Factory big block trucks?

[Mike C]

My guess is you are seeing the limits of 350 cfm on a 400 cubic inch motor. The 2 bbl engine is just out of fuel at a much lower rpm than the 4 bbl motor. And based on GM's ratings, to the tune of 50 hp.

[Steeveedee]

I've seen plenty of big blocks with 2 barrel carbs, I worked for a Chevy dealer on and off from 1970-1972. I'd suspect that the cam would be different between the two barrel and 4 barrel, but have no proof. I've even seen 421 Pontiacs with a 2 barrel. Our body shop manager had a '68 Star Chief that got 20 MPG on the open road with that setup. Beasts like that had tons of torque, and even the big cars had tall axles.

[davepl]

Originally Posted by Mike C

My guess is you are seeing the limits of 350 cfm on a 400 cubic inch motor. The 2 bbl engine is just out of fuel at a much lower rpm than the 4 bbl motor. And based on GM's ratings, to the tune of 50 hp.

That was my guess as well. The 350 just squeaks by with the 2bbl, but the 396 taps it out.

I bet that's some seriously crisp throttle response though!