For the exhaust, you need to
decide if you want to use the 16V manifold or the 20V. The
20V manifold is a much more efficient design, however involves
more customization that the 16V. In both cases you will need
to weld. I'll cover both scenarios here.
Using the 20V Manifold
First of all, if you are reusing a C50 transmission you must
use the 16V manifold as the 20V header will interfere with
the starter. (Actually, someone just got done with his swap
and says that the 20V header fits fine when using the starter
on the exhaust side. So, YMMV.) If you have a C52 that has
starter humps on both intake and exhaust sides you will need
to move the starter to the intake side. I'll leave the relocating
exercise to you, as I don't have much experience with it.
However, I would recommend just using the C56 tranny as it
is better geared for the high 20V powerband.
At any rate, you need to mate the 20V header with the MR2's
exhaust system. If you currently have a nice exhaust and don't
plan on replacing it, you will need to either extend your
current downpipe to reach the header, or you will need to
extend the header down to reach the downpipe. I believe there's
about a 2" difference that needs to be made up. You will
also need a custom flange to mate with the header. If you
purchased a front clip, just use the flange off the downpipe.
I was building a whole new exhaust at the time, so I just
reused the 20V downpipe and built the rest of the exhaust
system off of it. The 20V downpipe is nice because it has
a flexjoint in it, so that I didn't have to incorporate a
typical flexpipe. Here's pics of my finished exhaust.
Using the 16V Manifold
If you use the 16V manifold (stock or a TRD) you will need
to expand the 'ears' of the flange. Here's pics courtesy of
Dave Spinetti from his web
Ears cut off, notice the gap needed to be filled: