Will I gain any bhp by fitting a fuel pressure regulator before my car gets mapped? I dont mean fitting it and hey presto, 10bhp. I mean will the mapper be able to get more out of the car with it fitted than just leaving the standard one in?

I am also fitting a Walbro and 550cc's

 

Sorry, but NO, you won't get any more power from fitting a fuel regulator, unless a lack of fuel is restricting you in the first place.

If you're fitting an up rated fuel pump, & 550cc injectors, and you're only running a VF28, you have way more fuel available than the turbo is capable of producing power.

Fit a 400bhp + turbo, and it may be a different story.

 

It'll be a VF35 thats going on it