Inliners International Forums General Discussion Engines Low CFM 4 barrel carb options?

All the Holleys from the Old Days say pre-1980 or so are rated at 3.0" Hg for 1bbl or 2bbl, and 1.5" Hg for 3bbl or 4bbl.

Some 4bbl carbs were rated at 2.0" Hg even back then and some are even rated at 1.0" Hg today so it helps to be sure.

So yes, the smallest Holley 2bbl is about the same as the Primary of a Holley 390cfm 4bbl.

And, the big Holley 500cfm 2bbl is exactly the same as the Primary of a Holley 780cfm 4bbl.

I will try to throw on some bigger carbs during the next carb shootout. Problem is, at my level about 175hp currently, I can run eg a 600-625cfm Carterbrock, but the floppenvalve basically just doesn't open, so its running on the primary plus secondary transition circuits, about 300cfm.

When I run a 450 Holley, the secondary opens maybe half way, so again its at 300-plus cfm.

On a 600 Holley my bet is the secondary wouldn't open at all so in effect I'd have a 1-1/4" primary 2bbl.

And the 780 would be a good test as it would be the same as running a "500cfm" 2bbl, only heavier. It would be a good test of launch and low-end though.