Fuel Economy- A Funny Thing Happened

[SGS]

This is going to be a very long post. Thats your warning.

None of the new diesels get the fuel mileage that the pre 02 non EGRs did. The power is awsome on all of them stock or modified. In addition to 02 emmission standards that we have to live with, the OEMs continue to boost horsepower and the fuel mileage continues to drop. I have been thinking for a long time of trying to build a pickup to see what could be obtained for mileage. I have built plenty of hot rods and race cars in my life but never a diesel.

I was on a trip from East Tenesee back to Wisconsin. I was pulling my 3 horse 12' living quarters trailer. I would estimate my total gross weight to be pretty close to 18,000#. Just North of Nashville the intake pressure hose blew. It was a Saturday night about 11:00 PM and the odds of finding a Banks intake hose was 0. I was tired and wanted to get home so I kept on driving. The truck made a lot of noise and smoke. It definately lost power. The funny thing was that as sick as the engine was I was able to maintain a pretty steady 60 mph, sometimes 65, less often 70, and I never once dropped below 55mph.

I was curious and had the truck dynoed when I got back, before replacing the hose. The sickly thing pulled a whopping 97hp max and surprisingly 284 pounds of torque.

So now back to the project of building a top fuel economy truck. Question, If class 8 trucks pull 80,000 lbs at highway speeds with 12 litre engines why do we need 6 or more litres to pull 20,000 lbs in a pickup? Remember need and want are two different things. Wouldn't it make sense that 4 litres could pull 20,000 pounds efficiently? If I could pretty much maintain 60mph with 97 hp and 284 lbs of torque would 180 or 200hp and 450 lbs torque do an addiquite job on little fuel. remember i'm not talking about racing up a mountain just a good efficiant driver.

With that in mind I purchased a 1974 F350 crew cab 4x4. I purchased a 4BT cummins engine to install in it. 4BTs in marine trim pull 250 hp and 525 lbs torque. I don't think I need to go that high. the first gen 5. 9s were around 180 hp if I remember right. I am going to use 225x19. 5 high pressure tires to eliminate the extra friction of duals. Four 225x 19. 5s with forged aluminum wheels also have a lower rolling weight than six 2. 35x17s. A six speed . 73 overdrive trans will hook up to ether a 3. 54 or 3. 73 ratio rear end. I plan on using an electric fan and fuel pump to reduce parasitic loss. I may even go back to manual steering. {remember I'm old and had plenty of the old armstrong steering trucks} AC, no way. I am going to use a Piers Diesel high torque cam and will probably port and polish the heads. We will add a frontal cooler and try to find a turbo that spools fast but not exsessively high. 3" exhaust should be plenty for four litres. Our local injection shop recomended six hole injectors for a more complete burn and they want to play with the timing while on the dyno. We will use a large radiator and I think a reletively high temp thermostat will make it burn more efficiently. Synthetic lube throughout will be used. I think the 74 in single rear wheel trim will weigh in about 2,500 pounds less than my 06 dually.

My goal is 16mpg or more when towing total gross weight 16,000lbs. 60 or 65 mph works for me.

OK Gearheads, what am I missing?

 

[bkroupa]

I think a 2nd generation 2wd 5spd 3. 54 12V could get pretty close to that with that wheel tire combo & that cam. My '98 does pretty well pulling my tall TT. On flat level ground & no headwind at 60mph I'm sure it would get pretty close. I normally pull at 65mph & see high 13's to high 14's. Pulling 70+ it drops as low as mid 12's.

 

[SGS]

I think you are probably right. I thought about a 5. 9 and I had a million people tell me I would be sorry with a 4. 0. I still believe a smaller displacement diesel will rule the fuel mileage challenge. The 4. 0 will be a easier swap in the old F350. Speed really kills when it comes to mileage no matter what you drive. Aerodynamics will also have to play a part in this. I had an engineer tell me a lot of the aerodynamic drag comes from underneath. He said I should consider sheeting the crossmembers on the trailer. I will also be looking at some sort of bubble treatment for the flat front of the trailer at the rear underneath the gooseneck. My 06 has a Taylor wing and I know it helps as I don't get any bugs on the trailer. For this test I will be using my aluminum stock trailer. I will probably not use a wing on the 74 but will cut the nose of the stock trailer down to tuck it behind the cab. I am also going to move the goosneck coupler on the trailer back as far as possible to decrease the gap between the cab and trailer.

