i have a question about the carb on my friends 84 firebird S/E lg4 motor
i was not going to put this question on the tpi board and this is as close as you can come to carb
i was wondering if any of you fellow firebird owners would know what is the cfm on the stock 4 brl that comes on that car
he wants to put a bigger carb ut wants to know how big the original is so he has a starting point to go by

i was also wondering what size carb and what intake would you guys put on a lg4 with stock internals, flowtech headers and y-pipe, no cat, flowmaster 80 and a 5 speed tranny with 3.73 gears i was thinking the edelbrock rmp air gap for his car but ehat do you think
thatk you very much

 

There is a carb board closer to the top.....I thought they were 650 cfm in stock form.

 

The weaknesses of the LG4 are, in order: exhaust, from heads to street; cam; heads; then intake and carb. Until he does the other 3 things the carb and intake will make essentially zero difference, and may actually reduce performance overall.

The stock carb is plenty "big" enough up to about 350 HP. He has 145 now, so he's got a ways to go before he has to worry about it.

He needs to think of his motor as a system. Horsepower comes from flow; flow is limited by the most restrictive part of the system. If you think of the motor as being like a series of pieces of garden hose all hooked up together, let's say they're all 3/4" except for a couple of pieces of 1/2", and you take out one of the pieces of 3/4" and put in 2"; will more water flow through that string of hose? Not really. The engine is the same way.

He needs to attack the limits within his engine in the order they appear, not just un-bolt and re-bolt romantic-looking pieces that are easy to get to and sexy. He will be wasting his money.

 

There is one part of the carb that needs to be bigger - the air cleaner. That single snorkel air cleaner is a performance killer.

See the tech articles about q-jet mods. It's possible his current carb is restricted to 550-600 CFM, but that's easy enough to fix.

Like RB said, though, the carb isn't what's holding him back. The exhaust work is the right thing to do, then the cam will be the 1/2" fitting. Change that, then it's the heads. Change them, then it's compression. Up that, now the intake becomes the orifice. Fix that, and the q-jet is still fine.

Assuming the air cleaner was fixed before Step #1, that is...

 

Good answers everybody, kudos for everone. How'd this get on the tbi board?



Edit: That's more like it. I see you are getting some good info here on the carb board.

 

I would say the first thing you should do is swap the intake for something better (stock is very restrictive), I am quite happy with my performer intake. I'm pretty sure it picked me up a few Hp... much less restricted and it woke up the throttle response a little too. The carb isn't that important, but 600 or a little more is what you'd want to get if you decided to get off the computer. Also, the '84 LG4 came with 150 Hp... I'd say with my free mods, intake and carb I'm pushing 160-165 now.