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patt 8/30/2011
1980 Pontiac LeMans Base 4Cyl5.2L - Engine
1970 Pontiac Lemans Sport, 350 Engine, AT
Will there be any advantage, i.e. better gas mileage, in converting my 2 bbl carburetor to a 4 bbl carburetor. I am mainly concerned about better gas mileage. I currently get about 9 MPG in city and about 12 MPG on highway. The vehicle is all original
1 Answer
  • Jimm
    Jimm 8/30/2011
    You may realize a slight increase in fuel mileage - due to the smaller secondary venturis on the four-barrel carburetor versus the two-barrel. There are several cost-effective improvements you may also consider; tuning with seat-of-the-pants timing method (try advancing the distributor base timing just far enough with the highest vacuum gage reading at idle, and the vacuum advance disconnected) just before the engines starts to 'ping'. Changing the rear axle ratio to a lower numeric ratio; i.e from 3.50:1 to 3.00:1 or 2.80:1 as example - may help in reducing the engine RPMs at cruising speeds. You may also try; improving the exhaust (less restriction) with a more free-breathing muffler. Swap or upgrade the points ignition to a Pertronix Igniter (drop-in) electronic unit (hides under the stock dstributor cap). Upgrade the stock camshaft to an RV or higher torque-style of cam profile to give greater economy.
    patt 8/31/2011
    Thanks Jimm. You've been very helpful

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