[. . .] I am asking you folks for any recommendations on exhaust systems.
The muffler that was on it is an Ansa that looks similiar
to the "Monza" exhaust Victoria British sells for about $110. JCWhitney
also sells one that looks similiar, have any of you tried the one JCW
sells? Does the B get much performance boost from this type of exhaust
over the stock setup, especially when running the stock exhaust manifold?
Your best performance increase for the dollar will be to replace the
stock exhaust system behind the collector. Go with a system that has
only one muffler, and that one of the lowest possible restriction.
Flowmasters, SuperTrapps, and Walker Super Turbo mufflers are all
popular brands with autocross and race MGB owners. SuperTrapps have
the advantage of being tunable, that is, you can add or subtract
baffles from the exit of the muffler (which is the tailpipe) to move
the torque peak a few hundred RPM up or down the rev range.
Surprisingly, the stock exhaust manifold is pretty good. The worst
thing about it is the weight and the silly donuts that hold it to the
downpipe/collector. If you're feeling cheap, grind the exhaust manifold
openings about 1/16" larger than the exhaust gasket surface. That will
do most of what a header would on a stock engine. Pay particular
attention to the top of the openings, biasing to the front in the front
port and the rear in the rear port.
How much of a performance boost does replacing the stock exhaust manifold
with a header give? (My B has a Weber DCOE, the engine is stock other than
that.)
You might get 3 to 5 bhp, compared to 5 to 6 bhp with a good muffler.
Putting a muffler on the stock manfold is far better and more cost-
effective than putting a header on a stock exhaust system.
If I do get a header, what do you recommend? I've seen what look like two
different types, one (Longflow) has three pipes come together into one at
the bottom, the other has two pipes join together and then join the third
to form one farther down. Which is better?
The latter. It's the type called the "Long Centre Branch," and is probably
either a replica of or a development of the factory racing setup from the
Sixties. Seven Enterprises sells one for $225, order no. SXH0106 (why,
yes, as a matte of fact I *do* happen to have my Seven Ent catalog in
the office today! :-)
But Bob, if you're really serious about this, we've got to get rid of
that measly 18V engine you've got, with its single valve springs and
low-compression pistons. You might be able to get up to 80 bhp out of
it with the Weber and a fully developed exhaust system; the same mods
to an 18GK engine (with the big valves and dual valve springs) will
get you right up near 100 bhp. There are a couple of different ways
to accomplish this; only your checkbook and the rules of the sanctioning
body with which you autocross will be able to tell you which one works
best.
Next week I'll tell you what a Stock-legal porting job does (along
with a standard valve job) on an 18GK engine in fair condition.
They're finishing The Green Car's head today, I should be able to
pick it up tomorrow and install it over the weekend!
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