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My Dad had a 1974 Buick Lesabre with a 455/4 barrel. The car had a 26 gallon gas tank making it a great highway car. On the highway it used to get 18 mpg at 70. Around town it got about 12 mpg. My mom had 1973 Buick Estate Wagon with a 455/ 4 barrel (23 gal tank). That thing would get 15 at best on the highway. My dad and my mom both liked big engines.
I learned to drive on these cars in the late 1970s. They were boats but they could move pretty well off the line and when passing other cars. I had a lot of fun in these cars.
I had a Buick Electra 225 in the early 80’s was my fathers. Had a 455 and fender skits, was like riding on a cloud with the most comfortable seats of any vehicle i have ever owned. I loved the vehicles of my generation.
Carburetors, even at best, are a compromise, with respect to their fuel mixture. They're usually a little of the "rich" side, so as to not cause any damage to the engine, which an overly "lean" condition can cause. The car's computer, by way of the O2 sensor, can keep the fuel mixture ALWAYS at the perfect spot (late 80s, computer controlled carbs helped, but were not as adept as FI).
The real "step up" as far as fuel mileage goes, was the overdrive transmission. In an earlier post I mentioned that I have a late model Corvette, which will give me 31 MPG. At 65 MPH, in 6th gear, the engine is only turning around 1650-1700 RPM. Prior to this Corvette, I owned a late 70s Pontiac Trans Am. The car had a 4 speed manual transmission with no overdrive, and at the same speed, the engine in the T/A was spinning almost 1000 RPM more, and using that much more fuel to do it.
My modded 2013 C6 with a tuned A6 auto gets 31 on the highway if i keep it at 55mph and no stops and starts. City it will avg around 14mpg as i am hard on it.
I had a 1971 Buick LeSabre with Buick 350 engine (each GM division had own V8 back then) with stock 2BBL carb and TH350 automatic with no lockup. Somewhere around 4200 pound. Dont really remember but suspect 9:1 compression. Got 13mpg in city and 22mpg on long hiway trip. Really had to watch speedometer, very easy to be going 90 if werent paying attention. Once they detuned the engines in 73 or 74, similar car was more like 13mpg on long trip with same weight car and same engine. It was mostly in having right cam combined with right rear end gearing. Sure that thing with 5spd manual could got high 20s long trip. It was super comfortable car for interstate cruising, better than anything I have ridden in since.
Upstate John: was your Catalina with a 400 pretty darn close to the GTO "trim". Sounds awesome.
I dont know about that, but it did have the factory HO 400 in it, which was basically just a 4bbl carb. 2 door convertible, been repainted that crappy factory creme color. Why I dont know! It was blue. Had I kept it it was going to be fully restored to original, but I let it go for something with better mileage.
I remember Dad's Big Arsed Pontiac Catalina got 8 mpg at least the way I drove it. It had a 400 with a big 4bbl carb, It also once held 21 teenagers going home from pizza hut after dress rehearsal for a musical. So per person, it got 160 MPG
I remember the Courier! was it based on a British Ford or European Ford pickup chassis. seemed like the first 'smaller' pickup truck
I had a 72 Courier, tinny little thing, but it was geared right for actual pickup, thats why didnt get super great gas mileage. First gear was low and it only had 4spd. I cant remember but think original engine was 1.6L. I replaced it with 2.0L from a RWD 1980 Mazda 626. Bolted right up to the 4spd. And geared like it was with that extra power of 2.0L, it was great on back roads, even towing. Needed overdrive for highway, in 4th gear it was kinda buzzy. Yea all the Couriers were made by Mazda. That 72 had "Courier" written on tailgate. Maybe only that one year, most had FORD on tailgate.
I will say I had a 76 Datsun 620 pickup that I liked better. Handled better on hiway. None of these little trucks were something you wanted to go cross country with, but they were great grocery getters and got decent mileage. I wouldnt mind have either one in good shape now. There is nothing on market now anything like them.
I had a 79 Bronco with the 351M (boat anchor) and a 78 with a 400, slightly tweaked. MPG's on those trucks were horrible but they also had the aerodynamics of a cinder block. My 80 400 wasn't much better, even though it was a newer design. I did hit the extreme low double digits though (like 10/11ish), About 12 on my 80.
