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K30 military truck diesel to gas conversion

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by scotty1, Feb 6, 2002.

  1. scotty1

    scotty1 1/2 ton status

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    Well the 3/4 Burb I was gonna get was sold so I am re-thinking what I want. I like the mid eighties 1ton pickups but not crazy about the 6.2 diesel, I am more of a HP guy. I know there are folks who have the 350 SB in a K30 and would like to hear from you or maybe there is an article or thread to get good info from. Thanks

    Git there fastest with the mostest!
    Nathan Bedford Forest
     
  2. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I've done it (see my sig), Pete (pcorsmit) has done it, several others as well. It's practically a bolt in change. Same bell housing, same motor mounts, some models the diesel exhaust even bolts up (I wasn’t that lucky). Radiator hoses can be a small issue depending on what you got. You'll need the accessories and brackets for the gas engine. Accelerator cable and things like cruise will be different. Pretty simple mostly. Just get all the stuff along with the motor from the donor. The only problems I ran into came out of dealing with the military hybrid 24V/12V system (I converted completely to civi) and EFI. EFI was not bad, I just had never really taken the time to understand it before so I ran into a few surprises. Pete, Harry (HarryH3), Doug (AZBlazer) and several others here helped me through those issues and I have no complaints. If you do it, I and others will be happy to answer questions along the way.

    6.2 is not that bad though. If I had a good one in my K30 when I bought it, it would likely still be there, at least until an expensive repair came around. They aren't very powerful, but they are dependable when maintained and they will run upside down without complaint, at least until the bearings seize. That's what happened to my 6.2, completely toasted from running upside down after a roll over. The previous owner who did that was so shook up from the roll that he didn't even think about turning it off till it was too late. [​IMG]

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked, 4" lift, 42" tires
    Some day: massive cutting, shorter wb and rear overhang.
     
  3. Ben Malinski

    Ben Malinski Guest

    You'd be MUCH more happier installing a big block! Especially if you planning on keeping the truck for years to come. I swaped out the diesel in my 84 M1009 (Blazer) and installed a 454. I get better gas mileage then the small blocks! That's driving without stepping on the gas all the time. Cruising down the highway at 65-70 mph, I'll get around 18-20 mpg. Small blocks in the trucks are getting around 15 mpg. It all depends on your budget!

    I don't know the secret to success but the key to failure is trying to please everyone!
     
  4. Danno

    Danno 1/2 ton status

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    HP? Who needs that when you've got all that lovely torque!? Hehehehehe...

    I'd go with a big block over a small block if I were to ditch the diesel in my K5. I'd also go with EFI over carb.

    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  5. dyeager535

    dyeager535 1 ton status Premium Member

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    I gotta ask, how are you getting that mileage??
    if you're running stock tire size, haven't changed gears, and are over 5000lbs, I gotta know your secret.

    Dads truck at 6k lbs 454/q-jet/SM465/NP205/4.10's, OD, gets 11 at best on freeway, unloaded.

    My truck, 5k lbs 350, q-jet/Sm465/NP205/3.42's gets 18 AT BEST in the Oregon desert (flatter than flat) at night.

    both trucks are running correct speedo/odo's, verified by stopwatch/freeway speedometer check stations/tach readings

    I know this isn't the topic of the post, but I believe you are claiming/achieving Diesel mileage, with a 454.


    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
    Why insist on counting when the ring gear has the tooth counts stamped in?
     
  6. pcorssmit

    pcorssmit 1/2 ton status

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    &lt;blockquote&gt;&lt;font class="small"&gt;In reply to:&lt;/font&gt;&lt;hr&gt;&lt;p&gt;HP? Who needs that when you've got all that lovely torque!? Hehehehehe...

    <hr></blockquote>

    I found this on this site &lt;a target="_blank" href=http://www.uk.digiserve.com/col/chiltern/gmc.htm&gt;http://www.uk.digiserve.com/col/chiltern/gmc.htm&lt;/a&gt;

    160 BHP @ 3800 (Naturally Aspirated)
    Torque / RPM 290 lbft @ 1900 (Naturally Aspirated)

    (not that its neccesarily a credible site, but its all I could find. The specs page here on CK5 actually lists 130 hp).

    What torque? Thats right about where your run of the mill stock small block is. &lt;img src="http://coloradok5.com/forums/images/icons/wink.gif"&gt;

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  7. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Yeah, 6.2s aren't like most diesels. HP and Torque generally won't match a SBC unless you put a turbo on it along with other mods. From what I've seen, torque numbers are a bit bigger in the very low rpm range, but not by much. They really don't have much to offer other than relatively dependable (but nowhere near what most diesels give) and decent mileage (again, not up to par with other more powerful diesels). Like I said, if I had a good one, I would probably run it. But first time it gave me significant trouble, I would sell it or make a boat anchor out of it. Now consider a Cummins, IMHO, THAT is a REAL light truck diesel rather than just an overweight, underpowered, expensive motor that happens to burn diesel fuel.

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked, 4" lift, 42" tires
    Some day: massive cutting, shorter wb and rear overhang.
     
  8. Danno

    Danno 1/2 ton status

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    Er, OK. Well, a poorly running 6.2L will behave pretty much like you described, maybe. Mine's running great, and I wouldn't trade it for a small block ever.

    And when a Cummins gets over 27mpg highway, you let me know.

    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  9. Danno

    Danno 1/2 ton status

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    Yeah, the peak torque isn't very high, but there's still plenty to go around. I dunno, my K5 definately feels like it's got more in the lower RPMs than any other truck I've ever driven (all GM gassers).

