Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Polishing the combustion chamber

I notice that the combustion chamber is very rough when I cleaned the heads. I'm thinking about polishing them, but I'm not sure if they're left rough for a reason or not. If they are there for a purpose, what's the benefit?

I would not try this unless you have alot of experience porting and polishing. Whenever you start polishing the combustion chamber you are changing the volume of the chamber (do to the material being removed). Unless you constantly measure the volume you can cause serious problems do to variations in compression. It is possible, but if you haven't done this before I would not recommend trying this!

On a side note, although this does improve flow, performance may suffer. Why you ask? Well the rough surface in the chamber causes turbulance in the chamber which allows the fuel and air to mix more throughly (this is why CNC heads are so popular, the cutter produces tiny smooth ribs in the chamber). So in my opinion I would not waist the countless hours it would take you to properly polish the chambers since the gains you see, if any, will probably be very minimal. The best performance gains in the head will be found by port matching and widening anyway.

Removing a minimal amount of material can remove hot spots and have a great effect on performance. The combustion chamber doesn't provide any tumble effect other than it's general shape and position. The casting bumps should be removed.

Now what about the intake ports? Supposingly, there should be some roughness in there to help mixing the fuel better. But the E1 SVT heads have both primary and secondary intake passages extrude honed. So, logically speaking, it won't hurt if I port and polish both the primary and secondary intake passages on the E0 heads I have right?

Port yes, polish no.
EH does not leave a polished finish nor would you want it to. There are still some small surface imperfections.

The term port & polish is so overused.
The gains you see from polishing a port or combustion chamber are so miniscule compared to the amount of work it takes to do it is not even remotely worth the time or effort. Most of the time the gains can't even be quantified outside a static test on a flow bench. Real worlds numbers show no difference.

IMO CNC machining has replaced "old school" P&P work and if you look at it, it is by no means perfectly smooth.

Originally posted by DemonSVT:

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Port yes, polish no.
EH does not leave a polished finish nor would you want it to. There are still some small surface imperfections.

The term port & polish is so overused.
The gains you see from polishing a port or combustion chamber are so miniscule compared to the amount of work it takes to do it is not even remotely worth the time or effort. Most of the time the gains can't even be quantified outside a static test on a flow bench. Real worlds numbers show no difference.

IMO CNC machining has replaced "old school" P&P work and if you look at it, it is by no means perfectly smooth.

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I concur with this. Mild polishing might be beneficial, but it isn't worth the time and effort to do much more. One of the main reasons that polishing was done in the old days was strictly for the looks. It helped in selling a ported set of heads if they were polished too. It was just a Wow factor.