4.2 to 5.3 swap

Hey everyone, I'm not new to the forums but finally decided to make an account, anyway, I have a 2006 Trailblazer with 109k miles. Ive been wanting to swap in a 5.3. does anyone have a link to a swap thread or any info? I'm a mechanic so I know how to trouble shoot I'm just looking for a list of sorts. while I had been lurking in the forums ive seen a few people post about stuff but no solid list. Thanks


Well-Known Member
Hey, welcome to the forum. Theres a lot of stuff here if you dig around. One person who I always recommend is RevHardGarage. He had a 4.2 and swapped in the 5.3 and the man knows his stuff. I thought about doing one too but just decided to go the turbo 4.2 route. Good luck
Thanks for the quick reply lol. Yeah I know about him. id like to stay away from shops or anything like that that hasn't been tried and true. The trailvoy forum is dead it seems so not much help over there. I guess I have to start digging. I have a 5.3 already at home, just waiting for a weekend to do the swap


Well-Known Member
I mean he works out of his own garage, check out some of his threads. And not to be that guy but engine swaps are very involved, not typically your weekend job
Okay. Does anyone else have anywhere they can point me to? I appreciate the help @Traz but Id like some advice from someone who isn't banned. And have You ever done an engine swap? Its not that hard. ive swapped the engines in a focus about 3 times and once in my F150 so.


Well-Known Member
?? Alright?
I've worked at Roush and currently at Toyota, needless to say I've swapped hundreds of engines just at roush. But swapping out a bad focus engine for a working one is a whole different monster compared to putting in a whole different engine. Your talking exhaust work, mounts, wiring, pcm, fuel, all that extra stuff


Well-Known Member
I mean yeah it is, it would be awesome to just drop a 5.3 in and go but still.
I'm thinking if I had all the parts list and an idea I could get it done rather quickly. No offense but I'm going to keep looking for advice. maybe some competent advice


:popo: Alright gentlemen, let's keep it civil. You've both made your feelings known, you guys can let that go now. When someone else has some advice or input, they can chime in.


I've changed the title for better responses. Hello just doesn't cut it.

If you do a Google search for 4.2 to 5.3 swap, GMTN comes up on top and lists several threads:

Not having done the swap myself but owning both types and reading a lot, off hand, I can list most of the parts that may be required.

  • complete 5.3 motor (obviously) with pan for a GMT360/370
  • PCM, TCM and complete wiring harness (unless using a standalone system)
  • tranny bellhousing (AFAIK, the 4,2 torque converter bolts up and is supposedly desirable with higher stall)
  • front and rear driveshafts because the tranny will move rearward, also requiring moving the crossmember
  • rear diff from a V8 to handle the extra torque
  • engine mounts and brackets
  • radiator and hoses
  • fan shroud
  • power steering lines for 5.3 and pump tank
  • exhaust, at least to the muffler or more
  • BCM may need reprogramming to talk to new PCM
  • front springs for heavier engine (maybe)
  • bigger front brakes for V8 (recommended)

It might be useful to have access to a complete V8 truck for its parts since most are not obtainable new. This is not an exhaustive list and others may chime in with more.


Well-Known Member
Nice list Mooseman. I think Traz was just trying to say it's not a drop in and go type of thing. I don't doubt if someone was motivated and prepared they could knock it out in a weekend...getting the engine mounted is the easy part, it's all of the work with the wiring harness/ECM that will take some time. You didn't say what year the 5.3 was or if you got the engine harness/ECM/TCM that came with it, but that would be helpful info too. They made 5.3's for a long time so some will be 24x and some will be 58x, you'll have to make sure your engine harness/ECM matches whichever reluctor also.


One other thing I have read which I cant find much information as I want to do same thing is you is the pcm needs to be rewired for the 5.3 harness it's not a plug n play

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