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?

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.

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!

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?

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.

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

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.

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

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…

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.

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

Your truck is in the “correct all defects and accept the mileage given” situation. How much would you spend to put a manifold and carb on? how long would you have to drive at the better mileage to recover these costs from any (and that’s a big “if any”) mileage gains.

yeah haha now its running like sh*t i think its the distributor cap or plugs (the plug wires are brand new)and its running really rough and has no balls at all

If the carb’s set up too rich, that might cost you a couple of mpgs. Any way to get an exhaust check to see? If so, maybe new jets/rods/adjustment would help.

it runs a little rich. i just rebuilt the carb (done many many carbs) still no change in how it runs or the mpgs it gets so idk i pretty much just gotta deal with bad mpgs i guess

I had MAJOR problems with the carb on my 84 GMC S-15. I rebuilt one…but it had the same design flaw so the rebuilt only last about 30k miles. Ended up buying a Eldebrock carb…Best choice I ever made. Little less gas mileage…but I wasn’t playing with the carb every weekend.

get a 2-plane edlebrock performer. hi risers are for top end running.

stock manifolds are crap unless ported to an inch near its life.

For 3/4 ton pickup without overdrive, 9 MPG is pretty reasonable. The rear end is likely a 3.73. I don’t think you’ll see much improvement going back to the original intake and carb. If it’s not running smoothly you may want to have mechanic who knows how to work on carbs give it a once over.

Likely but maybe 2MPG. Not sure if its worth all the effort. Also it seems like a house of cards messing with the emmissions/carb on a 1984 truck.

Does the distributor have a vacuum advance pot? The light duty models in '84 had electronic spark control while heavy duty didn’t. Once the system is adulterated in any way complete de-smogging is necessary. Without mechanical/vacuum advance the timing will be fixed and power and mileage will be very liimited.