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Here's what I have: 87 RC, 318, 2 bbl, 3.21 gearing 4X4

I need more low end power for towing the boat. Gearing will obviously help and 3.55's are on the plan. But if I put in a bigger exhaust and a new RV cam, would I be helping or would the 2 bbl be limiting my gains.

This is a daily driver and boat puller, don't think I want a 4 bbl (I have one on the trail rig and that sucks down the fuel.)

Thanks,

John
 

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Yes, the exhaust would help, either a 3 or 3.5 inch single is most cost effective.
Altho, as you mention, the 2bbl is a limiter. You could adapt a larger cfm 2bbl to the existing manifold without much trouble.
However, IF you change the cam, the manifold would be off, and you could swap to a 4bbl manifold at that time with no major extra effort.
 

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IMHO i would swap out that 2bbl for a 4bbl. when i had my 318 with a 2bbl carter bbd carb i was getting maybe 10mpg on a good day.

i swapped it for an OEM 4bbl manny and dropped a 500cfm edelbrock on it and i started getting about 14mpg and a ton more power. combine this with a decent RV cam and you wil ldefinitely notice the difference. i also swapped the stock single exhaust for a dual 2.5 inch set up and it just made it better.

i thnik the problem most people have when swapping to a 4bbl is they go overboard on it, IMO a 600cfm (which is what shows up as a factory replacement) is to much for that 318. i tried both a 600 and a 500 and the 500 was ever so much better and infinitely more tuneable to the 318.

eric
 

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intenseimages said:
IMHO i would swap out that 2bbl for a 4bbl. when i had my 318 with a 2bbl carter bbd carb i was getting maybe 10mpg on a good day.

i swapped it for an OEM 4bbl manny and dropped a 500cfm edelbrock on it and i started getting about 14mpg and a ton more power. combine this with a decent RV cam and you wil ldefinitely notice the difference. i also swapped the stock single exhaust for a dual 2.5 inch set up and it just made it better.

i thnik the problem most people have when swapping to a 4bbl is they go overboard on it, IMO a 600cfm (which is what shows up as a factory replacement) is to much for that 318. i tried both a 600 and a 500 and the 500 was ever so much better and infinitely more tuneable to the 318.

eric
I don't think it's them going overboard with the sizing that makes the mileage drop so much; I think it's people likeing the sound of the 4bbl opening up.. so they keep thier foot in it more often. On my Roadrunner I almost doubled my mileage when I went to a 4bbl from the 2bbl.. I was up to almost 4 mpg by the time I was done with it.
I'd say give it a nice Thermoquad setup.. they're not as easy to fine tune as a holley, but if you drive sensibly.. you'lll get the better mileage.. and if you need or want it.. you'll have the capability for plenty of fuel.
RV cam is a great choice; and I too would suggest around a 3" exh.
Aaron
 
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As lean as these 2V's came from the factory, adding even so much as a better exhaust will tend to lean 'em out a little more, and slightly erode low-end power even more, but the exhaust is so choked up, anything will help. If you're gonna do this, do it right. Plan on better induction, cam, and exhaust. With the RV cam, you don't need anything radical. An Edelbrock Performer/500-625 AFB/and a decent exhaust. 3-inch is overkill, unless it's a single 3-incher, and even that is a lot for your application. Just these parts will add an easy 70+ ft/lbs torque to a fatter torque curve with the stock heads.
As for mileage, I remember an article about a wild 440-6pak Challenger. The owner asked if the 9mpg was due to a hole in the gas tank. The magazine responded that they doubted that, but it might have something to do with the 6 holes in the top of the engine. As long as you don't open the secondaries, you'll probably get better mileage. Better power from a fatter mixture (to a point) will actually improve mileage.
 

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On the gearing issue, swapping from 3.21's to 3.55's is hardly worth the trouble, not to mention the cost if you pay someone to do it. The difference will be hardly noticeable.
 
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