# Polishing ports... what are the pro's and cons?



## Neon Washer Nozzle (Mar 19, 2004)

I will be sending a head to the machine shop soon. I intend on having it ported, because I know that will help it flow better, make more power, etc. I will also be getting a valve job, and having it shaved a touch (just enough to get it flat). 
The thing I'm debating on is whether to polish the ports or not. I have heard that polishing is bad, because a slightly rough surface on the port will help the fuel/air mix blend better and will also induce a bit of turbulence into the intake, whereas a smooth surface will flow the charge in faster but will not aid in mixing it and will not add any sort of "turbulence". My machinist told me he won't polish ports unless its for a forced induction motor. He told me that polishing ports would be a waste of his time and my money unless I'm going to be running FI.
Yet every other 8v seems to have port/polish on its list of mods. So is polishing really where its at for 8v engines? 
What about the combustion chambers? Should the bowls be blended at all or are they good enough to leave alone?


----------



## 84_GLI_coupe (Apr 3, 2001)

*Re: Polishing ports... what are the pro's and cons? (Neon Washer Nozzle)*

There is a MAJOR difference between a smooth port and a polished port. The most I'll do is a 320 grit strip of emery cloth in a split rod in my die grinder. Intakes should never be polished. Exhausts can benefit from polishing because the polished surface will resist carbon buildup. Polishing the chambers and smoothing the piston tops can help to resist carbon buildup as well. Your head guy is spot on with the theory.
Get a catch-can for your oil breather, your engine will thank you.


----------



## Jason_Reuben (Jan 15, 2005)

*Re: Polishing ports... what are the pro's and cons? (Neon Washer Nozzle)*

There is a large gray area in there. Like the guy stated above me, a smooth exh. port will resist carbon buildup because there is nothing for it to stick to. Most people when they say a port and polish don’t polish to a mirror finish, its just a phrase that is commonly used. Most people will port match the intake and head runners to each other and smooth any rough edges and remove a little material to allow for larger CFM to flow. Its stupid to believe that only a FI engine will need a P&P. Not only is it cheaper to do it now while the head is going to be off the car and torn down anyways then later on down the line but all the bolt-on’s in the world only give you as much CFM as the smallest part in the system, And the head is one of them. 
It sounds to me like your mechanic is being lazy. IMO I would do it. But that is just me.


----------



## ABA Scirocco (May 30, 2001)

*Re: Polishing ports... what are the pro's and cons? (Jason_Reuben)*


_Quote, originally posted by *Jason_Reuben* »_Its stupid to believe that only a FI engine will need a P&P....... 
It sounds to me like your mechanic is being lazy. IMO I would do it. But that is just me.

Re-read the original post, this thread isn't about the benefits of porting and polishing a head, it's about the type of surface finish of the completed job. The guy's mechanic is telling him that polishing to a very smooth finish on the intake ports is pointless for an NA engine, he's not being lazy, he's speaking the truth. A very finely polished surface does nothing to improve airflow and if the surface is left slightly rough finish it helps to prevent fuel drop out, that's especially important if the engine's going to be carbed.


----------



## X K R O M X (Jan 19, 2006)

*Re: Polishing ports... what are the pro's and cons? (ABA Scirocco)*

I don't mean to be rude guy's but it seems you are still buying into common and old myths about head work and how it applies to modern engines and fuel delivery system's,alot of what has been said on the issue of smooth and rough intake port's does not apply to fuel injection,there is plenty of info out there that can lead you astray, so just be careful as to what cookie you bite into,as for your head If you want a quality job with no question's about the work check my Sig. and send me a PM,we can figure something out.


_Modified by X K R O M X at 10:50 AM 8-17-2006_


----------



## Agaeris (Mar 10, 2004)

*Re: Polishing ports... what are the pro's and cons? (X K R O M X)*


_Quote, originally posted by *X K R O M X* »_I don't mean to be rude guy's but it seems you are still buying into common and old myths about head work and how it apple's to modern engines and fuel delivery system's,alot of what has been said on the issue of smooth and rough intake port's do not apply to fuel injection,there is plenty of info out there that can lead you astray, so just be careful as to what cookie you bite into,as for your head If you want a quality job with no question's about the work check mt Sig. and send me a PM,we can figure something out.


I concur...And I will admit it wasnt that long ago that I myself thought that rough ports were necessary to atomize fuel. With carbs it is the case, but modern fuel injectors, even the old CIS injectors, do a pretty darn good job of it already.


----------



## MYTHOS (Dec 4, 2001)

_Quote »_
I don't mean to be rude guy's but it seems you are still buying into common and old myths about head work and how it applies to modern engines and fuel delivery system's,alot of what has been said on the issue of smooth and rough intake port's does not apply to fuel injection,there is plenty of info out there that can lead you astray, so just be careful as to what cookie you bite into,as for your head If you want a quality job with no question's about the work check my Sig. and send me a PM,we can figure something out.


You want to elaborate and let us know of your "know-how"?
It is a public forum, and I bet many would like to know.


----------



## X K R O M X (Jan 19, 2006)

*Re: Polishing ports... what are the pro's and cons? (MYTHOS)*

Modern fuel injectors have advanced so well they atomize the fuel upon injection into the flow of air entering the head,Older head used carb's and it was important to leave the intake ports a little rough in order to knock around the fuel and air to help better atomization.
I have an article from Race-car engineering that talks about it in better detail but that's the just of it.


