polished runners

Horsepwraddict

Pro Stocker
Mar 3, 2007
1,581
0
0
Princeton MA
OK, i have a feeling this might start a flame war but i want to hear opinions and facts.

The Topic: Intake runners on a cylinder head and intake manifold (wet manifold)... polished smooth or left slightly 'dimpled' or rough

my take on the subject (still learning myself here)

Rough finish- 'eddy's' on surface create turbulence and a small buffer area along the surface of the runners preventing the fuel from even coming close to the surface and condensing and puddling.

Polished finish-while good in a dry manifold application for air velocity, in a wet application (air/fuel traveling through runners) it causes pooling and poor mixture and actually creates turbulence because of the very very smooth surface.

Port velocity-Which is better in relation to port velocity. Bigger runner and rough surface for airflow or small runner with hi-velocity and polished runner, using the velocity to keep fuel atomized. Assuming both runners flow the same at lift point X. I already know that the if the same amount of air can be moved through a smaller port it WILL make more power due to increased velocity, but what happens when runner surface is factored in?

i think we need a physics section of the forum for stuff like this lol...let the games begin.
 

383malibufiend

Top Fueler
Mar 27, 2006
2,661
0
36
Lancaster PA
erik, i agree with you, i am also in the same boat as you, i am not a pro but im still learning, and have learned from listening, and an older guy that i know that used to port heads always said to me to keep the ports slightly rough if it is a wet manifold, it keeps the fuel from puddling and the rough surface keeps the turbulence up to keep the fuel/air charge mixed well. for street driving i would imagine you would want the high velocity runner for better power down low, and if its a high rev motor then you would want a larger capacity runner with less velocity down low. just how i understand it....correct me if im wrong though.
 

Horsepwraddict

Pro Stocker
Thread starter
Mar 3, 2007
1,581
0
0
Princeton MA
ya, this sort of thing fascinates me, its just so hard to get a straight answer out of anyone without somebody arguing the facts.
 

383malibufiend

Top Fueler
Mar 27, 2006
2,661
0
36
Lancaster PA
yeah this old guy i know that i mentioned above, i dont even know everything hes done in his life, but hes meticulous about everything and very exacting. if he says something i listen, hes got no alterior motives and hes not trying to sell me anything. good guy, and i hope hes around for awhile i still have a lot to learn.
 

540Malibu

Pro Stocker
May 22, 2003
1,432
0
0
Shrews., MA
i think the problem is what most people consider polished, i dotn consider smoothed with 80 grit polished, i would consider smoothed with 300 grit polished
 

RatDime

Frequent Racer
Oct 24, 2006
575
0
0
Ind
I agree with 540 malibu, I leave the intake rough-not alot, and use 300 grit on ex side. I was told this from a very respectable builder! Never flowed any heads before but proven on track with no other mods.
 

Horsepwraddict

Pro Stocker
Thread starter
Mar 3, 2007
1,581
0
0
Princeton MA
540Malibu said:
i think the problem is what most people consider polished, i dotn consider smoothed with 80 grit polished, i would consider smoothed with 300 grit polished

i was thinking along the same lines, how polished is 'polished'. Id like to hear more of you opinion on this spence, An old old thread you posted in on NEMS actually got me thinking about this a while ago.
 

Supe

MalibuRacing Junkie
May 21, 2003
15,116
0
36
Charlotte, NC
If it's not a near mirror finish, then it's not polished. If you can rub your finger down it and feel texture, it's fine for the intake side. Exhaust ports should feel like a piece of glass. I'm agreeing with Mitch in that 80 grit is almost ideal for the intake side as far as appearance goes, even a bit finer.
 

injected

Frequent Racer
Dec 21, 2006
432
0
0
Quebec , Canada
If you get your intake side to a miror finish it will make fuel pudle under 5000 rpm ! If your planing for the street ,forget about it !
 
A

Anonymous

Guest
It can vary by combo. Some will run better with a rough port and others run just as well with a smoother finish. I've seen some debate as to the finish just under the seat area as well. Some like to have a small band of rough finish under the seat. Even then what works on the flow bench may not work on the track.
 

MalibuRacing.com Gear

Stickers & Shirts!!