Now HDI's have got a Catalytic Converter but they are known not to be needed on these cars as they do not produce enough emissions to fail the test at an MOT even without one being in the exhaust.
However if the car was fitted with one standard then you still need to technically have one.
There are 3 types of exhaust setup that I have often seen for the 306 HDI. I will start at the cheapest and work upwards.
Modified Stock Exhaust £10-60
This is the cheapest possible way to get a free flowing exhaust on a 306 HDI.
What people tend to do on 306 HDI's is smash the cat out of the box it is in and then put the box back on the car. This basically involves taking off the catalytic converter and then shoving a peice of wood or metal bar through the centre of it to break the cat out. It creates a free flowing cat but wont increase the size of the exhaust. It can sometimes also cause turbulence in the exhaust pipe as any left over parts in the box will cause the air to swirl and buffet.
Once the cat has been smashed out the next part is the centre silencer. Most people remove the centre silencer on the HDI's and then just weld a piece of straight pipe in its place. This does the job really and will free up a little more flow.
Finally is the back box. Now this is the harder part to do on the cheap. The common way people seem to do the back box is either to take the regular centre section and put that in place of the back box. Or to just put a straight through pipe in it's place. The first way would need quite a bit of welding work and aligning to make it look neat. The straight pipe will often make the car quite loud but not overly stupid really.
Custom off the Shelf Exhaust £180-£230
The next cheapest option is to buy the exhaust parts off somewhere like eBay. On the 306 HDI there are 3 sections, the catalytic converter, the centre section and, the back box.
You can find on eBay a straight through replacement for the catalytic converter. If you search for "Peugeot 306 HDI Exhaust De Cat" you will get a big list of parts. The most popular one looks like this and is a straight fit for the original position. It costs around £50 and will fit in the original catalytic converter place.
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| 306 HDI De-Cat Pipe |
The next part that you would need is the centre section. Now as standard the 306 HDI centre section is not that restrictive anyway but replacing it will still gain a little bit of extra flow and performance. The centre section will cost about £40-£55 and can also be bought on eBay.
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| 306 HDI Centre Pipe |
Finally is the back box. This part on the HDI is known to be really rather restrictive as it has lots of baffles in it. You can find a few different back box's on eBay, Most of them are made by sportex. They would free up quite a lot of flow and will lower the RPM that the turbo spools at. You can also keep going up though the revs and the engine won't feel as restricted. They can be bough for around £90-£110 and are a direct fit.
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| 306 HDI Back Box |
For the perfect exhaust and best performance and look you can go for a fully custom exhaust. You can specify the size that you want and what sort of metal it will be made out of (Although Stainless Steel is always recommended) Usually people aim for around 3" and as straight through and free flowing as possible. This helps to spool the turbo up sooner and releases the potential of the turbo at high rpm and high flow situations. They are costly but if you want to do it properly then they are the best option so long as you go to a good reputable manufacture such as Miltek or Powerflow. They can be tailored to your needs and you can specify how many silencers and what type of back box you would like which makes it very easy to get what you want.
Thanks for Reading,
Jack
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