Posted by Gypsy Jim on January 09, 1999 at 01:02:56:
In Reply to: Re: Carbuerator comparison on dyno posted by T.L. on January 08, 1999 at 20:57:14:
:Theoretically, a 302 engine will draw into the cylinders 524 cfm at 6000 RPM. That's 302 cu in * 6000 RPM divided by 2 (each cylinder only draws in air/fuel once every two RPMS)and then divide this number by 1728 (the number of cubic inches in a cubic foot). This is theoretical in that it assumes that there is no resistance to air/fuel getting into the cylinder via the carb, intake, and valves. The less resistance you have for air to get into the cylinders, the more fuel that can get into the cylinders (i.e. a more radical camshaft with increased lift improves the performance of an engine). A 600 cfm carb is operating at 87% capacity (524cfm/600cfm) whereas a 750 cfm carb is at 70% (524cfm/750cfm). The 750 is going to definately let more air/fuel into the engine - if you have a "decent" cam and headers/low restriction exhaust.
Flow isn't the most important factor of a carb, though. The most important part of a carb is the fuel metering and atomization. You want the same air/fuel mix throughout the RPM range. Every carb has a specific profile and will work best at some range. To achive the best and broadest range of performance, manufacturers alter the fuel metering, jets, float set-ups, venturi/air horn design, and whether they are vacuum or mechanical. Each of these will effect the performance of the carb and your engine.
Just one other thought. You have to realize that while 302's need to be spun at high RPMS to produce HP, the actual amount of time you spend at 6000 + RPMS may be small compared to the amount of time spent driving around town - which is usually in the 2500-3500 RPM range. A large carb will cost you performance (throttle response) and fuel economy in this range. The bottom line, if you want an extra 20-40 HP, go with the 750, but be aware that you'll be sacrificing street performance in the low/mid-ranges. Otherwise, as T.L. noted, a 600cfm carb will flow fine on a stock/street small block.
What you don't seem to understand is that 750cfm is 750cfm. The horsepower will be the same regardless of what brand you use. What it comes down to is reliability, driveability (throttle response), and price. Another thing to consider is that if your wngine is less than 350 cubic inches, you do not need a carb larger than 600cfm. Not unless you have a super radical cam and radical cylinder heads with huge valves and ports. A 302 for example, will not flow more than 600cfm at 6000 RPM...
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: : Does anyone have the stats for 750cfm Holley, 750 Carter
: : and 750cfm Edelbrock? I would like to see what horse power
: : each carb produced on a dyno.