Buick Nailhead cfm

[Marx3]

For years I have been hearing wise people claim that Buick's Nailhead engines liked more cfm than other engines of same displacement.
I have been let to understand that the design of the intake and head runners was the cause of this.
Unfortunately most Nailheads only accept Carter AFB and 4-Jet carbs.
How do people in here feel about this ? Does it make sense to mount a 750 Edelbrock on a completely stock 364 or 401? Even though this carb is closer to squarebore than it is to spreadbore?

[omaha]

there was one year that the nailhead used the Q-jet, obviously the last year, 1966. If you could find that intake, you could run the Q-jet on a nailhead. As faar as running a 750 eldebrock or carter, I think it would work just fine on the 401 but I am not so sure if it would be a good choice for a 364. It probably would run just fine but I think a smaller carb would be a better choice, maybe a 600 or 650 (not sure of the cfm sizes for the "carter type" carbs.) I do not think that any particular engine series would "like" cfm anymore than another engine type. It's only going to use as much as it can, even at WOT. So, too small is bad but too big is not good either (but a little big is ok.) The nailheads did make a lot of torque though, that I do remember (the very first car that I owned was a '63 Riviera with a 401)

[Ethan1]

there was one year that the nailhead used the Q-jet, obviously the last year, 1966. If you could find that intake, you could run the Q-jet on a nailhead. As faar as running a 750 eldebrock or carter, I think it would work just fine on the 401 but I am not so sure if it would be a good choice for a 364. It probably would run just fine but I think a smaller carb would be a better choice, maybe a 600 or 650 (not sure of the cfm sizes for the "carter type" carbs.) I do not think that any particular engine series would "like" cfm anymore than another engine type. It's only going to use as much as it can, even at WOT. So, too small is bad but too big is not good either (but a little big is ok.) The nailheads did make a lot of torque though, that I do remember (the very first car that I owned was a '63 Riviera with a 401)

 Yep.

[Marx3]

Well, a Qjet is always preferred :-)
The saying is that these engine just handled more cfm better. I dont know...
I wonder which nailhead gave the best overall performance and feel, the one with the 4-jet/AFB og the late ones with the Qjet.

What cfm where the 4-jet?

[carmantx]

I just built an 800 cfm quadrajet for a mostly stock 401 nailhead.  Still some tweaking to do on the primary side, but when he drove the car, he was very excited about the performance increase.  He has run AFB's and has the duals on one car..  The nice thing about a quadrajet is that it only lets the air/fuel in that the engine is needing so you can't really over carb an engine when it is set up right.

There is technical explanation of head design, runner length and all that stuff that justifies the Buick need for more cfm than a Chevy engine.  I don't know the details, but I believe them and trust them.

[Schurkey]

Take a look on Buick web sites, and they're quite certain that any Buick engine--Nailhead, small-block, or big-block will magically need way more CFM than a comparable Chevy.

There is a way to explain that:  Restrictive intake porting.  Crappy manifolds, and tiny cylinder head intake ports respond to larger-than-expected carbs.  A Chevy 396 with "small" intake valves uses a fairly huge port, and a 2.07 intake valve.  A Nailhead 401 had a goofy intake port, small and curved; with a tiny intake valve--under 2" if I remember correctly.  Even the Buick Big-Block has (almost) Chevy Small-block sized intake valves.  Takes a "Stage 1" cylinder head to get a 2.12 intake valve, and the port size is still the same as with the tiny "typical" valve.

Yep, that's one of the many attributes of the Q-Jet:  Can be tuned to work on anything from Pontiac 6-poppers to Cadillac 500, and most anything in-between.  Including Ford 385-series Big Blocks.

[55super56R]

Keep in mind that Crappy is in the eye of the beholder!!  The great thing with long restricted intake runners on large displacement engines like a Nailhead is that they result in very high intake air velocities and great low end torque.  That's also the reason Nailheads like bigger CFM carbs - high intake velocities result in more efficient venturi operation and response.  A large venturi does not function properly with low air flow velocity because the pressure differential between the venturi bore and the fuel bowl is not high enough to lift the fuel from the bowl to the venturi port. 

For a street engine in a heavy car there is no substitute for stump pulling torque.  The 401 and 425 Nailhead delivers the torque and great throttle response with mild mods because of the intake manifold, long head runners, and intake valve/port geometry. 

The biggest mistake most of the Chevy small block crowd makes is too much CFM (oversize venturi size) for the application.  It's fun to brag about the shiny 750 or 850 CFM lump on top of the intake manifold with the hood up but the doggy low end response really sucks.