I knew the results would be bad, but I finally calculated the gas mileage for the NOM 454 in my 68 convert. 21 fill-ups from April 2016 to now had 198.2 gal for a total of 1737 miles. That's 8.76 mpg. The car has a 454 with flat top pistons installed by the PO, 4 speed, 3.36 rear axle. I added square port alum heads with 119 cc comb chamber, Lunati Voodoo cam with .542/.554 lift, Weiand dual port intake. Addl upgrades were HEI ignition, Hedman long tube headers, 750 cfm QFT carb, electric fuel pump. Fortunately the low compression ratio allows me to use regular gas, but long trips are limited to low mpg and small gas tank capacity. But............the car sure sounds fierce and is fun to drive.

 

Sounds about right. I have averaged 9.1 over the last 13 years. Your foot might be just a little bit heavier than mine. Common problem with big blocks, especially if they have been tweaked.

 

has your HEI been recurved and are you using vacuum advance?

 

EFI and 5-speed helps. My 71 LS5 454 is tweaked quite a bit (aluminum heads, roller cam, headers, etc) and I get 11-12 mpg driving short distances in town and 21 mpg highway.

 

If I was driving a BB 68 I would not care what my mileage was...I would just be smiling!

 

I have never checked fuel mileage on my 65 427 390hp but if I had to guess somewhere around 10 or less.

 

Figured $20 for 20 minutes of driving literally worth every dime
When its empty you gotta fill it anyways guess I never really gave it much thought

Id be lucky if my sbc got 6 around town hwy much better but who cares

 

My 70 LS5 seems to get around 10-12 mpg. That is running 70-80 mph, with m20 trans and 3.08 gears. I suspect if I was going slower it would have better mpg. Dads 70 LT-1 with 3.70 has gotten best of 15 mpg, but not sure the speed.

 

That's pretty much my attitude too. I bought the car because I missed the exhaust sound of a big V8, so I got my money's worth with this car. Loud, hard riding, hard to park with manual steering, but I find many excuses to drive it rather than taking one of my other modern vehicles with PS, PB, AC.

 

Stock curve and using vac advance. The distrib has several settings for the advance, but I have not changed from the setting that came out of the box. Not sure how much it would help gas mileage, but after I do some addl internal engine mods this winter I may play with the distributor when I do my dyno runs.

 

Never ever crossed my mind what kind of mileage I would get when I was stuffing a 454 in my 76. I do know that every time I go for a cruise I seem to have to put gas in it.

 

My '70 LS-5 likes gasoline! That being said, if I wanted fuel economy I would drive a Prius. Part of the allure to piloting a big-block, 4-speed C3 is the sound, smell and thrill of acceleration. I like to tell Prius owners that my car is a hybrid ..... it burns gas & rubber!

 

"It's a hybrid.....It burns gas and rubber" Love it!!! Can't wait to use that line on one of my friends who complains the car is too loud.

 

Some of us children just never grow up!

 

Those little numbers don't turn around. So maybe 35 to 40 MPG in an L36 Roadster?

 

In my stock 69 427 L36 with an M20 and 3:08 rear I get 11 mpg at 60 mph on the highway. Just for comparison the C5 Z06 I had got 31 mpg at the same speed and my C6 Z06 gets 29. I would rather drive my 69 even if it was only 2 mpg.

 

I'm curious as to what you were "expecting".

I have a 63 Impala w/ 409/425 engine. It will pass anything but a gas station.

Probably gets <10 mpg as well, but it's not my DD so who cares??

IMO, these cars get more smiles / mile than any piece of modern iron on the roads today.

 

I just came across this older thread looking or fa general answer to the mileage question. I just got my 69 tri-power back from a full rebuild (and other work, including a rebuilt rear replacing the 4:11 gears with 3:55). The shop found a couple fueling issues and replaced some fuel lines and added an electric fuel pump. Unfortunately, they also neglected to sufficiently torque the fuel line connector to the front carb, which delivered the treat on my first start up at home of 94 octane spitting and dripping all over the manifold. I stopped the leak, but it has made me nervous about losing fuel while driving. For some reason, the fuel gauge is acting up, and I was not confident in the reading, which changed depending on what the car was doing. So, I decided to fill up much sooner than I thought I should have. It took exactly 7 gallons. I wasn't sure on mileage but it was definitely under 70.

When I thought about it, getting less than 10 mpg would not be shocking. As many members have commented, I didn't buy this car to care about gas mileage. If anything, it is a little bit of a badge of honor. Who knows, before I die, it might be a felony to dump as much fuel through 3 carbs as will flow to generate that glorious sound and smell. I don't care modern grocery getters put up as good and better numbers, nor do I care electricity increasingly can do the job once the sole purview of fossil fuels. Who cares about mileage? Well, I do. At least until I am convinced I am not losing some somewhere other than through those 3 beautiful carbs.

 

I love watching the gas gauge move almost as fast as the speedometer when I punch into my '70 LS5

 

NO ONE , should buy a Corvette if they care about gas mileage