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hank63
12-26-2006, 09:19 AM
Not long ago, somebody asked how big a carby could be used.
The only formula I've ever known, is "engine ci x max rpm x 0.5 / 1728" which gives the answer in cfm.
Assume 289ci and max 5000rpm => 289 x 5000 x 0.5 / 1728 which gives 418 cfm. If you don't mind revving to 6000 rpm you get 501 cfm.

Carbies are only capable of maximum wide-open throttle efficiency in the upper 40 – 45% of their flow potential. Fitting an oversize carby will only mean that the maximum wide-open throttle efficiency comes in at a higher rpm. Also, don’t forget how the secondaries open – vacuum opening is definitely the way to go for street driving.
/H

DEEPNHOCK
12-26-2006, 11:16 AM
Most Yankee's are running the Edelbrock AFB carb for ease in tuning and great driveability. Also has the right bolt pattern for a Stude 4 barrel manifold.
http://www.edelbrock.com/automotive_new/mc/carbs_acc/performer.shtml
Some good reading can be had by downloading their carb application guide, available at:
http://www.edelbrock.com/automotive_new/mc/carbs_acc/pdf/carb_app_chart.pdf

500 cfm for a 259 V8, and a stock 289 V8 engine
http://www.edelbrock.com/automotive_new/mc/carbs_acc/images/1403.jpg
P/N# 1403
500 cfm, Manual or Electric Choke
CALIBRATED FOR PERFORMANCE
Designed and calibrated for small cubic-inch engines such as 305 c.i.d and smaller Chevrolet; 302 c.i.d. and smaller Ford and dual-quad applications such as Edelbrock C-26, F-28 and Street Tunnel Ram. Match with an Edelbrock Performer or Performer EPS manifold and other brands of similar design. Includes both timed and full vacuum ports for ignition advance. Comes with: Metering Jets – Primary .086, Secondary .095; Metering Rods – .065 x .052; Step-Up Spring – orange (5" Hg). Use Carb Studs #8008 or #8024 if needed, see Install Items. For auto trans throttle lever adapters and more, see Tuning Accessories.
500 cfm, square-flange, electric choke (non-EGR) #1403*
500 cfm, square-flange, manual choke (non-EGR) #1404*

Or.....

600 CFM (for a hot Stude engine)
http://www.edelbrock.com/automotive_new/mc/carbs_acc/images/1406.jpg
Electric Choke
CALIBRATED FOR FUEL ECONOMY
Designed for small-block and small displacement big-block engines, these carbs are recommended only for stock to Performer level applications. They are not recommended for use on RPM or Torker II intake manifolds. Match with an Edelbrock Performer or Performer EPS manifold and other brands of similar design. Calibrated 2% leaner than #1405. Includes both timed and full vacuum ports for ignition advance. Comes with: Metering Jets – Primary .098, Secondary .095; Metering Rods – .075 x .047; Step-Up Spring – yellow (4" Hg). Use our Carb Stud Kits #8008 or #8024 if needed, see Installation Items. For auto trans throttle lever adapters and more, see Tuning Accessories.

600 cfm, square-flange, electric choke (non-EGR) #1406*
600 cfm, square-flange, electric choke (non-EGR) w/ EnduraShine finish #[u]14064</u>* (OOoooohhhh shiney!)


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DEEPNHOCK at Gmail.com
Brooklet, Georgia
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Dick Steinkamp
12-26-2006, 11:53 AM
quote:Originally posted by hank63

Carbies are only capable of maximum wide-open throttle efficiency in the upper 40 – 45% of their flow potential. Fitting an oversize carby will only mean that the maximum wide-open throttle efficiency comes in at a higher rpm.


Hmmmm....I'm probably reading the above wrong, but the carb WILL flow 100% of its RATED CFM (dry), if you suck on it hard enough (or blow through it hard enough). Per your example, a 289 CID engine (at 100% volumetric efficiency) will flow a 500 CFM carb at max at 6000 RPM.

http://www.csgnetwork.com/cfmcalc.html



Fitting an oversized carb will result in poor low speed performance driveability issues), a "bog" when feeding in too much throttle from a start, and poor fuel economy.



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Dick Steinkamp
Bellingham, WA

Mike Van Veghten
12-26-2006, 12:18 PM
Dick...most of what you say is correct, and more would be happier if they stayed closer to 500cfm, for stock and mildly modified 259's and 289's, (The BG carburetor line now has a 525cfm carb.).

Except the "bog" part isn't totally on track. If not tuned correctly, a "bog" can be found with a two barrel carb. An Edelbrock 1403/1406 can have/develop a bog if not tuned correctly. Conversly, a 750cfm carburetor can be tuned to "seemingly" work just fine on a stock 259 engine. It'll just be down on milage, power and driveability. If tuned correctly...no bog will be present..

Now I suppose if one were to install a Holley Dominator of the 1050cfm or larger..."that" most likely produce a bog that wouldn't be tunable...but that would be a real chore and quite a few bucks to buy and install!

Mike

studeclunker
12-26-2006, 05:39 PM
Mike and Dick,
I installed a 650 CFM Holly on my Champ (259) because that's all I had on hand. Is there a way to work with this? I can see what you mean by stumbling on a start. It does. Right now it's necessary to work with what I have on hand. Kinda short on cash...

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Lotsa Larks!
K.I.S.S. Keep It Simple Studebaker!
Ron Smith
Where the heck is Lewiston, CA?

Mike Van Veghten
12-26-2006, 05:58 PM
The 650 Holley is a big carburetor for this engine.

That said, nice thing about the Holley is the tuneability.
If you have a stumble...there are several places to look -

1. Idle mixture screws correctly adjusted
2. Throttle blade angle within a usable location within the transfer slot.
3. Accelerator pump cam swap.
4. Accelerator pump nozzle swap.
5. Power valve sizing correct (vacuum wise).
6. Ignition timing.

These all have to work together.

Save your money and get something a little smaller. In the mean time, have fun working the Holley out.

Mike

hank63
12-27-2006, 12:36 AM
One problem with oversized carbies is the air flow velocity. When too low, fuel vaporisation isn't what it should be, leading too poor response and chronically bad fuel consumption.
I expect that can be improved with special manifold and hi-rpm driving, neither of which comes cheap.
I'd stick with max 500cfm. If I had a bigger carbie, I'd try to swap it (if cost is an issue).
Mind you, if cost truly was an issue, we should all drive little 4-cylinder egg beaters made up of plastic and electronics (and replace 'em every 2-3 years).
/H