quote:Originally posted by Joules5:
...besides MME elevated the stakes offering 725 HP and a 2 year guarantee...
Unless you are involved in true competitive racing where a trophy, prize money or a title are at stake, what does it matter how much bhp your motor makes? What matters is the powerband and throttle response. Doug makes a point worth repeating over and over, you've got a 500 bhp radiator (at best), a 550 bhp transmission, and a chassis prone to cracking. In 1972, Panteras racing in the world endurance racing series were able to attain top speeds of 170 mph with 500 bhp motors. 500 bhp is enough to spin a 335 section rear street tire for hundreds of feet. On the street, where we accelerate from stop lights, the car with the best low rpm torque, throttle response, and that hook the tires up the best with the asphalt will win the race. I've always advised owners building street motors to shoot for a powerband of 2000 to 6000 rpm, and the rest be damned.
quote:Originally posted by Joules5:
...Webers on an IR manifold can support up to maybe 500 HP and then they drop off as the Independent Runner manifold is restricted in per cyclinder flow rates in comparison to an open plenum type design. Is that true, valid to a point or urban myth...
I don't have experience with Webers on a 7 liter motor. I have read before that the 427 FE motors used for road racing in the sixties did have Webers larger than 48 mm. On a smaller motor the 48 mm variety provide plenty of capacity. Keep in mind the reason road racers run Webers is for throttle response coming out of a corner. Power quality, not quantity. Regardless of the size of your motor, if they get you to 6000 rpm before flattening out, that's good enough for a street motor in my book.
Lets play with some numbers. These are rounded off numbers. A Weber 48 mm carb flows about 600 cfm, thats 300 cfm per venturi, or cylinder. 300 cubic feet is over 500,000 cubic inches. A single cylinder of a 427 cubic inch motor displaces 53 cubic inches. Running at 6000 rpm, that 53 cubic inch cylinder will inhale 160,000 cubic inches of air per minute. The single venturi of the 48 mm Weber can supply 3 times that much air. There's more to it than this of course, such as depression at wide open throttle, but you get the picture.
To summarize, the reason to equip a motor with Webers is for the throttle response, the pull coming out of a corner or off the line, the looks, the sound. Whatever you might give up in maximum bhp will not be missed, unless you take your car to a dyno day shoot out. On dyno day, the guys with large single four barrels on a high rise manifold will probably win.