engine tuning, carby'd

[hks_kansei]

ok, getting my first car soon, and i was thinking of giving it a bit more power, but then i realized, i don't know shit about tuning Carb'd engines.

i was thinking of exhaust, and intake mainly. because their cheap (i'd love to look into stroking and boreing, but i know they are expensive)

so, what are some cost effective engine mods for carb'd cars?

[drdisque]

bigger carb, better intake manifold, better heads, more agressive cam (notice a trend here?), the mods are basically the same as for a fuel injected car. Also you won't really need an "intake" for a carbureted car because they don't have the tubes and airboxes that fuel injected cars have that you're replacing with a "cold air intake"

[Omega_5]

Well.. if you want to mod up a carb engine, and you wanna look at the mods first.... go here:
www.jegs.com

I like to call it heaven....

[curtis73]

The only real difference (at this level) between EFI and carb tuning is that with EFI, more is often better, but with carbs, less is often better

Since the intake carries air and fuel, the weight of that charge affects its flow greatly. On an EFI car you could swap between a short fat intake runner and a skinny long runner without much change to the power band. On a carbed car you'll get huge differences.

with EFI you usually go one step up; a higher flowing TB, bigger intake, and exhaust usually bump power without much of a penalty to the powerband. With Carbs its more common to go one step down. If you calculate that you need 625 CFMs of carb, don't get the 650, get the 600. Drivability and mileage will be much better and it might cost you 1 or 2 hp. Same with intakes. For the street, keep a dual plane manifold with modest runners. A single plane will allow the fuel to drop out of suspension and puddle on the walls since the idle charge will be moving so slowly. Then those puddles shear off and get sucked in which further contributes to the drivability issues associated with really hopped-up engines.

Same thing with cams. Overlap is critical. Since carbs rely entirely on flow and vacuum, the heavy overlaps on some performance cams make tuning a nightmare. EFI is as easy as telling the injectors to squirt X amount of fuel. The greater the valve overlap (larger duration, smaller LDA/LSA) the worse the vacuum signal to the carb and idle and part throttle drivability tend to suffer.