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Author Topic:   Rochester CFM Question !
ddoti1
Dirt Roller

Total posts: 23
posted June 03, 2002 05:16 PM
I have a Rochester 2 brl ( 2 Jet ) from a carb shop that is suppose to be 625 cfm, Can anyone tell me if one can be built to be say 750 cfm, or is that unheard of for a 2brl of this size ? Because these carbs aren t that big. Is the 2jet the largest of the 2 brl carbs or is the 2g ? Does anyone know of a site that has info on Rochester carbs for specs & so on ? Thanks !

powerglides
Dirt Full Roller

Total posts: 69
posted June 04, 2002 06:40 AM
The 2 jet and 2g are the same carbs and yes thats the biggest rochester 2 barrel there is. The largest stock ventury bore is 1.375 As far as flowing 625 cfm, unless the choke horn is carved up that is a misstatement.

KPLugnut
Dirt Freak

Total posts: 408
posted June 04, 2002 12:21 PM
The above post is correct. The largest venturi diameter ever made in ANY Rochester 2bbl carb was 1 3/8". The largest throttle bore size ever made was 1.687". That stock-type configuration was rated at about 450cfm at the MOST.
Now...
Carb shops that build 2jet/2G/2GV/2GCanything Rochester 2bbl related that is advertised to flow over 600cfm, well, they HAVE to be modified inside.
Venturi diameter bigger than 1 3/8", and throttle bores larger than 1.687" have to be used. Not to mention many other littler more subtle mods have to be done to the carbs for them to flow the proper amounts of air and fuel at all rpms.
Our largest "outlaw style" 2G ever made was able to flow close to 700cfm, but the idle quality of a carb of that nature absolutely stinks. It is ALL top end, boys. Forget idling at below 1000rpm. BUT....if WOT performance with HP up in the 7500rpm range is what you want, then that is the carb for you.

Just some info....other carb builders' results may vary....

KPLugnut.

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