Weber Dcd Venturi Sizing

[rob83ke70]

Just wondering if someone can tell me from experience what size primary venturi should be used in a 28/36 DCD on my worked 4k engine. Both the DCD's that I have at the moment are the stock 26/27 diameter venturis, and the stock carburettor is 21/24 diameter venturis. I can't find what diameter a 32/36 dgv is, or that much solid information at all.

 

I've been told to use either a 24 or 25mm diameter primary venturi, but how do I work out which one I need? how much of a difference will this make? has anyone run a 4k with a 26mm diameter primary venturi?

 

Robert.

[rob83ke70]

http://datsun1200.com/modules/mediawiki/index.php?title=DGV

 

This seems to think the venturi sizes of a DGV are 26/27mm for most models.

 

according to:

 

http://www.csgnetwork.com/cfmcalc.html

 

I only need about a 150cfm carburetor... a standard DGV apparently is 270cfm, so a standard DCD should theoretically be above 200cfm easily.

 

Therefore, a 24mm primary venturi tube wouldn't cause any dramas at all for me and would be worth forking out the $60ish AUD to get one....

 

please someone feel free to contribute and correct me on this!!

 

Robert.

[Felix]

In David Vizards books he claims you should have 2-2.2 CFM per HP. A DCD with 26/27mm venturis flows around 220 CFM.

 

The venturis you have will be ok, though you would find improved low-mid throttle response with a smaller primary venturi. Obviously it would work way better than a 32/36 DGV (32mm primary throttle plate), with the DCD's 28mm primary throttle plate.

 

The 26/27mm venturis came standard in the DCD's fitted on mk1 1500gt cortinas. They had a 1500cc non-xflow pushrod motor, with a 270 degree cam and extractors. Perfect for a warm 5k.

 

My original DCD came from a Fiat 1500, it had 25/25 mm venturis in it, and was fitted to a 4k with 270 degree cam, mild headwork, 9.8:1 CR and 4-1 extractors/exhaust. I later tried the 26/27mm venturis but found throttle response to be a bit soggier on the primary. I went back to the 25mm primary, but left the 27mm secondary for a bit more topend. I believe a 24mm primary would be the sweet spot on a 4k with a decent amount of work done to it.

 

Imp website gives a little insite into DCD tuning and compares the DCD to twin Strombergs (very similar to SU's).

 

Neil Lenton on Weber 28/36 vs. twin Strombergs (the paper filter and diaphram comments would not apply to SU's):

 

* A Weber 28/36 never needs mixture adjustment

* A Weber never needs re-balancing (as Strombergs regularly do). Re-balancing is an awkward job on an Imp

* A Weber does not have diaphragms that may split or o-rings that might leak

* A Weber takes up half the space, so it's much easier to get at and work on

* Its throttle and choke linkage is less complicated

* Throttle response

It can be very economical when driven on primary choke. When floored, the second choke also operates and gives extremely good acceleration. Twin Strombergs operate best on light throttle and tend to feel flat when floored.

* Air filters are cheaper. Paper elements are vital on an Imp. An early Mini 850 air box can be adapted to fit the Weber. (T.J. filter B.94)

Edited June 26, 2010 by Felix

[rob83ke70]

I did have a flip through that a while back - took me a few minutes to work out he must have been talking about stromberg CD side draught carburettors - whenever someone says stromberg I keep thinking the pissy little things fitted to holden 6's.

 

my su's definitely go better with some throttle control, if you mash it at lowish revs it feels a bit "boggy" but when you've got high revs happening they go well.

 

Kylie assures me the throttle response was better using the old weber dhsa2 (28/36 vac secondary) and that was with a heavier flywheel.

 

Maybe Keith was onto something using a pair of hs2's instead of hs4's! I spoke to a few people when I was originally contemplating the project and they thought a pair of hs2's would be too restrictive up high and they reckoned the hs4's would be the right ones.

 

the next point to ponder in the project is air filters. I've got a ramflo to suit the dcd, and the top and bottom (slightly rusty) for a rectangle paper filter. I'm no longer going to have the heat shield over the extractors, but I will be cleaning them up and wrapping them in fibreglass bandage when this project eventuates. I was thinking about obtaining a plenum/snorkel type arrangement for the DCD if possible (maybe making one?) and using an airbox out of a later corolla or camry (zze122 or acv20r/acv36r) mounted where the battery is and moving the battery to the rear seat area or boot. That way I can get cold clean air, easily available filters, and relocate some front weight. anyone done this or something similar?

 

Robert.

[altezzaclub]

You'll want to keep the top of the carb as low as possible to avoid the Dyna's problem where the intake closes the entrance of the carb off.

 

How about a hole up through the bonnet... :lol:

[rob83ke70]

http://www.knfilters.com/images/l/85-8921.jpg

 

single 2.5" inlet hose..... probably match up with the standard air ducting for the dyna, and probably also match up with the air ducting for an ae or zze corolla airbox.... looks to have more room in the plenum than the original on the dyna too. I'm yet to find out if they will fit a DCD - maybe the adaptor plate is slightly different to the dgv?

 

Robert.

[altezzaclub]

ooohh!! Sexy... and its black AND finned to make sure it absorbs all the heat of the engine bay!

 

That's the sort of thing, but you'd need to make sure it gave maximum flow without creating drag spots.

 

Start off with this..

 

http://www.bccp.nl/shop2/contents/media/42DCNF.jpg

[rob83ke70]

you can get plain alloy ones. dgv doesn't fit dcd either, so I'll have to get something made or find an adaptor thingie to suit a dcd. the dgv on the dyna should be straightforward.

 

trying to eliminate as much heat as I can - remote air filter sucking cold air, wrapping extractors..... if only I could do something about the radiator and heat generated from that.

 

Robert.