Question about the 4bbl intakes

My 2 cents:

You are going to need more than larger exhaust to get any benefit from a four barrel on a slant six. One needs to up compression, air flow by porting and oversized valves, and some sort of header tube or Dutra Duels. Camshaft upgrade from stock is needed to allow engine to spin fast enough to pump enough air to be able to utilize the secondaries. Also recurving distributor to take advantage of cam and compression changes will be needed, as a lot of fine tuning of the 390. Probably rear gear changes would be desired to take advantage of the faster spinning modified engine.


As you may know vacuum secondary carburetors only supply the amount of air/fuel the engine can use. So if you stock engine is only capable of 250 cfm, the second half of the 390 cfm carburetor will just be window dressing masking a two barrel engine with drivability issues due to being over carbureted.

You best bet would be to drop in a Super Six factory setup to get a little bit of power and drivability gain without spending a ton of dough on a ton of changes to a stock engine.

Disclaimer:
I have modified engine equipped with Holley 390 that spins to 6300 rpm with 3.55 Suregrip.