The need for a "progressive" two-barrel came from the high revving four-cylinder Japanese engines (i.e Toyota 2-TC 96 CID with redline of 7000). A significant amount of air needed at 7000, but very little needed at idle and off-idle. A conventional two-barrel with sufficient airflow to meet the 7000 RPM requirement was too large for sufficient air velocity at low RPM's, hence the progressive two-barrel.
The American manufacturers also used these progressive two-barrels (notably Pintos, Vegas, four-cylinder Chryslers). These carbs were surplused during the early ??? mid ??? 1980's. We could have bought a semi-truck load new at $5.00 per carburetor. Due to the price, we did a lot of experimentation and testing with these at that time, but were unable to make them perform as well on larger engines (ie Chevy 216, 235) as the stock carburetors.
The only real benefit we could see was cost. Due to our inability to make them perform as well as original units, we only bought the one we used for testing.
I understand from reading these forums that others are using them, and seem pleased with the results.
It would be interesting to see some testing of these compared to good originals.
One reason many aftermarket products get rave reviews is that most are sold when the original being replaced is in need of work. Often, comparing an unworn anything to a worn-out original gives a less than favorable comparison for the worn-out original.
Jon.
