L36 Composite Upper Intake Manifold Swap to L26 Aluminum UIM

Here is an interesting link to a conversion from using the infamous composite upper intake manifold (plenum) found on the SII 3800 engine to the newer redesigned aluminum upper intake manifold used on the Series III 3800 engine.

Project L26 (http://www.conncgp.net/gallery/Project-L26?page=1)

Alot of work but I have heard of at least two successful conversions. However, one owner noted that his gas mileage dropped significantly to around 15 mpg and had not figured what happened.

This thread will be left open for any comments.

http://www.conncgp.net/albums/Project-L26/DSC01087_002.sized.jpg

Credit goes to No_Boost of ConnCGP whoever he may be.

Hey guys. Came over from pcmos's invite to lend a hand with the L36 to L26 swap information.

Read over what you've been discussed and seems as though the thoughts are pretty much on the right track.

Couple of things FYI:

- The L26 is a direct bolt on replacement for the L36UIM

- I did notice some gains after installing the L26UIM and I believe this pic is they key to that. The inlet on the L36 is 'oval' whereas the inlet on the L26 is actually round. Imagine that... it matches up to the L36 TB rather than creating a "turbulance ridge"...

- The 'throat' of the L26 is longer than the L36, making space a little cramped in the airbox/CAI area.

- Your PCV, EVAP, EGR systems will still work with the L26UIM!

- The EGR 'stack' however will need to be cut down (I had to go ~ 1/4").

- You will need a TB adapter plate (Gen V to L67/L36 TB adapter plate from ZZP will work fine)

- You can and will want to re-use the runner inserts from the L36. They fit perfectly into the L26.

- You will need to plug two (2) ports which are not used/needed for the L36 engine

- You can use a stock L36UIM gasket (your original if it is decent shape).

- Recommend using some "Right Stuff" made by Permatex (avail. @ Advanced, Kreger, Wal-Mart, etc.) just for extra insurance. I found I had a small leak on the TB side (gasket problem, not the L26 to L36 mate).

This is available through GMPP (www.gmpartsdirect.com (http://www.gmpartsdirect.com/))

GM PART # 89017555
CATEGORY: Engine Fuel Intake Manifold
PACK QTY: 1
CORE CHARGE: $0.00
GM LIST: $196.08
OUR PRICE: $116.24

Also available through Ed Morad from time to time.

I currently have ~40k since the swap with ZERO issues. The swap from start to finish took me about 3.5hrs (LoL, same time it took to install my GMPP suspension). Less mechanically inclined ppl with require a little more time.

Hopefully, there's enough info here to help convince you that the L26UIM is the way to go. Mind you, I did this ~2yrs ago, and relying on my pics to refresh my memory. But trust me, it's all there.

The only other thing I can think of is to make sure you know the torque specs and pattern for re-installing the UIM. If anyone needs that, lemme know (I have factory manuals to refer to).

The Dorman UIM and even the "new" plastic GM UIM WILL EVENTUALLY WARP! Yes, I said that. They are both made out a different injected thermo plastic with some 'new' polymers and fillers, but they are still plastic. I'm the supervisor for the production shop which makes IMM robot and automation systems for Delphi (who used to make the UIM for GM), and have seen quite a few UIM's the sent us for testing. Just trust me, it'll warp.

I drive my '98 hard. 120k on the odo as of tonight and have been lucky to not have many issues. Fuel eco. is around 20 city / 25 hwy. Don't know how that compares to the rest of you, but I'm okay with it.

This is an investment you will not regret guys/girls.

Hope this has helped. Feel free to contact me if you have any other questions.

:popcorn:

Oh, btw, here's the link again to my gallery with all the pics: http://www.conncgp.net/gallery/Project-L26

I disagree on the new improved design UIM's being doomed to warp. They come with a new EGR stovepipe that puts more space between it and the plenum reducing the chance of warpage.

Is that on the revised GM UIM Plenum 89017272 Rich? There is a lot of debate as to whether the one GM offers has any significant improvements compared to the aftermarkets like APN 229679 or Dorman/Motormite 615-180. Some guys at other forums (no name mentioned) are going as far as saying '99 and up GM SII 3800 cars are prone to the EGR stovepipe problem as much as the '95-'98 cars even with the improved stovepipe. Of course, alot of people will take issue with this claim. I am not fully convinced this is true. I would agree a small percentage of suspected UIM failures in '99 and up but not like the '95-'98 failures. Supposedly the plenums in '95-'98 were made by Rochester. Then Delphi took over making them and the revised Delphi showed up on circa '99 model GM cars with the SII 3800. There will be a data label/barcode that says Delphi by the area of the PCV valve. That is why I have been saying revised but not necessarily improved. However, the GM UIM gasket 89017554 was improved.

Then the aftermarkets like APN go a step further by modifying the stovepipe hole and adding a steel metal bushing and some structural/materials improvement in addition to the smallest EGR stovepipes available.

APN UIM (http://www.automotivepartsnetwork.com/store/pc/viewPrd.asp?idproduct=229679)

Basically, I see the aluminum UIM conversion as another option for people that decide there is a need to do it not that I would arbitrarily do the mod but that would probably depend on the circumstances.

I disagree on the new improved design UIM's being doomed to warp. They come with a new EGR stovepipe that puts more space between it and the plenum reducing the chance of warpage.

Even though you get a 'new' EGR pipe, it's still a factor of radiant heat which actually heats the inside edge of the TB, then transfers the heat to the neck of the UIM, thus causing warpage.

A question you have to ask, is why did the S3 come out with AL UIM's?! It has nothing to do with the L26UIM being lighter... cause it sure isn't. :banghead: And it has nothing to do with GM wanting to 'avoid more recalls' due to the warpage issue, cause it costs more to sand cast AL than it does to produce UIM's using injection molding. And the cost of a new L26UIM is only about $20 more than a Dorman intake.

It's all a matter of what you perceive as being 'the best, cheapest, easiest' fix. And the L26UIM adds a certain 'bling' to the 10yo GT. :rofl: