Thinking about an engine downsizing

[kenm78]

I bought my 82 K10 4x4 that has a stock 454 in it about a year ago. I got it with no intentions of it being a daily driver but it has turned out to be one . I'm thinking about down sizing to a stock 350 becouse I'm only getting around 9.5 MPG with the 454. How much of a increase in fuel economy would I get by doing this? I would think it would be getting around 13-14 MPG with a 350. What are your thoughts? Not sure if I should have posted this in the engine forum or not.

[Your41Plague12]

Depends on how you drive. I imagine you're only getting 9.5 highway with the 454, right? Because I got 7 on the highway with my 350, and I drove like a grandma. It depends on the truck, its uses, and how well it's tuned. With a well tuned 350 I think 12-13 should be manageable on the highway.

[kenm78]

Not true highway, the county roads here have 45-55 MPH speed limits so I usually go around 5 over. On the highway the best I have ever got was 12 and that was when I first got it on the trip home, Haven't really been on the highway since. I'm averaging 9-9.5 on a regular basis. The engine runs great and I love the torque but it just drinks the fuel. I had a old 2wd and it got around 14 in town and 18 on the highway. I just figured a 350 would natuarlly get better fuel economy.

[bitchin85]

in my opinion, youre doing good with almote 10 with a big block. i got a 355 thats pretty mild and i get about 8. i mostly drive slow but sometimes i think i have to race from light to light

[Your41Plague12]

Yeah, It depends on the truck. A 350 will get better economy for sure than a 454, but the difference can be mild to wild. Depends on how it's tuned, really. The 350 I just put in my truck got about 12 in the truck I took it out of, but I get 5-6 now. My old 350 got about 8 in my truck, but I had to swap it due to the electric fuel pump annoying the **** out of me.

[kenm78]

I think my gearing is 3.08 or 3.42 no sure but I think its 3.08 becouse doing 63 mph its just a hair above 2000 RPM. What is your gearing?

[cableguy0]

It will take you a very long time to make up the cost of the swap with savings in fuel burnt. I would be surprised if you get anything more than 12 mpg with a 4wd regardless of engine. You might lose mileage going to a 350. A heavy 4wd truck with the aerodynamics of a brick needs torque to move down the road. The less torque the more you will be in the throttle to stay moving.

[Your41Plague12]

The stock gear ratio was 4.10 (with 235/85/R16), but that's changed a lot with the 38x15.50 Mickey Thompsons. That's the reason for my major drop there. But the motors were two different beasts. My first 350 ran like a top and was efficient, but had little to no balls at all. This new old POS I just swapped in has some power to it, but it burns oil, has a rough idle, and has WAY too big of a carb on it for its own good. It sputters badly when you jab the gas quickly, but if you accelerate gradually it's fine. The carb is another huge part of my efficiency problem. Then again, driving a 28 year old 3/4 ton 4x4 isn't the best idea if you're looking for efficiency.

[kenm78]

Might just be time to put it up for sale and by a 90 model 4x4 with overdrive then.

[Your41Plague12]

You could always add a beefed-up 700-R4 behind the 454 and have overdrive. That would help your highway mileage, for sure.

[lilpoindexter]

Buy some fuel sippin POS for the daily duties.

[kenm78]

Originally Posted by lilpoindexter

Buy some fuel sippin POS for the daily duties.

Maybe if the price is right.

[bluex]

When I checked it I averaged about 12-13 with my .060 350, 700R4 and 3.73's. It was worse with the 3.08's that were stock because the engine lugged in overdrive and was constantly downshifting for hills.

The engine also has flat top pistions, a summit 224/224 @ .050 cam, reconditioned heads, edelbrock performer rpm intake and 1406 carb. So it wasnt built with gas milage in mind.....

[ont_guy_38]

I agree with Cableguy..a few years ago gas around here went to approx $1.35 a litre thats over 5 bucks a gallon and everybody was trading in their year old big suv and losing thousands of dollars . Even at 5 bucks a gallon you can buy one hell of a lot of fuel for the 10 grand you just lost on your trade in

[496 BB]

I doubt any saving will occur. A SBC has to work harder to get the brick moving. For example the 2500HD's (2001+). I have an 8.1L (496ci) and get around 7-9 city and 12-14 highway. Take the LQ4 6.0L in same truck and its not too far off. Thing is I can stay in throttle and play alot and get same mpg.

If your really wanting to get mileage and money or recouping costs are a concern drop in a newer LSx block from a newer truck. You should get 12+ city from one of those easy. More efficient motors.

Honestly Id stay where you are and find a Honda or S10 if your looking to save some coin on gas. You can find late 80's and early 90's S10s with the 2.5L or 2.2L 4 bangers for cheap...under a grand easily. Might look like a Sanford and Son truck but its money savings.

[Altec]

My dad swapped a 700 behind his cammed 350. Around town driving saw no real increase. That was with 4.56 gears on 35 mts. That was getting about 15.

Later we swapped the 350 for a 454. Haha. Even switching to 3.42 gears, and 33's the fuel use pretty much halfed. Saw about 8. But, to be fair the 700 had seen better days by this point.

We also had a 305 from a 84 Monte Carlo SS we put in it. With the same gears and tires as the 350 it was getting about the same 15.

Get a diesel for the mpg's.

I think gears play a big part in things 3.08's take a lot more power to spin.

Truck In question was a RCLB K10.