Internally polishing cylinder head

[mrbeige 0]

I'm just polishing my cylinder head at the moment and wanted to know what grit sandpaper to take it down to?

 

Is 240 grit too fine a finish?

[Supercharged 2]

240 to fine!?!

 

I would have thought you'd want to go up to 800 grit at least to get a fine finish...

[Guest]

If you want it to look like chrame then you will have to go to 800 - 1,200 grit and then polish and wax it.

 

Dennis

[flusted 0]

Are we talking internal or external?

[mrbeige 0]

Well spotted flusted....

 

Internal port polishing! Sorry for my inital vagueness!

[flusted 0]

Inlet slightly rough,exhaust as mirror finish as you can get to prevent carbon build up

[mrbeige 0]

So, something like 240 grit on inlet and 800-1000 grit on exhaust?

[zarman 0]

I've heard polishing the intake ports is a bad thing. Reason being is you need some turbulence to mix the air and fuel well. If it's too smooth this doesn't happen and you might loose power. Take it for what it's worth.

[Guest]

Internally is a little different, you want to remove the casting marks and increase the airflow without greatly increasing the voluume. You want the intake a bit rougher then the exhaust to help with flow. Port matching the intake is also important as it helps increase the flow by reducing turbulance. I have read that 16V like the power matching and they really do well with cleaning of the exhaust ports in the head. There are some areas that really need cleaning up in the exhaust ports so I would clean up in there but don't worry about the intake too much as most tuners say the exhaust is where it needs help. I have also read that port matching the exhaust isn't the best idea on normally asperated motors as this reducies low rev scavaging which will hurt the bottom end. Here's a link on porting that I found, I don't know if it will help DIY Porting, I've never taken the time to read it but it may help.

 

Another point to keep in mind is that port injection doesn't need to mix air & fuel, the fuel is injected right into the intake port. Older cars with carbs use a wet manifold where fuel is introduced well before the port so it is important that it mixes before valve. A fuel injection car has much better atomization of the fuel and as it is innjected at the port I think a smoother intake would be fine a bit rougher around the intake port would work well.

 

Cheers, Dennis

[zarman 0]

Yes, port matching the exhaust is bad for reversion (the is the flow of exhaust gases back into the combustion chamber). You shouldn't gasket match the exhaust ports on the head. You need a bigger port on the exhaust manifold and a smaller port on the head. That "step" up helps prevent reversion. However, you should gasket match the exhaust manifold ports. If you want to go further, shave down the lip on the downpipe (the 2 ports that connect to the exhaust manifolds). If you look inside the downpipe you can see that they have welded on inside of the pipe to connect the flange to it. That little bump of welding is restrictive. Reweld on the outside of the flange and shave the inside weld down. The exhaust manifolds and downpipe should be as smooth as possible. This will increase flow. I have also ceramic coated the inside and outside of the exhaust manifolds and downpipe. The surface is smooth. The ceramic traps more heat and keeps it inside the pipe which increases the flow of gas out of the head.

[flusted 0]

or use a 4 branch 8)

[zarman 0]

No aftermarket header has proven to be better than stock. It's a total waste of money. Many people have come to an agreement on this. Just like aftermarket exhaust. There are almost no gains with them and most systems will loose power.

[stevemac 0]

No aftermarket header has proven to be better than stock. It's a total waste of money. Many people have come to an agreement on this. Just like aftermarket exhaust. There are almost no gains with them and most systems will loose power.

Unless the car is "force inducted" - as this type of engine requires very little back pressure, a well designed aftermarket manifold & exhaust will greatly improve torque & consequently bhp. :wink:

[zarman 0]

Theoretically yes. Any aftermarket system has the potential to be a better design. I'm not talking about theories but what is out there. And there isn't anything that has led me to believe is better while they cost a lot of money too.

[mrbeige 0]

Thanks guys.....8)

 

So, port match inlet manifolds, and polish to semi smooth on the inlet ports removing casting marks (240grit), and smooth exhaust ports well removing casting marks(1000grit)

 

Thats what I'll do then, and I'll try to get some photos up to!

 

Cheers