StarGeneral

Purely out of curiosity...does anyone have a ballpark on the MPGs a 1965 Delta 88 with a 1970 455 4 Barrel would get?

ah64pilot

For reference...1972 Cutlass Supreme with a mild 455 and 3.42 gears got around 10-13 MPG.

Also for reference, same Cutlass with the engine in my signature gets 6.98 HWY 5.93 CITY...lol!

Steve

jaunty75

I agree. You're going to see generally in the low teens, maybe mid-teens on the highway. I don't think it matters too much what engine the car is in for the most part, assuming it's generally a medium- or full-size car.

rocketraider

11-13 around town, depends on how heavy your foot is. Steady-speed highway driving with good fuel might surprise you. I have known 88/98 from that time to deliver 20-21 mpg in highway driving at steady 65-70 mph.

But with this rotten-*** ethanol fuel garbage we're forced to use, you can count on about 30% less fuel mileage per gallon than you'd get otherwise.

Something to consider is that back then, gas economy wasn't a big concern like it is now. Frugal people would buy Volkswagens or six-cylinder cars, though a lot of times a small V8 such as Chevy 283 or Ford 289 was within a mile or two per gallon of the six.

And then in 1974 along came the first politically motivated and engineered gas shortage. Then as now, environmental interests were intent on bringing the US to its knees over fossil fuels. I cannot understand a mentality that would rather see a country enslaved to a foreign oil producer than to allow it to supply and produce its own oil.

I forget- the objective is to eliminate fossil fuels and personal, privately owned transportation.

StarGeneral

thanks for all the replies...its got an automatic three speed th400 so i thought maybe mpgs would be worse on the highway because of the high rpms but i guess not

MDchanic

The highway RPMs may not be that high - what's your rear end ratio?

- Eric

rocketraider

What happens in highway driving is that the engine is running at a more or less steady speed with trans in high gear, and a 4-barrel is usually running on the front 2 bores. The way a QuadraJet works is it has metering rods in the jets that meter the fuel as needed. If the rods are not opening up to allow more fuel thru the carb, increased economy. Under those conditions you are also covering more distance per gallon of fuel burned.

In-town, stop-and-go driving when the transmission is shifting between 1 and 2 most of the time, the engine is: 1) turning up higher RPM in lower gears to travel the same speed, 2) traveling slower and not as far distance under steady-speed conditions, and 3) idling a lot. If you're stopped in traffic with engine idling, you are getting zero miles per gallon as you are not moving, but the engine is still consuming fuel.

Make sense? sometimes I can't verbalise things as well as I can show.

Jetstar 88

The first gas crisis was a response from OPEC to the Yom Kippur war in the middle east. We supported the Israelis, who were fighting the arabs, who controlled OPEC, who told the west to bug off by cutting off fuel shipments. We freaked out, because cars had been evolving away from efficiency and towards raw power, meaning most cars got about 14 miles per gallon. Even before 1973, the government had started to enact emissions regulations, which were meant with a stiff wall of resistance from car companies, who seemed to be so full of spite as to patch junk on to the engine to meet regulations, instead spending a little bit of money and changing the design of the cars. I hate to make this political, but when people can't go outside because of air quality in some cities, there's something wrong.
Thanks to all this, we now have engines that get twice the mileage of any '60s performance car engine, while making more power per cubic inch than anything in the '60s widely available to the public. They're more expensive, and tougher to fix, but that's how it is.
Maybe in 40 years, our kids will complain about the damn electric cars, how the Audi 4.2 was so simple to work on, and how easy it was when you could get gas almost anywhere for only $3.50 a gallon.

Ethanol is rotten garbage indeed, giving corn state politicians precious votes and everyone else headaches. I just wish they would ban it already.

And you're right about people not really caring about mileage. There were still a few economy champions left from the 1958 recession, but for the most part, buying a 6-cylinder was to keep the cost of the car down. Most Volkswagens were sold to people tired of Detroit and their shennanigans who wanted something different, as well as for mileage. VW was one of the few compacts that really took hold, as the rest (Renaults, weird British imports) were pretty much gone by 1965. The focus was shifted, with performance then being as important as mileage now. Cars that got good mileage, weren't foreign, and weren't basically taxicabs were few and far between (Corvairs, OHC Pontiacs) and never caught on in the marketplace.

And a 455/4-bbl combo in a Delta should average 12.

Vega

The answer is "terrible" haha. I think its funny when people bring up fuel economy in an engine build (not saying the OP is, just a personal observation) as far as camshaft, head, intake, or other components are concerned. The difference is merely going from "terrible" to "awful" haha

ah64pilot

To clarify my reference from above...carburetor has a lot to do with economy. On the first engine I mentioned I was using a Carter (Edelbrock Performer - 750) with vacuum secondaries. The current engine is using a Holly HP 950 with mechanical secondaries. As with both cases I am turning 2800 RPM to go 65 MPH, the former carburetor does it with primary jets only whereas the latter Holly is dipping into the secondaries at that RPM / throttle position.

The true answer to your question is going to rely heavily on what rearend gears you have and what carburetor you are using. I don't mention heads, cam, or other things because you mentioned a stock 1970 455. If you give us a little more information (gears & carb) we could give you better IDEAS of what you may get, but it will change based on your particular driving style.

