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Pump up the volume! (6.2 on the diesel scale)

Discussion in '1982-Present GM Diesel' started by elacruze, Mar 23, 2004.

  1. elacruze

    elacruze 1/2 ton status

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    I've heard that the pump on 6.2's shouldn't be turned up much. Why not?
    Since I have a spare on the bench, I gave mine about a 3/8 twist. Wow! it
    actually runs the way I expect it should have. Certainly not a 7.3TD, but
    something actually happens when you step on the pedal.
    What can I expect to happen? How long will the pump last, and what will it
    do if it quits? What pieces go bad?

    Thanks

    Eric
     
  2. BlueBlazer

    BlueBlazer 1/2 ton status

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    Pump should be able to take it easily, but the EGTs have got to be really high, get a pyrometer if you plan on keeping it turned up.
     
  3. elacruze

    elacruze 1/2 ton status

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    Seems like I saw 1200F as acceptable for 6.2NA motors. Is that correct, and for how long?
     
  4. azblazor

    azblazor 1/2 ton status Premium Member

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    [ QUOTE ]
    Seems like I saw 1200F as acceptable for 6.2NA motors. Is that correct, and for how long?

    [/ QUOTE ]

    Whether NA or Turbo the limit (stock pistons) as far as I have researched is 1100 Deg F. IE If you are hitting 1100 back off. I try to keep my EGTs at 1000 or lower, but when pulling real strong and all other temps are good it's a little exercise in self control to not bump into 1100 or a little more.

    See this post:
    http://coloradok5.com/forums/showflat.php?Cat=0&Board=deisel&Number=879774&fpart=1&PHPSESSID=
     
  5. arveetek

    arveetek 1/2 ton status

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    I turned up the pump on my 6.2L about a 1/4 turn. Made a lot of difference.

    As far as the limit for EGT's, I go against what everyone else says. This is due to my own personal experience. The n/a diesels don't have near as much a problem with high EGT's like the turbo diesels do. I have run my 6.2L for hours on end pulling a large load at 1350 degrees. I've even spiked above 1400 degrees several times. If I tried to keep my truck below 1100, I'd never get anywhere.

    Personally, I wouldn't worry about running up to 1300 degrees. I've put over 120,000 miles on my 6.2L since I rebuilt it 1996, and thousands of those miles are with my foot buried to the floor. No problems yet!

    I have never, ever heard of a melted piston or scored cylinder wall on a n/a diesel, only turbo diesels.

    Of course, keeping the EGT's low can't hurt. However, you'll never realize the full power potential of your engine. I know my 6.2L runs best when worked hard, really hard!

    With a turbo installed, it will force more air into the cylinders cooling the exhaust down a bit. Plus, more oxygen will burn the rest of the fuel being injected. Therefore, a turbo diesel running at 1100 degrees will have more power than an n/a at 1300 degrees.

    So, to sum all this up: Max EGT for 6.2L turbo: 1100 degrees. Max EGT for 6.2L n/a: 1300 +.

    That's my story and I'm sticking to it! /forums/images/graemlins/thumb.gif

    Casey
     
  6. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Casey, was your rebuild using stock pistons or are they aftermarket?

    Rene
     
  7. BlueBlazer

    BlueBlazer 1/2 ton status

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    Where is your pyrometer probe located?
     
  8. arveetek

    arveetek 1/2 ton status

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    Stock pistons. I have no idea how many miles are on them now. I bought the engine used from a salvage yard. The inside of the motor looked like new. Just honed the cylinders and installed new rings and bearings.

    Casey
     
  9. arveetek

    arveetek 1/2 ton status

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    Probe is located in the driver's side exhaust head pipe, about an inch below the outlet of the exhaust manifold. Pyro is an Autometer Pro-comp 2 5/8" guage.

    Casey
     
  10. azblazor

    azblazor 1/2 ton status Premium Member

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    I'm not refutting what your experience is. I am trying to understand your temperatures and what I've read in the Banks manual. I have had some education in metalurgy and heat transfer and fluid flow just so you don't think I'm coming in from left field. How can it matter to the piston (that is seeing a certain temperature) whether the initial charge into the combustion chamber was pressurized with a turbo or not?
     
  11. arveetek

    arveetek 1/2 ton status

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    Well, I don't think I can answer that very well myself. It has to do with raising combustion pressures. A turbo will add more than just 10 psi to the compression. It somehow raises the overall pressures in the process.

    Think about head gasket failures. Sometimes adding a turbo will blow head gaskets. I doubt it has to do with the extra 10 to 15 psi the turbo adds. It raises combustion pressures way up.

