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  1. #1
    Join Date
    Feb 2000
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    Montana
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    If you were building an engine for maximum fuel economy, which would you choose?

    1- A non-turbo 6.2L.
    2- A TD 6.2L.
    3- A non-turbo 6.5L.
    4- A TD 6.5L.

    I'll add more later, but I wanted you guys to think about fuel economy and what it takes to get it.

    MP

  2. #2
    john8662 Guest

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    This is purely based on my 86 pickup. Non turbo, with C series calibrated injection pump truck geared with 3.08 and 700 trans.

    I vote for Non turbo 6.2L

    I'ts all in the gears and a light right foot

  3. #3
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    Apr 2001
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    CA
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    My first answer would be N/A 6.2L, but....
    There are too many variables.

    What vehicle will it be in? 1/2, 3/4, 1 ton? Pickup? SUV? Other?
    What type of driving is to be expected?
    Towing?
    Drivetrain requirements?
    Power requirements?
    On/off highway?
    Driving habits?
    Speed expectations?

    The list could go on.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  4. #4
    Join Date
    Mar 2010
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    Hey everyone new here, thought I'd post in this because it's basically what I'm gonna ask.

    I have a 1988 Grand Wagoneer, currently with 3.31 gears (could change that)
    lookin at a 2-4" lift with 32s
    probably all onroad driving (never been offroading)
    And I am not a heavy footed driver, though some power isn't the worst thing in the world

    I was curious what everyone thought would be the best engine choice of the 4 for me?

  5. #5
    Join Date
    Sep 2006
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    363

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    Quote Originally Posted by jMedia View Post
    Hey everyone new here, thought I'd post in this because it's basically what I'm gonna ask.

    I have a 1988 Grand Wagoneer, currently with 3.31 gears (could change that)
    lookin at a 2-4" lift with 32s
    probably all onroad driving (never been offroading)
    And I am not a heavy footed driver, though some power isn't the worst thing in the world

    I was curious what everyone thought would be the best engine choice of the 4 for me?
    Either a GM 6.2 or Cummins 3.9 4BT. Do you have overdrive? The 6.2 likes to cruise at 1800 rpms and Cummins is a bit lower like 1500-1700 rpms. The 4BT would likely yield better fuel economy. However, a 6.2 that is set up with fuel economy in mind can yield close to 30 mpg.
    1990 ¾ ton 4x4 Chevy Suburban
    -Cummins Diesel - 12 valve - factory rebuilt
    -6 speed bullet proof manual transmission - NV5600
    -Gear Vendors Overdrive
    -Upgraded Holset HX-35 turbo
    -NP205 iron transfer case
    -3.73 gears

    1982 ½ ton Chevy Suburban
    -6.2L diesel - high nickle crack free 1982 block
    -Stans headers
    -Ported heads
    -Timing gear
    -4 speed automatic
    -3.08 gears
    -30 mpg on freeway

  6. #6
    Join Date
    Mar 2010
    Posts
    14

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    Unfortunately because of CA dmv I cannot do a Cummins swap.
    But 30mpg?? I have heard so much less from others. How would you set that up?
    I am in search of a whole knew drive train so I will be picking up some sort of OD transmission

    Quote Originally Posted by Edahall View Post
    Either a GM 6.2 or Cummins 3.9 4BT. Do you have overdrive? The 6.2 likes to cruise at 1800 rpms and Cummins is a bit lower like 1500-1700 rpms. The 4BT would likely yield better fuel economy. However, a 6.2 that is set up with fuel economy in mind can yield close to 30 mpg.

  7. #7
    Join Date
    Sep 2006
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    363

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    Quote Originally Posted by jMedia View Post
    Unfortunately because of CA dmv I cannot do a Cummins swap.
    But 30mpg?? I have heard so much less from others. How would you set that up?
    I am in search of a whole knew drive train so I will be picking up some sort of OD transmission

    Here’s what I did to get 30 mpg (US) on my 82 Suburban.

