real racing engine for a racing car that would bring more success to the company. Mackrle turned to prof. Ing. Josef Kožousek from Brno technology, who helped build the new engine, and thus a two-stroke in-line turbocharged six-cylinder with counter-rotating pistons was created, similar engines were produced by, for example, the German company Junkers (they, however, usually used diesel as a drive). The car with this engine had promising results. The Z 6V reached a top speed of around 175 km/h and had very good acceleration, but also had many problems such as a tendency to burn through the bottom of the pistons controlling the exhaust port. Therefore, the car was not at all suitable for long and demanding races. The car racer Bedřich Soffer was supposed to help solve these problems. who was testing the car before the Ecce Homo race, which took place on September 16, 1928. However, during a test drive on September 5, Soffer crashed and did not survive the accident. Ing. Mackrle took this tragedy very personally. He was already very embittered by the tragic accident of his friend Čeňko Junko in the summer of the same year at the German Nürburgring. The death of Bedřich Soffer led Ing. Mackrle to resign from the position of chief designer in Zbrojovce. He went to Škoda plants in Pilsen, where he worked until the occupation.

In some sources, this Z 6V racing car is referred to as the Z 2 with the M 2 engine.

Technical description
The 6V was a two-seater sports-racing car. The M 2 engine developed in 1927 was located at the front and the car had rear wheel drive. It had a two-stroke inline six-cylinder engine with counter-rotating pistons with a cylinder displacement of 1085 cm3 (bore 48 mm, stroke 50 mm, i.e. total stroke of both cylinders 100 mm). In the construction of the engine, the designers of the Czech Republic Armory in a bold, even pioneering way, the engine did not have a cylinder head. The engine block was equipped with two crankshafts connected by a toothed gear, allowing the intake and exhaust to be controlled by the edges of the pistons with a small offset. The pistons in the upper dead center defined the combustion space against each other. The fuel mixture, ignited by a dozen Champion spark plugs connected to two Scintilla aviation magnetos located transversely by the flywheel, was prepared by two Zenith TD 30 triple-diffuser carburetors. Impingement cooling of the engine with liquid with forced circulation. Supercharging by two vane compressors mounted on either end of the upper crankshaft (originally Zoller vane compressors, after a later conversion two Roots compressors were used). The oversized Zoller supercharger characteristically ran through the front and protruded in front of the radiator.

With an output of 55 kW (75 hp) at 5500 rpm and a three-speed gearbox with reverse gear (3+Z), the car reached a maximum speed of 175–180 km/h. The car was powerful, but had an unreliable engine with a tendency to burn pistons. The spark plugs and pistons of the engine were very difficult and reluctant to cool, and usually after some time the pistons burned out. So the car raced mainly on short tracks.

The body was made of aluminum sheet on a wooden frame. The chassis had a rectangular, ladder frame design that was riveted from pressed steel U-sections. The solid-axle car was suspended by longitudinal leaf springs and Hartford friction dampers. The wheels were Rudge & Whitworth wire and the brakes were mechanical, drum with balancer. The wheels were fitted with 4.95x28 tires.

Competition history
According to not entirely confirmed reports, the engine of this Z 6V car was supposed to have been used for the first time already at the 2nd year of the Praděd Circuit (June 19, 1927). The Zbrojovka Brno factory team started with three cars. Rychard Müttermüller won the laurel in the category up to 1.1 l, which was run for 10 laps (224 km) for Zbrojovka from Brno in a time of 3:06:15.7 h. Zetka's success was also completed by the third place of Maj. retired, Karel Stohanzl (racing from that date under the pseudonym "Flieger", which he chose as a former military pilot in the Austro-Hungarian army) and the sixth place of Bedřich Soffer, who drove the fastest lap of the class in 18:10.9 min. All armorers rode the Z 18 Sport type, however, Soffer's car was to be fitted with the new Z 2 engine. It was a 1085cc two-stroke turbocharged six-cylinder with a displacement of 1085 cc, designated M2, and this engine was later fitted to the Z 6V sports-racing special. Soffer finished in 6th place, although in the 3rd lap he rammed into Káš's Imperia, which skidded and remained standing across the road. Soffer saved himself by braking hard, the car went into a skid, and his front tire burst. The repair cost Soffer 3 laps that the others missed. He finished the race more than 65 minutes behind the winner.

