84 L31 Swap
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4th Gear
Joined: Sep 2025
Posts: 4
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84 L31 Swap
I looked into top end kits and a Holley sniper 2 to get rid of the Crossfire in my car but also talked to a local well known engine builder who said if I brought them a 350 donor they could get it in the neighbor hood of 400hp for around 3500 VS the 6500 to modify the L83. Ironically a friend just totaled his 96 K1500 and offered to sell me his L31 for 150. I am also planning on getting a rebuilt 700R4 when I do the engine swap to alleviate the chances of the original not taking the extra power. Would I run into any problems with engine mounts, wiring harness and transmission interface?
Pro
Joined: Sep 2024
Posts: 526
Likes: 114
I looked into top end kits and a Holley sniper 2 to get rid of the Crossfire in my car but also talked to a local well known engine builder who said if I brought them a 350 donor they could get it in the neighbor hood of 400hp for around 3500 VS the 6500 to modify the L83. Ironically a friend just totaled his 96 K1500 and offered to sell me his L31 for 150. I am also planning on getting a rebuilt 700R4 when I do the engine swap to alleviate the chances of the original not taking the extra power. Would I run into any problems with engine mounts, wiring harness and transmission interface?
The way I would approach this project is pull your original engine and put it next to the L31. Swap everything over all in one day, then dump it back in. Essentially, look at the L31 as a long block. Use all the C4 accessories and wiring from your car and plug it back in.
Le Mans Master
Joined: Aug 2017
Posts: 6,939
Likes: 1,488
From: New Jersey
Flex plate might be different. I vaguely recall having to reuse my l31 flex plate during the rebuild instead of the one with the rotating assembly as the torque converter bolt holes were in different spots. (Though I would tend to say the I may have been sent the wrong flex plate) despite being the same tooth count.
Probably won't have the water pump bypass drilled on the truck block... though I have seen some where it was. Not sure what application that would be.
Only other thing I can think of is the starter bolt pattern may be different.
Probably won't have the water pump bypass drilled on the truck block... though I have seen some where it was. Not sure what application that would be.
Only other thing I can think of is the starter bolt pattern may be different.
Burning Brakes
Joined: Sep 2017
Posts: 931
Likes: 165
I looked into top end kits and a Holley sniper 2 to get rid of the Crossfire in my car but also talked to a local well known engine builder who said if I brought them a 350 donor they could get it in the neighbor hood of 400hp for around 3500 VS the 6500 to modify the L83. Ironically a friend just totaled his 96 K1500 and offered to sell me his L31 for 150. I am also planning on getting a rebuilt 700R4 when I do the engine swap to alleviate the chances of the original not taking the extra power. Would I run into any problems with engine mounts, wiring harness and transmission interface?
Melting Slicks
Joined: Dec 2009
Posts: 2,231
Likes: 284
Make sure you get all the external engine bolts as they might be metric whereas the hardware for the 84 will be sae. I ran into that swapping a vortec 4.3l and was like "why aren't these bellhousing bolts starting?"
