Re: Question about exaust flow..
If I understand you right - you are going from the smaller head port to a larger manifold header?
If so, that sure is far better than going from big to small!
Expanding is best done a little farther down stream, but sometimes ya gotta do what ya gotta do.
If there's room, see if you can adapt with a taper - as smooth on the inside as possible. A "step", even a step up to larger, creates lots of turbulence. Even if the taper is only 1/2 to 1" long, it lets it expand without much restriction - the longer the taper the better.
A muffler shop may be able to expand something to make the taper - I'm sure it's worth the effort.
Try something -- dig a small trench about 1" wide in your garden - sloped gently downhill. At one point, make a square cut and expand it to 3" wide. Run water slowly down the trench from the small to the big part. You'll see where it expands the water swirls around because of the step . It's the same thing as the gasses do flowing down a tube or pipe when they come to a step up.
Expanding means the velocity in the pipes becomes slower, nodes and peaks are moved up toward the engine, but not really a problem.
You did the intake but not the exhaust -- better - a little better than stock. When and if you can, open the exhaust up too. ANY restriction, intake (choking) or exhaust (constipation) limits power just like it affects a jogger.
About the same as Athsma - you can inhale, but exhaling's difficult.
By the way - the backpressure myth - if the exhaust dumped right out of the head's port - no pipes, that's 0 backpressure -- hardly will run. Adding any sort of backpressure to that - restriction - makes it even worse!
Adding an exhaust system DECREASES backpressure to LESS THAN 0 - to NEGATIVE PRESSURE (you can measure it with a very fast vacuum transducer right at the port!) The exhaust "system" uses the pulses to extract, clean, or scavenge the old exhaust from the chamber so new AF mixture can get in with a fuller charge.
More A/F = more power.
The myth that you need backpressure comes from those that opened the exhaust up too much and killed the scavenging effect.
NO? Isn't a potato stuck in the exhaust pipe a restriction? More backpressure? Try it.