The first truly confirmed start was participation in the 5th year of the ČAMS (Czechoslovak Automobile Club for Moravia and Silesia) club race to the Brno-Soběšice hill (May 13, 1928). The race had a certain "sensation" when cars from Zbrojovka from Brno won in 3 categories. The latter sent to the race one Z 6V car with a six-cylinder, two-stroke engine (M2) with a displacement of 1085 cm3 with two compressors (Bedřich Soffer) and also 2 two-stroke two-cylinder cars with a Z 4V compressor (Rychard Müttermüller and Karl "Flieger" Stohanzl). Although these cars had not yet completely left the trial stage and were sent to the race, one might even say experimentally, they managed to win for the first time in the hands of excellent drivers. In the category of racing cars up to 1.1 l, Soffer won without competition in his category and even set a new track record for this class in a time of 2:53.6 min. Third place in this class was taken by Leo Karger on Zetka. "Flieger" with Müttermüller took the first two places in the class of sports cars up to 1.1 l on the Z 4V (M6 engine - two-piston two-stroke two-cylinder, longitudinally doubled, displacement 0.995 l, max. output 34 kW/46 hp). "Flieger" broke the record for this class with its performance. The success of Zbrojovka was completed by the first 3 places in touring cars from 18 to 1000 cc, where the drivers behind Zetky occupied the podium in the order of Karel Divíšek, Jar. Najman and engineer Václavíková-Zichová. Until III. year of the Praděd circuit (June 3, 1928) Zbrojovka sent 7 riders, most of whom drove new six-cylinders with Z 6V compressors or two-cylinders with Z 4V compressors. Karl "Flieger" Stohanzl already looked like a certain winner on Zetka. He was still leading after the 10th lap, with only two laps to go. Here he was caught by a breakdown, which eliminated him from the fight and cleared the way for Liebig to win at Amilcar (12 laps/268.8 km). This category had a serious accident. Soffer skidded in a corner, smashing the car and also smashing two spectator motorcycles with the back of his car. His mechanic suffered a broken leg. But strangely enough, the drunkard, who was sleeping almost at the very spot of the accident, escaped unscathed, and apparently only woke up when the entire accident had already taken place, Národní listy wrote. Fr. Liebig in an Amilcar won in 3:38:35.8 min ahead of Arnošt Procházka, Josef Mamula, Vodička and Karel Divíšek in Zetky (2nd-5th place). The honorary award of the Ministry of National Defense for the fastest lap (in the 3rd lap) of a Czechoslovak-made car was awarded to Leo Karger in a Z 6V, which he drove in 16:03.7 min (82.2 km/h). Of the seven armored vehicles at the start, 5 were classified.

The race (VIII open race to the Schöber hill) took place on June 17, 1928. 46 vehicles were entered, of which 40 started and 38 reached the finish line. Of the Czechoslovak factories, only Zbrojovka Brno officially participated in the race. In sports cars up to 1.1 l and in the category of sports cars of all classes, Karl Stohanzl on Z 4V won in a time of 3:13.6 min and in racing cars up to 1.1 l, Josef Mamula won in 3:15.6 min on Z 6V and won the Schöbru silver cup.

For the 5th year of the national race to the Knovíz-Olšany hill (June 24, 1928), 39 machines came to the start, including 21 motorcycles, 6 sidecars and 12 cars. In racing cars up to 1.1 l, Bedřich Soffer won at Z 6V in 2:37.4 min, and in sports cars up to 1.1 l at Z 4V, Josef Mamula, who broke Soffer's record at Sénéchal from 1927. Overall, the Junks won the race. Both started in Bugatti racing cars under 2 l: Čeněk in 2:08 min. and Eliška 2:13.5 min. That was Ceňko Junko's last winning race before his tragic crash at the Nürburgring.

After a one-year break due to track repairs, on April 28, 1929, the 12th edition of the international race to the Zbraslav-Jíloviště hill attracted 100,000 spectators. This year also brought new records in a number of categories. In sports cars from 750 to 1100 cc (category G), Karl "Flieger" Stohanzl won at Z 4V in 3:52.4 min and at the same time set a category G record, for which he received a crystal cup from the organizer of the event (AKRČs.). Anton Kahle with the Z 6V also won in his class of racing cars up to 1100 cc, also in the category record.

