What is a good diameter for quick spool on the up pipe of a standard TD05 turbo running mid 300 bhp ?

Does this Up pipe look to fat of a bore size ? I notice is narrows at the turbo end, so having a big bore then narrowing, would that make it a good up pipe ?

I know its hard to tell from a pic but this one looks a bit on the chubby size, now wanting quicker spool I don't want to swap my standard up pipe for a laggyer one

cheers

 

cant tell from a pic but the design is ppor at best regardless of size / you need a Harvey Smith 'trick' up-pipe custom made to suit the job.............

no ideas who you could possibly be the sole manufacture of them mind

 

Ha not biased much lol

Why is it a poor design ?
I thought the wider bore to start with allows for large flow yet as it narrows reduces pressure to aid spool ? I'm no expert tho lol , haven't had chance to measure bore size yet

 

there is no expansion joint for a start and if it was the correct size there would be no need to crudely taper it at the top........