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Old 01-05-2011, 11:08 PM   #1
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Default UIM Porting

SO I have a L26 Upper, I notice after I pull the runners out there is casting that holds the runners inline. Would it behoove me to Port my intake. I am going to be installing a HV3 insert.
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Old 01-06-2011, 12:59 AM   #2
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Wish I had a real answer for you, but here'* what I know about the UIM (besides the fact that it gets old and leaks coolant before you discover the joys of GM Forum and socket sets).

The runners seem to direct airflow through the UIM. However, like the MAF post in your throttle body, directing airflow means either reducing volume due to obstruction, or reducing velocity*due to directing. At high RPM'*, there'* enough air velocity that the runners actually slow things down (hence the existence of the HV3); however, at low RPM'*, the runners are needed to properly move air through the manifold; otherwise, the air would just slow down and stagnate. Proof: It'* been shown (by ZZP themselves, I believe) that completely removing the runners adds high-end horsepower but absolutely kills low-end torque.

Long story short, it seems doubtful that you can port the UIM to get more power out of it. On stock runners, I think reducing its height and therefore shortening the path the air takes through the manifold would be your best bet. (But bear in mind that I studied computer science, not mechanical engineering.)

However, I would look into polishing. I forget what the inside of a UIM looks like, but like a LIM, smoothing out the air channels would help a tiny bit.

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Old 01-06-2011, 03:59 AM   #3
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Zeta, the L26 can't crack and leak coolant because it'* metal. I mean, it could crack with enough tons of weight on it, but then you've got other problems.

Polishing actually messes with the air velocity. You don't want very smooth stuff. The finest you should go is 120 grit if you are going to touch the intake ports, but it all depends on how the HV3 lets air out into the LIM. Could we have some pictures, please?
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Old 01-06-2011, 04:44 AM   #4
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Zeta, the L26 can't crack and leak coolant because it'* metal. I mean, it could crack with enough tons of weight on it, but then you've got other problems.
Oh yeah, I forgot he had a S3 UIM sitting around. Guess I'm just an old-schooler… barely.
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Old 01-06-2011, 04:50 AM   #5
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I remember my good old days with the nylon upper manifold. It cracked by the throttle body, and it didn't look as awesome as the metal one I have now. So, when are you top-swapping?
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Old 01-06-2011, 09:24 AM   #6
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I'll get some pics up after the the devil game tonight
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Old 01-06-2011, 10:11 AM   #7
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Oh yeah, I forgot he had a S3 UIM sitting around. Guess I'm just an old-schooler… barely.
Never too late to put on an S3 mani... you know where there'* a couple.
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Old 01-06-2011, 01:39 PM   #8
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Never too late to put on an S3 mani... you know where there'* a couple.
Don't forget to pick up an adapter plate and N* with a LQ4. Just saying.
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Old 01-06-2011, 02:30 PM   #9
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I have two sittin here... next to the two L26 manifolds, next to the two Gen V'*... I have problems eh?
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Old 01-07-2011, 12:52 AM   #10
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Here'* with the runner'* in
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Here'* the casting I'm looking to eliminate

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Here'* the insert.
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