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would a differen intake manifold improve gas mileage

i have a 1984 chevy scottsdale 3/4 ton and it has an edelbrock hi rise intake wwith a 4 barrel and im getting about 9 miles to the gallon. would going back to the stock manifold and carb improve my gas mileage?


  • edited January 2010
    If you still have all the original parts, it might make a difference. If you have to buy the original parts and pay someone to do the work, you might not get a return on your investment. Do you know if there were other performance modifications to the engine? If it has a performance camshaft (quite possible since often done to get most out of the bigger carb) and runs more advanced timing, the original carb may not work well with the other mods.

    If you can find a carb knowledgeable mechanic it might be possible to disable your secondary barrels. The primary barrels run the truck and the secondaries (which are much bigger) kick in when you press down on the gas petal. Sometimes the secondaries are opened by a mechanical linkage, and in other carbs they secondaries are sucked open by vacuum pressure.

    If you can find a way to keep the secondaries off line, you'll save gas. Of course, when you want power you'll have to live with a lot less of that.
  • edited January 2010
    The guy who put the Edelbrock on probably wanted more performance, and was not worried about gas mileage.

    If you don't mind a loss of power, there were some small ventury "economy" carbs (even smaller tha the standard) made that would trade off power for economy. Budget about $500 or so plus labor, unless you can find one from a parts yard.

    Make sure no other mods were made, such a s "performance " rear axle or camshaft!
  • edited January 2010
    i dont have any of the original parts i bought the truck from a friend of the family for 200 dollars and i dont think it has a diffrent cam shaft but i really dont know much about the truck so i could be wrong i would go ask the guy but he passed away in september and i just lost my job so i cant afford the gas for it so how could i tell if i have a different cam in the motor?
  • edited January 2010
    Maybe, maybe not. You have not stated what gear ratios are in the truck, type of terrain driven in, what engine, and what type of carburetor is on it.

    If the truck has a 454 with a Holley then it's doing very well fuel-milage wise.

    Assuming the driving habits are not aggressive, the ignition timing is not a mile off, etc. then the truck should do much better on fuel economy than it is.
  • edited January 2010
    it has a 350 with an edelbrock 4 barrel im not sure about ggear ratio on the truck but its a 2 wheel drive with a 3 speed automatic transmission, i drive on all types of terrain and i dont hot rod it around the timing is set accoriding to factory specs and im still getting 9 mpg no matter where i take it or how i drive it. this doesnt make sense to me. my friend has an almost identicle truck and he is getting 12 mpg
  • edited January 2010
    The Edelbrock carb is a pretty good carburetor. (Got 3 of them myself with 2 currently in use)
    My hot rod Ford 302 has dual Edelbrock 600s (CFM overkill I know, but it looks cool) and it gets 20-21 on the highway, which stunned me the first time I checked it. I was praying to the automotive gods for 12 MPG when I first got it running.

    You might try decoding the rear axle tag and make sure that you don't have a set of real low gears in it. (4:10s, etc.) With a 3 speed auto a ratio like that would really have that engine winding up.

    This one is hard to decipher without truck in hand but some possibilities could be:
    Timing not advancing as it should?
    Weak engine due to wear? (piston rings, valves, etc.)
    Transmission slipping?
    Partially clogged catalytic converter? (assuming the cat is still on the truck)

    If you do your own tinkering I would suggest purchasing a vacuum gauge. This tool is cheap, bone simple to use, and is one of the best tools in the toolbox in my opinion.
    Connect it to an intake manifold vacuum port and it can reveal any one of a number of potential causes within a few seconds.
  • edited February 2010
    302 is a great motor. Timing is advancing right just did the rings and the tranny is brand new it is an 84 and cats were an option, my truck never had them
  • edited February 2010
    Lets see, your carb is a copy of a Carter AFB I think..It has main jets and metering rods that can be changed. After you learn how the carburetor meters fuel into the engine, you can start experimenting with the jets and needles and perhaps improve your mileage a little. Part of this process is learning how to read spark plugs so you know when you have reached the lean limit. If you over-due it, bad things can happen (burned exhaust valves) so knowledge is important here..
  • edited February 2010
    If it's an 8 lug nut 3/4 ton, 12 mpg would be about the best you could expect if back to original. If it's a 5 lug, 14+ might be possible. I really can't understand why anyone would waste the time and money to install high performance parts on such a work dedicated truck. It's kinda like me spending $500 on a pair of track shoes and wearing them to push a car around the shop.
  • edited February 2010
    i didnt put the hi rise or carb on the truck i bought it that way and it is an 8 lug 3/4 ton and im getting about 9
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