The DGV carburetor has a number of things going for it.
First, it's a dime a dozen. This carburetor was installed on virtually every
four cylinder engine at some point
in history. It's probably the most common carburetor to be found in the junk
yards.
Second, it's delightfully tunable. The combination of jets and such make this
carburetor flexible like virtually
no other.
Third, it's a progressive. This means you can set the primary up for economy,
and the secondary up for
power, and get the best of both worlds, at least in theory.
Fourth, nothing moves, so nothing goes out of whack. Once you've got it set
up, it stays set up.
For some reason, this carburetor has gotten a bad rap around Triumph groups,
and I don't know why. It's
a common hop up carburetor for many vehicles equipped with Hitachi's and such.
If you look at hot rodding
japanese and american 4 cylinders, this the the numero uno carburetor. Why?
Because it works.
The manifold design isn't bad. Even those with the dog leg that lowers the
carburetor. In fact, it flows
quite well, having only one "bad" area, that under the carburetor throats
forming the plenum. Those long
sweeping curves are quite good for flow. Manifolds of this design are the
replacement type for straight
legged manifolds like those used on stock 2.3 Fords and such. Straight runners
form kinks where they
meet the head, and kinks are bad for flow.
There are some problems though. Some can be overcome, some cannot.
First, there is an inherent fuel distribution imbalance by the positioning of
the carburetor throats on the
manifold. Those runners nearer the primary will get richer mixtures at low
loads. At high loads, the
runners under the secondary throat get richer mixtures. Edelbrock and others
worked on this extensively
for Ford four cylinders, playing with different types of ribs and wyres to help
distribute the gasoline.
Very small wyres worked best as I recall.
Second problem has to do with the firing order of the engine. This causes
problems for SU's as well.
At each end of the engine one cylinder fires, then the other, then there's a
pause. In musical terms,
it's two quarter notes followed by a half note rest. This means the first
cylinder draws air in with
no existing carburetor signal, so it gets less flow and a leaner mixture. The
second cylinder draws
in a richer mixture and breaths better because of the signal the first
cylinder created. SU manifolds
really have a problem with this because of the balance port (screws up the
first cylinder on each end
by restricting air flow), as well their extremely short runner length. For a
street driven car this amounts
to only the loss of a little power. It's only on racing engines living at the
extreme edge that it becomes
a matter of life and death, quite literally for the engine.
SU carburetors eclipse the DGV on their flow and power potential. But (always
a but), it takes
constant attention to keep them there, if you can get them there in the first
place. The Weber
works reasonably well out of the box, and quite well with some tuning. Then
you can forget it
and leave it alone for the rest of the cars life.
I suppose it I was to assign classroom grades to these two fuel systems I'd do
it thusly:
Tunability and Performance
Weber DGV = C+
SU = B
Ease of use and Reliability
Weber DGV = B+
SU = D
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