I'm at work now and can't check on that dent question, but let me gas on about
the last two.Last year Grassroots Motorsports did a series of dyno tests of
bolt-on MGB engine mods. One of the huge shocks from their point of view was
the difference--around 4%--made by bolting on stub stacks to the mouth of the
SUs, and letting them reside under K&Ns, which also provided a power gain of
around 4%. Unlike standard bell-mouthed velocity stacks, the stub stacks are
about 1/2 in. high with a rounded opening edge that, as dealer ATF products (I
think that's their name--information also at home) says, provides "a nice
radius" for the SU carb opening. In short, I guess it just fools the air flow
into thinking the carb is bigger, and the flow is increased. Cast versions of
the stacks are around $19 each, and that's what Grassroots tested. When I
ordered mine, the cast versions were out of stock, so I got the billet versions
for around $30 each. I also got K&Ns at the same time, going for the open
element design that eliminates the metal pots.
I am here to tell you that the combination of K&Ns and stub stacks makes a
SIGNIFICANT difference in performance throughout the power range, from lowest
RPMs up to readline, and yes, it seems to allow the ancient B engine to keep
accelerating at higher revs where previously it seemed to run out of gas. The
bill--around $200 and 15 minutes install time.
So here's my ultimate cheapie, no-risk, quick-install performance boost
recommendation: A Petronix ignition, K&N filters and stub stacks. Buy, bolt
and burn.
Jay Donoghue72 B-GT66 Mustang (also with Petronix and K&N)
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