James,
After 31 years of tearing up or wearing out various exhaust systems on
my '65 (stock, Ansa, custom, Abarth, and now the complete PECO system
header, pipes and muffler) I recommend replacing the entire undercar
section of pipe from the down pipe to the rear muffler with one
welded-in piece, and have a good muffler shop do it for you that is
experienced in custom work (i.e., NOT Midas!). Forget about a front
muffler, it is not needed if you get the proper rear muffler.
Your old Thrush is most likely too small for pleasant sound, so you may
want to consider a new muffler too. When I looked into exhaust systems
recently I found a good discussion of muffler design in Peter Burgess'
book "How to Power Tune MGB 4-Cylinder Engines", and that is what
prompted me to spring for the $500 PECO system, the one he likes and
recommends, but there is no reason you couldn't come close to
duplicating it for less.
Peter points out that there is a great variation in the quantity and
quality of the packing material used in straight-through mufflers like
the PECO, and this has a dramatic effect on the sound, as well as
maintaining the sound over time. Lesser quality packing disintegrates
or packs down over time leading to more noise. And, the PECO system has
larger 2" pipe and a HUGE straight through muffler, about two feet long
and 8" in diameter! I was surprised how big it was when I first saw it.
I have also read on other lists that the Walker Turboflo line is very
good, you might want to see if you can find one about this size when you
replace the pipe, which you could also increase to 2" for improved
flow. Though the pipe will flatten a bit as you inevitably scrape
bottom, it will not break or significantly restrict flow, and it will be
pretty inexpensive to replace when needed.
Have fun!
--
Stuart MacMillan
'84 Vanagon Westfalia
'65 MGB (Driver since 1969)
'74 MGB GT (Restoring)
Assisting on Restoration:
'72 MGB GT (Daughter's)
'64 MGB (Son's)
Parts cars:
'68 & '73 MGB, '67 MGB GT
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