Plenum porting surface roughness question

[mike100]

Long explanation short- gonna leave as much of the rough texture below the injectors as possible, but as far as the ported I/H lengths and plenum radius- should I purposely rough up the sides? They are far from polished, but feel smooth to the touch.

Does it really matter?- I'm sure the volume increase is going to add hp as it is a well documented mod.

the plan is to open up the head primary a little -maybe about 1 inch down from a semi-tapered i/h port to about 35mm on the bottom.

[sammy]

i would pm loco bob on your ?his work is amazing and he freely shares with those that ask .

[Locobob]

The research I have done on the subject seems to indicate that surface texture is at best a minor consideration. A very smooth, polished surface is generally thought to be counter productive as far as air flow is concerned. It does however help inhibit carbon deposits. Fuel puddling is largely thought to be a non issue for direct port fuel injected applications. On an LT-5 the injectors have a relatively narrow stream and are pointed almost directly at the valves anyhow. I usually just finish the intake side to 40 or 60 grit since those are readily available and allow consistency, I see no advantage to going finer. Trying to purposefully rough up the port beyond that is going to be difficult to do consistently and may end up being counter productive if it results in jagged edges. I prefer a much finer finish on the exhaust in the interests of keeping carbon deposits in check.
From the stock and ported intakes I have inspected after use, I have noticed less carbon buildup on those with a rough sanded finish vs unfinished castings. Obviously this is far from a controlled scientific test.
I'm always on the lookout for new research on the subject, if anyone finds something interesting on this topic post it up. :cheers:

[LGAFF]

From what I have read the 60 grit is good, just like when you drive a car in the rain, the water drops on the windshield move slowly even at higher speeds, because you develop someone of a "dead zone" above the surface if too smooth.

The guy who fixed the set of ported heads I bought actually bead blasts the surface flowing the flow of the air path. This leaves very lightly disturbs the surface, but feels fairly smooth to the touch.

But lets face it, we are probably splitting hairs at this point. As long as the runner does not look like the Rockies I think you are OK.

[flyin ryan]

A 'Sharp' 80 grit or dull 60 grit is my preferance...years of experiance :redface:.