Weber DGV's

[Tourniqet]

I just got some twin weber DGV's (thanks to thefastestz) and a 6 to one header with a 2.5' exhaust. Does anyone use these carbs or a set up like this? I was just wondering some popular mods for these carbs and full exhaust. I did not really want to jump right into a cam, but it may be the next step. I was also wondering about the different 240z heads and what the difference was. Also if there are different intake manifolds. Anyway, just tell me what you think.

[ZMunkey]

I've got DGVs on my 73 240 racecar, with a 6-1 header and a slightly built motor (I'm not sure just how built yet). My impressions are this:

1. Buy a book on tuning Webers-invaluable material, and you'll know more than others...

2. a DGV carb with both barrels open *should* flow more air and fuel than an SU... its a 68mm opening vs a 40mm opening, right? That's more air in my book

3. No one on this list thinks a race car will run well with the DGV carbs...

4. A DGV should only see 2.5 to 3 PSI of fuel pressure! This, evidently, is critical to preventing the fuel from overflowing the float bowl and leaking into the throttle body, causing all sorts of driveability and fuel issues. 6 Webers on a V-12 Ferrari will run on 2.5 psi, as long as there's enough fuel flow to back it up!

5. Don't just install a honking big electric fuel pump and clamp the return line like my previous owner did to raise the fuel psi at the carbs!

6. I'm installing a 2.5 psi adjustable fuel pressure regulator, a return line T fitting with a flow jet installed to prevent too much flow from returning to the tank immediately, and an in-line fuel psi gauge to measure exactly how much pressure the carbs are getting, and all new fuel lines. I'm going to cap the return line from the fuel rail above the motor. No sense in sending hot fuel back to the tank! I will probably construct a fuel rail heat shield out of aluminum, then polish it like my valve cover (I'm a nut for that stuff!)

I think they (Weber DGVs) look *very* tuneable, both for low speed and high speed operation... the trick is to realize that the "idle jets" control the extra flow of fuel at the venturis when the throttle plates are barely cracked open (because fuel won't flow at the main jets yet-air speed too slow to pull the gas out). Bumping up this flow prevents the "weak spot at 3000 rpm" that everyone complains about when the second throttle plate begins to open. The other trick is to make certain that the "air correction jets" are sized properly for high speed operation. If not, the engine will run progressively leaner as rpm and air flow through the carb speeds up. Yet another trick is to increase the size of the primary and secondary main jets, which simply increases the flow through the mains (as the throttle plates come fully open).

Now the primary is *smaller* than the overall single-barrel SU carb it replaces, so you should want to adjust the linkage to open the secondary butterfly a little sooner than 3000, but its going to depend on your motor and your cam. Since DGVs also have an "accelerator pump" similar to a Holley carb, you can up the size of that orfice too! That would give you an extra shot of gas when you suddenly whack the throttle wide open,! Much better for making mincemeat out of lesser cars at the line! While their ECUs and sensors are still trying to figure out how much air is flowing into their cold-air intakes, you'll be happily steaming off into the sunset. Believe me when I say that my car revs VERY fast!

A couple of caveats...

1. My racecar hasn't won an event yet (I haven't taken it to an event yet) so my advice is still theoretical... Many many championships were won by Ferrari, Porsche, and the others using Weber carbs though...

2. I'm still in the process of rejetting mine because the previous owner (who built the car) installed over sized "air correction jets" thinking that they were the main jets... Instead of making the mix richer at WOT, it is becoming dangerously lean... hence his comment "Race gas wears out plugs fast." Its not the race gas, its the mix coming close to detonation, burning too fast and too hot...

3. If you buy nothing else, buy a Weber book FIRST, then call Pierce Manifolds 2nd... They were terriffic at helping me out. Doug there deserves a standing ovation! MUCH better service than REDLINE!

Any questions, don't hesitate to ask

[redline240z]

There is not much info on tuning these on the Web. Another guy with a 240 w/DGVs took a shot at tuning them. There's a large thread over at hybridz.org.http://www.hybridz.org/phpBB2/viewtopic.php?t=17642&highlight=