Has anyone swapped a 3.5 to 3.9 liter engine. I have a 2006 Monte Carlo with a 3.5 liter with a blown head gasket and will be swapping the engine. Was curious if I could swap from the 3.5 to a 3.9 since it looks like the stroke(3 inch-3.5 liter, 3.3 inch-3.9 liter) is the only difference I know of. Thanks

 

I have not heard of anyone doing that swap. I believe the 3100/3400/3500/3900 GM v6 engines are all 60* v6 engines, based off the same block (the 3800 is a different animal and is based off a 90* block). If that is true, you could probably do a 3500 to 3900 swap with minimal issues. You would need to a PCM tuned to handle the 3900.

My bigger question, if you just have a blown head gasket, why not fix that (as you don't need to remove the engine to do that job and it would be cheaper and probably easier in the end)? Or did you drive on it too long and cause further damage, hence the need to swap the engine?

 

I have found engines from $300-$600 so for me the engine swap atleast with the 3.5 is less expensive than machine work. Also my 3.5 has 196,000 miles on it.

 

I looked up the PCM part numbers for both the 3.5 and 3.9 on a 2006 Monte Carlo at rockauto.com and found that they have the same part number which is ACDELCO 19210735. That makes it look like a possible direct bolt in.

 

On a daily driver, you do not always require machine work on the heads. I know on some of the 3100/3400 engines I have worked on, GM tells you in the shop book to check the mating surface of the head with a straight edge to see if it is warped. Pretty simple and easy test.
At your mileage, I can see the attraction to an engine swap. I did head gaskets on a 3100 once with 180K on the car (and that engine even with the failed head gaskets ran really good). Drove it until I sold it with 215K, still running.

There are some variables with the PCM. If you swap to a 3900, do you intend to also take the transmission? Even though both engines have been bolted to a 4t65e, the gearing might be different. If you don't plan to take the trans, you well need to compare the donor car trans information to yours and ensure the gearing is the same. If it is the same, the PCM should be an easy swap since they use the same hardware (as I said, I believe you might still need to have the VIN updated).

 

I was planning on keeping my original transmission since it was rebuilt recently. It's not a have to swap for me but if I do swap the engine and it's just as easy to go 3.9 I would consider it for a little extra power. Thanks

 

I totally see the point in moving towards an engine with more power if the difficulty is the not very high.

I wish I could provide more input. From what little I know about those engines (and it really is little), it should be almost a straight swap, short of the PCM tuning.

Since the Impala and the Montes are basically the same and the Monte production did not run as long at the Impala production, I wonder if there are any Impala guys that did what you are looking to do. If so, they may have information that many of us here do not.

If you can find more information, please feel free to share, as it may help others.