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I have a 351W in an F250 which has a 287 cfm 2150 carb.
The previous owner took this & rebuilt it from the 302 that was in the truck originally, then swapped it to this motor.
How limiting is this carb on a 351? Apart from an RV cam, the engine is stock. It doesn't get revved high, it's a work truck - seldom over 3000rpm.
Economy isn't bad - it's giving 20 mpg (imperial), but not the power I would expect. Am I going to lose one to get the other, by going to a 1406 or something similar?
It's also a feedback carb. I was going to replace it so I could do away with the computer ( Californian EEC-III) & all that goes with it, because it's been partially disabled anyway, but unless this carb is a big restriction, I wasn't going to do it immediately.
I have an Offenhauser chart that says for a 350 cubic inch engine (closest in the chart to 351) turning at 3000 RPM, 304 CFM is required. The carb you have on there now isn't too bad, but it will starve it slightly. After all, it was meant for a 302. Your motor will really wake up with a 4 barrel carburetor. An Edelbrock 1406 with a 4 barrel intake would be a good choice. As a side note, feedback carbs are very problematic.
I'd maybe expect around 15 mpg (US) with that setup, depending on how you drive it (maybe a little less, maybe a little more). You might try asking in the small block forum (289/302/351W); some guys over there with that actual setup could tell you their numbers. The nice thing about 4-barrels is if you keep your foot out of it, you just drive on the primaries and can actually get better mileage than with a 2-barrel.
The manual choke version of the 1406 is simply the 1405.