tehsil4d

out of curiosity i was looking at pictures of ported and polished rotary motors. now several of the pictures i viewed, i noticed that the intake ports were polished to a mirror finish. beside a VERY basic understanding of how a rotary works, as far as adding performance im a total newb. anyway here's my question, on a cylinder motor, the intake ports would never be polished, and are generally left slightly roughed up, this is to cause enough turbulence in the air fuel mixture to prevent the fuel from beading up and sticking to the walls of intake port. is this not the case in a rotary?

Aaron Cake

iTrader: (1)

It's open for debate.

On school of thought says that mirror smooth ports will promote very smooth flow. Another school of thought says that eliminating the bumps in the casting removes the boundary layer, hurts laminar flow and thus costs flow.

I don't know if testing has ever been done as it is hard compare tests on a static flowbench to real world results as the port shape changes during induction.

One thing that is for sure though, is just polishing the ports does nothing. It is a waste of time.

global247

so why do the people do it??

tehsil4d

people will polish in addition to the porting, but my question was specifically on the polishing aspect of this performance mod.

When i ported and polished the head on my SR20, i didnt bother with polishing the intake side, as i was informed by many people that if i polish the intake side fuel could bead up on the walls of the ports. So all i did was gasket/port match whatever you wanna call it, and took out the casting imperfections. But the reason you polish on the Exhaust side is to prevent the build up of carbon, though the inevitable will eventually happen, and carbon will slowly build up again. but i digress, i brought up the polishing side, because i saw quite a few pictures of 13b intake ports having been polished. i was just wonder why i saw polished intake ports on a 13b, when i almost never see polished intake ports on a cylinder engine.

(when i say polished i mean to an almost mirror finish)

Aaron Cake

iTrader: (1)

Because people are stupid.

While I don't know of any testing comparing just the difference between polished ports and rough ports with an equivalent port job, it has been proven that just polishing the runners and inner port area without changing the port shape does nothing.

I agree with polishing the exhaust sleeves to help eliminate carbon, but it is only a short term thing. Carbon will still build up. Proper tuning is what will eliminate carbon buildup.

Also, another reason people polish the port runners on the rotary even though there may be no benefit is because it looks really nice in pictures.

sashanos

So what would be the horsepower increase when street ported either mild or more aggressive?