The Stovebolt Site Forums The Shop Area The HiPo Shop 4 barrel?

i was looking through a catalouge and i noticed an intake manifold for my 235 that could hold a 4 barrel carb. i thought this would be best because more air = more power. but would it be too much CFM? its a totally stock engine with a planned exhaust of fenton headers, 2 inch pipe, a universal x pipe, and 2 flowmaster 50's. but other than that, its just a stock engine. Would a 3 barrel Carb or 2 barrel carb be a wiser choice. (fuel economy is not a factor, it is only going to be a sunday driver)

There is more to sizing a carb than number of barrels. CFM is the important measure, but also think in terms of how fast the air is moving between the carb and the valves. If the air is moving briskly, usually from a smaller opening, response is likely to be crisper.

Unless you really are racing sizing a 4 barrel with small openings and only opening the second barrels when really needed probably makes a more pleasant driver.

Too much air going slow doesn't equal more power, it equals a pause while the motor catches up. On a mild motor I'd be really cautious about too much carb.

Of course someone else will have different ideas...

thanks. i just don't want to spend my money and realize it would have beedn wiser with a different set up. so the 2 carb or 3 carb is the wat i might go

the ole man's got a clifford 4 brl intake with a 4360 holley and it work's great on his 235 .

There's a reason the GM engineers only put one 1-barrel carburetor on those engines for over 30 years- - - - -they work that way! A 4-barrel or a fancy multi-carb setup is only eye candy. It does nothing to improve performance, and usually makes the engine super-sensitive to slight changes in throttle position. If you want a rig that stumbles stalls, farts, snorts, and backfires a lot, go ahead and put too much carburetion on it. A race-modified 261 engine can benefit from extra carbs, or a 4-barrel, but increased intake flow capacity on an otherwise stock engine is only a small part of the total performance package. If you've just got to have that dual-carb setup for looks, find a manifold for an old 216 with the close stud spacing, and put the smallest-venturi 1-barrel Carter carbs you can find on it. Then you'll only be slightly over-carbureted, and if you do a good job of synchronizing and tuning those carbs, the performance won't suffer as much as if you use two of the big Rochesters designed for a 235. I think there's a very low-volume Carter 4-barrel available, but it's still got more than twice the CFM capacity a 235 needs.
Jerry

Simple bolt-on modifications, and proven...I've seen plenty of the small Holley 4-bbls, as well as the multiple 1-bbl setups on all sizes of 6's. With headers and a cam, they're HOT. Without the cam, the improvement is marginal, and some tuning may be required. But, I've never talked to anyone who didn't like it! Remember, a performance improvement generally involves an efficiency improvement...just keep your foot out of it!

I would be hesitant to put a 4-barrel carb on a low-revving, smallish engine like the 235. With an appropriately sized and tuned carb, you could get driveability that's just as good, with a little more power for getting on the freeway. I would recommend a 390 cfm Holly, or a small (I think it was 425 or 450 cfm) Rochester Quadrajet.
The Rochester has very small primaries, so it really does provide responsive driving at lower rpms. The secondaries are absolutely huge, so you'll never run out of air with your foot planted. The smallest Quadrajet came stock on the 4.3L V6 (262ci). It's about 11% bigger than your straight 6, and it winds up a little higher, but I don't think the stock carb from it would be absolute overkill. I always promote Quadrajets, because I think they've gotten a bad rap. The Holly is a good choice, too. Both of these carbs are progressive, vacuum secondary, so you shouldn't be over-carbureted, even if you have more than you need.
I can't speak regarding multi-carb setups. I think they're sexy as hell, but I've never worked with them, and they scare me. It seems like if they're progressive, and you don't drive like a [censored]-off teenager, they should still serve you well.
My final opinion would probably be to go for a two barrel. These trucks were originally designed to be driven like tractors, so they're rather undercarbureted from the factory. Stepping up a notch without going overboard wouldn't hurt anything and will probably give you a noticeable boost. Once you've got your headers I think you'll really reap the benefits.

The early-70's Pontiac Firebird 230 cubic inch OHC six had a Quadrajet available as optional equipment. The calibration of that carb would be pretty close already, without a bunch of jet or metering rod changes. It might be a challenge, getting that one adapted to a 235, but it's probably possible to use the 4-barrel manifold that's already available, with an adapter plate of some sort. It would definiotely be a conversation piece with that carb installed!
Jerry

The key to selecting a carburetor to use would be the footprint of the available manifold. Manifolds are available as square-bore (Carter WCFB, Carter AFB, Holley 4150, 4160, Rochester 4-GC, etc.) and as spread-bore (Carter TQ, Rochester Q-Jet, Holley 4165? not sure of the Holley number, we don't use them).

Adapters from square-bore to spread-bore and viseversa are available, but should be used only if clean, and then as a paper-weight! (My professional opinion, others will have differing opinions).

As Jerry mentioned, a Q-Jet was available for the Pontiac Sprint 230. However, these carbs were early Q-Jets, and extremely problematic. The later Pontiac Sprint 250 engines also used Q-Jets, and these Q-Jets were excellent carbs. Downside...very rare, and quite expensive (both criteria also apply to the 230 Q-Jets).

To say the engine would be overcarbed is somewhat untrue, as Pontiac, in addition to the 230/250 Sprint also used a 4-barrel on the 195 CID 4 banger; and GM (Buick, Olds, and Pontiac) used a 4-barrel on a 215 CID aluminum V-8.

Power increase, although measurable on an engine dyno, would be extremely modest on a stock engine; and may not be noticable by the "seat of the pants" gauge. IF YOU DO YOUR HOMEWORK ON SELECTION AND TUNING, driveability should improve. Fuel economy could go either way, depending on your driving habits.

Jon.