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Thread: 8.1 4l85e

  1. #1

    8.1 4l85e

    Are there any general guide lines with these as far as how much timing and setting up trans for fuel mileage and not taking out the TCC like the 8.1s like to?
    I just got one for a tow rig and ofcourse I want to mess with the tuning. I found a few old threads about it but most of them post a tune and say here base it off of this and you cant see the tune file anymore.
    I plan on taking a little torque management out but not a ton to help the trans.

    Ps yes I know you dont get an 8.1 for fuel mileage, but if you can make it a little better why not.
    Thanks

  2. #2
    Tuner 1970ss8.1's Avatar
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    I mostly tune only 8.1 motors. They like different things than LS motors. What mods have you done to it? I?m guessing you have a burb or a avalanche those were the only 4L80 combos. Trucks came with Allison. A few has 6 speed manual. What year motor? Load a tune file for me to look at. I?ve tuned just about every combo of mods you can throw at these. Right now I?m building a tune for a highly modified one in my chevelle. towing 12k stock I was getting 6mpg after light mods and a tune I was getting 9-10. After heavy mods (cam/roller rockers/modded intake/90mm TB) 10-12mpg. Mine is a 4x4 Allison 6 sp 4.10 gear. If you have a 80e Burb or Avila it will have 3.73 and you could get better mileage. With the stock cam, k&n cai and the plug mod I was getting 16mpg empty. I can help you get this tuned.

  3. #3
    It's a 04 yukon xl, so yes a suburban, all stock. Just got it. Plan on a few small mods later. I can post the stock tune and the one with the few changes I made already tonight. I have not tried my new tune yet as I'm looking into a torque converter slip issue with it. It does have 4.10 in it
    Last edited by dmaxs10; 01-07-2020 at 10:58 AM.

  4. #4
    Tuner 1970ss8.1's Avatar
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    04 is when they made the changes for the better. You have floating piston pins not pressed and all the upgraded sensors. So you are already ahead of the game. Change your plugs out to AC Delco 41-993 and gap them 0.045. Get the Accell ceramic spark plug wires. Install a K&N air filter and get some free flowing exhaust, I use two Dynomax super turbo 3", they flow very well.
    You can get rid of 50% of the TM and change up the shifting a bit. If you lock up the TCC sooner you will pick up some MPG. Be carful with spark tuning these pistons like to explode with det. I have experimented with a lot of different AFR for PE and it tows great at 12.5 but these motors really love 13.1 I now run 13.1 and it has a lot more power than 12.5-12.0. I towed at 12.0 for 600 miles one time and it pulled good but drank so much fuel I raised it before going home. The biggest killer on these are the timing reductions, IAT is a killer in the tune. They pull so much from IAT because the factory doesn't allow these to ever see over 14.6. Once you get some fuel in there you can take away the IAT retard. Also ECT and Burst Knock are really raping these as well. you will want to change Stioc to 14.22 for the E10 fuel we get and the timing is way low in the low rpm low map values. There is a lot to go through in the tune to get these to their prime. When I first re-did the timing table in the low area I would break the tires loose from any stop sign and I run 19.5 tires. I had to tone it down, way too much torque from a dead stop. Also the MAF curve is a joke from the factory, I was throwing a code at WOT above 3,000.
    The factory has tuned out about half of the power these motors can make.
    Are you going to install a wideband?
    My Avatar is my Wife and Proud of it!!
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  5. #5
    wow that's a lot of info. I plan to do plugs, mess with intake, add electric fans, maybe exhaust. But some of it will take time. Would like to go into head cam and intake but that will be a long time if I do. I don't have a wideband for it yet, I have one in my s10, so I wasn't planing on messing with the ve table or maf yet until I get one in this spring. Exploding pistons sounds like fun lol.
    Here my tunes. I removed some of the added timing at cold IAT. When I took it for a short drive with the scanner it was pulling KR about the same amount as the IAT was adding so I'm going to see if that makes a difference too.
    Changing stoich to 14.22 I keep reading about it but always forget about it.
    Thanks
    Attached Files Attached Files

  6. #6
    Tuner in Training
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    Nice info 1970ss8.1
    I have a buddy with a 2005 GMC 8.1 and Allison. Any suggestions for a basic tune I can load without having to drive a log. His truck is bone stock.