    And I'll eventually have a turbo under the hood to keep my engine happy. :-)

    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  10. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I've never seen a dyno graph of a 6.2 but I've heard they do make bigger numbers down low, and I believe that. That's why I would have run the 6.2 if it had been good in my K30. Ideal for rock crawling. However, I've driven 6.2s that were running right, I've really never been that impressed. And I've seen peak numbers similar to the ones Pete posted. I can easily believe those numbers (or even less) based on my experience. And as for 27 mpg, sorry, I just don't see it happening. It's been a long time since I knew someone who drove a 6.2 but, IIRC, he was bragging about 21-22 or so compared to my 14-15. He was a diesel mechanic (working on a fleet of GM diesels) and always kept his truck in top form. I may be wrong about the exact number hew as quoting but no way was it anywhere near 27, and I've never even heard of anyone getting any where near 27 in a 6.2. I could certainly be wrong, I'm in no way an expert on the 6.2. I don't have a ton of data or printed material to back it up but, if they were that good, everyone would be clamoring for them instead of trying to swap them for gas burners or Cummins...

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked, 4" lift, 42" tires
    Some day: massive cutting, shorter wb and rear overhang.
     
  11. pcorssmit

    pcorssmit 1/2 ton status

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    I did actually get 27, once. I have no doubt that my Cummins is capable of mid 20s, either, if I were to run it down the highway at 55-60 mph, but I've never tried it, not do I really have any plans too. I also remember pulling the hill after Georgetown on I-70 at 35 w/the 6.2; even when stock the Cummins had no problem at 85. Shortly after I bought the Dodge, I took it to Grand Junction. I hit 5th when I got on I-70, left it there till Glennwood canyon when my bladder was about to explode, then left it in 5th to Junction.

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  12. Mr.Chevy4x4

    Mr.Chevy4x4 1/2 ton status

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    I can vouch for the 27 MPG figure. I have a goof friend that has a 6.2 K5 all stock that he drives 46 miles each way to work and he averages 24-26 MPG out of it all of the time. Not to mention the fact that it has over 200K miles on it with only having the injector pump rebuilt once. He is a diesel mechanic(Cat) and he did turn the pressure up on it just a hair. Supposedly this helps power and mileage on those engines.

    '85 K5 : 330 HP-350/350/205/FF14/D60/36 inch TSL's
     
  13. Danno

    Danno 1/2 ton status

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    Well, I've hit 27mpg every time I've driven between Colorado and Indiana so far. I normally get around 18-22mpg during everyday driving, which is a mix of city and open road at 60-75mph.

    The 6.2L does have a smaller operating range of RPMs compared to a gas engine, and I sometimes wonder why GM didn't use better transmissions with these engines. I think the tranny setups really play a major part in how a diesel feels, and a 700R4 with 3.42 gears isn't a really good match. I'm shooting for an NV4500 in the future for my K5, and probably better final drive ratios too.

    The 6.2L is a good light-duty diesel. No, it's not a Cummins, but it still is a good engine that I think fits a K5 perfectly. Just need better trannies!

    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  14. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Cool, I stand corrected.

    The mileages I was thinking of were more mixed conditions I guess so the 18-22 does mesh with what I remember. I still don't care for the 6.2 but if it gets that kind of mileage on the open road in a K5 then, maybe it is worth considering for some people. I don't know if I could live with it in the mountains though. I do remember cases like Pete mentioned where the 6.2 bogged down pretty bad with relatively light loads on a hill. Anyway, sorry for the noise, I guess they are capable of better mileage than I realized.

    Russ

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked, 4" lift, 42" tires
    Some day: massive cutting, shorter wb and rear overhang.
     
  15. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    On the original subject, the gas swap is easy, I also did it way back. There is some nice stuff on the diesels, like the secondary fuel filter that's good for about 100K miles on a gas motor. And hydroboost.

    On milage, my parents tell me they used to get low 20's from my K5 when it was a 6.2L. Up to about 24 if I and they remember right. I was down to about 17 when I took it out, that was with a little lift and some 31's. With highway gears and no lift, I can see mid 20's and maybe edge up from there depending on the wind.

    Maybe more relevant here is what you can do with a modified truck. The only one I'm really familiar with is Jim Allen's "stinky" and he was reporting about 18 mpg on the highway with 4.10's, 35's and 4" or so of overall lift. This dropped to mid 16's with the Doubler compared to the NP208 by itself.
    AND, the big bonus was with the turbo he was getting 385 ft-lb of torque on a chassis dyno in Denver. My 383 put out 315 on an engine dyno at similar altitude. Once again not a cummins but a cummins doesn't exactly bolt into a K5 either. Or better yet come stock! boo hoo.

    Making the world better, one truck at a time.
    SW-ORD
    <a target="_blank" href=http://www.offroaddesign.com>www.offroaddesign.com</a>
     
  16. Danno

    Danno 1/2 ton status

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    Yeah... My K5 isn't very peppy over 10,000 feet with the stock air snorkel installed. I'm slowly making the engine breathe better, and I've noticed a major improvement when I'm in the mountians these days.

    My 27MPG figures are under optimum conditions. Open highway, cruising around 70-75mph, running with a light load.

    And I didn't want this to sound like too much of an arguement, just hoping to get people thinking about diesels. With a little work (and a turbo), you can get some really nice power out of a 6.2L, and still get pretty decent mileage.

    Take care...


    1984 K5 Blazer 4x4 Silverado
    6.2L diesel, 700R4, 3.42 gears, 31x10.5" tires
     
  17. scotty1

    scotty1 1/2 ton status

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    Thanks guys for all your input. I am still kicking myself for not acting sooner on the 3/4 Burb but thats the breaks. I would not mind a diesel if I could get good gas mileage and power but I need it to pull mountains with a decent load. Add in the 35" tires and lift to clear them with proper gears and I am afraid the equation gets pretty messed up.

    Git there fastest with the mostest!
    Nathan Bedford Forest
     

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