Posted by Chris W. (216.172.142.27) on April 11, 2001 at 05:09:04:
In Reply to: Engine breathing ability posted by Ken on April 10, 2001 at 22:48:13:
Something else to think about. On a street engine you said that a carb needs to be sized for high air flow at cruising speeds.(I assume most people with "street engines" that are concerned with their mileage wouldn't use anything larger than a 600. Also, even though we're talking about 4BBL, most people don't cruise around with all fours open.) A smaller carb (like an Edel. 500) has pretty small venturi's, which would keep the velocity quite high. Then the fuel flow rate would have to be up to match the higher air velocity. Switch to a 600 with a little larger venturi's. These would then lower the velocity slightly. The lower velocity would then slow down the air/fuel mixture entering the engine. Then wouldn't the fuel flow rate also slow down?
It sounds kind of confusing, even to me. I'm just trying to say that the smaller carb., with the higher velocity, is going to "suck" the air and fuel into the engine faster then a larger carb. with less velocity. So you might increase your mileage with a little larger carb.
We ran a 600 on my Dad's 400 and then switched to an 800. Mileage improved from about 10 mpg to at least 15 mpg on the highway. Sometimes it's even a little better than that. Power improved big time also.
I'm not saying that everybody should stick a big carb on their car, but if you have something a "little" bigger then you running now, try it. It might surprise you.