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Diesel V.S. 350 injection

Discussion in 'The Garage' started by Scott39, May 6, 2005.

  1. Scott39

    Scott39 1/2 ton status

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    I have a 350 TBI with 88,000 miles on it in my 91 blazer.
    My buddy has a 6.2 turbo diesel 1985 truck that has 134,000k on it, but he has not ran the engine for about 1.5 years, because he rolled his truck, but the engine was still good, so he pulled it out.
    I asked him if he would want to trade straight across, my 350 for his diesel, he said yes.
    Is this a better deal for me?
    What MPG out of the turbo diesel?
    Would I notice better horse power, or take of power with the diesel and turbo?
    I`am running 38" tires, dana 60,70, 5.86 gears, 700r, 241 SYE kit.
    I drive this blazer to the trails.
    Thanks,
    Scott
     
  2. Zeitler

    Zeitler Registered Member

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    i would take a diesel anyday instead of a 350..but here old 6.2s go for 2-3000 $$..

    both power and mileage should improve ..hard to say how much...

    expect atleast 15 mpg probably more
     
  3. joez

    joez 1/2 ton status

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    The gearing in your axles will both help, and hurt you. With those gears a 6.2 TD will probobally get up and move very nicely, and have plenty of power. But on the interstate, your RPM's will be up arround 2500-2700. The motor will be plenty happy with that, but you are then out of the torque curve and fuel economy will suffer a bit. IIRC tRustyK5 is turning similar RPM's on the interstate at 65mph, and with 39.5 TSL's pulls down 16mpg.

    For comparison, i run a 36" tall TSL, with 3.73 gears and am only turning ~1700 RPM's on the highway and average fuel economy is arround 20mpg, I have recorded as high as nearly 26 before.

    That said, I would swap motors in a heartbeat. No comparison to the off idle torque of a diesel.


    EDIT: Forgot to mention that both mine and tRustyK5's are both N/A, no turbo's. You may be able to squeeze 17mpg or so out of it with the turbo. Unless you keep your foot in it all the time, that is.
     
  4. steve_kibbe

    steve_kibbe 1/2 ton status

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    can you drive the diesel or is it out already?
    IMHO I would rather have the turbo diesel. I think I have some diesel fuel in my veins.......
    Your milage should definately go up, even with steep gears like yours. The only draw back is you won't get the rmps out of the diesel you do out of your 350. I'm not sure, but you might have to get another torque converter aswell, I believe they are different from gas to diesel.

    my $.02 for ya

    Steve
     
  5. DesertDueler2

    DesertDueler2 1/2 ton status

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    Also the gov. in the transmission is different.

    Dan
     
  6. 1977k5

    1977k5 3/4 ton status Vendor

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    Just because the engine is out of the power band does not mean that it will get worse mileage. For an engine, there is a power curve and a mileage curve, and they very rarely match up.
     
  7. joez

    joez 1/2 ton status

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    It does on a 6.2. I didnt say every engine, i said that that is how the 6.2 is.
     
  8. mrk5

    mrk5 The Sticker Guy Moderator Vendor GMOTM Winner Author

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    I'd go for it.

    I went from 6.2 to 350, and I kinda miss the diesel. I was getting 20mpg with 33's and 3.08 gears.

    With your gearing, I wouldn't be concerned at all.
     
  9. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    With a 6.2 the peak cruise rpm for fuel mileage is approx 1800 rpm. Every 100 rpm more than that loses 1 mpg. The reverse is true also, meaning for every 100 rpm i can drop my cruise rpm I will pick up approx 1 mpg. Adding an overdrive to my truck will drop cruiise rpm's down by nearly 500 rpm and should net me 4-5 mpg better economy.

    Rene
     
  10. Scott39

    Scott39 1/2 ton status

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    THANKS everybody,
    I know alittle about diesels, I have been drving semis for 20 years now but I wasn`t sure about the 6.2.
    I will probably be changing the gears later after I put on 42" IROKS.
    KEEP THE INFO COMING.

    SCOTT
     
  11. Diesel Dan

    Diesel Dan 1/2 ton status

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    I wouldn't exactly count on it. When I installed my gearvendors there was less than 2 mpg improvement but driveablitiy was WAY worth it. The truck was an '88 V30 crewcab, 6.2L/Th400/4.10s running 235/85s all stock. Best of 18mpg.

    Now on my '98 CTD dodge I lost about 1.5mpg by going from 245/75s to 285/75s at same highway speeds and adjusted for the 8% difference in speedo variation. Rotating tire mass is real close since I replaced the factory steel wheels with aluminum Centerlines. We did see a gain of ~3 mpg by running 55-60 Vs 70-75.

    Some may call me anal on my MPG figures :blush: , I have all fuel reciepts for my dodge for the last 8K miles.
     
  12. mountain4x4

    mountain4x4 Registered Member

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    Just did a 1200 mi. road trip in my '90 Burban, 350tbi, 31" tires. 3.73 gears, 700r4, 4"lift (I have 33s, but don't run them much until I change gearing. I mainly drive in the mountains and am switching to 4.56s w/285/75/16s for my road tires, maybe some 38s or so in the future for off road use. Currently, with the 33s, I have to floor it ALL the time on the highway).

    Anyway, I got about 18 mpg cruising at 80 mph or so. This is on I-25 from Denver to Walsenburg, then to Alamosa, La Veta pass, then La Mancha pass, and through to Albuquerque. It is a relatively hilly, windy drive and I was not driving with fuel economy in mind. I'm sure low to mid 20s is possible given the right conditions.

    I get a few mpg. less around town. I believe with an intake, injector and tb spacers, high performance exhaust, and fuel pressure mods, the 350tbi is capable of good mileage. When I rebuild my motor (it has 215 K miles on it), I believe more effecient heads (Vortec or similar), a slightly bigger cam, and a 9.5 to 10:1 compression ratio, depending on cam choice, the SBC can get very good fuel economy. I can only speculate what the motor mods would do, but I'm hoping to have a Burban that gets no less than 20 mpg and produces 300 plus hp. Case in point is the ZO6 Vette, not exactly a big truck, etc., but it has a 405 hp SBC, and can get over 30 mpg. on the highway. It kills me how ineffecient stock trucks are. I won't get into why it must be this way, but major improvements in mileage and power can be had with some simple intake, exhaust, and fuel tuning...

    The way fuel prices are rising, maybe biodiesel will be a good enough reason to run a Diesel truck (besides massive torque). In New Mexico, biodiesel was a little cheaper than regular diesel.
     
    Last edited: May 9, 2005
  13. Diesel Dan

    Diesel Dan 1/2 ton status

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    If your getting that kind of mileage then why change anything? :confused:
    Keep it as a driver. My '91 V2500 sub had a new engine w/flattops, RV cam, Edelbrock TES headers, 3" flow master exhaust(single), 4L80E, 35" radials, 4.56s and got 11mpg on the highway. Going 600 miles from PA with it on bias swampers only saw 10mpg or so.
     

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