Difference in MPG between a car and truck

[Inventive1]

I'm interested in an older model vehicle for a summer time daily driver. I've considered a 67-72 pick-up or a full size Chevy from the same period. Keeping it stock would not be important, so an overdrive transmission swap, up dated brakes, etc. would be done to improve drivability and safety.

Trucks generally use more gas than cars, presumably because they usually have lower gears and more air resistance. Lets say the car and the truck have the same engine, transmission, AND rear axle ratio. Assuming these vehicles are equal as far as possible, does anyone have any idea how the gas mileage would compare?

[special-K]

The car would get better mileage

[Stocker]

Originally Posted by special-K

The car would get better mileage

^^^ This. There are so many variables involved that an accurate response is not possible. Safe to say that even with equal weight and equal powertrains, a truck's aero drag (even a lowered truck) will be worse than a car's -- and fuel economy will suffer as a result.

You can always do things to improve a truck's fuel mileage. Do the same things to a car, and it'll get better mileage than the truck.

[chevy88]

"If they were equal as far as possible" the car would always get higher mpg, to get closer mpg lowering truck would help and dropping lbs off the truck would help.

[406 Q-ship]

Originally Posted by chevy88

"If they were equal as far as possible" the car would always get higher mpg, to get closer mpg lowering truck would help and dropping lbs off the truck would help.

Exactly, except that 67-72 C10 is not really that heavy. My 67 SWB C10 was weighed to get it registered in Cali, it came in at a hair over 3800. I have a 1971 Monte that weighs 3800 and my Chevelle is approx 3600. I bet a full size Impala is heavier than one of our trucks so weight while important is not as apart from the cars. MPG differences have more to do with being a rolling billboard in the air, frontal area will kill mileage.

My 1968 Chevelle with a 330 hp/350 (GMPP crate), TKO600, and 3.31 pulls 21 MPG @ 75 MPH all day long. For comparison, my 1974 SWB C10 with a Goodwrench 350 (now called the 260 HP Crate), 700 R4, and 3.73's used to get at best 17MPG @ 70 MPH. Speed will do more to improve mileage in a truck than just about anything, slow down.

[Inventive1]

Lowering the truck is definitely an option, so long as ride quality is NOT sacrificed. Lowered 2 wheel drives look good! I'd also want a bed cover.

I haven't known anyone who built a full size truck for gas mileage. In my situation, such a vehicle would be ideal.

Would it be possible for a truck's gas mileage to reach the low 20's on the highway without going to a diesel engine? If so, what kind of drivetrain would it take?

[blackdawn]

im in the process of building a 69 stepside for a daily driver, i drive on the freeway probably 50 miles a day so im working with an engine builder to make a carbed fuel economy truck. my build will be a 327 engine (built for fuel economy and towing maybe 3 times a year) a 700r4, a 373 or 410 rear end and 29in tires. my engine building and i are optimistic about maybe hitting 20 mpg going down the freeway on flat ground, but thats about all the more to expect out of them with out either dropping a pretty penny and stuffing an lsx engine in or going to diesel. in the end no matter how low to the ground you go you are still driving a billboard compared to a car.

[mrein3]

I don't want to knock your engine builder but I find it hard to believe that any engine/trans combo in this model year of truck could get 20 or better even on the highway with a good tail wind.

I'll believe some people here who are seeing 18 mpg but anything higher than that I think is unrealistic.

Some people will claim that they drove on a full tank down to 1/4 tank and went 300 miles so they know they are getting 20 mpg. Well that is B.S. because we all know that the gas gauge is only an indication of what is there, not what is really there.

THE ONLY WAY to compute mpg is to first make sure your odometer is correct.

THEN fill up, writing down how many miles are on the odometer. Drive the vehicle. Fill it back up again writing down the odometer reading. Subtract reading #1 from reading #2 and divide by gallons put in at reading number two. ANY OTHER mpg computation is just a guess - and probably an optismistic one at that.

The only way I can see even coming close to 20 mpg in one of these trucks is a 2wd, short wheel base truck with a small displacement, VERY well breathing V8 (283, 305, or 307), 3.73 rear end gears, and an overdrive transmission. And a VERY light right foot.

