RS Motorsport :: Classic Speed Restored

If we considered a Weber 45 DCOE and a Weber 48 DCOE BOTH with a 38mm choke would there be any potential power difference between the two? Both should flow exactly the same amount of air so should make equal power?

I currently have a set of new 45's on my car as I have been waiting on parts to be made for my 48's (been a long long long wait!). Not sure whether to give up now and stick with the 45's.

Compare and contrast..............

Hey mate,

Although the same choke size may technically limit your total air flow to a similar overall figure as the 45's, you will increase the verturi effect with the 48's as there is a greater differential between the choke and bore. This can potentially help with some mid range power/tuning and throttle response perhaps??? can't really say how it will effect your motor exactly as i'm far from an expert but my understanding is that yes there are still gains to be had in the tuning of the thing with the increased venturi effect.

I'm sure there is someone out there who can give you some better first hand experience.

llewellyn

Any thoughts from others as suggested by Llewellyn?

Hi,

depends ...

If in both cases the inlet manifold is matched to the carbs there would be very little difference in top-end power between the two carbs. But because the 48's are bigger (at the throttle plate end) the air-fuel mixture looses more momentum, so low/mid range bhp could be down compared to the 45's.
We have 48's with 42mm chokes on the Pinto-engined rally car (BDG is being rebuild) but that is running one-off very light pistons and a very trick head plus rallycam. (220 bhp at the crankshaft).

Hope this helps, Leon.

38mm choke is the biggest choke size recommended for the 45DCOE.

Rule of thumb is no less than 7mm of bore size. (45-7=38)

I would have thought 48DCOE with 38mm choke would perform better since the 45 is at it's limit.