2- Has anyone had any experience with the triple weber carb set up ?
Weber carbs are certainly interesting. First off, I'll say that it is quite
likely you don't want to install them yet. There is a noticable difference
in power and better throttle response, if the carbs are put on an engine in
good condition, and are set up well.
The constant depression type carbs like Stromberg CDs or SUs have some things
in favor of them. For around town driving, and as the engines wear out, they
are quite acceptable. The carbs react to the demands placed on them by the
engine, as a response to driver input. That is, on an older, worn out motor
they will open the pistons more slowly and not as far, as the worn motor
sucks in less intake charge than a newer, well sealing motor.
The Weber carbs will flow more air, and more gasoline to go with it, of
course. If the engine isn't in condition to handle it, then you are wasting
money and losing power. They will bog when you hit the gas, not give you the
kick in the pants you are looking for. The most common problem with Webers is
that they are set for a full competition motor that doesn't spend much time at
low revs. So the chokes (aka main venturis) are sized for best flow at high
revs. At low revs when tooling around town, this results in reduced gas
velocity through the intakes, which yields poor atomization of the fuel, rough
running, excessive fuel use, poor throttle response, and a general feeling
that Webers are a pain in the toolbox, and with luck some poor schmuck on the
Triumph list may want to rid me of these things.
The motor need not be running a monster cam or high compression ratios, though,
to get some benefit from the carbs. A decent exhaust system is pretty much
required, though. On my autocross Spit, with a '76 9:1 motor, stock cam (in
truth, the least worn out of several stock cams) and no port work, the dual
DCOE carbs tend to work pretty well. Gee, if Bob Lang does some more work on
his TR6, it might be almost as fast as my little Spit! [Okay, cheap shot. At
Rockford, Bob actually had a better raw time than the Spit, but bumped a cone.
Wait until Texas!]
You will no doubt hear about Good's triple SU setup. He claims to get as much
power as Weber DCOEs, but I wonder about this. With the DCOE carbs, you get
one throat per cylinder. With the triple SU (or Stromberg) setup, each carb
feeds two cylinders. This is fine for the middle pair, which have their intake
cycles 180 degrees apart. The two front cylinders share a carb, but there is
a 240 degree phase difference betwen cycles. The same holds true for the two
back cylinders. What this phase difference means is that one of the cylinders
will be getting robbed of a full charge by the other cylinder, so one runs lean
and one runs rich. In a year or so when I have a dyno in my shop I'll see what
sort of difference, if any, this really translates to at the wheels.
So the bottom line is that with the proper care and an understanding of what
one is getting into, the $1,000 to $1,500 required to get three Weber DCOEs
working on a Triumph straight six can be money well spent. Used sets do crop
up from time to time, at the moment I have nothing available for the TR6/250
cars, just a single sidedraft setup for a Spitfire. But they do crop up from
time to time, with price tags of $500 to $750 or so. Installation and tuning
are extra.
Oh, and the downdraft DG* carbs are completely different. I still don't see
how people can add all those extra bends and restrictions to the induction
path and claim a performance increase. Another thing to check out on the dyno!
mjb.
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