350 /454 mpg differences - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Bowed · 09-15-2008, 04:55 PM

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** · 09-15-2008, 04:59 PM

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

swb85 · 09-15-2008, 05:05 PM

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 · 09-15-2008, 05:20 PM

agreed

gafiredog · 09-15-2008, 07:29 PM

Quote:

Originally Posted by Captkaos

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

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

Eyegore · 09-15-2008, 08:17 PM

Quote:

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 · 09-15-2008, 09:34 PM

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** · 09-15-2008, 09:38 PM

Ah heck, in all these cool rides who cares

But the DD thats another story

**78 Big10 454** · 09-15-2008, 10:25 PM

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 · 09-15-2008, 10:40 PM

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

Baresteel10 · 09-15-2008, 11:37 PM

A good or bad difference?

**Captkaos** · 09-15-2008, 11:44 PM

Quote:

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 · 09-15-2008, 11:47 PM

Quote:

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** · 09-15-2008, 11:59 PM

Quote:

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 · 09-16-2008, 02:07 AM

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 · 09-16-2008, 09:22 AM

Quote:

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** · 09-16-2008, 10:38 AM

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 · 09-16-2008, 10:46 AM

Quote:

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 · 09-16-2008, 12:03 PM

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** · 09-16-2008, 12:03 PM

Quote:

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* · 09-16-2008, 12:45 PM

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 · 09-16-2008, 03:31 PM

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 · 09-16-2008, 09:28 PM

Quote:

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 · 09-21-2008, 09:55 PM

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

Low84 · 09-21-2008, 10:00 PM

Quote:

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

09-15-2008, 04:55 PM	#1
Bowed Registered User Join Date: Oct 2002 Location: where it's hot Posts: 1,059	350 /454 mpg differences 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 ? .

09-15-2008, 04:59 PM	#2
Captkaos www.73-87chevytrucks.com Join Date: Dec 1999 Location: Birmingham, AL Posts: 6,935	Re: 350 /454 mpg differences 350 = 15 cty/19hwy 454 = 9cty/12hwy __________________ Chris Lucas 1973 Chevy C-10 1978 GMC Jimmy (2WD) - SOLD 1987 R10 twin turbo LS 1991 R3500 SRW CrewCab 1985 K5 diesel swapped project 1989 K5 2WD conversion w/ Vette susp Project Captkaos Customs 73-87chevytrucks.com

09-15-2008, 05:05 PM	#3
swb85 On a budget like Fred Sanford Join Date: Oct 2005 Location: Topeka, KS Posts: 2,031	Re: 350 /454 mpg differences 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. __________________ '85 Silverado swb: 383 stroker, 10.5:1, vortec heads, 232/238 roller cam, RPM air gap, performer 750 carb, stainless longtubes, 3" duals/super 44's, T56/4.11 383ci build / exterior refresh thread '98 Camaro z28: 370ci twin turbo 370ci build '01 Tahoe LT 4x4: 5.3, longtubes/ory, magnaflow duals, custom tune....wife's DD

09-15-2008, 05:20 PM	#4
stepside454 Registered User Join Date: Nov 2003 Location: st. louis area Posts: 1,551	Re: 350 /454 mpg differences agreed __________________ 75 GMC C-15 short/step factory 454, lowered

09-15-2008, 09:34 PM	#7
stepside454 Registered User Join Date: Nov 2003 Location: st. louis area Posts: 1,551	Re: 350 /454 mpg differences 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 __________________ 75 GMC C-15 short/step factory 454, lowered

09-15-2008, 09:38 PM	#8
scotts62 One day... Join Date: Apr 2008 Location: Tuttle, Ok Posts: 9,243	Re: 350 /454 mpg differences Ah heck, in all these cool rides who cares But the DD thats another story __________________ Scott 93 crew cab build Project 62

09-15-2008, 10:25 PM	#9
78 Big10 454 78 Big10 454 Join Date: Jul 2008 Location: Pismo Beach, CA Posts: 839	Re: 350 /454 mpg differences 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.

09-15-2008, 10:40 PM	#10
ton*loc Registered User Join Date: Feb 2008 Location: sioux city iowa Posts: 178	Re: 350 /454 mpg differences i went from a 305 to a 358 and i really notice a big difference. __________________ 1986 chevy c10 in the "build" process as we speak 358 flat tops, vortec heads, .500 lift cam, NOS power shot plate system, yada yada yada MMA PIX http://www.clgpix.com/MMA/Fighters/F...C/CoteTony.htm MMA RECORD 24-5

09-15-2008, 11:37 PM	#11
Baresteel10 Registered User Join Date: Oct 2007 Location: Ramona, CA Posts: 18	Re: 350 /454 mpg differences A good or bad difference?

09-16-2008, 02:07 AM	#15
Pyrotechnic Registered User Join Date: Feb 2007 Location: Austin, TX Posts: 3,930	Re: 350 /454 mpg differences 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. __________________ 1977 GMC Sierra Grande

09-16-2008, 10:38 AM	#17
Corts60 Just here to tinker Join Date: Jun 2008 Location: Holland, MI Posts: 3,697	Re: 350 /454 mpg differences 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... __________________ 78 C10 SWB Diesel #1 (wrecked)http://67-72chevytrucks.com/vboard/s...1978+silverado 78 C10 SWB Diesel #2 (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=650751 60 GMC Suburban (sold)http://67-72chevytrucks.com/vboard/s...d.php?t=445526 60 GMC 1000 (sold)http://67-72chevytrucks.com/vboard/showthread.php?t=298235 67 GMC 1500 (sold) http://67-72chevytrucks.com/vboard/s...d.php?t=803695 73 Chevy C20(Daily)http://67-72chevytrucks.com/vboard/s...d.php?t=852767 86 Suburban(summer unit) http://67-72chevytrucks.com/vboard/s...d.php?t=810697 88 Suburban 4x4(sold)

09-16-2008, 12:03 PM	#19
Richard D Registered User Join Date: Jun 2008 Location: Texas Ctiy TX Posts: 228	Re: 350 /454 mpg differences 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.

09-16-2008, 12:45 PM	#21
JCampbell Account Suspended Join Date: Apr 2008 Location: Hesperia, Ca Posts: 1,332	Re: 350 /454 mpg differences 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.

09-16-2008, 03:31 PM	#22
Alex1 Registered User Join Date: Jul 2007 Location: Ottawa Ontario Canada Posts: 1,156	Re: 350 /454 mpg differences 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.

09-21-2008, 09:55 PM	#24
Baresteel10 Registered User Join Date: Oct 2007 Location: Ramona, CA Posts: 18	Re: 350 /454 mpg differences Sorry for the hijack but, what octane are you guys running on with your higher compression motors?



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