  7. #7
    Tuner 1970ss8.1's Avatar
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    I just had another member PM me and I built him a ready to go tune for $100, because he bought his own license and will do his own data logging. If interested PM me and I can do the same for you. I would need your stock tune, They made changes to the tune every year so you cant just load any random tune.
    My Avatar is my Wife and Proud of it!!
    1970 Chevelle SS 8.1 Vortec T56 9" 3.00
    2006 3500HD 8.1 vortec Allison 6sp 4.10 4X4
    2013 Audi A5 Cab 2.0tfsi Quatro
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  8. #8
    Tuner 1970ss8.1's Avatar
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    Dmaxs10
    I took a look at your tune and your headed in the right direction. Your PE comes in late and has too much delay. The ramp in is too fast it will pull timing. Your PE RQ is too rich 8.1s don't like to be too rich, they bog down. If you had hard part mods it could take more fuel. The ECT correction is pretty good and the IAT is close but not quite there. The timing table could use some rework as well. Of cours this all depends on what you are doing with the vehicle. Towing, (how much weight), beating up on muscle cars, or granny driving. I have a tune for towing, playing, and commuting. As well as one that covers all three but there is a give and take. Also what octane fuel, I only run 91 now and love the way it drives. I have a set of 42lb injectors waiting to go in because I run out of injector at WOT above 3500rpm. So im excited to see what that does. Once I put those in Ill install my headman headers. Right now the truck is on hold until I get the 8.1 in my Chevelle dialed in.
    My Avatar is my Wife and Proud of it!!
    1970 Chevelle SS 8.1 Vortec T56 9" 3.00
    2006 3500HD 8.1 vortec Allison 6sp 4.10 4X4
    2013 Audi A5 Cab 2.0tfsi Quatro
    www.mcmnapa.com

  9. #9
    1970 thanks for the tips. I will make a few adjustments. I have not messed with the timing tables at all yet. I put the rpm delay in it to help with winter traction in cause the wife drives It at all. I have not test the tune yet. I will try it lower and see how it reacts. Its main purpose is towing, mostly a car trailer with about 4000 lbs on it for now, for driving in bad weather, and proably an occasional family trip bit not often. Wife's escape gets 24 mpg a lot cheaper to drive that!

  10. #10
    Got it out today. Changing the stoich helped out with a lot of the KR. Deffently need to adjust my PE throttle percent enable lower. I think i lowered the rpm down to 2400.
    Either way thanks again good to know I'm going in the right direction with it.

  11. #11
    Tuner 1970ss8.1's Avatar
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    Change the RPM enable to 0 and ramp up your PE EQ. You will want stioch at 800 and 13.1 at 2400 then interpolate to ramp up to it. Just remember now if your stioch is 14.22 you need to go 14.22/13.1. Use the EQ map to control how the PE works and try to set your trigger at 60TPS. Post your tune file you have now and let me take a look.

  12. #12
    vans and gmt400 hd's also came with 4l80/85e's

  13. #13
    Tuner 1970ss8.1's Avatar
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    Yes some those vehicles came with a 4L80 but not with the 8.1. Only one year of the express van had an 8.1 2001 and it had a 4l80. All 8.1 SUVs had the 4l80 and the GMT 800 trucks and the Kodiak and top kick had the Allison.

  14. #14
    Incorrect I own an 8.1 van and I can link many c3500hd's with 8.1's if you like

  15. #15
    Tuner 1970ss8.1's Avatar
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    What year is your van? I?ve been looking for one.
    I?ve never heard of a 3500hd before 2001 that had an 8.1. I would love to see what you are referring to.

  16. #16
    Tuner 1970ss8.1's Avatar
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    Wow just looked up the c3500 with 8.1. Learn something new everyday. I guess they had some chassis cab trucks left over when the 8.1 came out. I wonder if the came with the prototype motor or the production 8.1. The prototype 8.1 came out in 96 but I don?t know if they were ever installed in anything.

  17. #17
    1 ton vans 2001 and 2002 mine is an 2002
    https://www.commercialtrucktrader.co...500-5010488411
    IS an example supposedly 01 and 02 as well and 03 but havent seen any to confirm
    the trucks come with 4l80/85 or nv4500
    I also own an 01 2500hd with 8.1 05 5500 kodiak with 8.1 and have an 04 1500 with an 8.1 swap

  18. #18
    no prototype engines where different 4 bolt per cylinder heads etc different water pumps intake etc, raylar put a prototype engine in his c5 he also has a c4 with a 502

  19. #19
    Tuner 1970ss8.1's Avatar
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    Ok. I thought the 02 van might have come with one. I?ve seen some of your 8.1 work on other sites. Good work. Have you seen Larry?s new book yet on the 8100? Just got my copy a couple days ago.

  20. #20
    NO i need to buy the book but i am sure, it is chock full of things i already know. I eventually will be swapping an 8.8 psi engine into something. unfortunately the one i got came with an mt88 pcm which hpt doesnt support so i bought a 2013 6.0 harness and pcm to convert over to run it. 58 x big block with 6l90 should be interesting.