Reply to "Weber air cleaners"

There is a lot of mis-information on this thread. The first large downdraft Weber carb was the 45 IDM (M=Maserati) developed for the 1957 Maserati 450S race cars. These carbs were also used on very early competition Cobras. Then came the 48 IDA (A=Abarth) which were a modification of the IDM and slightly larger bore. This is the common downdraft Weber of the Cobra era. For a number of years, Weber stopped production, but now they are making them again in Spain.  Most versions of this carb have only two progression holes and are a little "tricky" to make run smoothly on the street. We always add a third progression hole even with vintage race engines. I am not sure, but the current production IDA's may have three holes. The 48 mm bore limits the effective use of this carb to about 350 cu. in. engines. These carbs can be bored to 50 mm to help a little on larger engines. Ford financed a very limited series of 58 IDA units for the 255 Indy engine of 1962. They also appeared on some larger displacement Can-Am engines. Next comes the 40 and 48 IDF (F=Fiat) units. These are far more sophisticated carbs as they were designed for street use from the start. They have three progression holes and diaphragm accelerator pumps instead of the old piston pumps of the IDM/IDA series. They are easily tunable for street use and are less expensive than the IDA series. The downside of this carb for race usage is it has poorer interior streamlining than the IDA and therefore does not flow as much air at full throttle. Ford specified 48 IDA's with 37 mm venturis for street applications and 42 mm venturis for race usage in the day. Today, we bore the venturis to 45 mm for a modern vintage race motor. We use 38-40 mm venturis on 289 street engines. IDF's can easily use 40 mm venturis on street 302-351cu. in. engines.