It's kind of interesting -- I've been around all sorts of MGBs, but
I've never driven one with a 45 DCOE.
However, I ran a 40mm DCOE on my old faithful roadster
"Black" for a number of years, and really liked it. It's the same thing
as the HS4 vs HS6 debate -- smaller bores means higher velocity.
I was happy with the carb, when I lived in San Diego, where the people
who would grow up to be TV weathermen end up being surf bums,
because the weather doesn't change (or so it seems). Back here
on "home" turf -- in Arkansas -- I had to change jets out for different
times of the year. Kind of cool in a gearhead geek way, but it can
be a pain, particularly if you drive in varying conditions and have to
buy a few sets of jets (and then have them stolen from your glove
box because some stupid druggie loser finds a little plastic baggie
with little round things in it).
That engine was 20 over, flat top, slightly milled head, ported and
polished, with a Piper 289 cam.
It's not so much that the DCOE is designed for power at high RPM,
it's a question of two things: 1) volume of air/fuel charge, and 2)
velocity of said charge. The problem with DCOEs on MGs is that
the venturi size (that most people select) is just way too big for
low RPM. It's not a part of the DCOE, its part of the application.
You can do the same thing with SUs, right? Put HS6s on a fairly
stock engine, and now you've got lots of potential volume, but
lowered velocity, and your throttle response/low RPM suffers.
There isn't anything "special" about high RPM operation, nor
is there anything "special" about the DCOE that makes it
only for "high" RPM engines. Yes, most every carb I've dealt
with works best at full throttle. The Weber (and copy) carbs I've
worked with even had some nice helps for throttle response, like
tunable accelerator kick circuits, not something you are going
to do easily on an SU (without changing other parameters).
Keep in mind that an engine that can turn 7000 RPM is drawing
72% of its max air/fuel flow at 5500 RPM (if V.E. is the same at these
rev points, which it won't be), and I will not believe that a DCOE
only works in the last quarter of its max flow capabilities. It's
not "opinion" nor a "flame", it's basic IC engine math.
(And define "high" RPM. There are plenty of MGB engines out
there that will rev to 7000, but passing 6500 with a Rover V8
takes some serious cubic dollars.)
In my experience it's just a question of being realistic about what
RPM you will use, and properly selecting and tuning the carb
for that use. And, to be honest, tuning a DCOE can be a
complete royal pain, at least to do right.
Safety fast,
-Keith Wheeler
Team Sanctuary
ps -- vi all the way.
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