PORT AND POLISH
One of the best ways to get extra ponies out of your motor is to port and polish your heads. Anyone who's been in the motor business for any length of time will tell you that one of the best ways to increase horse power in just about any engine is to (among other things) port & polish (P&P) the cylinder heads. How far you go with porting really depends what you are trying to accomplish with your motor and how you plan to drive it.
So what is porting and polishing?? Porting and Polishing (P&P) is the removing of material from the intake/exhaust ports as well as the combustion chambers for the reason of improving flow both in AND out of the combustion chambers. Stock heads are made from cast aluminum and if you look at the intake and exhaust ports, they are a very rough and have lots of sharp edges.
PORTING is when you carefully grind away this un-necessary material smoothing the flow paths for the intake and exhaust gasses. Every protruding little point in that path restricts the flow of air causing your engine to work harder both sucking in the fuel/air mixture and then pushing out spent exhaust gasses. By removing these large ridges and smoothing the flow path, you have enabled your engine to more efficiently ingest and expel air. If done correctly, this can translate into impressive HP gains.
POLISHING is. . . well just that. Polishing the surfaces of your combustion chambers and exhaust ports reduces the drag coefficient of those surfaces making it even easier to ingest and expel gasses.
I'm NOT going to get into specifics about "HOW-TO" P&P, or techniques which pertain to all out race motors and high HP off-road machines, because I don't have any experience with these. In fact, I'll be totally honest and say right now that this is only my second time carving up a set of heads. These few pages more or less just chronicle MY P&P job. I was kind of nervous since the heads used here were brand new and if I made a mistake I couldn't take them back and I could be out a couple hundred bucks!! Not a pleasant thought going into a project. ;-)
I guess now would be a good time to encourage all first timers of P&Ping to practice on an old junk head. You will soon learn how to, and more importantly, how NOT to manipulate the tools to get the results you want as well as learn each tools limitations. Believe me when I say that when a tool is turning @ 10,000+ RPMs, it only takes a split-second to do some SERIOUS DAMAGE to your new heads. So practice on a junk head or two, first!! Your local wrecking yard is FULL of good practice candidates cheap or even FREE.
Why did I want to P&P my heads, you ask?? Well my reasons go back several years ago... I used to have a dual Dellotro'd 1776cc in a Ghia several years ago that could hold it's own with most stock 6 cylinders of the day. In '93 I took it to the Northwest Bug-In to try my hand at bracket racing. While waiting to race, I was talking to another guy in the staging lanes about his engine and found out that he virtually had an identical engine to mine (identical displacement, cam, crank, ignition, flywheel, carbs, valve sizes etc, etc, etc.) with only one difference. The difference was that he had spent a couple hundred dollars for ported and polished heads. All I can say is that he SMOKED me in the 1/4 mile by over a second!!! That was my introduction to the value of porting and polishing. . . and it SUCKED!! :-)
Below are some photos of my stock "040" VW heads after disassembly. Note the rough casting in the intake and exhaust ports as well as the combustion chambers. These are pretty typical of stock heads.
For the INTAKE PORTS, since I'm going to only be running Weber 34mm ICTs, I'm not going to be removing much if any material from the center of the ports, but rather I will be match-porting the intake manifolds and smoothing the transition from the valve seat to the port.
My goal with the combustion chambers will be to generally smooth out the roughness of the casting. I'm not going to get into polishing too much since I don't think that will be necessary for my heads application.
The Exhaust ports will be the real challenge. Here, I plan to smooth the port for the full length. This may sound easy, but being that it makes a 90 deg. bend, it makes getting tools to the proper areas difficult at best. This will take a considerable amount of time for me. Again, I'm not going to get really into "polishing" but rather plan to use progressively finer emery cloth.
After all this work is complete, I will CC them to ensure all the combustion chambers are all the same size so I can ensure proper compression ratio calculation. Then take them in to be opened up for 90.5/92mm cylinders as well as treated to a 3 angle valve job