Hi Ron,
The best carburetor size for ANY engine is given by this little formula:
Carb. size in CFM = (Displacement in cu. in.) x (Max. RPM) x (Volumetric
Efficiency) / 3456
Street engines usually have volumetric efficiencies around 80% to 85%. I'm
going to assume red line on your 289 is 5000 RPM:
CFM = 289 x 5000 x 0.85 / 3456 = 355 CFM
According to this, you need at least 355 CFM. The closest Holleys are 465,
570, and 600 CFM.
A typical performance carburetor has four barrels. The primary barrels are
usually the front two. The secondaries are usually the back two. I would
recommend vacuum secondaries on a street car for driveability. Mechanical
secondaries (like "double pumpers") are best suited for race use. Vacuum
secondaries open up based on engine demand. Mechanical secondaries are
linked directly to the throttle like the primary barrels.
If you can fit a spacer between the carburetor and manifold, then use
one. It will help to keep the carburetor cool. If a carburetor gets too
hot, fuel can boil in the fuel bowls. This is called percolation. It
usually leads to bad things like a lean air/fuel mixture and stalling. Of
course, making everything fit under the hood is usually a bigger priority.
Original equipment on most Ford engines was a Holley carburetor. Edelbrock
carburetors are based on Carter carburetors. Most carburetors come with
either square bore or spread bore mounting configurations. Your intake
manifold will determine whether you need a square bore or spread bore
carburetor. Holleys are usually square bore, and Carters are usually
spread bore.
That's all the time I have for now. Inquire further for more detail.
- John
At 10:55 AM 5/1/2004, you wrote:
>Hello-What is the BEST carburetor setup for the Ford 289? Do you need a
>spacer between the manifold and carburetor? Is a Edelbrock taller than
>the Holly?
> What is the BEST CFM for a mildly modified engine? What is the better
>carburetor..Holly Vs Edelbrock? I do not know anything about
>carburetors...Any
>help would be greatly appreciated.
>
>THANKS
>RON 65 Tiger Mark 1
|