DKW two-stroke motors require a finely tuned exhaust to provide optimal performance. The prewar F7 and F8 exhaust system was basically a straight through pipe, after making a 90 degree turn out of the engine. The company's engineers invested a lot of effort in designing the F9 exhaust system in 1939, consulting with two specialist exhaust tuning companies. In the postwar period, the exhaust system of the F89P Meisterklasse, which was powered by the same twin cylinder engine as the prewar cars went through several changes which progressively improved engine performance. After making the 90 degree turn out of the engine, the exhaust passed through a large dead-ended cylinder which bounced the pressure wave back towards the engine, before passing through another long straight pipe to the back of the car. An expansion chamber was later added under the driver's seat and later an expanded silencer at the end of the exhaust pipe.
The F93 exhaust system expanded and improved on the F89P's system. After leaving the manifold, the exhaust turns though a 45 degree expansion chamber, before moving on to a second, larger expansion chamber mounted under the driver's seat. Alarge, specially designed silencer was mounted at the rear.
Shortly after I purchased the car in 2012 I noticed the rear silencer was looking pretty shabby. Rot holes were beginning to appear in the silencer and it was weighed down with a built up carbon and oil.
When searching for a suitable replacement, some fellow DKW owners recommended a sports exhaust manufactured in South Africa. The exhaust was said to provide an increase in speed and performance.
The sports exhaust was basically a straight through pipe. Once I had it fitted I observed that it provided excellent performance for freeway driving, giving an uplift of about an extra 5 miles an hour. However, this came at a considerable cost. Most of my driving is done on suburban streets at around 40 to 50 miles an hour and it really wasn't suited to that power band. The engine ran really rough at a lower speeds and, most importantly, the un-dampened exhaust note was quite deafening!
After a few weeks of driving I had the sports exhaust removed and replaced with it a modern exhaust. This substantially reduced the exhaust noise and generally performed okay, but the engine and exhaust continued to vibrate a lot and performance at speed dropped from a comfortable maximum speed of 75 miles per hour to around 65 miles per hour. It was time to go back to an original style exhaust.
After these two unsuccessful trials, I decided to obtain an original silencer. I eventually obtained a NOS exhaust from Germany from Ralf Muller (info.ralf.mueller@t-online.de), who has a great stock of original spare parts for most DKW models. Gary from Custom Exhaust Specialists in Osborne Park fitted the exhaust (http://customexhaustspecialists.weebly.com/). The difference in performance between a clean, original exhaust, with the modern and sports exhaust was amazing. The exhaust note is extremely quiet again, top maximum speed has been returned and the vibration and rattling in the exhaust system has stopped.
Original rear silencers are expensive and hard to find, but they are worth the investment. Reproduction exhaust systems can be purchased from DKW Klose https://dkw-klose.de/Abgasanlagen/
Similarly, I also tested a modern air-intake filter and noticed similar performance challenges. It did increase the airflow and gave the engine a lot more get up and go, but the loss of the steel dampener around the intake resulted in an unacceptable increase in engine noise. If I were rallying the car, it would be an option but not for general driving.
The engineers at DKW really knew what they were doing.
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