    1. I used 1982 heads with small pre-combustion chambers and large valves. These heads get the best gas mileage but suffered from cracking. Of course mine had cracks in between every valve seat so I installed liners between each valve seat.
    2. Ported / polished the heads
    3. Stan’s Headers – Made a big difference in power since stock power was 130 hp
    4. Free flowing exhaust – Dual 2-1/2” with H-pipe and Thrush tube mufflers.
    5. DSG Timing Gear
    6. Ported / polished J code intake manifold
    7. 700R4 automatic with overdrive
    8. 3.08 rear end
    9. Tall & skinny tires – 30x9.50 with 50 psi of pressure

    And of course, the most important, an easy foot. To achieve 30 mpg, I have to keep it under 60 mph. Over that, it drops off rapidly with the square front end on the Suburban. For example at 75, it’ll drop down to about 23 mpg. The 75 mph gas mileage can be increased considerably with aero mods but I rarely drive that speed so I have not done any aero mods on my Suburban.

    >> Unfortunately because of CA dmv I cannot do a Cummins swap.
    I don’t believe the 88 Jeep Grand Wagoneer was ever offered with a diesel in the U.S. So technically, CA DMV won’t allow installing any diesel. However, if you push the right buttons, I believe you can get it through even with a Cummins. PM me if you’re serious about doing this swap and I’ll tell you how.
    1990 ¾ ton 4x4 Chevy Suburban
    -Cummins Diesel - 12 valve - factory rebuilt
    -6 speed bullet proof manual transmission - NV5600
    -Gear Vendors Overdrive
    -Upgraded Holset HX-35 turbo
    -NP205 iron transfer case
    -3.73 gears

    1982 ½ ton Chevy Suburban
    -6.2L diesel - high nickle crack free 1982 block
    -Stans headers
    -Ported heads
    -Timing gear
    -4 speed automatic
    -3.08 gears
    -30 mpg on freeway

  8. #8
    Join Date
    Feb 2000
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    Montana
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    The vehicle will be a factor in answering the question as to which engine produces the best fuel economy. Also, part of the fuel economy equation is determining the intended use. We'll talk about all aspects....

    Was this a trick question?

    MP

  9. #9
    Join Date
    Dec 2002
    Location
    Terre Haute IN
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    I would use a NA 6.2J stuffed in an 80 Olds Cutlass with a 700R4 and a rear gear ratio tuned for 1700 RPM at 70 MPH.
    99 K2500 GMC Ext Cab, 6.5TD, Heath ECM reflash, TDC Offset -1.80, Bumped Optic, FSD Isolator, Turbo Master, KD 3.5" Exhaust, 4.10s and 33x11.50, Intercooler is next.
    98 Burb 350 1/2T/4l60/246/10Bolts - Wifes Ride
    80 Olds Cutlass 6.2/Studded/700R4/12Bolt 3.30s/IP=4544 Juiced by JK/Best MPG=30
    79 Olds Cutlass, 410ci/700R4 - Currently Restoring
    1992 Mitsubishi Eclipse Turbo, currently 12PSI max boost
    39 Chevy Rat Rod
    2004 Sportsman 600
    2002 Scrambler 500
    2007 Sportsman 90
    2003 Kazuma 50
    2001 XR50
    1990 Murry 46"
    43 Total pistons!
    Email= Dr.Diesel@gmail.com WA9SDJ

  10. #10
    dieseldummy Guest

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    I would say it doesn't matter what engine. My answer is any engine with the IP calibrated to only deliver XXmm3 of fuel. Then it can only burn so much fuel as well as only have so much attanable HP.

  11. #11
    catmandoo Guest

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    well just from my experiences,my old 84 c10 with 6.2 and 700r4would run about 25-26mpg,and my 92 c1500 with n/a 6.5 with nv4500 ran a high of 27mpg on a half dozen occasions.i have since put my banks turbo on it and turned the pump up and man lots more power,yet i have still pulled 27 on occasion.they both use 3:08 gears.so if i had to chose i would probably go 6.2 with the 4500.but i really don't think it will be much more,i've been thinking of a way to hit 30mpg.but just haven't got there yet.

  12. #12
    Join Date
    Feb 2001
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    Fort Worth, Texas, US
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    945

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    lots of compression, hardly any fuel delivery, small T3 based exhaust housing and wheel with about 6 pounds of boost from a T04 H3 inlet wheel. That's enough inlet air for around 180 hp, yet fuel delivery would probably be around a stock 135-140 hp c code engine. Wouldn't matter which engine as long as it had the correct pre-chambers. I'd also put it in one of our out of date bodied craftsman trucks......could weigh in at just over 3K pounds. And it deffinately needs a T56 from a late model camaro or firebird.

