350 /454 mpg differences

[Bowed]

In 2 trucks exactly the same except one having a 350 and the other a 454 , how much of a difference would there probably be on mpg for the added cubes ?


.

[Captkaos]

350 = 15 cty/19hwy
454 = 9cty/12hwy

[swb85]

Depends what components are in each motor. If your 350 is built with huge heads/cam/intake and the 454 is a low compression stump puller, the bbc may get better mileage. Captkaos is probably pretty close if both are stockish low compression builds.

[stepside454]

agreed

[gafiredog]

Originally Posted by Captkaos

350 = 15 cty/19hwy
454 = 9cty/12hwy

are those numbers based on late model type motors with EFI? Art

[Eyegore]

Originally Posted by Captkaos

350 = 15 cty/19hwy
454 = 9cty/12hwy

I measure my 454 by the number of gas stations I pass, typically 6

[stepside454]

my mild built 454 averages 11MPG, with 31" tall tires & 3.73s. best I ever recorded was 13 MPG, all hiway, no AC running around 60-65 MPH. 70-75 MPH it gets noticably worse

[scotts62]

Ah heck, in all these cool rides who cares
But the DD thats another story

[78 Big10 454]

Bowed: My cousin has a 78 Big 10 350/350 and I have a 78 Big 10 454/400. Trucks are exactly the same, except for the engines/trans. We both get about the same mileage, 10-12 mpg.

[ton*loc]

i went from a 305 to a 358 and i really notice a big difference.

[Baresteel10]

A good or bad difference?

[Captkaos]

Originally Posted by gafiredog

are those numbers based on late model type motors with EFI? Art

No, you can expect about 2-3mpg gain on a TBIsetup.

[Low84]

Originally Posted by Baresteel10

A good or bad difference?

x2 I've heard from a lot of different people the 305 is actually just as bad or worse at fuel consumption than a 350.

[Captkaos]

Originally Posted by Low84

x2 I've heard from a lot of different people the 305 is actually just as bad or worse at fuel consumption than a 350.

I wouldn't believe that.
My 305 in my R10 gets 17/22.
My 350 in my R3500 gets 13/17.

These are actual averaged numbers as I check these regularly.

[Pyrotechnic]

I think mileage has to do with how efficient a motor is running for that particular application. I think a 454 that has been worked over with raised compression, improved cylinder head flow, a larger but not overly radical cam, and a free flowing exhaust could actually get the same or better mileage than a low compression smog 350.

[swb85]

Originally Posted by Pyrotechnic

I think mileage has to do with how efficient a motor is running for that particular application. I think a 454 that has been worked over with raised compression, improved cylinder head flow, a larger but not overly radical cam, and a free flowing exhaust could actually get the same or better mileage than a low compression smog 350.

You're exactly right. The old 355 I had in my truck was a low compression (8.5:1) smog motor making ~300hp on it's best day. Best I ever got was 13mpg, usually averaged 12mpg. The 383 that's in the truck now is making ~450hp and consistently pulls 15-16mpg. I added over 150hp and 30 cubic inches and my fuel economy increased by 25%.

[Corts60]

I just ran the first tank through my new '80 scottsdale 10 4x4, with a stock 350 and a 4-speed and averaged 13 MPG. And this truck was sitting for the last two years! I am going to rebuild the carb next and do a complete tune-up and see where it goes from there...

[Pyrotechnic]

Originally Posted by swb85

You're exactly right. The old 355 I had in my truck was a low compression (8.5:1) smog motor making ~300hp on it's best day. Best I ever got was 13mpg, usually averaged 12mpg. The 383 that's in the truck now is making ~450hp and consistently pulls 15-16mpg. I added over 150hp and 30 cubic inches and my fuel economy increased by 25%.

Ditto, over the summer me and my dad built a 383 similar to yours that is getting 14-15 MPG highway on a rough tune (still messing with the carb and timing).

[Richard D]

I'm getting 14MPG out of the 350 I swapped in place of the 305. Used the same TBI. Haven't really done any fine tuning yet, will probably do better.

[Palf70Step]

Originally Posted by swb85

............. I added over 150hp and 30 cubic inches and my fuel economy increased by 25%.

Until our foot gets heavy

[JCampbell]

I get about 11 on the highway in my 454 powered '77 dually. That's running around 65 mph. The faster I go, the faster my tanks empty.

I get around the same in my '88 K20 'Burb with the 350 on 33's.

My theory is that little 350 is working a lot harder than the 454-hence the mileage discrepancy.

[Alex1]

My 1980 step with 454 is pretty hard on gas - at the most 12mpg - if I beat on it, I can almost see the gauge go down.

[ton*loc]

Originally Posted by Baresteel10

A good or bad difference?

well its hard to compare the 305 was a stock 86 with a edlebrock 600 and the 358 is a 10 to 1 compression with a holley 750.

but the 305 was around 16-17ish on average

the 358 was really ****ty on my last trip on the highway trying to keep it at 80mph with a th350 tranny was probably the problem got 11-12

[Baresteel10]

Sorry for the hijack but, what octane are you guys running on with your higher compression motors?

[Low84]

Originally Posted by Captkaos

I wouldn't believe that.
My 305 in my R10 gets 17/22.
My 350 in my R3500 gets 13/17.

These are actual averaged numbers as I check these regularly.

That sounds more logical.

I was getting 6.5 mpg on my running on a miracle 350 right before it gave out