Does everything, accessory wise need to be 8.1? Are there parts that are any easier if they are my factory stuff?
Easier put. Do I just need to plan on putting a totally complete 8.1 in, and connect the dots accordingly? Or modify some of my accessories to this motor?
Seems computer and wiring can be done with some head scratching. What about heater core and radiator and stuff like that? I assume the radiator may need to grow?
End of the day, I guess I’m hunting a realistic parts list.
The easiest 8.1s to swap come out of a GMT400 or an Express/Savanna van. I used the engine wiring harness out of the van, converted it to stand alone and married it to the L31s harness near the firewall connector. I took both fuse boxes apart and moved the connections from the van fuse block to the Tahoes. Then cut the wires that went to the engine harness of the Tahoe from the firewall connector and soldered the 8.1s matching wires in one at a time. I used a 6.5 diesel pedal and the van TAC module and throttle body. Most of the inputs for the TAC module that come from the body side of the Tahoe already existed in the cruise control wiring. I had to move a few wires around to match the diagrams. The Van TAC module bolted directly in place of the cruise control actuator. My air intake is a late model 6.5 diesel air box with a forward facing air outlet. I used a 90* elbow out of the air box, connected the Tahoe MAF directly to the 90, then connected a straight section of aluminum tubing with a straight coupler to the MAF. At the throttle body end another 90" coupler connected right up. I used a K&N filter for a 6.5 diesel. My exhaust is long tube headers for a 454 TBI, dual 3" piping with thunderbolt 3" high flow cats and a dual 3" in, single 4" out magnaflow with a 4" diesel tail pipe. I have dual batteries and dual AD-244 alternators. I used the stock small block Tahoe radiator because it was massive 34" wide double row anyway and an electric fan setup from a GMT800 Tahoe mounted upside down. I used a 4.3 V6 torque converter in the 4L80E and it stalls about 2,500 rpm behind the 8.1. Works very well with the 420 hp HP2 Marine cam. I can roast the P305/50R20s with light throttle powerbraking despite having 3.42 gears. I need to put together a swap thread and take pictures of it all. That is if I could ever pry my Tahoe out of my brothers hands.
I did a complete front suspension rebuild while I had the truck down. New control arms, 2500 Suburban front sway bar, variable rate HD front springs for listed for a 454 SS truck, inner/outer tie rods and adjusting sleeves, 454 SS steering gear box, new idler and pitman arm, new rag joint, new KYB Monomax shocks all around, HD rear springs and added a rear sway bar setup from a Suburban. I also upgraded the front calipers to SRW 3500 calipers and rebuilt the drum brakes. I also swapped the motor mounts to polyurethane inserts and used a polyurethane trans mount from Energy Suspension. The stock rubber mounts will not last long with a big block sitting on them. I added a massive trans cooler next to the OEM pusher condenser fan and added an OEM power steering cooler from an earlier TBI Z71. When I set the cruise at 85 mph on the toll road it was like driving a new truck down the road. No steering wander, no bouncing, no botteming out, just a nice tight handling truck that rides like an unloaded 3/4 ton. I was at 85 mph for more than an hour and still got better than 15 mpg that trip. I run 1,850 rpm @ 70 mph and 2,300 rpm @ 85 mph with the 4L80E, 3.42s and 32" tall tires. The 8.1 is slightly oil thirsty though. I have found I burn about 1-qt every 1,500 miles which is better than most but I discovered the intake gaskets on both of the 8.1s I have torn apart had come apart the same way the L31 gaskets do. Saving grace on the 8.1 is they do not contain coolant passageways and only caused vacuum leak at the intake runners of the heads. Both engines had multiple cylinders with intake runners coated in oil they were pulling through the gaskets.
Attached is the GM dyno graph for the HP2 8.1 from the now defunct page on GMPowertrains website. 2md chart is the HP1 stock Marine engine which uses the stock truck cam. Since I will never tow more than 7K with the Tahoe, I used the higher HP marine cam. 400 ft/lbs at 1,200 rpm moves the Tahoe effortlessly at lower RPM and when I stab the throttle the converter flash stalls 2,500 rpm which makes the torque difference between the cams at low rpm largely irrelevant. As it is I cannot pin the throttle to the floor from a stop with this setup anyway without ALOT of wheelspin.
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