quad downdraught carbs

poo slinger · Post by **poo slinger** » Sun Aug 16, 2009 9:57 pm

how come you see alot with ida / idf or drla carbs but not dcnf?

dcnf carbs are smaller so i would of thought they would be better to use?

kiwicar · Post by **kiwicar** » Mon Aug 17, 2009 9:58 am

Hi
DCNF carbs were designed for ferrari and Maserati who user 70 ish degree V6 and V12 engines, as a result the banks are closer together and the ida/idf would not fit in a north south arangment as you get on most installations, putting them across the engine would have meant having to mount them higher on a "swan neck" manifold (and have them stick out the bonnet). So the the DCNF has the chokes much closer together so the carb can be mounted on a straight shot manifold further down in the valley. (lamborgeni got around this by putting the inlet port in the middle of the head and using DCOEs).
The upshot is that as I said the chokes are on a closer pitch so you would have to make a different design of manifold to use them.
Best regards
Mike

poo slinger · Post by **poo slinger** » Mon Aug 17, 2009 2:49 pm

i was thinking this as dcnf carbs are alot cheaper than ida's.

would 40mm dcnf's be undersized for a 4 litre engine?

kiwicar · Post by **kiwicar** » Mon Aug 17, 2009 3:31 pm

Hi
I would do some research on the carb before you jump into this, you may find they use a different set of jet sizes, this may lead to limited tuning potential. I am not saying it is the case but it may be. As for size, it is a clasic case of "it all depends", 8 x 40 mm chokes should be able to support 250 to 320 bhp without being reatrictive on a 4 litre engine maybe a little more, but it does depend on alot on where and how that power is made, I presume this is for a rover? if so you may have to make a manifold that has overly long inlet runners and again mounts the carbs very high so as not to have overly tight curves, may be fine.
If you are going to go to the effort of fabricating a manifold for these carbs, why not fabricate a set of Fuel injection throttle bodies in 45-48 mm size while you are at it? Then the saved money on a controler?
Mike

poo slinger · Post by **poo slinger** » Mon Aug 17, 2009 4:16 pm

so overall you doubt dcnf carbs will be lower down than ida's?

kiwicar · Post by **kiwicar** » Mon Aug 17, 2009 4:27 pm

I think you will have to measure it all up, consider the design and work out what your priorities are. If you can go for a set up like a chevy dual quad or 4 duces set up using them then it can be what height you like. If you want a tunnel ram look alike or an individual runner set up then you may be looking at somthing higher.
Best regards
Mike

poo slinger · Post by **poo slinger** » Mon Aug 17, 2009 5:35 pm

kiwicar wrote:If you can go for a set up like a chevy dual quad or 4 duces set up using them then it can be what height you like.

explain this bit please

ian.stewart · Post by **ian.stewart** » Mon Aug 17, 2009 5:41 pm

Sounds like the height of a Tunnel ram, you can buy them at different heights of manifold.

kiwicar · Post by **kiwicar** » Tue Aug 18, 2009 10:40 am

A "dual quad manifold is a 50's/ 60's style low rise manifold for two 4 barrel carbs, depending on type they were generally an open plenum under each carb that fed 4 cylinders. Efectivly they were a simple case of joining up the holes. A four Deuces set up is basically an open chamber in the middle into which all the inlet ports ports connect via the most direct route possible on top of this chamber are sat 4 solex '98, 2 barrel carbs (Deuces) and a linkage that opens the carbs in pairs so that up to about 1/3 throttle you only run two carbs, then as you use more throttle more carbs open.
They were more about looks than power, and getting the whole lot to fit into an engine bay.
Best regards
Mike

poo slinger · Post by **poo slinger** » Tue Aug 18, 2009 11:52 am

could dcnf carbs be used like 1 barrel per cylinder and mounted the same way that idf / ida carbs are mounted?

kiwicar · Post by **kiwicar** » Tue Aug 18, 2009 2:22 pm

That is how they were originally used, so yes they can, that is why you get to the issues I mentioned above of runner length, which way you mount them, resultant height etc.
It is an issue of how much fabrication you want to do to match the carb to head, and as I hinted at before, is it more work than building your own individual throttle bodies and use EFI? Bear in mind if to did use short throttle bodies and individual runners to each you could have an inlet tract length of about 4.5" or less.
Mike

poo slinger · Post by **poo slinger** » Tue Aug 18, 2009 4:15 pm

i thought dcnf's were originally mounted in a straight line, not 2 on each side.

HairbearTE · Post by **HairbearTE** » Tue Aug 18, 2009 11:45 pm

On old V8s and V12s they were often mounted in a straight line as you put it but they have also been used successfully side by side on some 4 cylinder engines, most notably as an upgrade for the ford CVH engine. I would think that as with most carbs there will be different variants and things such as linkages may vary. If your planning on buying the carbs on ebay and fabbing up the linkage yourself it may pay to do a little homework and make sure you know what you're buying before parting with your hard-earned. Inglese induction do an inlet for the chevy small block - they might be able to help with the linkage.