I currently own a 1984 Z28 with these mods: Edelbrock Performer Intake Manifold Edelborck Headers, and a total aftermarket exhuast with a high flow muffler. I plan on putting a new cam and Heads in very soon. I was thinking about the Speed demon but what cfm? I wanna really make some hp!

 

Is this a 305HO with Q-jet carb? Don't you have a computer on that? If so, then plan on replacing more than just the carb. Without a CC carb, your computer will screw up your timing, so you will have to get a non-CC distributor.

With the 305, don't go too big with the carb. You could do some mods to the stock Q-jet, check the tech articles. You can get over 650 cfm out of a stock Q-jet. Depending on the cam/head combo you go with, I think 650+ cfm would be plenty for a stock short block. As far as Hp, what is your goal. Or how fast do you want to go(1/4 mile)? Later.

 

The guy i bought the car from took off the computer controled stuff and put on a Webber Carb. I have no idea what size it is. I would like to see myself doing the quarter in 12.5 mybe a little higher.

 

Assuming no nitrous or huffer, your dreams will probably stay just that.

Could mid-12's be done with a NA 305? Probably. Major cam, major head work, better exhaust and intake than you've got, rotating assembly good for spinning up to about 8 grand, steep gears, serious suspension work, sticky tires, about an 800 pound diet, really loose torque converter in front of a built transmission, kiss driving it on the street goodbye.

Oh, about a 750 DP Speed Demon. Or a stock q-jet.

Now, want to be realistic? Basic bowl and port work on World S/R Torquer 305 heads, nice cam, slightly higher stall converter (assuming auto tranny again), gears, suspension work - you could be in the high 13's. It's still real horse power. Streetable horsepower. Now you're talking about a 600 CFM VS Demon. Or a stock q-jet.