The original fuelrail is single feed and quite small innside dimmension which lead to uneven fuel distribution to the injectors:

This is why the number 4 sylinder is most likely the first to experience knock when raising the boost.
This dualfeed rail with a larger bore distributes the fuel evenly over all four injectors.

Fitting it was easy besides a litte accident when taking off the stock rail.
For some reason there was a lot of pressure on the returnline and not the feed line.

I ended up spraying my face with gasoline. Very funny stuff...
I might be a petrolhead but drinking unleaded 98 is not my cup of tea...
The new fuel line plumbing including the split for the second feed line: