Max fuel economy?

[john8662]

I think in all fairness for this excersize MP is referring to using a 6.2 for best mileage in a vehicle that came factory equipped with a 6.2L. Mainly Gm Pickups, Blazer/Jimmy, Suburbans, and vans.

I think that most follow Scenario # 2 in that we measure the fuel mileage on the interstate going between 70 and 75MPH. I know I for one, never look at mileage in town or in mostly mixed traffic because It'll be bad no matter what. When it needs fuel, I put it in.

But when traveling on the highway, I always measure fuel economy, this helps me tell the condition of the engine and or powertrain.

I've seen a best 24MPG on the highway with my rig, but I couldn't get that the last trip I took, it was a mere 19.

Things I would do to improve fuel economy:
-Cruise Control
-Proper Sized Tires for Gearing (insure accuracy of miles driven)
-Max Air flow (make note of Black smoke)
-High Gear Ratio (but matched for speed and engine power output)
-Probably best Fuel Economy at 1900 RPM
-Total Weight Of Vehicle (good bye tool box full of junk).

[cschneider]

I am missing something here? All things being equal a turbo diesel will produce better fuel economy than a N/A engine. Efficiency is improved in a turbo engine becuase the fuel is more efficiently burned in a compressed state and the ingition of the fuel air mixture is more powerful. If the injection pump delivers the exact same amount of fuel in both engines, the turbo engine will produce more power per stroke than the N/A engine, correct?

[G. Gearloose]

nope, not if you only need 30 hp to roll down the road.

[20050420|7|006071|000022|69.19.2.78]

so hello,

When i have a lite foot, i can come to 7.5 liter diesel on 100 kms, in my nova 6.5 NA/4L80 combo with 2.73 gears, i think it can be better with a bigger exaust, timing gears and k&n airfilter.

[catmandoo]

convert,i'd like to check those out when your done.those buicks are some cruisers.

[Edahall]

It was very interesting following this thread. I have a 1982 Suburban with the original 6.2 diesel and Scenario #2 is what this rig is set up for. Last year, I took a road trip around the US and added 15k miles on the odometer. Since fuel was much more expensive than it is now, I kept my speed 60 mph (1600 rpm) since I was not in a hurry and this is where I could pull in the best mileage. I consistently got 28 mpg and got at high as 32 mpg on several tanks.
Here's my setup:
2 wheel drive
3.08 gears
700R4 transmission from 1989 truck
30”x9.50 tires
Ported and polished heads – 1983 heads
Intake manifold runners matched to heads and casting smoothed out
Exhaust Headers
Dual 2-1/2” exhaust with H-pipe
Timing gear
Injection pump turned up ¼ turn

I also tow a 26 ft. Airstream which weights around 6000 lbs. I tow in 3rd gear and 2nd gear on the hills. I can manually lock the torque converter to keep the temperatures down on long grades. I get 16 mpg with this setup.

Some things that I could do improve economy:
Super Tune engine using glow plugs.
http://www.ford-trucks.com/forums/59...he-engine.html

Hydrogen Generator
http://pesn.com/2007/01/08/9500445_B...rolyzer_Plans/

Aerodynamic mods such as front air dam and rear fender skirts

[NH2112]

I think the turbo will get slightly better fuel mileage, if all other factors are the same, because it completely burns more of the injected fuel. Add propane and you completely burn about 95% of injected fuel, as opposed to 80% or so in an NA engine. More injected fuel being completely burned = more power at a given throttle setting = less throttle needed to produce x hp from a turboed engine (and propaned, perhaps) than from an NA engine. Obviously that's "theoretical" and what you see in the real world will be different, but not too far off.

[More Power]

Scenario #1 -

[img]smile.gif[/img] dieselhumvee and I think alike....

Just about any year El Camino would be a real sweet fuel economy rig. An N/A 6.2 or 6.5 that was professionally rebuilt, balanced, gear drive timing set, 6.2L "C" series cylinder heads, port matched and running a DB2-4911 and matching injectors defueled for N/A use. Dual 3" mandrel bent exhaust with crossover pipe and free-flowing mufflers. These car/trucks weigh about 3800 lbs and have a better drag coefficient that a truck/Sub. 30-mpg could be possible with 3.42 gears and a 700R4.

Otherwise, a 2WD 1500 series pickup or Suburban, lowered a bit, and geared with 3.42's or 3.73's and a 700R4 should deliver fuel economy in the mid 20's with a non-turbo 6.2 or 6.5 - maybe a little better if driven at no more than 65-mph. The 1982 GMC K1500 4x4 I owned would deliver 24-mpg if driven at 65-mph or less. Alltime high was 27 at 55-mph.


Fuel consumption rate for an N/A 6.2L diesel.

An N/A engine is more efficient than a TD in light load applications. Pushing exhaust through a turbo and its more complicated exhaust manifolds takes energy. At lower power requirements, a non-turbo is more efficient. I'd stay with the 21.3:1 pistons. [img]smile.gif[/img]

MP

[ 12-22-2004, 02:32 PM: Message edited by: More Power ]

[john8662]

Heads?

Using C series pre-cups, but I wonder if using the 82 Model heads would yield better fuel economy as they have largest valves?

[dieseldummy]

Ponder this, '86 or so Lincoln town car with a 700r4. Late model 6.5 with 25:1 compression ratio, '82 heads ported and polished, splayed mains, fuel rate set to "C" engine specs supplied from a DB-4 pump, injectors set to pop at 3000+psi, free flowing exhaust and intake. With the high compression ratio comes thermal efficiency and fromt the DB-4 pump comes the capability to supply high injection pressures for extended periods of time which in turn raises effeciency by better atomizing fuel spray. The splayed mains would help the block better cope with the high stresses involved with 25:1 compression and the '82 heads as John mentioned have the bigger valves capable of flowing more air. Not only would you have a car with all the creature comforts, but a drivetrain capable of delivering 30+ mpg...

[More Power]

I owned a 1982 "C" 6.2L diesel that I had rebuilt. The largest valves came a couple model years after the introduction of the 6.2 in an effort to improve power. GM abandoned the large valve heads because of a much higher likelyhood to crack. I've seen a couple sets of large valve heads, and I sure wouldn't use them. I'd leave the compression ratio at factory specs. The head gaskets are the concern here with higher CR, plus I don't think you could raise CR much because the 21.3:1 piston protrusion through the cylinder head deck is already taking up all of the room.

I like the idea of a DB4....

To get max fuel economy, think low vehicle weight, minimize drag force, maximize engine efficiency and drive at efficient vehicle speeds with appropriate gearing. Got to stay below 65-mph. With a light vehicle, slower speeds and correct gearing, a non-turbo 6.2/6.5 built as was mentioned above would get you the very best fuel economy.

MP

[moondoggie]

Good Day!

More Power: Is there an article and/or project in the future here? Since mpg is my only hobby, my interest is VERY high, although my ability to duplicate anything you might do is limited.

I'll be watching this topic.

Blessings!

Brian Johnson, #5044

[More Power]

Moon... Might... I have lots of photos of special stuff that would work for a fuel economy article...

2- Scenario #2- You run at 75-mph on the Interstate most of the time in your pickup/Suburban without a load.

Wind drag increases exponentially, with drag becoming an ever more increasing factor above 65-mph. At 75, you need a turbo. The efficiency loss of pumping exhaust through a turbine is now overcome by the increase in power and efficiency offered by a turbo when operating at the higher power requirements of 75-mph.

Still, a 6.2/6.5 built as the above N/A 6.2/6.5 would apply, but we simply add a turbo and a single 3" mandrel bent free-flowing exhaust system. Gear the vehicle for 2000-rpm at 75-mph, and shoot for somewhere in the vicinity of 3-5 psi boost pressure at 75-mph on a level highway.

As mentioned above, wind drag is significant at 75-mph. Anything you can do to decrease drag will pay big dividends in fuel economy. Under-bumper air dams reduce drag, as does lower vehicle ride height. Lose the exterior accessories (like bug deflectors, etc.) and run narrow radial highway tires with maximum air pressure.

Differentials..... Open diffs have lower drag than limited slips.

MP

[john8662]

The 65MPH theory is true, thats when I got my best MPG at night traveling doing the night time speed limit of 65.

[More Power]

A few facts and trivia concerning my 1982 6.2L GMC K1500 pickup.

When I first got the truck, it was four years old. The previous owner had gotten tired of fixing the 700R4 and had installed a TH350 3-speed auto without overdrive. I drove the truck in that configuration for about 9 years, which roughly corresponded with the relaxing of the speed limits.

Once the speed limits were removed here in Montana, I quickly learned not having an OD was a problem. So, I had a performance built 700R4 installed. I just wished I'd done that years earlier. The improvement in driving pleasure was astounding.


circa summer 1988 at a remote F/S campground in western MT.

This truck had 3.42 gears and produced 17-19 mpg with the TH350 at about 60-mph. Once installing the 700R4, fuel economy jumped to 22-24 mpg. When kept to no faster than 65, it would deliver a consistent 24-mpg.

Then I added a Banks turbo. Fuel economy actually dropped to a consistent 22-mpg, but who could resist not using the extra power. I suspect if driven exactly the same, fuel economy may have been a little closer to when N/A.

