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6.2 rebuild

Discussion in 'GM 6.2 Diesels' started by 1994ch, Nov 25, 2016.

  1. 1994ch

    1994ch Active Member

    297
    60
    Dec 6, 2008
    South Carolina
    Starting to pulling apart a 6.2 (was told it had an 80 or 81 code stamped on the block) have not learned/looked into that to confirm it. Future goals are to have good fuel economy and hopefully have enough power to "get out of its own way" but it does not need any more than that.
    Is a stock 6.2 reasonable for that or should I look into putting a turbo on it?

    If a turbo is kinda a toss up of opinion for what I am shooting for then the following questions arise.
    If I go with a turbo my understanding is that I will need to change out the precups. So if I want to stay open to the possibility of putting a turbo on it down the road should I go ahead and change the precups or should I not change them until I put a turbo on it?
    In other words are there any draw backs to having turbo precups on an N/A 6.2?
     
  2. Will L.

    Will L. Well-Known Member

    6,066
    3,443
    Jan 25, 2013
    Boulder City Nv
    Big precups only! Turbo as soon as you can afford it.
    Balanced 2350psi injcetors from day 1.

    My hummer was N/A. I replaced the long block with an optimizer longblock so it will have in it the turbo precups. I drove it for years as an N/A, it got the same mileage with the optimizer block. It had the small precups in the stock heads, the optimzer ha sthe big ones. Put the big ones in the heads! How you fuel the engine has tons more to do with it. Unshrouding the valves, port heads will have a much bigger effect than the precup size.

    Later I added a gm6 turbo (homemade turbo master) and turbo injectors from a used engine with around 70k on it. I turned up the db2 fuel screw more than twice as much as was needed to get the IP from N/A to turbo.

    I also added my steel roof/ slantback and top bars at the same time adding 1,000 of weight (no joke), and a taller profile and wind resistance.

    I accelerate much faster now and can climb freeway speed inclining hills that before I would loose speed horribly-

    Power and engine heat:
    One hill on the freeway here is about 3 miles long. Start at 70 mph. &190* f and at top of hill 40 mph and 230* f. Throttle floored. If ambient temp was over 100, I had to do 45 mph the whole way, then pull the over for a couple minutes to cool down.

    Add turbo: starting same speed and temp I can maintain 70 half way up the hill until temp rises to 210, then I back out of throttle to 55 mph to the top of the hill, never hitting 215 if ambient temp is over 100*f. If outside temp is in the 50's I can do 65-70 up hill entire way and never hit 210.

    Mpg?
    Better with turbo even though I added too much fuel from the IP. I timed myself on flat road driving accelerating at same slow speed I could do without a turbo and saw almost 20% increase in fuel mileage. I wonder what it would be if I set the IP to proper spec and used new injetors.

    You can easily swap injectors around, adjust fuel screw to play with it for free. You could swap turbos with some more effort. But do the inside of the engine once, and leave it alone.

    In the fleet where we had parking lots of 6.5 trucks we (I mostly -It was a nice calming break from the other chaos.) rebuilt injectors. BALANCED 2350 psi was the best setting we found for mpg and power for daily driven turbo trucks. We ran them in N/A trucks and it improved power and mpg there too, but not as much as it helped the turbo ones. Long term N/A was around 2100-2200 psi.
     
  3. cornemuse

    cornemuse Active Member

    104
    37
    Jan 11, 2013
    San Diego north county
    Just how big a hurry are you in?? I've been driving diesels since 1979, (Rabbit diesel, a Datsun diesel), & 3 6.2 Chevs, & now my 300cd turbo Mercedes. For the most part they are underpowered (except the MB). I have just adjusted to the low power mainly getting on the freeways, the low power has never really been a problem. They all get/got decent mileage except my '84 Blazer which is a real 'gas' hog. The 1st was an '82 sold in 81, supposed to be 'allison assembled', w/ 700 trans, that truck did fly! & high milage! '84 suburban about the same. Blazer w/t-400 trans is a pig but I love it. I have never been in too big a hurry so they suit me fine, as/was is, , ,
     
  4. deejaaa

    deejaaa Well-Known Member

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    Sep 19, 2008
    Texas
    i'm working on the 6.5 again and had to remove the turbo to try and diagnose it. i have an N/A manifold in the shop and am seriously considering putting it on and going 6.5 N/A. i am not in much of a hurry.
     
  5. 1994ch

    1994ch Active Member

    297
    60
    Dec 6, 2008
    South Carolina
    @Will. L Thank you for the great info. Where is a good source for pre-cups?

    Another question that is arising.... I may end up buying a whole parts truck instead of scrounging up all the parts I need. The two that I know of for sale right now are a 89 and 93 6.2. Is there any advantage in the later blocks? or heads? One of them is reported to have a cracked piston and the other a rod knock. I don't have an IP yet and I can get either of these trucks for about the price of an IP... and all the accessories and brake booster.

    I got both the heads off and found two cylinders that have some goo and rust (hopefully not too bad) everything else looks pretty good. Will try to get some pics up here soon.
     
  6. Will L.

    Will L. Well-Known Member

    6,066
    3,443
    Jan 25, 2013
    Boulder City Nv
    Junkyarding used to be a good sorce, but not anymore here. Too rare here now. Maybe see if Leroy can order some. Post in the for sale/ wanted section- maybe somebody here has some they will sell/trade.
     
