Join Date: Jan 2019
Location: Sedgwick, Kansas
Really, "too much" carb is kind of a hard thing to judge. A lot of it has to do with the boosters, etc.
What you need to be asking is how will the car be used, and whether it will support good atomization in the RPM range it's most commonly seeing.
I think a better rule of thumb is figuring out how many horsepower the engine will realistically be using, and size the carb for that, because that way you've got a better idea of how many CFM you need at WOT to prevent loss of power from too much intake vacuum.
With a typical 4V setup on the street, you're better going "a little bit too small" than "a little bit too big", because with a big carb, the air going through your boosters will be so slow, all you'll get is big fat drops of gas as you run around town. Your car will run "rich", get lousy mileage, and foul plugs, even though it acts "lean". A smaller carb will have better atomization and much crisper throttle response.
For a car that only sees use on the strip, going "too big" may be just right, because who cares about cruise or idle, so long as it runs? You want every last horse you can wring out of it, and having little to no vacuum drop at WOT (from carburetor restriction) is an effective way to get that. While 900 CFM is kind of silly for a 500 horsepower motor being street driven, on the top end, it might make 5-10 more horses than a 750.
Annular boosters are awesome on the street, because at any speed, they are very effective at creating a fine mist of fuel/air for your motor to burn. Some racers feel that they cause too much restriction to be effective for track use, but I think it's more that not too many "performance" carbs have them, and the carbs that do tend to be smallish/hard to tune/find parts for - like the 4100.
Last edited by Grimbrand; 04-17-2019 at 05:17 AM.