I picked up a 4-1 exhaust manifold at the Stoneleigh show this year – link here: http://parts-shop.westfield-sportscars.co.uk/index.php?route=product/product&product_id=174&search=manifold
Fitting it gave me a chance to investigate a rattle from the exhaust that had cropped up. Initial suspicions were that the catalytic converter was breaking up. With the misfires from the coils dying a couple of times I suspect the lifespan had been shortened a touch. Still surprised it’s this soon though. Took the silencer off and it sounded like it was full of lego. Gave it a little shake and was greeted by these:
First impressions were good, it was a bit of a deeper sound at idle and took the edge off the raspy exhaust a touch.
A week or so later, I took it to the rolling road to see what kind of difference it had made.
I put the figures into excel to make a better comparison. As you can see, it’s largely up on the mid range but as the rev climbs the difference drops and then becomes negative. I think the dying cat is strangling the exhaust somewhat, not allowing the air to flow at high rpm. New silencer required, such a shame! Actually at the time of writing, a Wunoff repackable exhaust is in the garage awaiting the link pipe to be made…
edit: for those researching the manifold, I’ve since replaced the silencer and it drives much better – top end is really opened up. I’ll get it back on the rolling road soon.