This seams to come up from time to time so I would offer to add my insight
and several years of experience in multiple carb setups for what it's worth-
As with any type of carburetor, including Webers if PROPERLY sized for the
application they can be made streetable, including triple Webers on a TR6.
Again, as with any carb, it's a trade off. With the slight exception of
constant depression types (Stromberg/SU's) or vacuum operated secondary
types which are more forgiving in term of sizing because for the most part
the engine will only use as much carb as it can with these types. Unless
the carb(s) are too small for the max rpm you are seeing, effectively
strangling upper engine performance through pumping losses, then bolting on
6 3" SU's or Strombergs or anything just to be bigger WILL NOT make any
difference, except that you will have a performance LOSS at lower
rpm/engine conditions. If you want a streetable mostly stock engine, then
you size the Venturi for the rpm you will be cruising at plus a little
extra for a bit of power when you need it. It is foolish on a stock or
slightly modified engine to size the carb(s) for 8000 rpm when you will
NEVER see this. With carburetors, if you size them for a high flow for a
given pressure drop, at a higher RPM then you will trade off low rpm
tractability. If on the other hand you size the carb(s) for low rpm then
you sacrifice high rpm power because of the inherent design operation of
the Venturi. The only real gotcha with multiple carb setups is complexity.
They do look cool, and can be made perfectly tractable and reliable. You
can get just as good and sometimes even better mileage, and performance,
through proper manifolding for better cylinder to cylinder distribution,
from multiple carb setups IF SIZED AND SET UP PROPERLY. To get all the
performance and power from a given engine without the carburetors inherent
drawbacks consider fuel injection, where Venturi size is not a determining
factor which will soon be on the V6 :-)!
Barry Schwartz (San Diego) bschwart@pacbell.net
72 V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire (long term project)
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