Just wondering about the 2bbl...

Do you know of anybody that has used a performance 2bbl on their engine?

Right now I have a 2bbl and it's in bad shape. I was looking at performance carbs because I was thinking about changing to 4bbl. BUt I came across some different performance 2bbl(I know they only put out 500cfm), but I was wondering if they were even worth trying. I was just going change intakes and go to 4bbl, but right now I just want a smooth running car that doesn't suck too much gas.
This is all just a thought. So what do you all think I should do?

 

The only guys I know who use a 2-bbl are those who are racing roundy-round and have to because of their class.

Seriously, a decent Q-jet will get better performance AND mileage, but it'll depend on your right foot. The smaller primaries are way more sensitive/efficient that a 2-bbl. I went from a 2-bbl to a Holley (yuck) to a Q-jet, and it's the only way to go, imho. :Smarty:

 

I have an old Quadrajet on there now. But it's in bad shape. What's the usual cfm of stock 2bbl quadrajets? And what about those Demon 2bbl carbs? Are they any better than Holleys?

And would a square-bore carb fit on the stock intake?

And another thing, how is cfm categorized? because when I was looking at the 2 bbl carbs it seems that the 350cfm was more expensive than the 500 cfm. ????? wouldn't it be the other way around or am I mixed up?

 

From the Doug Roe book on Rochester carbs: :Smarty:
"Rochester has rated their 4-bbl carbs at a pressure drop of 1.5 inches Hg, and other carbs at a pressure drop of 3.0 inches Hg", and lists Rochester 2-bbls from 227cfm up to 435cfm. Because the cfm ratings are a measure of air friction as it goes through the carb, and (unless I've got it backwards) it was easier / more accurate to measure the big 2-bbl (primaries) at a higher pressure drop.
All that so say that you really can't compare the cfm of a Rochester 2-bbl to a Holley 4-bbl, because their ratings are based on different standards. Which is why GM could put a "tiny" 435cfm 2-bbl on a 455 and it would actually run.

Anyway,

The difference in 2-bbl sizes and costs you're seeing is due to the relative "popularity"/availability, not so much because of cfm ratings. LOTSA boats and trucks used the bigger 2-bbls, so they tend to be cheaper.

You can get an adapter to put a Holley / Edelbrock square-flange carb on a Q-jet spreadbore manifold, but I don't like them, because the bores don't line up, and the flow has to do some sideways turning between the carb and manifold.

I have no idea about Demon 2-bbls, but I'll bet that's a racing carb, and you could do better in a street-driven car. But I'm just guessing...

I don't like Holleys for non-race cars in general, in my not-so-humble opinion, they are cheaply designed and engineered, which is why there are so many aftermarket parts out there to solve their inherent problems, like blown-out power valves, etc. Besides, setting the float level while the engine is running and gas is coming out of the carb isn't my idea of a smart thing. :spank:

Seriously, I'd highly recommend sending your Q-jet off to somebody like John Osborn, it'll cost at most about $250-300 with shipping, and you'll have a dead-on carb set up perfect for your car. Best of both worlds, performance and mileage (again, it's up to your right foot... :Brow: ) I've even known of guys who wire the Q-jet secondary lockout in place so that the secondaries never open, so that they only have the primaries to drive around on. Doesn't hurt a thing on the carb to do that...

If nothing else, you need to get a copy of Doug Roe's book "Rochester Carburetors", published by HP books, and add it to your stack of bathroom reading materials, there is a TON of good info in it! :Smarty:

Hope this helps! :beer