Speed hurts.... At 65, I saw close to 22 or a little better. On one 700-mile Interstate round trip between Missoula, Montana and Billings, Montana, I drove the 6.2TD GMC at 80-85. Fuel economy on that trip dropped to 17.5-mpg. Was fun though.... At that time, the "Reasonable & Prudent" rule applied to MT's Interstate speed limits.

Seemed prudent.....

MP

[ 12-21-2004, 02:04 PM: Message edited by: More Power ]

[grape]

6 speed manual is in order most deffinately. I would also like to have the rear end out of the vehicle to put on my fixture to make sure it is exactly true. As the come from the factory they are within an 1/8" which in our world at 180 is unacceptable. There are also a few various things I'd like to do to the ring and pinion and the axle bearing surfaces.

[G. Gearloose]

I concur the manual OD trans. The 700R is efficient but not tops.

Could a 6.2 be stuffed in a late model Camaro?

[convert2diesel]

I too have spent a great deal of time trying for fuel economy, using various engines, mostly to allow me to continue driving my "Yankee Tanks" without draining my bank account.

One of the first things I had to wrap my head around was I was not trying for peak horsepower, but "effective" use of horsepower at the speeds the engine would be run at. One of the great things about diesels is that they are "naturalized", meaning that at part load they are over aired and the amount of fuel directly effects the power out put.

In designing an engine for peak horsepower, you are trying to cram as much air fuel mixture into the combustion chamber as possible, while still allowing the combustion process to proceed as efficiently as possible. Ergo long duration cams, turbo chargers, high flow exhausts etc. When you are designing for fuel economy, then what you want is to produce the most efficient burn at or close to, the peak torgue RPM of the engine. That is how industrial engines are designed. In our case that is 1,800 RPM. Now it becomes a question of how much horsepower you require to operate your vehicle at a given speed.

From an efficiency standpoint, the 6.2/6.5 is not a stellar performer compared to most other diesels but it does do an decent job in the power/wieght category. Fuel consumption for this engine starts at .42 lbs/SHP/Hour for the economiser and tops out at .47 lbs/SHP/Hour for the last variant 6.5. In industrial terms, that is god awful, as the engine manufacturers are consistanly producing engines in the .33 to .35 area, with some of the huge ship engines down to .28. In order for us to achieve these figures, a major redesign of the engine and fuel system would be required.

That doesn't leave much that we can do with the engine itself to increase efficiency, other then to gear it correctly to allow it to operate at it's most efficient speed. MP corrected this when he installed the 700R4. He just dropped the RPMs down closer to that magic number of 1,800 RPMs at highway speeds. Increasing or decreasing the the amount of fuel will just serve to increase or decrease the speed of the engine. Increasing the amount of air (turbo) at part throttle will have no effect what so ever except to increase the load on the engine and thus require more fuel. The advantage of the turbo in this case is that it flattens out the torgue curve, thus allowing for substantial HP increases at RPMS higher then 1,800. At part throttle and low loads, the engine is still over aired, so a turbo is not needed. As far as changing the compression ratio, it will always be a trade off. If we increase the ratio yes we will marginally increase combustion efficiency but the added power necessary to rotate the engine may negate any advantages. If we lower the ratio, then we would have to add a turbo to make up for the loss in efficiency. IMHO we should leave well enough alone and just do the mods to make this engine breath (and exhaust) as efficiently as possible and endeavour to run this engine as close to 1,800 RPMs as possible.

Any significant gains in fuel mileage will be realized in wieght and aerodynamics. Unfortunately the trucks that most of you operate have all the endearing aerodynamic qualities of a grand piano with the lid up. Perhaps the suggestion made previously about lowing the body plus adding some, more then cosmetic airdams, may be money well spent. But then some of the usefullness of these vehicles may be lost. Again that trade off thing!! Wieght is another thing. Most studies have shown that within reason, wieght is only a factor below 40 MPH and in climbing hills. It becomes a major consideration in day to day city driving, but on the highway aerodynamics is the great enemy.

Sorry for the long winded disertation, but I thought it would help the discussion get away from building a "stump puller" and into designing a mileage machine.

All the best

Bill

[catmandoo]

mp i noticed on my 92 with the 6.5n/a that after i put the banks on it i too dropped about 2mpg,but as you mentioned the banks seems to make the right foot feel heavy,but if i drive it at 55 religiously i can duplicate the same milage as when it was n/a.this is with maybe 1/2 to 1 lb of boost at the most,can a turbo be made to spool right off idle,or could a smaller turbo be used that would be spooling up at idle.my thinking is if i could cruise at my 55mph with 5-6 lbs boost wouldn't the extra boost offset any loss of power driving the turbo.i think thats how i want to say that!

[catmandoo]

must a been typing at the same time there,and you have a very good theory there on the turbo convert.