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Quick briefing... 78 inline 6 1 barrel carb... I want a 4barrel carb, and i know i have to change out the cylinder head, to change out the intake.
my buddies dad said since i have a 250 it would be best to go with a 2 barrel carb, instead of the 4 barrel, you'd be getting more power out of it... i didnt ask his reasoning... but this isnt true is it? i mean more gas=more power right?
It would be pretty easy to put too big of a carb on a six. Many of us run Holley 8007 4 barrels with vacuum secondaries. At 390 cfm, they are about twice as big as the stock 1 barrel (200 cfm). The good part is that the secondaries open when needed, and the primaries act like a two-barrel the rest of the time. Since they are a "square bore" carb, the primaries alone are around 200 cfm. There are also some Holley 4 barrels around 450 cfm. The V8 guys run bigger 4 barrels, 600 to 750 cfm mostly.
I think most of the 2 barrels are 350 to 500 cfm. Those two big barrels would open all of the time. I would guess that your buddy's dad doesn't know that there are 4 barrels that are smaller than some 2 barrels.
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'72 Nova in orange/black int/black rallys/250 inline
Tom Langdon (stovebolt engine co) is a great reference on these engines. He worked as an engineer at Chevy and is more that willing to help you out with your questions. For carbs on these engines, he recommended the Holley 390 CFM 4 BBL or the Edlebrock 500 CFM 4 BBL
Back in 1983, I started upgrading my recently re-built L6 (it had about 5K miles), and the first thing I did was swap out my single-barrel set up to an Offy intake and a Holley 390 4-barrel carb. That switch alone gave me enough power to break the rear tires loose (I was never able to do that before), and I went from about 15.5 mpg to 18 mpg (combined freeway and in town driving) - my best freeway mpg was right at 21 mpg (20.8 mpg if memory serves) driving back and forth from home (Central Valley in NorCal) to Los Angeles (700 mile round trip). I think the efficiency of the 4-barrel's primaries, and staying out of the secondaries when I didn't need them was the difference over the single-barrel. Anyway, that was my experience with making the induction switch from the single-barrel Rochester to the 390 cfm 4-barrel Holley.
4b carbs are rated differently then the 2b carbs. a 390 4b is basicaly smaller then the 350 2b. If not about the came . Many have also up graded from the 1b to a holley/webber carb from Tom Langdon Ihave even seen them used on the offey instead of a Normal 2 or 4b.
this is the carb i was looking at a while ago, 390cfm vaccuum secondaries... and i just didnt understand what my buddies dad was talking about, cause it'll run as a 2 barrel until you get on it then all 4 barrels open up... and as you guys said the primaries on a carb like this are smaller than a 2 barrel so your gonna get better gas if your not hot rodding it right?
What do you folks recommend as the order of importance for upgrades on a 194 inline six? Exhaust, intake, carb, cam, transmission, etc? I am wanting to improve performance and mileage at the same time and am more concerned with mileage with the current gas prices (I already have a 68 El Camino which drains my wallet). The only thing I have done to the motor so far is install an HEI which seemed to make the car start better and run smoother, but I am confused about what to do next.
In the 70's I ran an Offy intake and Holley 450 CFM carb on my 230. It was the best performance and economy upgrade I made. Properly setup, a Holley 470 CFM carb should be fine on a 250
It is something that is mostly done to a high performance motor. Or to one that has had a cam swap. It puts the advance/curve matched to the cams rpm range. Meaning changes of the springs and weights in the dist. This is best done on a dist. machine, But it can be done in the car.
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