Thread: The Black-art Of Carb Sizing

Tweet

The reason I labeled it a black art is because of the controversy when it comes down to it, everyone thinks they have the simple answer. L@@k at this feed back so far. Many different answers. Some of which are fine points and others that a fine opinions.


Everybody including myself, wants a street engine to perform like a street engine with street engine manners, drivability, economy, etc etc............. But what is the harm in running a more power ful carb WITHOUT GIVING UP ANYTHING ON TORQUE. If you were to go back and reread my article, you will see that I am not shooting for highest hp numbers only.


The most common racer mistake is to assume that bigger CFM equats bigger HP. The next most common mistake is to assume that a carb can have to many CFM for an engine.... Confused by the contradiction there?? The problem isn't with the carb having too much CFM but, not enough booster signal to go with the available CFM. Given enough booster signal for atomization, you can give an engine all the CFM it needs at top and still deliver down low.

CHECK OUT THIS COMBO:

Chevy 355
9.8 CR
Comp 268H
Roller tip rockers
Chevy 186 heads
Edelbrock Performer RPM
Holley 750 reworked to flow 820cfm
1-5/8 headers Dynomax 2-1/2 mufflers


RESULTS:

TORQUE: HORSE-POWER:

@2K-353 152
@25-356 178
@3K-375 205
@35-398 265
@38-406* 288
@4K-404 314
@45-398 345
@5K-395 373
@55-368 377
@58-347 381*
@6K-335 380
@62-310 374

THAT IS A NICE, DIRT CHEAP COMBO THAT IS VERY MUCH AT HOME ON THE STREET. I RAN THIS ENGINE FOR ABOUT 3-1/2 YEARS WITHOUT A SINGLE PROBLEM. IT HAD A SMOOTH IDLE AT ABOUT 725, PULLED MORE VACUUM THAN I KNEW HOW TO USE, AND HAD A STOCK CONVERTER WITH A 3.42 REAR GEAR. I HAD IT IN A '76 NOVA AND RUN 12-90s @ 107. SHIFTED AT 6500 WITHOUT EVER A GLITCH UNTIL ONE-DAY AT A STOP LIGHT I JUMPED OFF WITH A STANG AND LOST OIL PRESSURE AT THE TOP. PICK-UP FELL OUT THE PUMP AND IT WAS BRAZED, JUST NOT GOOD ENOUGH. NOW I BRACKET THEM AND BRAZE.
THIS WAS MY EVERDAY DRIVER CAR FOR WORK AND ALL.