FWIW, before I started messing with my 72 Chevelle, the stock 307, stock 2bbl carb, stock th350, 14" tires, and stock 2.73 rear end gears got 21 on the highway. I got better mileage with the windows up and AC on than with them down and AC off.
I owned a 1971 Monte Carlo with same rear end, same th350, 15" tires, and a 350 with a 2bbl and it got 23 on the highway. A lock-up torque converter on that vehicle might be all you need to get you to 25.

Based on my observations, and to answer your question, I'd say you could build an A-body (not full-sized like you're thinking) with modern OD tranny and small displacement V8 and get as high as 25 mpg on the highway. The very best you could do with a truck is 18 mpg.

[68gmsee]

Originally Posted by mrein3

......The only way I can see even coming close to 20 mpg in one of these trucks is a 2wd, short wheel base truck with a small displacement, VERY well breathing V8 (283, 305, or 307), 3.73 rear end gears, and an overdrive transmission. And a VERY light right foot....

Even that won't do it. My 68 (250) three speed standard with 3.54 barely squeezes 17 on the highway -with tail wind.

My 96 Tahoe with a 350 would get close to 20 on the highway but again it was with a tailwind and flat west Texas roads. My two rangers with 3.0 V6 get around 18-19 on the highway and my 07 Trailblazer gets the same.

Trying to squeeze 20 out of these old trucks requires a lot changes. Maybe a 3.08 rear axle with 4 or 5 speed standard shift and an extemely well built small displacement carb and a reasonable engine -a 327 or 350 wouldn't be a bad choice if blueprinted and with tuned headers and exhaust.

[Vintage Windmills]

Build for peak torque in street RPM range and maximize your compression ratio. Also make it breathe as well as possible.

I'm curious what my K20 will get with all the mods I'm doing but I know it wont be great because its a K20 for crying out loud. I am expecting good MPG as far as 4x4 3/4 tons go though. The engine is built for 9.4:1 compression and peak torque in useable rpm range and if you look at efficiency calculations on engine design, it shows peak efficiency at your torque peak. Also efficiency is directly related to compression ratio. Most guys go wrong because they select cams for horsepower which means better performance at higher rpms than you run on the street. Torque in the useable rpm range (street range) suffers as a result, and therefore efficiency.

['72customdeluxe]

Drop it, soft tonneau, partial restriction behind grill (ala srt-10 ram), etc. You could make the small 88-98 factory air dam piece work without looking bad (saw in on here somewhere). A 5.3 swap would kick the mileage way up and run circles around most small blocks with just headers and a tune. If not, it would with a baby cam. An aluminum block lh6/lc9/l33 would save weight, have better heads, and a tick more compression. The gen iv motors (former two) have a better intake manifold. Don't fear the gear with an ls and o/d trans
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[junksaver]

If you are worried about mileage, then buy a cheap little econo box and keep your truck for the weekend. I bought a 95 Civic for $300 and drive it daily. I average between 30-33 mpg. Your truck will probably average about 14 mpg if used on a daily basis. For the difference in mpg and the price of fuel it is worth having a cheap little car and then use your truck as a truck and not worry about what mileage it gets.

[webfoot]

The heavily modified 383 in my 70 chevelle (about 475 HP) gets 12.67 mpg which beats my stock k20 by a couple MPG.

[jablack]

I built an 83 Chevy C10 short bed 2wd back in 02 and I always got around 20 mpg. Of course this was also when we still had real gas. I lost it in some ice at the end of 04 and took the engine and trans out and put it in my 88 Camaro I had. I averaged 28 mpg if I kept my foot out of it. It had a higher gear than the truck but it moved down the road much easier than the truck since it was more aerodynamic.
I now have an 87 R10 lwb 2wd daily driver that gets around 20 mpg, but averages more high 17 to 18 more often. It has a tbi 350 and a 700r4. I'm sure if I could fine some real gas without ethanol I could do better.

[Inventive1]

Jablack, Do you know what gear ratio is in your truck's rear axle?

I used to drive a 93 Caprice with a 305 tbi, 700R4, and some 2.56 or 2.7? gears. It would regularly get 28 mpg. (The EPA rated it at 26 if I recall correctly) I've wondered how a drivetrain like that would work in a truck. The Caprice obviously had a much more streamlined shape than any truck.

The 5.3 engine is probably better than a tbi in most every catagory. Wouldn't swapping in one of the LSx engines cost considerably more than a tbi?

