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The big difference is that the DGV (manual choke), DGAV (water-heated choke) and DGEV (electrically-heated choke) are all PROGRESSIVE carbs; so are the DF_V series, which are basically a mirror image of the same carb (some engines need a "left-handed" carb and some need "right-handed"; I'm told a DF is a more direct replacement for a Solex, but either will work on a V4.)
"Progressive" means that when you step on the pedal, only the throttle plate in the primary barrel opens at first. When it's about 3/4 open, the secondary barrel's throttle also begins to open, giving you increased throat area and more power. The two continue to open together until both are wide-open at full throttle. Theoretically this gives you optimum fuel economy, since you do most of your driving on the small carb throat, then add on the second throat only when you need it. Again theoretically, it's good for throttle response, because air moves through the small throat more quickly and can respond more rapidly to small changes in throttle opening.
The DCNF is a SYNCHRONOUS carb, meaning that both throttle plates open simultaneously. In theory this is best for all-out power, but requires careful tuning to get good part-throttle response and economy.
The joker in all that "theory" stuff is the manifold. The old Saab/Ford 2-barrel manifold that's used with the DF/DG carbs carbs is kind of convoluted -- the air passages have a fairly straight shot to some cylinders, but have to snake around sharp bends on the way to others. This makes it hard to get an even mixture distribution: some cylinders can run rich while others run lean. The MSS manifold that goes with the DCNF carb has been hand-fabricated to provide a straighter, smoother path to all the cylinders. The carb sits fore-and-aft, so basically the front pair and rear pair of cylinders each gets its own carburetor barrel (although the two halves of the intake tract aren't physically separated.) This gives much more equal mixture distribution, which negates some of the theoretical fuel-economy and throttle-response advantages of the DGV carb.
So a lot of your choice has to come down to other factors, such as:
-- If you want to use a DGV, can you find a manifold? They turn up fairly often on eBay, but you're still depending on being able to find a used part. The MSS manifold is modified from the much more common single-barrel manifold (you have to send in your old manifold as an exchange) so supply should be no problem.
-- How much tweaking are you willing to do? The DCNF system is still very new; only a few of them have been sold so far (mine is stamped "3," which MAY mean I'm only the third person to get one!) MSS is very helpful with setup info, but there's still not a huge knowledge base about which jets and settings work best on engines in various states of tune. The DFV/DGV setup has been around a long time, and a lot of people know how to make them work.
In terms of power and torque, I think the DCNF setup has a definite edge. I haven't used a Weber DF/DG on my car, but I *have* used a Solex 34/34 TDID, which is a similar two-barrel progressive carb that was standard equipment on late-model 96es in Europe. I never did dyno or 0-60 tests with the Solex, but I have gone to some open-track days at a race track, and with that carb I would generally see top speeds around 89-90 mph at the end of the longest straightaway. I'm still dialing in my DCNF, but even without ideal tuning I've been seeing 94-95mph at the end of the same straightaway.
(Incidentally, my engine is otherwise stock except for an MSS exhaust system -- you need some kind of low-restriction exhaust to get the full benefit of either carb option. My car is a Sonett III with the standard motor mounts, and the DCNF fits fine with the low-profile air filter that comes in the kit.)
The way I see it, the DCNF kit has more power potential if you don't mind being a bit of a pioneer when it comes to setting it up. The progressive DF/DG carbs don't offer as much of a performance boost (although still a significant improvement over the stock 1bbl) but there's a bigger experience base to help you tune them.
So if you like having something a little different and enjoy experimenting to get the most out of your engine, take a look at the DCNF, and if you want more of a bolt-on-and-go project, lean toward the DF/DG. That's my take, anyway...
posted by 68.13.13...
, Wed, 18 Aug 2004 16:58:24, Fri, 15 Oct 2004 12:46:19
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