Gregski

Some old timers say that the most common mistake is over carbing your engine, so I am just wondering if you can build a modest streetable 300 horse power 302 V8 engine under a two barrel carburetor, or do I need to be looking for a four barrel?

I have the Motrocraft 2150 carb on mine with the 1.21 venturi size which crresponds with 351 CFM according to this chart, but they go up to 424 CFM.

These numbers are for 2V carburetors only (2100/2150). The first numbers are the Venturi Size, the second is the corresponding CFM.

.98 = 190
1.01 = 240
1.02 = 245
1.08 = 287
1.14 = 300
1.21 = 351
1.23 = 356
1.33 = 424

kalli

--> Some old timers say that the most common mistake is over carbing your engine
correct

well if you want 300 horses streetable you can do that with changing the carb/.cam/intake/heads/exhaust/

however to get to 300 horses you probably will have to spin past 6000, which means you'd probably need at least 550cfm. it's all just guesstimating, but I doubt you will ever get 300Hp using a 289 coupled with a 400cfm carb

the HP numbers given with the mustangs are misleading. A 225HP a code probably does 180HP, and the K-code probably put down 225 stock (the 271 was measured differently i the past)

From that if you're going from a stock 289 2 barrell your goal would be to nearly double the HP. Hardly with the same carb.

On that note I don't believe a 500cfm 2 barrel can be as efficient and economic as a 4barrell 500cfm (or at least not that easy?)
undercarbing can become a problem as well.
For example you use a holley with a 6.5PV in the front, you floor it, the revs climb up, A/F is ok and as soon as the carb runs out of breath and the engine demands more, you will start to get more and more vacuum in the carb where you should have none at WOT. Once you pass 6.5inches of vaccum the PV will close, the whole lot will lean out so much that it can lead to desaster for the engine

Deviousfred

I bet a lot of dirt track guys would say "yes." Cheap, probably not.

Norm Peterson

Keep in mind that 2-barrel flow ratings are nearly always measured at 3" of vacuum, where 4-barrel ratings are conventionally taken at 1.5". Apples and oranges, sort of.

It is certainly possible to pull more than 350 cfm through a carb rated at 350, but in order for that to happen you'll need to have more than 3" pressure drop across it. That costs you in overall volumetric efficiency, and I think for every added psi of intake restriction you should plan on about a 7% power loss compared to what you'd have without it.

With respect to what Fred posted, here's a link, and it only deals with what you do to the carb itself. Nothing at all about the rest of the engine.


Bottom line for streetable power is (still) a small-cfm vacuum secondary 4-barrel.


Norm

Deviousfred

Great info Norm! One of the things I see in these dirt track engines is ridiculous camshaft that could not be driven on the street and I'm sure they have a lot to do with those hp numbers.

jimmy428

i have a magazine with a 60s dodge wagon that runs 11.10s in the quarter mile using a 273 2bbl engine.... with the 2bbl still on it!!! no joke. if i can find that mag i will definitely post it. no nos either. does takes a lot of skill and know how.

Norm Peterson

And I'll wager some really deep gears, maybe even deeper than 5.13's


Norm