Brněnská Zbrojovka commissioned engineer Vladimír Souček, who joined Zbrojovka on January 1, 1929 (after the departure of engineer Mackrle), to rework the Z 6V and prepare it for the sports car race at the Grand Prix of the Sports Car Nations, which took place at the German Nürburgring on July 14, 1929. The Z 6V was lowered, the engine was moved a bit back (the compressor no longer "peeped out" in front of the radiator), the suspension of the axles and the brake system were redesigned. It was fitted with dual Bosch magneto ignition, new Roots superchargers and the stressed pistons were cast with a copper cooling liner. In the class from 750 to 1500 cm3, Ernst (Arnošt) Procházka-Karel Divíšek started in a Z 4V (st. no. 50) and in 2 Z 6V cars Karl "Flieger" Stohanzl-Anton Kahle (st. no. 54) and Josef Mamula (st. no. 56). The race lasted 18 laps, i.e. 508.77 km. The factory driver Karl Stohanzl led his category for almost the entire race, but in the penultimate lap he blew his pistons again. Josef Mamula with the second car heroically finished with a dislocated gimbal bearing (loose joint shaft bearing) which prevented him from shifting gears, and all wet with hot oil in second place in the category, but unfortunately after the time limit, so he could not be classified. Karel "Tunal" Divíšek finished third in Z 4V, but due to a defect also after the time limit, so nothing.

According to other sources, Stohanzl finished with a blown piston but after the time limit and Mamula dropped out after lap 4 with a gearbox fault. Be that as it may, the failure was felt by Zbrojovka's board of directors so strongly that it immediately sold both Z 6V cars to private individuals and intended to abandon racing activities for good. After the failure at the Grand Prix of Nations at the Nürburgring and also after the tragic accident of Bedřich Soffer, Zbrojovka stopped the entire Z 6V/Z 2 and Z 4V project. Zbrojovka sold the produced prototypes to private riders. On September 22, 1929, Karel Divíšek in his blue Z 4V won the category of racing cars up to 1100 cm3 in the race to the Ecce Homo hill and at the same time set a track record for this category. Divíšek was basically the initiator of the creation (in 1930) of subsequent Zbrojovka racing cars with the engines of engineer Vladimír Souček M8 (Z-S30) and M15 (Z13 or Z 14).

The 6V without an engine was sold to Antonín Beránek, who gradually installed six different engines in it and raced it on circuits and uphill races, but without much success. Gradually, the car was converted again to BZV6 and was equipped, among other things, with a Vauxhall K14 engine. His biggest success with the built-in Bugatti engine was second place in the under 1500cc class, respectively sixth place in the racing car category (19th overall) in the 1936 Ecce Homo hill race. On September 5, 1937, E. Laufka took 2nd place in racing cars at the 17th Ecce Homo in Šternberk with this machine, behind Florian Schmidt in a Bugatti T51A, but ahead of Bruno Sojka (Bugatti T37A).

Literature

 * Popelka, Jan, Petr Cincibuch. S písmenem Z na chladiči. Praha: UNIUM, 1999. ISBN 80-902542-2-5
 * Skořepa, Miloš. Dějiny automobilových závodů, Praha 1973: Olympia, s. 320, příloh 88
 * Kuba, Adolf. Automobil v srdci Evropy, Praha 1986, NADAS, s. 312, S.118-124
 * Šuman-Hreblay, Marián. Encyklopedie automobilů, Brno/Praha 2018, CPres v Albatros Media, s. 272, S. 202–206, ISBN 978-80-264-1852-8
 * Tuček, Jan. Auta První republiky, Praha 2017, Grada Publishing, s. 356, S. 89–93, ISBN 978-80-271-0466-6
 * Popleka, Jan. Automobil "Z" Českolovenská Zbrojovka a. s. Brno (Autoalbum), Brno 1988, 735. ZO Svazarmu při pedagogické fakultě Univerzity J.E. Purkyně, s. 67