Stepping up exhaust pipe sizes

I am building my own exhaust system and I was wondering if anybody had some experience on this. I'm installing a 400hp 383 V8 and will be using 2 1/4 pipes true duals from the header for about 2 feet then 2 1/2 pipes to a 3 inch dual muffler. Will that be sufficient?

 

^^^^
Yes,
Duel 2-1/4 inlet muffler to 2-1/2 single outlet would be big enough, ""tube/pipe size.""as long as you merge properly,
The muffler construction / internals will determine if restrictive,

 

2.25" all the way out would be sufficient for that motor. Agreed that mufflers and crush bends will do more to determine restriction.

~Peter

 

More then sufficient I'm sure.

 

While you're at it you may as well get yourself some electric cutouts you'll never regret it!