----------



## S4mig (Sep 18, 2003)

*Re: Polishing ports... what are the pro's and cons? (Neon Washer Nozzle)*

Most real world applications will benifit from a slightly rough finish to the intake ports and a good polish on the exhaust ports. The rough intakes help keep the air and fuel in suspension and the polish on the exhaust ports helps to prevent carbon buildup. The same holds true for combustion chambers with polishing. Bowl work is where a good port job is made. You want to keep the runners of the 8v head small to keep up velocity and the bowl should provide a smooth transition into the chamber. HTH.


----------



## mgordon (Jun 25, 2004)

*Re: Polishing ports... what are the pro's and cons? (S4mig)*

I also spoke to a machinist who does alot of VW heads, and he thinks that the most gain comes from cutting the valve guides, and Rifling in the Intake Manifold gives slight gains as well.


----------



## X K R O M X (Jan 19, 2006)

*Re: Polishing ports... what are the pro's and cons? (S4mig)*


_Quote, originally posted by *S4mig* »_Most real world applications will benifit from a slightly rough finish to the intake ports and a good polish on the exhaust ports. The rough intakes help keep the air and fuel in suspension and the polish on the exhaust ports helps to prevent carbon buildup. The same holds true for combustion chambers with polishing. Bowl work is where a good port job is made. You want to keep the runners of the 8v head small to keep up velocity and the bowl should provide a smooth transition into the chamber. HTH.

Everyone has there opinions on this issue, and I have seen and heard them all, I am only Stating what I know to be true from my own experiecne with the flowbech and other data tools.


----------



## onewiper (Aug 29, 2002)

What's the point of roughing up your intake runners to keep the fuel atomized when your injectors spray just before the intake valve? As stated earlier carbed engines benefit more from rough surfaces in the head and intake manifold then fuel injected engines because the air fuel mixture has a much longer distance to travel and the fuel tends to drop out and cling to the surfaces of the runners. A rough surface creates vortices that keeps the mixture agitated to prevent fuel separation. Even on CIS basic the fuel is injected just before the intake valve, not much time for fuel separation.


----------



## ABA Scirocco (May 30, 2001)

*Re: (onewiper)*

It's well established that a slightly rough surface helps keep the fuel supended in the air better than a smooth one, but as has been mentioned already, that's only really important for carbed engines. However there's debate in some circle as to whether a slightly rough surface will flow dry air better as well, I'm not going to enter into that debate except to say that the evidence I've seen is, at best, inconclusive. 
So in a nutshell, afaik, in a fuel injected engine, shiney dead smooth ports won't really help you much but they won't hurt you either but for a carbed engine you want a somewhat rough finish.


----------



## Neon Washer Nozzle (Mar 19, 2004)

*Re: (ABA Scirocco)*


_Quote, originally posted by *ABA Scirocco* »_
So in a nutshell, afaik, in a fuel injected engine, shiney dead smooth ports won't really help you much but they won't hurt you either but for a carbed engine you want a somewhat rough finish.

I think I'll leave them slightly rough and save myself the time/expense of smoothing them because it just seems like overkill. Who knows, the engine might end up carb'd someday


----------



## X K R O M X (Jan 19, 2006)

*Re: (Neon Washer Nozzle)*


_Quote, originally posted by *Neon Washer Nozzle* »_
I think I'll leave them slightly rough and save myself the time/expense of smoothing them because it just seems like overkill. Who knows, the engine might end up carb'd someday









Hmmm I dont know guy's my personel Race head with smooth intake ports flows over 260 CFM







this is a 2.0 16v head with alot of work but It is very rare indeed to see those kind of results.
I have heard of 275cfm around the horn but I will leave it where it's @ and not risk damaging a good thing.


----------



## ny_fam (Apr 3, 2004)

*Re: (Neon Washer Nozzle)*

Seems were splitting hairs here.
This type of conversation is hard to have via the web. You really have to see a ported and polished head's ports to see how smooth they are.
Please correct me if I'm wrong here I'm not expert.
But this may help.
When I've tried to talk about the surface left after porting I talk about lines and surface texture.
Lines are very straight, dips bumps, inconsistant surfaces are removed. Depending on the air flow direction curves are shaped with clean transitions.
the surface is not rough like sand paper but also not like glass.
If you can see non polished lines they are as think as a human hair, and no bigger.
http://www.innovations-report.....html
Interesting note about CIS injection above- When the injectors are flowing all 4 are flowing as the same time. That means that some of the valves are closed when the injectors are flowing. Thus in the bowl/inside radius area of the intake port their will be gas dropplets. 

Cheers


----------



## ABA Scirocco (May 30, 2001)

*Re: (ny_fam)*

There's an interesting article on cylinder head porting on wikipedia, I'm not prepared to critique it but here's an excerpt from that article germane to this discussion.

_Quote »_ A mirror finish of the port does not provide the increase that intuition would suggest. In fact, within intake systems, the surface is usually deliberately textured to a degree of uniform roughness to encourage fuel deposited on the port walls to evaporate quickly. A rough surface on selected areas of the port may also alter flow by energizing the boundary layer, which can alter the flow path noticeably, possibly increasing flow. This is similar to what the dimples on a golf ball do. Flow bench testing shows that the difference between a mirror finished port and a rough textured port is typically less than 1%. The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means.


----------



## X K R O M X (Jan 19, 2006)

*Re: (ABA Scirocco)*


_Quote, originally posted by *ABA Scirocco* »_There's an interesting article on cylinder head porting on wikipedia, I'm not prepared to critique it but here's an excerpt from that article germane to this discussion.


This is a good read.


----------

