VW Head Porting and modifications

Its said that most the Horsepower gains are all in the head. There are several cylinder head modifications techniques targeted at different functions of the head that increase horsepower and torque. Very good reference atricle on Wikipedia http://en.wikipedia.org/wiki/Cylinder_head_porting The different functions fall into a few categories, each with its own modification techniques :

Air flow:

• Port and polish
• Bigger Valves
• Thin light weight valve stems
• Bigger cam

Increase Rotational capacity:

• Heavy Duty (HD) valve springs
• Titanium retainers

Increase combustion efficiently:

• Increase compression by Deck or milling, different pistons to reduce combustion chamber volume
• Index spark plugs
• Polishing combustion chamber
• Decrease piston to head clearance squish zone to .050" or bit less. (stock is .07" or more)

When the compression is increased combustion chamber turbulence increases and with increased turbulence quicker and more efficient combustion occurs. 

Picture of proper high performance valve Job and port and polish on a 87 GTI hydro 8v head, Installed on a Rabbit GTI with a fresh rebuilt 1.8 JH bock.

Work performed on this head:

• 39.5mm intake valve with thinner 7mm valve stems.

• High performance radiused seats

• Back cut valves

• Port and polish

• Polished combustion chamber 

Test Flow Data: 

 Higher Numbers indicate more restriction, and less flow.  Lower numbers indicate less restriction and more flow.