    It's all rather complicated and over my head, but all I know is what I know! /forums/images/graemlins/smirk.gif

    Casey
     
  12. BlueBlazer

    BlueBlazer 1/2 ton status

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    A turbo raises cylinder pressure due simply to the fact that when you force more air in the same space, then compress it just as much as before then the pressure will be higher. Boyle's law (I think thats the name) would prove my point better. It shows how when there is more gas in a given space, the pressure goes up, so between NA and turboed engines, the volume at BDC and TDC are the same, but since there is more air forced in at BDC, the pressure at TDC is greater (hope that makes some sense). As far as different EGT limits for an NA engine versus an NA engine that has been turboed, as long as pistons and valves (and other components in the combustion chamber) arent changed, I dont see how there could be any difference. Obviously, the forced induction of a turbo cools EGTs until you add more fuel by turning up the screw, but I dont think that the EGT limit should be any different. Sorry for the ramblings guys, its late. /forums/images/graemlins/smirk.gif
     
  13. azblazor

    azblazor 1/2 ton status Premium Member

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    Well as I ponder this it comes to me the phenomenon may be the duration of the burn "event".

    If the stock piston is exposed to 1100 degrees for a longer time in a turbo engine, due to advanced timing (earlier injection) and more fuel (longer injection) to burn, it stands to reason that it could melt, whereas in a NA engine it could withstand 1300 degrees for a shorter time with out melting. I am assuming times in the milliseconds here. But when you are talking changing states of a material ( from solid to liquid/semi-liquid) the difference is all about how much heat is transfered into the material. And time of exposure to a given temperature is obviously a significant factor.

    OK - I've satisfied myself. I wonder if the clevitekid would agree with this?
     
  14. BlueBlazer

    BlueBlazer 1/2 ton status

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    That may be true, but were talking about turning up an NA diesel also, so if you turn up an NA 3/8 of a turn like Elacruze did, then your injection duration would be longer than the 1/4 turn that Banks recommends after you add a turbo. So all things being equal, max fuel the same between and NA and turbo and base timing the same I dont think the EGT limit should be any different.
     
  15. azblazor

    azblazor 1/2 ton status Premium Member

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    My intuition leans towards the same conclusion as yours. But the empirical data is straightforward. I trust arveetek when he reports his NA EGTs (1300-1400 degrees). I know there has been a lot of damage reported by guys pushing 1100 degrees with a Turbo. I have yet to put a pyrometer on a NA 6.2L diesel, but soon I will have done that. So in the meantime - I do believe arveetek and therefore there IS an explanation for the different allowable temperatures. I offered a possible explanation that satifies my understanding of what is going on in the combustion chamber. It may not be wholy correct, but I am pretty sure it is at least partially correct. I suppose I will ask the experts over on TheDieselPage, ie the clevitekid comes to mind.
     
  16. BlueBlazer

    BlueBlazer 1/2 ton status

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    I am pretty sure that most damage on turboed 6.2s would be from the increase in cylinder pressure, not EGTs.
     
  17. azblazor

    azblazor 1/2 ton status Premium Member

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    I see from your profile that you work at Cat. You ought to have access to some real experts on diesel combustion theory. Maybe you could ask around?
     
  18. BlueBlazer

    BlueBlazer 1/2 ton status

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    I could, but I dont think there is one guy in the building that has worked with an NA engine nor knows the characteristics of them. We'll see though.
     
  19. 6.2Blazer

    6.2Blazer 1/2 ton status

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    1100 EGT is 1100 EGT, whether there is a turbo or not, so I don't see how the limit would change. The difference is that with a turbo you should be able to pump more fuel through the engine, as compared to a NA, without exceeding the max EGT.

    I don't doubt that people have more failures running around 1100 with a turbo as compared to the NA, but I would have to say there is more to it than just the EGT. The higher cylinder pressures and more overall power being produced puts a lot more stress on all of the engine components....so there is more overall stress on a turbo engine running at 1100 than a NA engine running at 1300. The EGT therefore is not the problem in itself, but rather just a measurement that shows when other factors can cause a failure.
     
  20. arveetek

    arveetek 1/2 ton status

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    [ QUOTE ]

    I don't doubt that people have more failures running around 1100 with a turbo as compared to the NA, but I would have to say there is more to it than just the EGT. The higher cylinder pressures and more overall power being produced puts a lot more stress on all of the engine components....so there is more overall stress on a turbo engine running at 1100 than a NA engine running at 1300. The EGT therefore is not the problem in itself, but rather just a measurement that shows when other factors can cause a failure.

    [/ QUOTE ]

    Very well said! /forums/images/graemlins/waytogo.gif That's what I was trying to say, but just couldn't find the words to do it.

    Casey
     

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