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Port & Polish to a mirror finish

Port & Polish to a mirror finish

Port & Polish to a mirror finish

Hi gentlemen I had just recently completed a port and polish on my 1.8T 5v head. I ported both intake and exhaust and only mirror polishing the chamber and exhaust ports, the intake ports are to scotch brite/satin finish.

I'd appreciate any comments or insight on having such a surface finish involved in the combustion chamber. My intitial intentions were to decrease hotspots caused by carbon build-up and to create smoother surface for better flame propigation.

Here are some pics of the work...Thanks in advance :)

The Intake ports will remain a #4 finish.

Next are the valve faces and a 3 or 5 angle valve job...should be good  =)

RE: Port & Polish to a mirror finish

Nice finish;  should do what you wanted: reduce formation of deposits,  and eliminate detonation-causing hotspots.

RE: Port & Polish to a mirror finish

I was told that having a high polish in the combustion chamber my lead to need to run a higher octane fuel.  The high polish reflects more heat and increases the likelihood of spark knock.  The benefit however may be and increases in thermal efficiency.


RE: Port & Polish to a mirror finish

otx12- definately could be a possibliity. I've heard that well polished aluminium can have a reflectivity ~99.9%

RE: Port & Polish to a mirror finish

A highly relflective surface would have a similiar but lesser effect as thermal coating the chamber.

RE: Port & Polish to a mirror finish

My experience leads me to believe that the chamber finish in the photos does reduce carbon build up and reduces detonation by reducing hot spots. If you get more heat retained in the combustion gasses, but less heat in the metal, it should give more power by better thermal efficiency, but higher compression can also be run before onset of detonation due to substantially lower maximum point temperatures. Also reduction of carbon build up maintains original compression and also reduces the likelihood of glow plugging of the carbon.


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RE: Port & Polish to a mirror finish

Ok, I have to know what you did to get that finish! Besides a lot of elbow grease ;)


RE: Port & Polish to a mirror finish

otx12 - After porting I used a series of custom polishing bits with different grits finished by a diamond grit wax. My place of work uses these items on a daily basis. The port and polish took about 80 hrs not including the valve faces that still require poilishing.

If in fact you are interested and want to save the time and money on getting supplies. I suggest you look into www.gethoned.com

...and for a more in-depth look at the process you can visit www.extrudehone.com

RE: Port & Polish to a mirror finish

Could polishing the chamber potentially reduce combustion efficiency by reducing the in-cylinder charge tumble and turbulence that helps keep fuel suspending in the charge?

RE: Port & Polish to a mirror finish

I think tumble and turbulence are macro effects and that the surface finish could only be considered a contributing factor on the micro-scale.

RE: Port & Polish to a mirror finish

Very pretty work Don but you may get better power from the inlet ports if you scratch them up a bit with about 60-80grit paper perpendicular to the air flow. Several people I know who do heads for a living insist that the roughness gives tiny localised eddy currents or swirl which improves fuel atomisation and thus power. Exhaust ports can be smooth to reduce carbon buildup.
cheers, derek

Derek White

RE: Port & Polish to a mirror finish

Derek, thanks for the input and it seems like a good idea but after realizing that the injector nozzle is situated close to the valves I'm not even sure plenty of tumble is involved. I beleive most of the atomization is a result of the specific injector design and function...

Courtsey of SFW vid on the Bosch 440's (Performance Upgrade) in comapison to USRT 42# Injectors (Performance Upgerade as per orig design and function)

Bosch EV1 42#

Bosch EV6 42#

The specific injectors that will be used on my application are the 60# Siemens DEKA that have a very wide angle spray pattern for better atomization over the 3 intake ports.

Here are some examples of fuel intjector patterns...The specific ones that would provide better atmomization for this specific head application would be the bent split spray or wide cone.

I have already tested the Bosch EV1 42# which is a pencil spray pattern over the Delphi 42# Injectors (features 3 bent cones @ 20°) and I saw a reduction of almost 2 volts on my knock sensors via datalogging on my car and setup that boasts over 300+whp.

This is what the chamber & exhaust ports look like after cleaning :)

RE: Port & Polish to a mirror finish

Hi Don,

The tumbling air along the port walls may
also help keep the fuel suspended in the air
 and stop it sticking to the walls.

Send me some info on what setup works well
for you as later this year I'll probably be
building an approx 600hp Audi 4.2 V8
(essentially two of yours glued together.)

cheers, derek

Derek White

RE: Port & Polish to a mirror finish

Derek, that is going to be impressive. You going with forced induction of any sort or strictly naturally aspirated?

I will indeed keep you posted on my results :)

RE: Port & Polish to a mirror finish


I´ve heard about that finish in the exhaust ports reduce the carbon buildup, and reflection of the radiation diminishes the heat transfer to the port walls.  In the intake ports It´s cool to have a tiny groove perpendicular to the air flow for better air/fuel mixing.  

RE: Port & Polish to a mirror finish

try diamonex coating the entire chamber and ports but mask the surface that come in contact with oil or coolant.

RE: Port & Polish to a mirror finish

The Diamonex coating seems like a good idea however, it's max operating working temps is 500°C. I'd be a little reluctant in applying it to the chamber on highly boosted motor. I would venture to say that applying it to Crank bearings, rod-end bearings, Piston Pins, Piston skirts, Cams, vlave train...and bascially any other load bearing application would be ideal.

In regards to the intake ports they have been ground smooth to a 120 grit finish perpendicular to air-flow.

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