I swapped UIMs last night, and noticed an interesting trend in my intake runners. The UIM mirrors what you see in this pic, and where the TB bolts to the UIM the entire surface area of the runners is the light brown 'oily' color with no evidence of carbon.



Something else very interesting......on the old UIM I had opened up and smoothed out the runners (I did the same to the LIM as you can see in the pic, but I am NOT removing that sob, lol). The new UIM has the stock roughened surface on the inner area of the runners. The car is *much* smoother below 3k rpms now. Previously it has been jerky and bucked on/off throttle at rpms below 3k or so. I attributed this to my portwork/overlap and/or my spec 6 puck clutch. Now I can lug the motor if needed and accelerate smoothly from off idle . Very happy. I assume this has to do with increased turbulence and laminar flow.

Comments, suggestions?

 

It's all in your head Rich But seriously, that's an interesting observation...

 

looks like my LIM...unequal flow?

 

Mine as well. Do the exhaust and secondary inlet cycles overlap?

 

wasn't there a thread on this before? I can't find it but remember it being discussed

 

Easy. You have two sets of throttle plates - primary and secondary. The primary plate goes to the two center "tubes" in the UIM/LIM, and to the two intake ports in the middle iron housing. 90% of your driving on the street will be just on the primary throttle plate - the secondaries will be closed. With the secondaries closed, their intake tract is basically dead space, and gets reversion of oil and gas fumes and other crap.

It's normal, and there's really nothing much you can do about it.

Dale

 

When you reinstalled the UIM, you probably synchronized the TB primary throttle plates accidentally somehow . At very small throttle openings (such as those at 3K rpms and below), there is already so much turbulence created by the intake tract pulsations and the throttle plates that "laminar flow" is basically non-existent at that point. Any benefits from portwork won't be seen until you start getting some airflow through there (as in higher rpm/full throttle applications).