  13. #13
    Join Date
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    There are 3 or more scenarios that we'll discuss concerning engine/vehicle requirements and maximum fuel economy.

    1- Scenario #1 - Fuel economy supercedes all other prorities for your fullsize street legal pickup/Suburban.

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

    3- 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.

    MP

  14. #14
    NH2112 Guest

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    Well for scenario #2 I'd use a 1/2 ton with OD tranny and gear it so that when in OD and at cruising speed I'm turning about 1800rpm. That would put you at about 55-60mph when turning 1800rpm in direct so your mileage while not on the interstate wouldn't suffer too badly.

  15. #15

    Post

    How about a budget fuel economy buidup. I vote for a 6.2 na in an 70's el camino with 2.56 gears and an overdrve trans.

  16. #16
    convert2diesel Guest

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    To answer scenerio 3, I have been driving the Buick Roadmaster wagon conversion now for a little over a month and this is my initial experience.

    The conversion is a "J" code tested used engine from Diesel Depot with a Hummer intake, 3 in single exhaust using low restriction muffler and resonator. 3.23 gears through a 700R4 (gasser torgue and tranny...soon to be upgraded to full diesel specs before I do our yearly sojorne to Florida in April with the Coleman).

    Drives in the city like it's butt is on fire (certainly gets alot of suprised looks) and still gives me 22 - 25 MPG (CAN), about 18 to 20 US. If I can ever get the return lines from leaking, maybe another 10%???

    2 100 mile trips on the highway at 70MPH gave me 30 and 34 MPG (CAN) respectively. Will have to change the timing gears and chain over the holidays and that should allow me to set the timing correctly. Once the temps get over 30 degrees F,with the proper timing and using 100% bio-diesel, I don't think 37 MPG is out of the question.

    Car was designed to tow and is spec'd for 7,500 lbs. The 6.2 may be a little light for this kind of wieght (will see. Friend has a 7,000 lb. Airstream that I'm going to try when the snow clears). From what I've seen to date, the current setup should have no trouble what so ever with my 2,500 lb Coleman.

    The thing that really impresses me is how smooth and effortlessly this car performs. With it's old gasser, anything over 60 MPH and this thing was humping. Add the trailer and you'd think I'd just stabbed it's mother. With the 6.2 I have a hard time keeping it under 70MPH on the highway and with the exception of the diesel rattle (music to my ears, bone of contention with my wife), it is not any noisier then the gasser.

    Will keep you appraised of further testing.

    Bill

    [ 12-19-2004, 06:11 PM: Message edited by: convert2diesel ]

  17. #17

    Post

    I like the idea of a 6.2 or 6.5 in a car, the mileage potential is much greater than in a pickup. Not to mention you can use a big, rear heel drive GM full size 70's or 80's car that wil provide a lot more room than any VW diesel car and be much less expensive on maintenance than a mercedes diesel. I would like to have a full size GM diesel car for work and just everday driving, and an Elcamino would be even better, I could pick up stuff from home depot or haul other light loads with ease.

  18. #18
    catmandoo Guest

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    convert what years your roadmaster?

  19. #19
    convert2diesel Guest

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    DieselHumvee and Catmandoo:

    I am trying to build up a conversion "Kit" for the 91 to 96 "B" body GMs. Peggy Sue is a 91 Roadmaster wagon with the trailer towing package, including the factory air shocks (ergo the single exhaust...why pray tell would they mount the compressor under the car where it gets all the road spray??)

    This chassis is basically the same as the "A" bodys built since 1978 and our kit should retrofit any of these cars easily. Probably there is more room in the "A"s. Hope to have a website up and running early in the new year.

    Oh and by the way, a full size wagon with the rear seat down, allows you to carry a 4x8 sheet of plywood with the gate up thereby negating the need for an Elcamino, though that would be a great conversion. The air shocks are good for 750 to 1,000 lbs.

    Bill

  20. #20
    Join Date
    Dec 2004
    Location
    Janesville, WI.
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    35

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    All things being equal, a 6.2 NA, should give the best mileage.
    87, GMC, G25, 6.2, 700R4.

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