Bore out/tune stock exhaust manifolds ?

[Racer57]

 Growing up and talking to my areas respected engine builders always told me that intakes need a semi rough surface to help atomize the fuel and that if stock manifolds are used they need to be polished to allow gases to escape faster. Anyone messed with this ?

[Chryco Psycho]

Always , no engine I have ever built goes back together stock !!
Port matching to gasket size , raising the port roofs narrowing the valve guides & working the bowls excessively , as well as modifying intake & exhaust manifolds are just std proceedure , why not get the most out of any engine build , they cost enough to build , might as well get 100% of the power !
I never lower the floors or smooth them a rough floor can trap liquid fuel allowing it to atomize before entering the cylinders .

[torredcuda]

My road runners 383 is built for power while looking 100% stock so I`m modifying the intake and port matching and smoothing the exhaust manifolds as deep as I can. Extrude hone is another option but I don`t think it`s cheap and heard there is a possibility it may crack old manifolds.

[redgum78]

Growing up and talking to my areas respected engine builders always told me that intakes need a semi rough surface to help atomize the fuel and that if stock manifolds are used they need to be polished to allow gases to escape faster. Anyone messed with this ?

No doubt match porting and a good port job make a big difference.

I think the semi rough finish on the intake to help atomize fuel is a bit of a stretch. Be good if anyone could provide hard data on this one. I have heard it before but always had my doubts. 

[Chryco Psycho]

I would agree with leaving the floor rough as the liquid fuel can drop out of the air flow .
I use a very unique trick inside the intake ports that is hard to describe , maybe I can draw it out & take a picture of the port work I use

[fc7cuda]

My road runners 383 is built for power while looking 100% stock so I`m modifying the intake and port matching and smoothing the exhaust manifolds as deep as I can. Extrude hone is another option but I don`t think it`s cheap and heard there is a possibility it may crack old manifolds.

I've had 3 sets done and never a crack, start with good originals. 

[RUNCHARGER]

I touch them up but I generally am pretty conservative so the manifolds don't get too thin.

[HP_Cuda]

Now you know why folks go with centrifugal blowers.

The blower takes away the inefficiencies in the intake and exhaust because it pushes air through those inefficiencies.

There is a caveat: very large constrictions will not be helped by a blower (i.e. putting a tiny exhaust on a race setup)