Can you get 300 hp from a 2 barrel carb?

[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

 

[78CobraII]

You can probably make 300 HP with a 500 cfm 2bbl. However it would be happiest at wide open throttle and would not have great throttle response or efficiency at part throttle because of the venturi size.

In some cases a small(er) 4bbl will have better fuel mileage and throttle response due to its smaller venturis. Of course you have to stay out of the back barrells to get the higher fuel mileage...

For your project engine I might go with the 500 cfm 2 bbl.

The 302 in the MII will greatly benefit from the usual flow improvements...a higher rise dual plane intake, matched (to the manifolds) intake and exhaust ports, a higher lift cam, and higher flowing exhaust.

The mid-late '70's 2bbl 302's (like the MII) were rated at about 140 HP SAE. These engines really aren't much different from the mid-60's 2bbl 302's that were rated at 200 HP (non-SAE). The polution controls that were on the later engines were probably only taking 15-20 HP off of the engine in the range where HP was measured, so most of the difference between the early and late measurements were in the method. What I'm getting to is that the mid-'70's 302's were much closer to the mid-'60's output than anybody gives them credit for.

If you want a cheap factory 4bbl aluminum intake and carb to play with, look for the '84-'85 5.0L HO engine factory 4bbl intake and carb. Its only a 465 or so cfm carb, and the intake is pretty low profile (fits under the MII hood with no mods!), so its not a high-performance part, but it should be cheap. A better choice performance-wise would be the '68 302 4bbl and intake, but those are probably pretty rare these days.

Of course any swap-meet aluminum dual plane 302 4bbl intake will be a higher performance part than these factory parts. Just stick with a small 4bbl or the 500 cfm 2bbl.

 

[gregski]

wow great advice

thank you very much for your very detailed recommendations, I have learned a lot and agree that measuring gross horse power in the 60s vs net horse power in the 70s does make the 302s similar in output

I guess I was intimidated by the 4 barrel carbs before I knew how they worked, I guess for the most part they run on 2 barrels and only when you gun it the other 2 barrels kick in, I thought they ran on 4 barrels all the time, I much rather have an efficient 4 barrel carb now rather than a huge 2 barrel

I like the tip on the OEM '84-'85 intake manifolds and will keep an eye out for them, however I bet they are EGR as well, and I want to delete my EGR and the accomodating spacer for asthetics mostly and to keep things clean and simple

of course if I can score an aluminum intake that would be best, we'll see I'm trolling Craigslist daily, LOL

thank you very much for your advice, much appreciated

 

[Wart]

.. I thought they ran on 4 barrels all the time,

Depends on the driver.

I like the tip on the OEM '84-'85 intake manifolds and will keep an eye out for them, however I bet they are EGR as well, and I want to delete my EGR and the accomodating spacer for asthetics mostly and to keep things clean and simple

You could try locating a set of intake gaskets without the exhaust passages.

Or plug the passage(s) in the intake. Long as a 'normal' spacer seals. Or a spacer could seal off the passages with the right spacer and gasket combination.

Or get the EGR spacer and "hack" off the "extension" and plug the ports.

All sorts of possible ways around it.

Thing you need to know is with a carb set up to work with an EGR will run lean in hte mid range. The EGR adds inert gas(es). Removal of these gases creates a O2 rich / fuel lean situation. May make a difference, probably not.

I mean, it IS a low compression '70s engine.

OTOH, a malfunctioning EGR and the engine doesn't idle worth a crap and probably not make full power.

What a trade off.