2004 Suburban 1500 towing issues: Engine or gears?

Discussion in 'Engine & Drivetrain' started by Martinjmpr, Sep 6, 2018.

  1. Martinjmpr

    Martinjmpr Full Access Member

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    (Crossposed from Expedition Portal):

    Closing in on 3 years now of using the 2004 Suburban (1500, LT, 5.3, 4x4, 4L60, 3.73 gears) as our primary tow vehicle. Previously we had a 2,000lb [email protected] trailer but in January we upgraded to a ~ 3500lb R-Pod 179.

    The "issue" I'm having is when climbing steep, high passes (here in CO you can't get from the Front Range cities to the mountains without crossing at least an 11,000' pass.)

    As I slow down, of course the 4 speed 4L60 drops into a lower gear. 2nd gear is actually pretty good for climbing and I can typically keep up with traffic at around 50 mph even in 2nd. But as the hill gets higher, the weight bogs the rig down and speed drops. When it drops below about 35, the truck wants to kick the transmission down a 1st gear - which of course makes the engine spin around 4500 rpm (screaming.) That typically only lasts a few seconds before it shifts up to 2nd but then it bogs down again and drops back down to 1st. This sometimes happens 5 - 10 times while ascending a steep pass (think Eisenhower Tunnel or Berthoud Pass, for those familiar with them.)

    When we had the [email protected] this never happened, we could stay in 2nd gear the whole time. But our trailer weight has nearly doubled and I can really feel it when climbing those steep passes.

    Not only is it a bit of a shock to feel the truck dropping down into 1st gear, I'm worried about what those hard shifts and high RPMs will do to my transmission and engine (transmission was rebuilt 2 years ago @ 150,000 miles and has worked fine since then.)

    So my question for the GMT800 Hive Mind is this: If my goal is to be able to ascend passes more easily, should I be looking at doing something to boost power/torque or should I be looking at lower gearing?

    I'm not looking to spend a ton of money and I don't want to put too much stress on an already middle-aged drivetrain (170k) so I don't think turbo/supercharging would be a good idea for me. Are there less "radical" power mods that would boost the power of the engine?

    EDITED TO ADD: I'm not a huge fan of things like Cold Air Intakes or air box removal - I'm just skeptical that they really improve power. Ditto for "reprogramming" the computer, as I think that assumes that the "tuners" know more about the engine than, you know, the people who BUILT it. Adding power and sacrificing reliability or utility would pretty much defeat the purpose of what I'm trying to do here.

    Or would it be a better idea to simply change the gearing to, say, 4.11? And if I was to do this, what would I be looking at, cost-wise, to replace the front and rear gear sets (and ideally retaining the G80 locker in the rear?)

    Anyone else had this issue with a 1500 'Burb towing? (If I'd known we were going to be getting a heavy trailer like this I might have held out for a 2500 but that's 20/20 hindsight at this point.)

    Thanks in advance!
     
  2. Scottydoggs

    Scottydoggs Full Access Member

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    4.10's might do the trick, but your gonna have to trust a tuner to change the gear in the tune or your speed o will be off by a bit. easy grand for both axles if not more id think.

    and tuning unlocks power/performance the factory robs you of.

    i had 2500 hd pick up with 4.10 gears, and the 6.0 that back in 03 had only about 300 hp, and a 80le trans. i used to tow my 4,000 lb boat all over the place. id forget it was back there some times, pulled it like nothing.

    had a 97 3500 with the last of the 350's, had a tb injection, less then 300 hp i want to say 270. same gears, also pulled that boat like it was nothing.
     
  3. SnowDrifter

    SnowDrifter Full Access Member

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    That's definitely odd. I've towed a 6k trailer through the cascade mountains(3000-4000ft depending which route I go) going 60. Had to do it in second, 5.3 didn't have enough oomph to do it in third. It's clear it's not a tow rig, but it wasn't complaining and still had some power to give.

    I just poked at some math. at 11 thousand feet, you're only at 66% of normal air pressure. Do you have difficulties only at the higher altitude? Or is it like that even when ascending a grade starting from sea level or close to?
     
  4. Martinjmpr

    Martinjmpr Full Access Member

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    Didn't EFI basically eliminate the old "no power at high altitude" issues cars used to have? I thought the oxygen sensor in the engine leaned out the fuel mixture to allow for more air (thus more oxygen) at altitude?

    Haven't noticed any difference at lower altitudes but to be honest I live in Denver and we go to the mountains almost every weekend, so going to a LOWER altitude isn't something I do very often. ;)
     
  5. Scottydoggs

    Scottydoggs Full Access Member

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    being at that elevation will for sure hurt your power.

    i know a guy from out west in the mountains (6,000 feet) from anther site. we both have the same car pretty much, only hes got more mods then i do, hes got a cam and heads on his, and on paper he should kick my ass, yet i run a second faster in the 1/8 mile then he does. im at sea level pretty much, iirc my track is 1000 foot up or so. but i live literally at sea level lol

    thin air is like breathing through a straw for a engine really.
     
  6. SnowDrifter

    SnowDrifter Full Access Member

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    Less air is less oxygen. Can't add as much fuel. There's no way around physics
     
  7. SnowDrifter

    SnowDrifter Full Access Member

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    Imagine: You're basically running with a brick under your throttle. As far as your engine is concerned, that's exactly what's happening
     
  8. SnowDrifter

    SnowDrifter Full Access Member

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    Thinking about it more: This would be an ideal use case for a turbo. As a matter of fact, this use case is exactly why forced induction was invented. It was originally for aviation so the planes could overcome the thin air at altitude. An altitude correcting tune would allow your vehicle to make the designed power level at all altitudes. Zero boost at sea level, and increasing in proportion to a decrease in atmospheric pressure. Now whether or not the cost/reward ratio is appropriate is a decision you need to wait.

    You could accomplish something similar with a supercharger, but I think you'd run into issues with boosting beyond stock at lower elevations
     
  9. Scottydoggs

    Scottydoggs Full Access Member

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    not to piss in your cheerios, but the guy i know out west is supercharged, as well as i am. (on the 3800 engines) you still cant make the same power at elevation, the thin air kills everything. you cant make up for lack of air.

    whats really nuts is he cant get over 18º wot timing, hes been on e85, e85 with meth injection, still cant go any faster. where im on 93 gas rockers, diy ported heads a fsic and meth, running 21º wot kr free. where hes got kr at 18º. he tends to run about 16 most of the time but turns it up at the track to play with it. and still has kr on the street with 16. he also had a intercooler that did 100% nothing to help him. so i bought it off him. his track times stayed the same, where mine picked up. and im actually able to run a smaller pulley on the sc then he is. im on a 2.8 he could never get past a 3.2.

    being you cant get all the timing you'd like to have up there, when you come down to lower elevation you wont blow up, cause your timing is already lower then it should be. having a tuner would be nice if you took trips up and down the mountain for any amount of time. a flash takes 30 seconds, lap tops take up no space really.

    where adding forced induction will help over stock. its still not 100% the power you'd get at a lower elevation.
     
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  10. Scottydoggs

    Scottydoggs Full Access Member

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