Funny thing is that I dropped in a 73 Lincoln 460 in my 79 when my 351 failed and if I drove it sane, I got the same MPG's as my brothers new 88 fuel injected 351 Bronco (14), Even better on highway trips. Now if I got on it I could literately watch the gas gauge drop on acceleration and unfortunately that was more the norm. Why else would I have swapped in a 460?
when Consumer Reports would provide gas mileage information ay various speeds ( the practice ended for 1970 and gas mileage was just a range to be expected in normal driving and gas mileage on a 300 mile trip), I recall the 1968 Cadillac Sedan De Ville recorded 7-15 mpg in normal driving but at a steady 30 mph the car actually recorded 18 mpg
The '69 Plymouth Fury recorded 11-21 mpg in normal driving and at a steady 30 or 40 mpg 25.5 mpg
does this mean you could generally add 3-4 mpg to the top number on the upper range at a steady 30 mph??
for example, a 73 Plymouth Valiant with a 225 registered 12-23 mpg in normal driving and 18 mpg on a 300 mile trip
would then my old 71 Duster (essentially the same car) with a 225 get about 26 or 27 mpg at a steady 30 mph?
These results are consistent with a Motor Trend and Oldsmobile test of 1967 and 1968 Cutlasses and Delta 88s. They showed a gain of 3-4 mpg at 30 mph over their highway test loop. They also showed a loss of 1-2 mpg with the air conditioning running on the highway test. The 1968 models, with larger engines and numerically lower axle ratios, had both better acceleration and gas mileage.
Another article compared the 1967 442 and the Cutlass Turnpike Cruiser. The 442 got 12-15 mpg, while the Turnpike Cruiser got 15.7-18.1 mpg. The 442, with a 4 bbl carburetor and 3.08 axle ratio, did a 15.5 1/4 mile, while the Turnpike Cruiser, with a 2 bbl carburetor and 2.41 axle ratio, did a 16.5 1/4 mile. The production Turnpike Cruiser had a 2.56 axle ratio, though.
Let us compare these figures to a modern vehicle, the 2020 Buick Enclave AWD. At 4589 lbs, it is 100 lbs heavier than the 1968 Delta 88. While the highway tests are not comparable, the Enclave got 21 mpg, while the Delta 88 got 16.4 mpg. The Delta 88 had a 16.9 1/4 mile, better than average for its time. The 15.5 1/4 mile of the 1967 442 was typical of muscle cars of that era. Driving a muscle car caused loose morals, or something, especially if you were a teenager, according the the common wisdom of the time. The 2020 Enclave has a 15.1 1/4 mile, so it's faster than your father's or grandfather's muscle car, but nobody seems to be complaining. Isn't technology wonderful?
I could talk about mileage and performance during the emission era before modern technology was available, but that's a depressing subject. Let's just say those vehicles were slow and thirsty.
As far as your 1971 Duster, emission controls hit hard starting in 1971. Although your compression ratio is the same as the 1970 slant 6, you probably had poorer efficiency.
Let us compare these figures to a modern vehicle, the 2020 Buick Enclave AWD. At 4589 lbs, it is 100 lbs heavier than the 1968 Delta 88. While the highway tests are not comparable, the Enclave got 21 mpg, while the Delta 88 got 16.4 mpg. The Delta 88 had a 16.9 1/4 mile, better than average for its time. The 15.5 1/4 mile of the 1967 442 was typical of muscle cars of that era. Driving a muscle car caused loose morals, or something, especially if you were a teenager, according the the common wisdom of the time. The 2020 Enclave has a 15.1 1/4 mile, so it's faster than your father's or grandfather's muscle car, but nobody seems to be complaining. Isn't technology wonderful?
The Delta 88 had a very low numerical first gear ratio (around 2.48:1 with automatic) and usually a numerically low axle ratio such as 2.93 or 3.08. Most modern cars have a lower ratio for both 1st gear and overall.
1960s ('70s) tires had a traction problem. It's not uncommon for the 1/4 mile time to drop by 1/2 second or more with just wider tires.
One magazine (Motor Trend) tested a '67 427 Camaro. The stock tires could in no way handle the power. The testers put on either wider tires or slicks (don't remember which one) and the 1/4 mile time dropped one full second, from 14.0 to 13.0.
The fact that many muscle cars could run 13s on skinny, stock tires was a feat in itself.
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