exhaust collector on Fiat 1.6 sohc

[fiatuno]

exhaust collector is 4-1 flat type 0000 in one outer diameter 60
i hawe now exhaust pipes outer diameter 35cm on Fiat 1.6 liter sohc engine
my exhaust valve is 36mm diamete
the car is equiped with 302° camshaft and racing springs and dellorto dhla 45 carbs with 40 chokes
compresion ratio is by my calculatio aproximatly 13,7/1
my car is now for drag race in sonner future will be for relly when put the 314° camshaft

my question is which should be the inner diameter of exhaust pipes
now is outer diameter 35cm inner is 33,4
i hawe read that the inner dimensions of exhaust pipes must be the exhust valve + 5mm
that means that inner dimension shoul be 40mm
is thath true?
will i get better or worser with that dimensions?
i had also read that with to larger diameter will lose
will i get more power if i do larger pipes on the collector?
will i get better risponse?
what should i do?

thanx and best regards from Dorian

[Acki]

13.7:1 is very very high?! What fuel do you want to drive?
About the manifold, look at GC's engine. Here is a thread about a engine where you can see a good working exhaust manifold.