I have a 83 305 firebird , and I'm thinking of changing the intake manifold, cam , and carb. What size cfm carb would be best for me ? 600 , 650 , 750 , Help please

 

The size of the carb depends upon the RPMs the cam allows the engine to spin to. The standard forumla is max RPM times cubic inch displacement divided by 3456. If you use a dual-plane intake manifold (probably a good idea, if a street-driven car), add about 15% to that.

With a 5-speed, a double-pumper type carb is a very, very good idea.

Can we assume you've upgraded exhaust already?

 

For street use, I'd pick a dual plane manifold and a carb with a vacuum secondary (if Holley, probably 600 CFM).

 

NOT a good idea with a manual tranny, regardless of street or track use.

 

Yes I have upgraded the exhaust , Heddman off-road headers and y-pipe , no cat , Hooker super comp. cat back . And I think the cam gives me redline at 6500rpms instead of stock 5500rpms .

 

You should go with an RPM or Stealth type manifold to get the upper RPM range capability. Their dual plane design will maintain some low RPM manners for around-town driving.

With the formula, you get 575 CFM (roughly). With the dual plane factor, that bumps you up to about 650. If you try to go WOT with a 650DP on a 305 below about 1400 RPMs, you'll probably bog.

 

I was planning on the edelbrock performer rpm intake manifold w/matching cam and lifter kit. And I was thinking of valve springs since the heads will be open to put the lifters in.
And I was planning on a edelbrock 4-barrel carb. but after reading the carb. info page I don't know which one to get.

 

Later grinds from Comp, Crane, Lunati, Isky, etc., will produce the same peak power #'s and help a whole heap with torque in the lower RPMs. Of course, such a cam & lifter kit will run you $150 instead of $80, so only you can decide if the extra $'s are worth the extra umph.

If you're considering the Edelbrock carb, you might was well keep the q-jet. The only advantage the Performer would have over the factory carb is being slightly less confused at idle with excessive cam. Do some research on demand-type secondary carbs and how they open & close the secondaries, you'll understand why I keep saying a double pumper (AKA mechanical secondaries) is the way to go with a manual transmission. Doesn't matter if it's a Performer, Thunder AVS, Holley or Demon vacuum secondary, q-jet, etc. - same story. Especially with a T5.

 

I say from experience go with a Weind Stealth intake. A Crane Blue Racer .442/.465 cam ( I've been running one for 38,000 miles, great cam for the money) Holley 570 Street Avenger, and some hedders. You won't believe the performance and mileage. And excellent driveability. Also nobody has mentioned if you change the carb you will also have to change out the distributor. I'm running a Mallory HEI. By the way this will be good for mid 14 1/4 mile with 3:42 gear and good traction.

 

Whys that?

 

When you ditch the computer-controlled carb, you have to ditch the computer-controlled distributor also...unless you want to try some type of PROM.