Dual DCOE or DCNF?

tigeravg

tigeravg

True Classic
Aside from having to hack the trunk firewall, any huge differences between the prformance/tuning of these two carb set-ups. Need some input. Thanks ahead of time.
 
Check the ultimate SOHC thread. If your looking for dual DCNFs, I have a set with manifold, and filters for sale. They will need rebuilding and covers for the pump jets.
 
That's a given, I meant the structural beam that runs from side to side at the top may have to be notched as well as cutting out the sheet metal.
 
PBS reported that the twin DCOE setup provided much better performance than the twin DCNF setup.

"The ultimate carburetor setup for the 128-X1/9 engines, from a performance standpoint, is a pair of 45 DCOE side-draft Webers. Unfortunately, however, they won't fit in either the 128 or X1/9 cars without modifications to the car for clearance. In the 128, the heater inlet box must be removed or at least cut down for clearance. The X1/9 installation requires cutting clearance into the rear trunk area for the carburetor air horns and filters. The box member, across the top between the engine bay and the trunk, must be cut out along its bottom for clearance. Then a piece of sheet steel must be welded back in higher up to box in this area for structural integrity. Customers who have tried both the 40 downdraft carburetors, and the 45 side-draft installation, say that the extra performance of the 45 side-drafts easily justifies the extra effort required for installation. In addition to allowing somewhat better breathing at high speed than the downdraft carburetors, the DCOE carburetors are also less sensitive to cornering, etc. The same comments about low speed fuel economy apply to these carburetors as well as the twin downdrafts, of course."
​
The PBS documentation is posted on mirafiori.com at https://www.mirafiori.com/pbs/pbssohc.html

Paul
 
Actually pbs don't say it provides 'much better' performance at all... the term they use is 'somewhat'

"allowing somewhat better breathing at high speed than the downdraft carburetors"

somewhat
ˈsʌmwɒt/
adverb
  1. to a moderate extent or by a moderate amount; rather.
    "matters have improved somewhat since then"
    synonyms: a little, a bit, a little bit, to a limited extent/degree, to a certain degree
And that is when considering 45dcoe's... take a look at the inside of a 40dcoe and you will see it's far more restrictive to airflow than a 40dcnf is.

When you take into account the manifold differences IMO the DCNF wins hands down from a flow and performance standpoint.

You can cut just the sheetmetal and not the box section and the carbs will 'just' clear... but to remove the carb tops to do any float level adjustments then requires the removal of the complete carburettor... so the box section needs to be cut and rewelded.

SteveC
 
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DCOE vs DCNF is a very interesting argument, but there are not huge differences in their performance on the Fiat SOHC engine. I suggest you have a read on this link for 2 different opinions on the topic, https://t124.com/forum/forum/fiat-fans/fiat-fans-aa/14314-track-day-x1-9/page2.
They are both equally tuneable, I would suggest if you decide to go for DCOEs, use 45s not 40s, the auxiliary venturi body in the 40s is too restrictive (37mm ID) for max performance. And yes, you will definitely need to modify the cross member.

Hi Steve, looks like you posted while I was typing.
Greg
 
The modifications needed to the rear trunk area for the DCOE carbs is not worth the trouble for a street-driven car. Based on PBS's advice I opted for the side-drafts, but I was building a race car, not a street car. In the picture link you can see the stock cross member was cut out and replaced by a smaller boxed section for clearance. I have used both setups (DCNF and DCOE) but they were on different engines with different mods, so it was hard to compare them.

http://i1121.photobucket.com/albums/l511/racerron1/myx19_webers_zpsb027c81c.jpg
 
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