Author Topic: 77 GMC K35 - 8.1 w/ 8 Spd Automatic Swap  (Read 6482 times)

Offline BlackTomC

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77 GMC K35 - 8.1 w/ 8 Spd Automatic Swap
« on: August 17, 2015, 09:44:42 am »
Morning Fellas,

Figured I'd start this thread now considering the truck will probably be here before the weeks out. I've got a 1977 GMC Sierra Classic K35 on the way with a stock 350, 4spd manual, and some rusted out rocker panels.

After talking with Jesse up at True Blue Motorsport in NJ, I have been thoroughly convinced to drop in a Vortec 8100 with an 8 speed (8L90??) transmission. However, there's one problem, right now Jesse can reprogram the ECU in the 6L series to work with 3rd gen LS engines, but can't seem to hit the nail on the head with the newest tranny's that just came out.

I'm willing to wait until that happens todo the swap, was hoping that someone on here has some knowledge of BDU100 ECU reprogramming and could possibly steer us in the right direction so we can make this beauty come alive. If this isn't the right section let me know, but this is the last question we have before ripping the guts out of this truck and dropping in the 8100.

The bottom line has dropped

Offline blazing816

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Re: 77 GMC K35 - 8.1 w/ 8 Spd Automatic Swap
« Reply #1 on: August 17, 2015, 01:29:09 pm »
Just curious why not just buy an LS Gen IV so the 8 speed is plug and play??
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1988 Chevy R20 Scottsdale Crew Cab (350/TH400/4.56)

Offline BlackTomC

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Re: 77 GMC K35 - 8.1 w/ 8 Spd Automatic Swap
« Reply #2 on: August 17, 2015, 05:02:58 pm »
Alright, it looks like we are going with the 8.1 with the 6L80 tranny
The bottom line has dropped

Offline Engineer

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Re: 77 GMC K35 - 8.1 w/ 8 Spd Automatic Swap
« Reply #3 on: August 23, 2015, 06:05:19 pm »
I have one of the über-rare 8.1L Vortec big blocks with the ZF S-6 650 6speed manual (most 8.1s were with the Allison) in a 2002 SilveradoHD. It is nasty.

I know one thing is for sure an LS engine with a supercharger can be nastier (more nasty?).
2002 Chevy 2500HD 4x4 8.1/ZF6sp RC/LB
2001 Chevy 2500HD 4x4 6.0/4L85E EC/SB
1997 Chevy Blazer 4x4
1994 Chevy K-2500 4x4 C6P 5.7/4L80E
1979 Chevy K-30 4x4 4sp 4.10
1977 Chevy K-30 4x4 4sp 4.10 454

Dad of an Eagle Scout, and a Life Scout

Offline pholliday1

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Re: 77 GMC K35 - 8.1 w/ 8 Spd Automatic Swap
« Reply #4 on: August 23, 2015, 09:08:58 pm »
I ordered an 03 2500 HD with an 8.1L with six speed and it was an animal. I had trouble keeping a clutch in it and didn't have any success back then with the after market. In 04 I ordered my next 8.1L with an Allison and wished every since I had the six speed. Really nice truck looking forward to your project.
VETERAN AND LIFETIME NRA MEMBER. WHAT DO YOU STAND FOR?
1991 V3500 CREWCAB SRW 454TBI GMC
1991 v3500 crewcab SRW 454tbi 480le 6" lift
1990 V3500 crewcab Dana 60 FF 14b 5:38 ratio 40 inch 11" lift
1989 v3500 crewcab 454TBI 5" lift

Offline ehjorten

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Re: 77 GMC K35 - 8.1 w/ 8 Spd Automatic Swap
« Reply #5 on: August 24, 2015, 02:44:27 pm »
dang you Paul and your crew cab collection!  ;D
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline fitz

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Re: 77 GMC K35 - 8.1 w/ 8 Spd Automatic Swap
« Reply #6 on: August 24, 2015, 08:26:04 pm »
I can't help on the technical side, but I'm waiting to see the outcome.
This looks like a great project.

Offline pholliday1

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Re: 77 GMC K35 - 8.1 w/ 8 Spd Automatic Swap
« Reply #7 on: August 25, 2015, 07:20:59 pm »
 :))))
VETERAN AND LIFETIME NRA MEMBER. WHAT DO YOU STAND FOR?
1991 V3500 CREWCAB SRW 454TBI GMC
1991 v3500 crewcab SRW 454tbi 480le 6" lift
1990 V3500 crewcab Dana 60 FF 14b 5:38 ratio 40 inch 11" lift
1989 v3500 crewcab 454TBI 5" lift