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  1. #1

    Default 8.1L in a 1999 Suburban?

    Just wondering if anyone here ever swapped an 8.1 into the GMT400 body style. I know the 7.4 would be a pretty easy swap since its the same generation, but what about the 6 and 8.1? The 5.7 will haul my 5000 lb boat fine but she heats up after a while when going over 80. I was hoping it would be cheaper to buy a 6L or 8.1 and install heavy duty leaf springs than to buy a newer 3/4 ton. Also would appreciate if anyone with experience with all three engines (6, 8.1, 7.4) could lend me some wisdom about them. I know the 8.1 is a gas hog, but I'm averaging 12.5 with the 5.7 now so.....
    Thanks!
    Jake
    Last edited by '99Suburban; 11-07-2012 at 07:50 PM.
    MONTANA CADILLAC

    Proper noun. Used to describe ones large, lifted, comfortable, gas guzzling SUV that is driven primarily in the backwoods. Synonym for Chevy Suburban/ GMC Yukon XL.
    One corporate Suburbanite says to the other, while sipping his overpriced latte, "Check out the hick in that Montana Cadillac!" Both giggle as they wait for AAA to come pull their Audi/ BMW/ Mercedes out of a snow filled ditch

  2. #2

    Default

    Any one of them would require getting a new tranny and drive shafts. It would be easier and cheaper to better cool your tranny and engine oil. Also why are you towing anything at 90?? Thats extremely unsafe. Yes the 7.4 would be fairly easy to swap in it would require switching engine mounts, upgrading to a 4L80e transmission, new tranny mounts, new front and rear driveshafts (if 4x4) because the 4L80e is longer and the 7.4 takes up more room. The 5.7 should have no problem with that size boat.

    Still better plan is better cool your tranny and oil plus you can add some aux fans to help cool the engine. In adding the fans you may need a bigger alternator, but still alot cheaper then having to get a whole new drivetrain.

    1996 Chevy Tahoe LT 5.7L V8 4X4 205,000+ miles. Built proudly at Janesville Assembly in Janesville, Wisconsin
    Basic mods: Lights all over, bunch of electrical work, and a couple cooling mods.

    Check out my other mods in My Garage: http://www.gmtruckclub.com/forum/sho...t-Tahoe-4-Door

  3. #3

    Default

    Towing over 80? Really dude? I tow a 30ft camper that weighs about 6500 loaded with my Burb and never go over 65. Most trailer tires are rated for 65mph....maybe you should check yours so you don't end up hurting someone.

  4. #4
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    Quote Originally Posted by 98BIGBLOCKBURB View Post
    Towing over 80? Really dude? I tow a 30ft camper that weighs about 6500 loaded with my Burb and never go over 65. Most trailer tires are rated for 65mph....maybe you should check yours so you don't end up hurting someone.

    This is very true... Also pulling that much weight at that speed is just not safe...

    The 8.1 Sub's I think were built on a Truck frame not a 1500 frame so not an easy install.. Also 8lug not 6 so differant axels.

    Keep an eye out for a nice Red Cladded Avalanche with a Cowl hood. Thats Jake he lives in Rockaway also
    08 Z71 Avalanche Mods to date: K&N CAI,Hellwig Swaybars and End Links, Corsa Sport Exhaust, Superchips Programer,IPCW LOF & 3rd brake light and tails, AMI Gas door,Show Hooks and Door locks, Enkei Wheels, with Pirelli tires, StreetScene Bowties, Grant Steering wheel,Muth signal mirrors,SSBC Big Brake kit,Huskyliner Mug gards,Floor mats and Hood shield, McGard Lug nuts and locks, Bedrug, Cervini's Ram Air hood,35watt HID Fog lights, Sylvania bulbs all around ZXE's Highs and Lows, WhiteNight Back up lights,Sirius and HD Radio, SnugTop sitting on deck now Got a Softopper on now,Tempress Boat Hatches.... New Bilstein shocks are on... New Mods coming soon..... X

  5. #5
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    The 8.1 is not a great engine, the 6.0 has more useful power and torque band. You would be better off getting the 383 (it is designed for your truck and tranny)from GMPP and adding a shift kit for your current tranny. Why on earth would you drive that fast towing anything?
    99 K1500 Suburban LT "THE BEAST"
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  6. #6
    Jr. Engineer Jamm3r's Avatar
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    Quote Originally Posted by '99Suburban View Post
    Just wondering if anyone here ever swapped an 8.1 into the GMT400 body style. I know the 7.4 would be a pretty easy swap since its the same generation, but what about the 6 and 8.1?
    I'm assuming that your 1999 'burb is a 2500. That being the case you already have the 4L80e transmission so the 8.1 would bolt right up. Not sure about clearances or the PCM but the times I've thought about swapping my 5.7 for something bigger I've always presumed that the 7.4 is the way to go. The 8.1 has a fairly large oil cooler in front of the radiator that you'd have to shoehorn in somehow especially if you're having cooling problems already.

    The 5.7 will haul my 5000 lb boat fine but she heats up after a while when going over 80.
    Not sure that displacement will help with that, maybe adding some cooling to your 5.7 would though.

    I was hoping it would be cheaper to buy a 6L or 8.1 and install heavy duty leaf springs than to buy a newer 3/4 ton. Also would appreciate if anyone with experience with all three engines (6, 8.1, 7.4) could lend me some wisdom about them. I know the 8.1 is a gas hog, but I'm averaging 12.5 with the 5.7 now so.....
    I get 13 mpg with my 8.1 burb by itself. Towing at 75 mph I get 7 mpg but that's with an 8,000 pound trailer. I don't tow any faster.

    Quote Originally Posted by vncj96 View Post
    The 8.1 is not a great engine, the 6.0 has more useful power and torque band. You would be better off getting the 383 (it is designed for your truck and tranny)from GMPP and adding a shift kit for your current tranny.
    I like the 8.1. It churns out the ponies at lower RPM and makes for a smooth, quiet ride.


    Why on earth would you drive that fast towing anything?
    Who knows? I don't judge anyone on speed alone. Some trailers can be towed safely at higher speeds depending on weight distribution, hitching, aerodynamics, brakes, and tires. I'm comfortable at 75 mph with a ProPride hitch, a MaxBrake controller, and suitable tires, and can stop from 75 in a straight line in the same space it takes to stop without the trailer.
    Minneapolis area - 1997 K2500 regular cab long bed + 8.5' Western Unimount plow + modified transmission + 2nd battery + modified camper charge circuit + 1971 Cayo camper -and- 2004 4x4 Suburban 2500 8.1 + Maxbrake controller + 2nd battery + modified trailer charge circuit + Reese receiver, pulls 30' Airstream trailer

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