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Thread: Max fuel economy?

  1. #21
    catmandoo Guest

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

  2. #22
    NH2112 Guest

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    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.

  3. #23
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    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 ]

  4. #24
    john8662 Guest

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    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?

  5. #25
    dieseldummy Guest

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    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...

  6. #26
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    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
    Last edited by More Power; 03-08-2009 at 16:42.

  7. #27
    moondoggie Guest

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    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

  8. #28
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    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

  9. #29
    john8662 Guest

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

  10. #30
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    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 ]

  11. #31
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    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.

  12. #32
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    I concur the manual OD trans. The 700R is efficient but not tops.

    Could a 6.2 be stuffed in a late model Camaro?
    1996 K1500 6.5, 1984 K5 6.2 Banks both \"Stock\" (tilting hand side-side like Sammy Davis in Cannonball Run)<br /><br />Got Boost?

  13. #33
    convert2diesel Guest

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    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

  14. #34
    catmandoo Guest

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    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!

  15. #35
    catmandoo Guest

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

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  17. #37
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    I give up......you guys think hp is magic and not math. total amount of air decides hp, displacement decides when that power will be made (rpm), the bigger the engine the quicker target power can be attained. A turbo allows power to be made quicker with the same cubic inches as a N/A engine if the turbo is designed correctly.......guess why, cause it makes the engine bigger. And "big" turbo and "small" turbo is about as vague as saying I'm lost somewhere in the United States, can you help me find out where I am.

  18. #38
    dieseldummy Guest

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    convert2diesel,
    I agree with what you are saying, I guess all I was getting at with the motor mods is that theoreticly some gain can be had from going into the motor.
    grape,
    Idealy the car designed for max fuel economy won't take that much HP to push through the air so in reality adding a turbo may add a parasitic loss on the engine by restricting exhaust flow. The only time adding a turbo becomes effective is when you have more fuel than air, and in this case I don't think that will be an issue... Sounds like your stuck in the world of big HP racing to me...

  19. #39
    convert2diesel Guest

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    Grape:

    Who P@#$%ed in your cornflakes this morning?

    If in fact you are trying for maximum HP then you are dead right. What MP and Cat were talking about was making the engine more efficient at part throttle.

    Not all of us are trying to pull stumps down on the farm nor are we interested in taking on the local piston heads in their HunToyIssans. We are just looking for good functional vehicles that can be operated economically.

    What Cat was asking was a question of volumetric efficiency at less then optimal flow. Unfortuantely if you size (Using math) the turbine for low exhaust flow, when you do put your foot into it the turbo looses it's efficiency and effectiveness.

    What MP is saying is what I am saying...namely at part throttle and low RPM "you don't need no damn turbo" Run your numbers any way you want. You'll come to the same conclusion.

    Bill

    [ 12-21-2004, 07:46 PM: Message edited by: convert2diesel ]

  20. #40
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    These are just opinions.... [img]smile.gif[/img]

    Scenario #3- You use your pickup/Suburban for all sorts of family and work related driving, including towing the 7K family travel-trailer a few times a year.



    This is the category that most of us fall into - to one degree or another. Let's talk about maximum fuel economy strategies for scenario #3.....

    MP

    PS. I had a hell of a time climbing the tree to take that photo...

    [ 12-23-2004, 02:49 PM: Message edited by: More Power ]

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