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Hey guys I was wondering if a 350 engine will increase MPG on a 1974 k10. I currently have a 391 big block on it and gets about 6 - 8 MPG. I was reading that a 350 small block will get around 13 - 20mpg
What transmission? Th350 or th400? If a three speed I would look at finding a non computer controlled th700r4 to get a OD gear. That's going to up your mpg more than a engine swap. I might be wrong but a 391 isn't a big block. It's usually a bored and stroked small block.
my mechanic said it was a 391 lol i mean i dont know too much about trucks other than the basics. i would like to keep my truck if i get around 12 13 mpg city
IIRC its a lifted truck??? Not going to get much better with big tires and lift kit. The 391 is a bored and stroked engine, and going down to a 350 wont help much.
You michg be able to go form premium fuel to regular and that would save a little, however unless you dive 50,000 miles a year, I do nto see how you will ever pay the cost of the change.
Keep your truck as second vehicle and buy a cheap used mid 00's compact car or mid size car as your daily driver OP
that way if you break something wheeling you still have a car to get around in a Ford Fusion, Honda Civic, Honda Accord, Toyota Corrola, Toyota Camry, Mazda 3 or Mazda 6 from the mid-late 00's should be fine
Hey guys I was wondering if a 350 engine will increase MPG on a 1974 k10. I currently have a 391 big block on it and gets about 6 - 8 MPG. I was reading that a 350 small block will get around 13 - 20mpg
I have a 97 tahoe with a vortec 5.7 350 in it gets 13-17 mpg.
IIRC its a lifted truck??? Not going to get much better with big tires and lift kit. The 391 is a bored and stroked engine, and going down to a 350 wont help much.
Actually it can do ok if you do it right. I had a gmc on 35 later 33s and I regeared to 4:56. From the stock 3:08 ratio. I still got about 15 mpg. Dropped two mpg from the old 17 stock.
If you don't regear yeah you gonna have crap for mpg but the OD will help. Of course inky until you smoke it from the OD going in and out from the big tires. If op is lifted he needs regear.
Unless your mechanic has the engine opened up, he's not going to know that the engine is a 391. I doubt he actually knows unless he built the engine to begin with. If it is a GM 391, it should be a gas eater and a hot rod. Otherwise, Ford has a 391 big block that is in the FT family of engines. I doubt you have a Ford 391 FT in K Series so it makes ya wonder if the guy is BS you or what. If you are running stock tires and gears, you should be able to get an engine that performs adequately and give you 15 mpg. GM has always had great engines, the rest of the truck is crap but the engines are good. But unless you just have money to throw away and into this thing, you're best move is to unload it on somebody and find a good used stock truck. The 5.3 GM Flex engine is a great one for gas mileage and performance.
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