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2x 40mm DCOE’s: Each cylinder can only be fed by one throat, they can’t get anything from the other three throats, so each cylinder only has 175cfm available to it if you are using 36mm chokes in 40mm DCOE’s.
2x HIF6 SU’s: Most of the time each cylinder gets one SU to it’s self.
And the line of resoning that would lead you to think that each cylinder hooked to a single SU gets that 240 CFM during it's turn would also lead you to figure that a single 240 CFM carb would do just as well a job feeding all 4 cylinders
1 SU can be better than 2 SU’s (Yes, I just typed that) the problem is building a decent manifold. If you imagine a SU mounted on the side of a D-Jet injection manifold you would have a tunnel ram just like what you see on a V8. That would make power, but it would drink fuel because half of it would fall out of the air stream before getting in to the cylinder.
Have a look at the single down draught manifold originally used by Volvo with a 36/36DCD. The DCD flows barely any better than a single HIF6, but they develop more power than twin SU’s because the manifold itself is better. If I had one of those manifolds, I’d put a 500cfm Holley on it (which actually flows 350cfm@1.5”Hg) it’s something a friend & I did to his 2 litre Pinto powered Escort & it works a treat. (They have a 32/36 DGAV on them originally)
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