i ported my series5 LIM today, but i couldnt get all the way inside up the inside of the runners... i smoothed it out a bit on the inside (where i could barely reach) but its clearly not as worked as the top by the entrances to the runners. i'll post some pics of it later.
will it really matter that i didnt cut away any of the middle of the runners?
also, will i see any kind of gains by polishing either of the upper intakes? the VDI one and top one look rather large compared to the LIM...

 

you don't want to smooth the inside of the manifolds. The turbulance created by the rough surface helps mix the fuel better.

 

.....

 

it's a debatable topic, but you know how the whole golf ball thing works I imagine.


I made mine smooth, but not mirror smooth, I stopped around 600-800 grit sanding parallel to the direction of airflow.

I think smokey yunick gets into this a bit in power secrets, I'll check the book later to see what he says.

 

Seems to me that maybe smoothing the manifold before the fuel injectors would be good, but not after.

 

Smooth polished manifolds are great if you have the adjustability in your fuel injection system to handle it OR don't mind the horrid driveability of this on a less adjustable computer.

The engine port runners (head in a piston engine) is where the you need to be very careful about using smooth and textured surfaces as you can induce some nice "tumble" into the large open area of the rotor housing (combustion chamber) that will actually aid flow. In a constant-ish diameter runner poslished surface will have the most flow.

One other issue in polishing runners is keeping the fuel atomised in the air. The smooth poslished runners will condense fuel like a bathroom mirror when the shower is on. After you port/matchport the 2ndary runners you should go back in and add ~80 grit striations perpendicular to runner flow under the 2ndary injectors so there is a thicker boundry layer to to protect against "whetting". Primaries can be fully poslished as the inj. are in the "block".

You will still whet like crazy at idle/low air velocity(especially w/ an extended port) as intake "pulsing" pushes the fuel from the injecors up the manifold runners. This is most pronounced when the manifold walls are cold. Easily adjusted for stock driveability w/ E6K.

I used a 1/4" by 10" long stainless shaft split to hold a roll of emery cloth.

Started at 80 grit in a bucket of water to carry off the material (this takes material off FAST- be careful) and worked up to 1500 grit (had to back sandpaper w/ cloth as I couldn't find 1500 grit cloth- and the 1800 grit "crocus" cloth has to be spun so fast to take anything off the internal cloth backing grooves the aluminum.)

Using the 3rd gen UIM I was able to poslish every inch of the intake and exhaust systems except the turbo intake and exhaust scrolls. I think you would have to cut up or extrude the TII UIM to polish it all.

Polishing/porting/match porting aren't the only thing to do on the manifolds. Make sure you relieve them as well. Pay attention on the LIM to the casting boss intrusion into the primary runners and the EGR intrusion (have to back weld material onto this to take it out). On the TB take out the 2nd set of 2ndary plates and round out the front of the edges and taper the backside into your UIM matchport (like an airplane wing- this is all subsonic flow) before you polsih. You can also take off the plates, reduce the shaft to an airfoil (when open) and set screw/locktite the plates back onto the shaft so there are no screw heads exposed. Knife edge the backside of the plates if you are crazy.

On all intake tubes and such you should port the edges into an internal knife edge so they meet the hoses on their outside diameter smoothly before you polish them. Thin IC tubes can be flaired at the end to hold hoses on instead of rolled (which leaves a bump inside the tubes)- this has held over 20psi of boost w/ no hose popping off on my set-up (T-bolt clamps).

Portmatch/ gasket match EVERYTHING. It is much easier to dowel or pin the parts for perfect fit-up than just match mark them- I wish I had doweled, it saves time in the long run...

Good luck, Ian.

PS- for God's sake if you do all this polishing work eliminate all sources of vapors and oils into the manifolds so they don't cook onto your polished surfaces and "powerfoam" once in a while to keep it clean.