 

[83 crew cab]

the 89 first gen I had with no mods 3;09 gears 16 inch tires and no overdrive got 22 mpg pulling a 24 foot enclosed car trailer and car proble around 6000lbs



not awhole lot of fun to drive top speed was 85

 

[Forrest Nearing]

you're missing the AC and the fact that a diesel doesn't really use much fuel at light load... go light, use a 5. 9, and do 55-60mph, you'll get great mileage

 

[DDeFreece]

I have a 78 Blazer with 4bt, 14bff w/ 4. 56, d60, nv4500, np205. 4bt is stock. I get about 25mpg empty. I just pulled about 5000 lbs load with about 400 lbs tools in truck 300 miles. I almost didn't notice the extra weight behind the truck. The bad thing is I didn't check mileage pulling but it didn't get bad mileage. Pulled in 5th gear.



I wouldn't think of pulling 10,000 lbs though - at least not far.

 

[SGS]

I would agree that a stock 4BT isn't up to 10,000 lbs. Most 4BTs I've found are 105 hp out of the box. At 180 to 200hp I think they will do it. Question, What is it about the early diesels in pickups that got them so much mileage?

We used to use the original GM converted V8 diesels in our delivery trucks. They always got upper 20s for mileage in 1/2 ton 2wd's. The 5. 7s did too. The 6. 2s were good but not as good as the 5. 7s. the 6. 5 turbos were a big step backwards in fuel mileage. None of these engines had a lot of horsepower. One of the replies to this post said his 1st gen cummins would get 22 pulling. I've talked to other early Cummins owners who agree that with the upgrades over the years to horsepower the fuel mileage always suffered. It's just that no one much cared untill now. Is it just the horsepower that causes this? You would think with all the advancements in electronics, at least before 02 emmissions and EGR the mileage would have gone up not down. All of these early diesels that got such good mileage were mechanical pumps.

What are your thoughts?

 

[Matt S]

My 90 W250 would get around 22 mpg at 55-60 mph consistantly. My new truck isn't as miserly. The VE pump did well for economy.

 

[dieselcruiserhead]

with a heavier load there is a chance the 3. 9 will not be as efficient as with the 5. 9. For what its worth. .

 

[JHerr]

SGS, I am with you. We are on the same wave-length. I have been thinking about creating an efficient commuting/go-fer truck by using a '67-72 Ford F100 and a 4BT in the last couple of weeks. I am not after any towing, just an efficient diesel pickup. I would even consider keeping the 4BT stock at 105-hp, at first.



You are correct about the GM 5. 7 and 6. 2, they were efficient. I never wanted to own one, however. I like the fact that they were diesels, but was leery about long-term expenses.



Regarding the truck: My heart isn't set on a Ford of that era. I could be talked into the GM truck of the late '60s. My thinking is that the weight of the truck itself would be lower, thus less ballast that you are constantly hauling around. The front axle should hold up a 4BT, right? They aren't that much more weight than a V-8, are they?



Trucks of that era are so much simpler: no power steering, no air, no FM radio... hmm, wait a minute. Tunes can be added for low dollars. This is just a scheme in my mind at this point. No dollars have been spent at this point. Please correct any mental mistakes that I am making.

 

[SGS]

Dieselcruiser head, This post is supposed to be mind expanding so I'll answer yours with one word, why?

Now a lot of words, I do appreciate the warning. If I find out I'm wrong I'll be the first to admit it. My theory is horsepower is horsepower and torque is torque. they don't know how many litres produced them. I feel if you have adequite power, not over power you should operate most eficiantly. I am basing my assumptions on a carrer in the trucking industry that goes back to a time when men argued about which had more power, a 220 Cummins or a 250. These were not pickups they were arguing about, they were class 8 semis pulling 80,000 pounds. Now the truth is these trucks were as under powered as todays 600 horsepowers are over. Some of the most miserly trucks out there are powered by M11 litre Cummins. The new Mack engine that was just introduced and is doing an outstanding job for power and fuel mileage is also 11 litre. So if you do the math, why do we need 6 litres to pull 16 to 20,000? There are a lot of 33,000lb trucks out there with 5. 9 Cummins or 7 litre Cat.

Now if you go back to post 1 you can see what can be accomplished with 97 hp and 284 torque. This was definetely underpowered and I'm not recomending it. But I don't think it would take a whole lot more to be adequite. My present truck is an 06 F350 with Banks 6 shooter 4" exhaust and Banks frontal cooler. This truck is incredible to drive but at the pump it is much less impressive.

If I'm wrong what is the worst thing that can happen? We pull the engine and put it in something else. What about the 74 F350? Well I guess we would have to put something else in it, maybe a 300 CI 6cyl gas.

 

[SGS]

JHerr, When I was dreaming up this project I also considered a late 60s GM, They were great trucks too. You are right that they weigh less than a Ford of that era. Both weigh much less than any of todays trucks. The truth is they also weren't quite the truck as todays ether. I went with the Ford because I wanted a crew cab. I agree with you about wanting a simpler truck. I would like to see the engine when I open the hood, I'm sick of seat belt buzzers, automatic locking doors, and windows that roll all the way down when you only wanted it 1/2 way. Life is rough isn't it?