  7. 1994ch

    1994ch Active Member

    297
    60
    Dec 6, 2008
    South Carolina
    The pre-cups I want are out of a 6.5 right? Any particular year? I do have a local LQK pull it yourself junkyard with two 6.5 trucks in it.
     
  8. Will L.

    Will L. Well-Known Member

    6,066
    3,443
    Jan 25, 2013
    Boulder City Nv
    Yes. If know square and diamond are both large.

    Isnt there a chart somewhere that shows pics and which is which?
     
  9. 79jasper

    79jasper Active Member

    230
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    Nov 10, 2013
    El Paso, TX
    [​IMG]

    Sent from my SAMSUNG-SM-G935A using Tapatalk
     
    Will L. likes this.
  10. WarWagon

    WarWagon Well it hits on 7 of 8...

    7,449
    1,434
    Nov 15, 2009
    AZ
    Have you ever driven a 6.2 NA? Drive one before you commit. Frankly a V6 gas of the same era is a close 1/4 mile race. The V6 had 160 HP till the Vortech got them to 200 HP. Simply be aware the 6.2/6.5 NA engines do not get out of their own way. In a world where no-assed small cars have power and deliver MPG this is a serious consideration.

    The smaller precups without the extreme weight of a Hummer to get moving were known for over 20MPG in 1/2 ton 2WD rigs on yesterday's diesel. Frito-lay had some econo 100 HP engines with extremely small precups in their delivery vans. (Seriously have to deal with fly-by's from bicycles...) This is all NA.

    Larger turbo precups used in NA: because they don't swirl the NA as much can cost some MPG.

    In Turbo-Land the small precups become a restriction and centrifugally separate the air and fuel from swirling it too fast. With the "asthma attack" GM turbo you really won't notice the smaller NA precups. The second you go to a bigger turbo that doesn't roll over and play dead past 2200 RPM the small NA precups become a serious smoke problem.

    Yeah, leave the paperweight GM turbo's in the junkyard.

    You have to be careful in junkyards because these engines are known to crack all to hell and are expensive to repair vs. the cost of starting with a low mile surplus military 6.2. Military surplus gets a new ring set and timing chain with gaskets. The other stuff may require machine work going oversize and the cost for pistons and the machine shop labor goes over the surplus used cost quick. Hear the engine run with a working cooling system to check for combustion pressure from cracks is the best way to buy used 6.2's.
     
    deejaaa and Will L. like this.
  11. 79jasper

    79jasper Active Member

    230
    96
    Nov 10, 2013
    El Paso, TX
  12. deejaaa

    deejaaa Well-Known Member

    1,480
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    Sep 19, 2008
    Texas
  13. ak diesel driver

    ak diesel driver 6.5 driver

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    Feb 7, 2009
    alaska
    If either of those has a 2 piece rear main seal and is in a 4x4 IFS the pan might net you a few dollars
     
  14. 1994ch

    1994ch Active Member

    297
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    Dec 6, 2008
    South Carolina
    I think they are both 2WD but I am seriously thinking about dropping the front axle out of the tahoe. Kinda want more MPG than I need a 4X4. If I decide to keep the 4X4 I would think I could cut and weld the pan to fit. I have a tig welder and know how to use it.
     
  15. WarWagon

    WarWagon Well it hits on 7 of 8...

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    Nov 15, 2009
    AZ
    Pretty sure the Suburban mentioned has made an appearance or two around the performance section here. I recall after the article came out it's 6.2 had like the second known BD Spool Valve put on a 6.X IDI. http://www.thetruckstop.us/forum/threads/another-bd-quick-spool-valve-install-with-a-c.39716/
     
  16. 1994ch

    1994ch Active Member

    297
    60
    Dec 6, 2008
    South Carolina
    Making some progress... I do not have a IP for this engine yet.... Is it best to go with new? Or is there a good source for overhauled?
     
  17. 1994ch

    1994ch Active Member

    297
    60
    Dec 6, 2008
    South Carolina
    Progress is slow... but I do have the engine going back together. I got some 6.5 pre-cups installed and now I am shopping for an IP. There seem to be alot of different ones out there for the different years... since this is a frankenstein I assume the best year to get would be a 93 (latest being the greatest?)

    Also I need to figure out which injectors it needs (as I bought an engine only I don't know by year what it needs) I have heard of long body and short body coarse thread and fine thread. Can I compare the ones I took out of my 6.5 to the ones that were in this engine and tell what I have?
     
  18. ak diesel driver

    ak diesel driver 6.5 driver

    11,795
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    Feb 7, 2009
    alaska
    there's really not all that much difference in injectors. The coarse thread ones were only used for 1-2 years. Other than than long and short. Nozzles are mostly that same too.
     
  19. deejaaa

    deejaaa Well-Known Member

    1,480
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    Sep 19, 2008
    Texas
    mechanical IP's were available later than 93. vans and P30's used them.
     
  20. WarWagon

    WarWagon Well it hits on 7 of 8...

    7,449
    1,434
    Nov 15, 2009
    AZ
    n8in8or likes this.

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