Inliners International Forums General Discussion Engines 2 Barrel vs 4 Barrel

Buying a new carb for my 230 inline 6 and am stuck on options. The motor is stock except for tube headers and an HEI and is in a 3500lb pickup. I was given an offenhauser 4 barrel intake years ago, and thought about spending the $350 for the Holley 390CFM, but I'm told it will be too much carb for the motor and if i got it to run right, would have no benefits over the stock rochester. Is this right? I also thought of maybe getting a 2 barrel and buying langdons adaptor to my stock intake. Cheaper route and its progressive with close to 270CFM, and maybe would suite better, but this one is off of a 4cyl car.... what do uyou think?


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I think any carb bigger than stock will give you more power,, up to a point.

A 2 bbl carb would probably better suite your stock 230 CI engine for the time being.

The Holley 390 will work also. Depends on what you are looking to get out of it.
Better mileage,better power.

If it was my truck, I would use the Holley 2 BBl or Langdons 2 barrel for better mileage.
If it was a 250 with a little more mods done to the engine,a nicely prepped Quadrajet.

For all out power from a carb or carbs,, sidedraft Webers DCOE's
Very streetable & provides a lot more torque. Pricey though $$$!!

MBHD

Bigger carb will add power until the WOT vacuum falls below about 1.5" Hg.
If it's not jetted correctly, it may reduce power (and mileage).

If you take 2 carb's:

390 cfm 2 bbl
390 cfm 4 bbl

You will get better throttle response from the 4 bbl than the 2. Its all about booster signal - smaller venturi - high air speed better signal & better driveability.

If you get a 390 4bll vac sec. and tune the sec. opening rate it'll work well.

But... 2 bbl. and 4 bbl. aren't rated at the same pressure drop.
A 2 bbl. identified by the manufacturer as 390 CFM actually flows 276 CFM @ 1.5" Hg.
A 4 bbl. identified by the manufacturer as 390 CFM actually flows 552 CFM @ 3" Hg.

I ran a stock 600 holley on my Stock 250 with the offey intake.So as long as you can tune that 390 in, you shouldn't have a problem running it on your 230.

CFM-wise you'd be fine either way.
The stock 230cid/140hp carb is about 140cfm (at 1.5" Hg).
Way too small.
My rule for carb CFM (at 1.5" Hg) is, "double your horsepower" - that's how much CFM you need. About 10% less than that works fine. Even less will work, too, you will just lose top end. Sometimes way MORE is ok too if it is a progressive carb or a light car with steep gears.

The 32/36 Pinto "270cfm" Weber is about 200cfm at 1.5" Hg.
Not quite enough for a 230cid but bigger than even the 230/155hp HiPo carb which was about 185cfm. So that would work fine.

But you could be just fine going bigger, my experience is same as Twisted's. I've run and clocked CFM's from 390 to 450 to 500 to 625cfm on my stock 250, no correlation between et/mph and CFM, even though they all were a bit big for the 170hp engine. I will say though, the only ones I could stomp on off the line without a "gasp" of air were the 390 and 450cfm Holleys. So if you ever plan to upgrade to a 292cid or build the 230 up, then the 390 Holley would be a better choice.

Depends on your plans -

Thanks for the help guys, I'm going to use the Offy intake and buy thr 390 Holley. I get the cool factor of an offy and a 4bbl, will get mileage and performance, maybe with some tuning but thats fine, and I will get a new carb and won't haver to deal with the 46 year old one.

There was a great article on tuning Holley 4-barrel carbs in the May, 2010 edition of Street Rodder magazine that may help you. It's located here: http://www.streetrodderweb.com/tech/1005sr_carburetor_setup_tips/index.html
Good luck.

Not impressed by the article:
a 350 engine multiplied by a 5,500-rpm redline, divided by 3,456 equals 557
That's for a single-plane manifold, still gets repeated every 5 minutes. Dual-planes can be much larger, as can vacuum secondaries and spread-bores.
(power valves are) available in different sizes to match the flow requirements of the engine.
They're all the same size, and they don't match any flow requirements. Ooppsss - does he know what the PVCR does?

He sounds like someone trying to re-write someone else's article, but doesn't know how the carb works.