The 4BT will do a great job in a half ton even in stock form. It all depends on what your after. It will give you fuel mileage, it's just not going to be a dragster. However there is a post somewhere in this forum by a guy who put one in a 1/2 ton Dodge and he says he can break both wheels loose.

As far as weight and the front axle goes, the 4BT weighs in at about 725 lbs. If you took your small block added a second battery a winch and heavy duty winch bumper you would be that much or over. You wouldn't buy a new axle for that mod would you?

It will probably be spring before I get this done. Right now the cab is off and the chassis goes to be blasted next week. The engine is coming apart and the cam lifters and head are going to PDS also next week.

Good luck with your dream.

 

[WDixon27]

i am in the long term planning stage of restoring my grandads 73 f350 camper special he bought new, for mom, i want a put a 4bt in it for mileage so i am in a similar boat but this thing probably won't do much hauling with my beast around

 

[Scot]

FWIW, the thing that got me on this bug was a truck my boss drove. I was working for DSI Transports in Houston ('81) and my boss had a 69-72 Chevy pickup with a 4 cyl Perkins and a 12(?) spd transmission. He claimed he was getting 33 mpg out of the thing.



I don't see why you could not do about the same with a 4bt.

 

[ezcurra]

I don't think it makes much sense to compare a 50,000 lb semi that gets 6MPG to a smaller 10,000 lb truck that gets 12.



Light truck owners expect a level of performance much different than that of a semi truck, and that has a huge effect in fuel economy. Apples to oranges.

 

[Jefff929]

I'd be intrested in the plates on the underbody.

In the last 15+ years the ground effects stuff on OTR trucks has improved.

I'd like to know how much it helps.

 

[SGS]

Ezcurra,



Thanks for the reply. I disagree however about not comparing fuel mileage of a semi to that of a diesel pickup pulling a load. What I am comparing is how much work or energy we can get out of a gallon of diesel fuel. Todays typical semi is 80,000 pounds not 50,000. This is over 4 times the weight of my fully loaded truck and trailer which should come in at about 16,000 pounds with 4 horses and gear. The frontal area of a typical semi is 114. 75 sq. ft. and my stock trailer is 57. 7 sq. ft. , less than 1/2.



A good driver with a fuel efficiant rig can pull easily 6. 5 and sometimes 7 mpg with 4 times the weight and twice the surface area.



I do agree with you that most diesel pick up owners would not be satisfied with the performance of a semi however at 3. 17 per gallon if this works and I can get 15 - 16 mpg loaded I will be very satisfied.



The last post asked about ground effects on semis. I assume you mean side fairings. Side fairings alone add about 1% to fuel mileage. There aren't many big things you can do to increase fuel mileage but lots of little pieces that all add up. Speed is the number one factor. The trucking industry feels that somewhere between 55 and 60 mph the amount of energy used to pull the load is equaled by the amount of energy used to break the wind. Every five miles an hour over this speed compounds that factor.

 

[SGS]

The project is well under way, The body is off, sand blasted, primed and coated with bed liner under and over the floor. Brakes, lines parking brake cables all new. The transfer case and transmission have been rebuilt and an Advance Adapter overdrive unit now sits ahead of the 4spd New Process transmission. The 4BT has been rebuilt, custom cam grind for torque and mileage. Head porting and polishing with 3000 rpm springs has been done. We are waiting for the injectors, pump and turbo to come back from the pump shop. That should be this week. We bolted the divorced case in the original position as well as the rear trans. mount. The entire assembly looks as it was made to order. We will probably trim the front crossmember so the engine sits level. This will also gain us some starter clearance. It looks like the radiator support and stock 460 radiator will come out in the right spot.



Todays question is: Who knows the best way to add cruise control to the 4BT 73 Ford manual trans?

 

[brodge]

Scot, FWIW, I have also seen the 6 cyl Perkins from Massey Ferguson Combines used, my buddy has this setup with the turbo in a later 70's Ford 250 Crew paired with a 5spd and claims upper 28-32 mileage

 

[tabell]

I have 4. 10s, 35" tires, 4" exhaust, superchips programmer at max setting, ATS transmission in my 99. I was at 18K GVW, at 85mph I got 13. 5 mpg at 65 I got 16 mpg. The trailer I was pulling was a 28' enlosed trailer, it did have one of those air bubbles on the front.



At that weight I did have turn off the overdrive on steep hills, so I could stay at 55mph.



I've noticed that my best fuel milage is when I'm around 1800 rpm or 2350 rpm.