On really cold days, sub zero, when the injection system is running very rich, it stinks.
But once upon a time all cars smelt like that on cold days.
Rusty bolts, 2 of the header bolts were rusty.
On one I had to use a bolt-extractor hammered on to it, the head was no longer a hex, just a rusty nubbin.
Performance wise, I think it is a bit quicker, but the real difference is throttle response and gear change.
I can now blip the throttle on down changes and instantly match engine speed to road speed.
Up changes can be made equally instant.
It also back-fires a lot, I’m suspicious I fire flames out the back on occasions on over-run over 5krpm, but that does seem to deter tailgating.....
You will need ear-plugs, it is LOUD.