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Second winter upgrade: exhaust It's been mentioned to me a few times that my exhaust looked small.. so rude. ...in all seriousness I had been considering this for a while to help the engine pump air more efficiently as is their way. I realise the normal route would be just to get a mandrel bent stainless setup made but I was intrigued that there are so many different combinations of part numbers on Etka for various Mk1-Mk2f Coupe/Hatchback applications; single/twin downpipes, 42.5, 45.5, 48.5, 49.5mm clamps, long/short middle sections, long/short silencer back boxes. Also there are a lot of exhaust parts available NOS from Volkswagen Classic Parts. So I made a spreadsheet of the options then started hunting. The Polo originally had a 895cc HA exhaust: HA single outlet cast manifold > HA combined single downpipe and middle section piece 38mm OD with no resonator or cat > 42.5mm clamp > short silencer I then upgraded this to a 1272 HH exhaust which would have been the largest available on a Mk1: HH twin outlet cast manifold > GK non-cat twin downpipe section (as HH would have had a port from the inlet heater) > 42.5mm clamp > flexible section > 42.5mm clamp > HH long middle section with resonator (as GK would have been too big at the end for my silencer) > 42.5mm clamp > short silencer I then tried the below ending with a Mk2f silencer but it didn't work as I'll come to: HH Twin outlet cast manifold > 3F non-cat twin downpipe section (no inlet heat, no cat, still 38mm OD each but 50:50 pipe join instead of side entry join and goes over flexible section not into it) > 45.5mm clamp > flexible section > 45.5mm clamp > 3F non-cat short middle section with large resonator > 48.5mm clamp (although Etka said it would need 49.5mm) > PY (G40) long silencer I'll go though some photos but where I've ended up is a Mk2 setup essentially: HH Twin outlet cast manifold > 3F non-cat twin downpipe section (no inlet heat, no cat, 50:50 pipe join instead of side entry join) > 45.5mm clamp > flexible section > 45.5mm clamp > 75PS GK long middle section with resonator > 48.5mm clamp > 75PS GK short silencer So it'll run though logically from the engine. The HA was a single outlet cast exhaust manifold with a V-clamp so I'd changed already to a HH twin outlet exhaust manifold. The PY (G40) cast exhaust manifold has very slightly larger twin outlets so has a different gasket between the manifold and downpipe (the same as some Passat) but all PY downpipes are cat so not something I thought I would have space for easily or wanted to do. All other cast twin outlet exhaust manifolds are the same outlet size so I stayed with the HH one. The HA was a coolant heated inlet manifold so had no interaction with the exhaust when I ran it stock or with the twin DCOE40s. Although the HH is an exhaust heated inlet manifold so would then have a flexible section down from the inlet manifold to take the exhaust gas into the downpipe near where the gearbox hanger is I have always run it with the twin Weber carb set up with no inlet heating. So I used a GK non-cat twin downpipe section as GK is also not an exhaust heated inlet engine, this had the two downpipes join by one entering the side of the other then the pipe where they joined going into the ID of the flexible section. I have upgraded this to a 3F engine code non-cat twin downpipe section which also has no exhaust port for inlet manifold heating, no cat strangely (there is a cat version) but notably it has a 50:50 pipe join instead of side entry join and it goes over the OD of the flexible section not into the ID of it so has a larger clamp. In the photo below 3F is top and GK is bottom. When I put the HH exhaust on I used a stainless braid flexible section as it was much cheaper than the corrugated original type ones I could find at the time. This time round I located the corrugated type (direct from Volkswagen Classic Parts actually during free-shipping Black Friday) but it's worth noting that the cat downpipes don't need these and the 3F/GK engines state a different part number but they are all the same part. The only difference is that 3F/GK parts clamp to the outside of the flexible section and others go inside the flexible section hence the smaller clamp. The HA engine middle section goes all the way from the single outlet cast exhaust manifold as a single 38mm OD pipe to the silencer back box and I'd been using a NOS VW back box which connected using a 42.5mm clamp. When I changed to the twin downpipe I used a HH long middle section with resonator which used a 42.5 mm clamp at either end. For the new arrangement I have used a 75PS GK long middle section with resonator which is over the OD of the flexible section so a 45.5mm clamp and then has a short engine specific silencer back box which uses a 48.5mm clamp. The below photo shows the difference with the HH going into and the GK over the middle section. In the photo below GK is top and HH is bottom. Prior to the final arrangement I had tried using a PY (G40) silencer back box with a 3F non-cat short middle section with large resonator. Unfortunately whilst the combination of short middle and long silencer did the same job as a long middle and short silencer in terms of lining everything up \9e.g. the rear axel dip) the rear valence got in the way. The rear valence of a Mk1 curves around quite a lot compared to the mostly vertical Mk2 and the Mk2f which benefits from a larger bumper too. The space between the rear axel dip and the mounting bracket is the same for each but the Mk2f's larger tail pipe takes up more space making its curves and also has almost no downward drop so the silencer box itself pretty much touched the rear valence even if the tail pipe was totally chopped off. The Mk2 GK silencer back box had a decent downward drop on the tail pipe which was similar to the Mk1 silencer back box but clearly the pipe was still bigger taking up more space past the exhaust hanger point where the rear valence curved into. In the photo below the PY is top -eft, GK is bottom-right and Mk1 is bottom-left and top-right. The photo below better shows the vertical drop on the GK tailpipe where the PY had almost no vertical drop. It all also shows that to fit the GK silencer back box I had to move the mounting bracket 1" back to allow for the larger tailpipe inside the rear valence. A friend removed this and tig welded it in place for me which turned out great and it sits happily in the Mk1 valence hole. The eagle-eyed amongst us will have spotted more progress with another winter upgrade but for now, Merry Christmas!