Steve

WoofWagon

My time working on engines and also flying airplanes told me that you have to figure out at what RPM your engine is producing peak torque. This means that the engine has the highest Brake Mean Effective Pressure in the cylinder. More BMEP means more torque to move the car. If you drive on the freeway at peak torque (with in stated speed limits of course) as a steady speed, you will see your highest fuel economy. I don't remember if anyone mentioned this, but pick yourself up a vacuum gauge and use a ported vacuum port off the carb. Drive so as to have the highest manifold vacuum as possible and you'll see decent mileage. Of course with big blocks, you're not going to win any fuel economy contests.......

ah64pilot

Good info Woof...I think you could cruise at the highest manifold vacuum but probably not at peak torque lol! At least I couldn't, peak torque wasn't until 4500 RPM and if I cruised at that I'd be calculating GPM rather than MPG haha!

Bluevista

If you have to ask how much you can't afford it.

My 4500 pound '92 Custom Cruiser/tank gets over 25 mpg on the freeway with a Chebby TBI 350, 3:23 rear, and overdrive trans.
It helps to not have the aerodynamic drag coefficient of a brick too.

Jetstar 88

That's why the new Corvette gets 30+ on the highway.

Destructor

My 71 Caddy consistently got around 15 on the highway if I didn't drive too radical. 11 or so around town.

WoofWagon

The nice thing about BBO is that they produce buckets of torque down low so you don't have to rev the snot out of them. RV type cams are best for that and typically will provide decent mileage in a light car but will run out of breath by about 4500RPM, depending on head work of course.

Texas Jim

WoofWagon,
Do you remember in the early to mid 60s, the Pontiacs, Grand prix and Catalina f/ example, had big vacuum gauges on the console, which were called your "fuel economy gauge." When you drove w/ your foot only feathering the gas pedal, the gauge would read in the "green" area f/ good fuel economy (high vacuum), and when you stood in it, it would read in the "red" area f/ poor fuel economy (low vacuum). LOL! I was a senior in high school during the early '70s fuel crisis and pumped gas part-time at a Texaco station. I remember well pumping gas on Saturdays until we ran completely out, (last number on the license plate) odd numbers one day and even the next. The military ended my gas pumping days shortly after that. LOL!

Neat thread.

oldcutlass

Fuel economy? As my tach goes up the fuel gauge goes down. I get 7mpg with 3:08's around town. I haven't driven far enough at hwy speed to guess what it gets on the hwy.

WoofWagon

Texas Jim, while I wasn't around in the early sixties to see those items first hand, I have observed them at car shows and relatives who've had similar devices on their vintage cars.

BMWs had or maybe still have a fuel economy gauge built into the instrument cluster. Shame you had to buy a crappy BMW just to get the gauge.....

StarGeneral

edit: never mind, I seem to be getting more around 12 miles per gallon average. but i am still checking with the previous owner what the carb and rear gear ratio are.

Update:

He says it is a stock GM rochester Quadrajet. He doesn't remember what the rearend ratio is, but guesses 2 something..."really high ratio more than likely"

442much

I've driven my 1976 442 with the 455 from Vancouver Island to Cape Cod and back. The manual says that from factory, my 76 gets 19 mpg on the highway and 13 in the city. The reality is I get 235 miles to a full tank (21 US gal) IF I drive at 60 mph with the 3:42 posi gears and a 4 bbl Q-jet. I need some sort of gas economy as I drive it all over North America when ever I get the chance. So far, 3 times across Canada, 3 times across the US. If you ever see this car on a trailer, call the cops, it's being stolen.

StarGeneral

Haha yep, I drive the Delta around all the time too. Can't understand why some people just let their projects sit around for years and never drive them when they are in better shape than mine. You only live once after all

Interesting that you get 11 mpg combined...maybe it's the fuel that we're using now? who knows...

Intragration

I get 12 around town and 17 on the highway in my '70 DeVille with 2.93s. When driving carefully, I get 15 around town in my '83 Cutlass 455 with 2.41s and an Edelbrock 600. I'd guess your '65 with a Qjet should be capable of similar numbers to the DeVille.

Djcoak

This is an old thread but it piqued my interest. I am currently considering my 68 455 to install in my trans am. This will be coupled to a od trans and probably run about a3.08 rear gear. With approx 425 hp and 500 ft lbs of torque. I figure with 27" tall tires the hwy rpm should be about 1800 or not much above idle.

This will be a Driver. Like some on here I can't stand seeing it in the garage and besides, if I pour all that money into it, the wife says I better dang well use it lol.

So I would guess since the ta is kinda aerodynamic and lighter than a delta, and the rpm slow I should geta. Decent hwy mpg? Or am I smoking crack?

matt69olds

I thought I would add my data to this discussion.

I averaged around 14mpg on Drag Week with my car. I was pulling a small single axle U-Haul trailer loaded with tools and spare parts. Keep in mind, I'm running 3.73 gears with a loose converter and Gear Vendor. One of these days I'm going to take a long road trip unloaded and see what the actual mileage is. I have no doubt the Q-Jet helps a bunch. I didn't think 14 in the state it was in was bad.

oldsmobiledave

Cruising @ 70 mph in my 1969 Delta Royale with 455 4 bbl , T400 & 2.56 gears wearing 28" tall tires I would get 13-14 mpg.


Cruising @ 70 mph in my 1980 GMC p/u with 455 4bbl T400 & 3.73 gears & wearing 28" tall tires I get 11 mpg.

Djcoak

What rpms are you turning?

Destructor

I'm averaging zero MPG. Come spring time the Cutlass will be loaded onto a flatbed and taken to the junk yard.

76olds

I ride my wife after 10 pm that saves on fuel ! Cold starts can be a problem.