Just after a few opinions..... I dropped my mk R1 2006 off at powerspeed exhausts kent to have a full system made up. Dave gave me an option of using a larger 1.75" pipe instead of a standard 1.5" pipe for the manifold and 4-2-1 collector simply for the look I think there was a cateringvan being done when I was there and looked very nice

Dave said theoretically it should affect bottom end, but has done a few bike engines and said this doesnt happen.

Then I also thought about the weight aspect although only slightly increase I would imagine. So what do people think keep with the 1.5 or the 1.75" dont really want to make an expensive mistake.

How confident is he that this doesn't affect power? Does he have dyno data, or is it just a "seat of pants" estimate.

What I mean is all R1's feel fast!

When I looked at the tables when making my exhaust using 1.5" primarys was the indicated size for an 893 blade engine but you could not get enough length in the system to place the collectors correctly.

I would follow his advise as increasing the size allows shorter lengths to be used although not ideal its all compromise.

I would go with the bigger size.

Dave Parris knows what he is talking about.

Bigger It is, Dave seems a top bloke cant wait to have her back though