Getting a small car for fuel economy is not the best choice. One of my family members has some health issues which makes entering and exiting a car difficult. That's why a truck or an SUV that sits up a little higher than a car would be a better option, if I can afford to put gas in it. (The next best choice MAY be an older 2 door car with LONG doors???) I also have access to a real truck for the occasional towing and hauling of heavy loads.

I appreciate all the ideas so far. Any more suggestions?

[Vintage Windmills]

Put tall skinny tires on. Drops your rpm's, less rolling resistance, and is easier than changing gears.

[xb9rguy]

How much money do you plan on spending on the vehicle and on the changes that need made to get it in the mpg zone you want? If a few mpg between a car or truck is going to make or break the bank then it seems the car would be the logical choice for saving money.

[jablack]

Not sure on the gear but if I had to guess I would say 3.08.

I also had a 97 Chevy Silverado extended cab long bed 350 vortec, 5 speed, and 3.08 gears back in 2000-01 and it averaged 19 all day long.

[68gmsee]

Originally Posted by jablack

Not sure on the gear but if I had to guess I would say 3.08.

You need to know for sure otherwise you might have a 4.11 and your mpg won't be good.

Trucks just generally push more air which contribute to lower mpg. Newer vehicles have been tested and massaged in wind tunnels specifically to improve their aerodynamics. These older trucks were not.

[C-10 simplex]

The current silverados and sierras get 20 mpg with a 4.3 v-6----which is a gen 1 small block.

[jablack]

Originally Posted by 68gmsee

You need to know for sure otherwise you might have a 4.11 and your mpg won't be good.

Trucks just generally push more air which contribute to lower mpg. Newer vehicles have been tested and massaged in wind tunnels specifically to improve their aerodynamics. These older trucks were not.

Hey 68gmsee, this isn't my thread. I'm just trying to help the guy out.

[68gmsee]

Originally Posted by jablack

Hey 68gmsee, this isn't my thread. I'm just trying to help the guy out.

10/4... I didn't pay attention to the name. The was you posted it I assumed it was Inventive1.

[MARKDTN]

Here is a close answer to your question. I have an '83 K20 that my uncle bought new. 700R4 and 3.42 rear. I bought a 34k mile '91 Corvette L98 TPI engine and 700R4. The case on the Corvette 700R4 was cracked in the wreck. The 700R4 in the truck died at about 140,000 miles so I bought another 89 4x4 case and had it rebuilt with the Corvette parts (not so much because they were Corvette parts but because the later 700R4s are much more reliable and I had a low mileage core). The truck always got 14 city and 17 highway-before and after the transmission. About a year later the cam lost a lobe on the original 350. I put the TPI engine in and my mileage went from 14 to 17 city and 17 to 20 highway. If you can find out what kind of mileage a '91 automatic Corvette gets, you could be close to an answer. The Google mileage I have found is 15 city and 20 highway, but I find that hard to believe that the truck gets better than that. I would like to find someone who has one and ask. The 6-sp would be even better road mileage because of the double overdrive so be careful not to compare to that.

[Stanley0910]

There is a lot of variables in this, 9.9 out of 10 times the car is going to beat the truck, the only way the truck would beat out the car is if the car had a larger frontal surface are creating more drag, and at highway speeds drag is worse than weight. There have been a lot of good tips above, and you can find a bunch on ecomodder.com. To get your optimal fuel economy you need to look at whether you will be doing more city or highway driving. Changing your gears, whether lower for city or higher for highway, to put your engine in the right rpm range for best economy. Who cares if you can get 25mpg on the highway if all you do is drive around town? Look at the new Prius C, it is meant for city driving so they cut the tail end off and put a smaller motor in for weight savings so it gets better city economy. The original prius has a longer tail with a "kamaback" to reduce drag and a bigger motor to effectively pass at highway speeds, netting it a higher highway mpg. Basically there are a lot of variables, but either way your gas mileage is not going to be too dramatically different if you set either vehicle up for economy driving. I plan to make my truck as economical as possible, without giving up fun, because it's my DD. It's not hard to make an old truck get the same or better mpg's than a new truck. Just look up some economy tips and apply, just be wary of snake oil gadgets that promise 50mpgs by stabilizing the voltage.

[special-K]

Get an El Camino