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Posted by: BeatNavy Nov 20 2021, 01:44 PM

I want to swap my current 2.0 late plenum with an early 2.0 plenum and the larger diameter inlets (trying to get more air to my Raby cam on cold start). I'm sure it's possible to do this in the car, but how big of a PITA is it? I can't recall off the top of my head if you need to remove or loosen the L/R cylinder tin in order to get the plenum off.

I know I'll have to loosen up the intake runners, and negotiating the old one off of those and the new one back on is sometimes finicky, even with the engine out. I'm pretty decent dropping the engine, but what's the quickest way here (or, the path of least resistance )?

Posted by: JeffBowlsby Nov 20 2021, 03:02 PM

In car, no problem.

Posted by: rjames Nov 20 2021, 03:26 PM

It’s not hard at all. The tin pieces don’t need to be removed. Cut the intake to plenum hoses for easier removal and replace with new ones.
If your plenum is in good shape and you want to sell, let me know as I may be interested in buying.

Posted by: BeatNavy Nov 20 2021, 03:57 PM

Thanks, Jeff, Robert. That sounds like a plan then -- swap with engine in. Glad there are no hidden gotchas.

Robert, I'll look around to see what my "inventory" is on plenums. I may have a spare (perhaps this one)!

Thanks, fellas.

Posted by: emerygt350 Nov 20 2021, 03:58 PM

How on earth do you unbolt it? I could not figure it out when I was worried there might be bad seams.

Posted by: 914werke Nov 20 2021, 04:05 PM

Im confused about what you are trying to accomplish?
While there are differences in early to late 2.0L plenums the dia. of the inlets isnt one of them?

In any event check each of those units carefully... ask me how I know.


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Posted by: BeatNavy Nov 20 2021, 04:06 PM

Unbolt it? It's held onto the case with a couple of tin screws and the intake runner boots.

Posted by: 914werke Nov 20 2021, 04:08 PM

...and a bolt on back spine of the case.

Posted by: emerygt350 Nov 20 2021, 04:10 PM

Exactly, where are those screws? Down those holes?

Posted by: BeatNavy Nov 20 2021, 04:11 PM

I'm pretty sure the 2.0 plenum has differences in inlet size -- the two nearest the dizzy. The early one has larger inlets than later ones. I've got both, unless I'm missing something.

Late on the left, early on the right. I think.

Posted by: 914werke Nov 20 2021, 06:17 PM

Ah! the vacuum ports. not the intake...gotcha

Posted by: BeatNavy Nov 20 2021, 06:35 PM

My fault...incorrect terminology I guess. Sorry!

Posted by: Montreal914 Nov 20 2021, 06:40 PM

...and how are you planning on using those larger vacuum ports to improve your colds start?

Posted by: emerygt350 Nov 20 2021, 06:43 PM

More air? Until I started working on a djet... I never would have said that.

Posted by: BeatNavy Nov 20 2021, 06:46 PM

I currently have the late plenum (on the left). I have a idle air control (IAC) valve off Hyundai Sonata (I think), that's connected to one of those vacuum connections. I just purchased a BMW 325i IAC that is significantly larger than the Sonata IAC (in fact it's huge in comparison). I've tested it, and it helped, but now I'm convinced the restriction is simply the size of that vacuum inlet. I want to try the BMW IAC with the larger vacuum inlet to see if I can get enough air for an off-pedal cold start and solid idle.

Posted by: Montreal914 Nov 20 2021, 07:02 PM

Thank you for the explanation. Please share results and setup after you try it. I believe I bought a BMW unit too for my build but I am very far from getting all of this running...

Good luck, I hope this will solve your problem.

Posted by: BeatNavy Nov 21 2021, 11:57 AM

Ok, got the plenum swapped and I think it's a winner. Potentially. The car started strong dead cold and idle immediately went to 1200 or 1300. I do need to make sure I don't have any other vacuum leaks I created when I did this (I reused the TB gasket and MAP sensor gasket -- I know, terrible!). I had tried everything I could think of to get a solid cold start including manipulating mixture, cold advance timing, and of course IAC settings. EDIT, I even drilled a small hole in the throttle body plate to allow more air to bleed through (as per Jake's recommendation on another thread relevant to the 9950 cam).

Now I need to completely go over my idle tune though. Except for cold starts, the other IAC and tune were working well, and I had closed loop doing it's job. Now I need to completely redo that

Swapping the plenum with the engine in car wasn't too bad. Funny, the parts I thought would be hard, like getting the intake runners on and off, was pretty straightforward. I think I spent most of my time trying to get the darn tin screws back in.

Posted by: rhodyguy Nov 22 2021, 07:49 AM

Is this the 2258 listed in your sig?

Posted by: rhodyguy Nov 22 2021, 07:49 AM

Is this the 2258 listed in your sig?

Posted by: BeatNavy Nov 22 2021, 07:51 AM

Why yes, yes it is as a matter of fact.

Posted by: Montreal914 Nov 22 2021, 11:07 AM

I love to hear about these debugging successes! Very encouraging for the rest of us.
Good luck with your re-tune!

Posted by: Wew Dec 2 2021, 12:02 AM

Hey Rob,

Have you also confirmed your aar is functioning properly. If it’s stuck open or closed it could cause trouble with cold or warm idle.

Ian Karl has a good video on how to clean them up and confirm they are functioning properly.

Best of luck.