Hi
Someone asked me why the tailpipe on the 500/126 is crimped? Something to do with backpressure or aesthetics??
Can anyone shed any REAL reason for this. Some after market ones don't have it.

Good question Tim, but I have no definitive answer. The cross sectional area is almost certainly the same as the main pipe and even if it was bigger or smaller it's not likely to be significantly so. If they wanted to improve performance, with such a short exhaust they might just have made the pipes fatter.
Being an Italian car, I like to think that the reason was simply related to styling. After all, it's a feature that has been mimicked in the modern 500.

I think you are probably right Peter. We have a modern 500 as well and whilst I have obviously noticed it has a flat exhaust tail pipe. I have never put two and two together and realised why until you pointed it out Peter.

The reason for this is by squashing the end of the pipe it actually reduces its cross section area, and therefore increases velocity of the gas flow. This can help performance at different rpm and also helps reduce noise levels.
Well at least thats all i could find on the internet.

"by squashing the end of the pipe it actually reduces its cross section area"...Ah, but does it though?
I'm not quite that sad (nor clever enough at geometry), but I bet it still has the same area in cross-section.
Although stylish, the Fiat 500 mainly sticks to that old design principle: "form should follow function".
I actually believe that it's simply to increase the clearance between the pipe and the rear engine support panel. With a fairly wobbly engine and tight clearances, that's probably saved quite a few cars getting knocked to bits at the back.

You may well be right Peter, but just to back up the theory, this is what i found.
I am no expert on exhaust manufacturing so who knows what the reason actually is for?

You did the math(s). I am amazed that is quite a difference.