Has anyone here ported one themselves, and did you match to heads as well as upper intake. Does anyone offer that service.... I have dremel set and have done that on different vehicle, but not familiar enough...yet

 

I port matched my LIM to the heads on my L36. Not to be confused with gasket matching. Gasket matching requires working both the LIM and the heads. I also plugged the coolant ports that go to the Tbody and expanded the coolant bypass.
Below is a link for a full write up with pics:
'04 Monte Carlo SS - Port Matched LIM

I was going to offer a service to fad these up for people, but when I tried to gauge interest, no one was really interested. I have a LIM in my garage that when I find a little spare time, I'm going to port match like I did mine, offer it for sale (just haven't had the time).

 

Jason I'm curious what effects this had on the car? Did it make definent sound and or performance differences? After listening to my engine a friend commented it sounded like this has been done.

 

This was put in at the same time I added the HV3 UIM insert, an L67 throttle body, ER Rockers and a PLOG. I honestly cannot tell you what effect this one mod made. I know when I was working on it, this was something seen more on Bonneville forum and those guys claimed it was the single best mod one could do (so of course I did it lol).

Honestly, I'm not sure how you could hear a change with this mod, I would think feeling a performance bump would be more expected. I honestly don't think this is a very commonly done mod.

 

Porting the LIM is certainly not a common thing on the 3800 N/A but worthwhile. You can gasket match the LIM ports without doing the heads, no downsides, the LIM ports are much worse than the head ports. You can also take off some material from the injector boss; reinstall the fuel injectors and rail, see where the injector sits and mark the bottom of it. You can port up until the lower injector seal, leave some extra room for security but there's a decent amount of the boss that can be removed.

 

You'll end up creating a step in the air flow (I was always striving for smoother airflow, less obstructions/steps trying to keep good velocity). If you are not going to port the heads, I think gasket matching sounds like a lot of extra work.

I never studied the injector boss for any gains. I did not want to disturb the injector mounting.

 

Its minimal extra work to just do the LIM matching and it does help. Regardless, anything porting helps the exit ports on the L36/L26 LIM, they're so poor.

The injector boss is molded into the L36 head, you can feel it just inside the port on the ceiling. That can be completely ground down if you ever do the heads.

I've also recommended porting the inner ribs of the UIM once the runners come out. I can't find a decent pic however, it's been years since I did this. The combo with a throttle body upgrade make a nice difference

 

Actually, the injector bosses are on the LIM for the L36/L26, they are in the heads on the L67.

I wondered about the ribs inside the UIM, how would air flow change if they were removed if someone put in a HV3 and removed the runners. But that's a mod I never saw anyone try or talk about. I know other UIMs for other cars don't have any such thing. Such as the 3.8 used in the '89 Turbo Trans Am and Grand National, it has a small UIM, and the LIM has long runners on it to the heads. No ribs or runner insert in the UIM.

I know at least with the L26 UIM, it had two different designs (I had both in my garage at one time).

 

The holes were never machined but the casting indentation was made into the head port on the L36 heads. You can see and feel it on the ceiling of the head port and it can be ground right down if you ever port the heads.

Good to know on the L26, I've never looked close enough, and thanks for the pics.

If you have a die grinder or corded drill, get yourself an aluminum carbide bit, otherwise it's a lot of aluminum material to remove and will take forever. The L36 plastic manifold is easier to port, I used the same aluminum bit and it goes through the plastic like butter.

 

Thanks for the info about that casting in the heads. I never knew about it! Learn something new every day
If I ever pull the heads, that would probably be the time I'd consider something like grinding those pieces out.

As for the different intakes, it's related to how the L26 PCV setup works (tube for the PCV runs right up the side of the snout). GM made two different snout castings. Not sure how they changed things, but they did.

If it's of value, here's some number info I found on the two (good is the UIM that has the larger inlet into the main chamber):
Good
Sticker: 12598924
Casting: 12573322 3

Bad
Sticker: 12598925
Casting: 12573323 7

I'm working on the "good" one and I ended up hogging out that opening a little more and feathered down a step in the snout. Still have a ways to go.

Nice to chat with another guy who grinds with a Dremel