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3.7L to 3.5L Swap

08H3

Well-Known Member
Messages
1,349
Location
United States
Yeah, you read that right, and I know, it's weird. I have a 2008 that needs a new engine. I absolutely refuse to pay what people want for a replacement junkyard engine. I do, however, have the potential to pick up a 2005 Colorado with a 3.5L for close to scrap value. My only goal is to get the H3 mobile again on the cheap, which is why I'd settle for a 3.5L. I know replacing a 3.5L with a 2008+ 3.7L is doable, but with a lot of work. I can't really find any info on the reverse though. Does anyone have any info on whether this is possible and what is involved? Thanks in advance.
 

EndeavoredH3

Well-Known Member
Messages
407
Location
Arizona
IIRC the 08’ I5 has an intake cam pos sensor, while the 06 doesn’t. Id assume there’d need to be either a tune or some programming to accomplish that. Given the difference in displacement I’d imagine you’d need to tune it to the correct motor as well.
 

alrock

El Diablo
Staff member
Messages
10,540
Location
Scottsdale
PCM/TCM differences too that might affect it and I would have no idea how to address. Your later H3 has the PCM and TCM as two different components while they are integrated on earlier H3s. 2006 transmissions lack a sensor that was put in 2007, and while that's of course not the engine it could affect the computer issue.

Sounds like it's time for a Cummins!
 

08H3

Well-Known Member
Messages
1,349
Location
United States
Not really. I know my limits. I'm confident I could pull an identical engine and put it back in. Given my skills, a swap like that would end in a pile of parts. I'm not at all denying that Cummins swaps are about the coolest thing you can do. I think being realistic about your abilities is an important considerations. I've seen dozens of cool project cars setting and rotting away because someone got in over their head.
 

08H3

Well-Known Member
Messages
1,349
Location
United States
No compression on 3. Have not dug into it to find the reason. I don't have the time or frankly probably the ability to do a successful rebuild. No one around here will even consider touching a 5 cylinder. It's totally foreign to anyone around here.
 

crwalkerasla

Well-Known Member
Messages
344
Location
Corinth, MS
I have an '06 that just went through a full 3.5 rebuild. I was intending to do an LS swap, but found out that in '08 there were a lot of computer changes, for the new systems/formats that would have required me to run 2 PCMs, 1 for the new engine & 1 for the old truck. This was one of the deciding factors in choosing to stay with what I had. I would definitely look into this if crossing the '07/'08 threshold.
 

atvspeed4

Well-Known Member
Messages
1,190
Location
massachusetts
I have an '06 that just went through a full 3.5 rebuild. I was intending to do an LS swap, but found out that in '08 there were a lot of computer changes, for the new systems/formats that would have required me to run 2 PCMs, 1 for the new engine & 1 for the old truck. This was one of the deciding factors in choosing to stay with what I had. I would definitely look into this if crossing the '07/'08 threshold.
You do not have to do that at all for a swap in a 2006. We swapped a 2011 6.0 and 2012 6l90 into our 2006 without running two pcms. Sorry someone gave you bad information its tough with the internet navigating something like a swap with so many different information sources. Check out some of the build threads on here there is alot of talented members that have done swaps.
 

crwalkerasla

Well-Known Member
Messages
344
Location
Corinth, MS
Well, I guess that's 'Murphy' at work. Can't find good information when you need it, and after it's too late, it's everywhere. Anyhow, she's running smooth now. just doesn't have as deep of a throaty rumble.
 
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