Toyota 20R/21R/22R Head Modifications
Head work is a true art, there is just no way around it. You can know everything there is to know about your head but without the skills and experience you or your machinist will never bring out the full potential of these, or any other heads. It is generally agreed that do it yourselfer head porting is a bad idea. Unless you really know what you are doing you should take the head to an experienced, reputable machinist.
There are surprisingly few things that can be done to the head itself. There is porting, polishing, milling (sometimes referred to as shaving), and CCing. Then there are valvetrain upgrades. More aggressive camshaft, bigger valves, stronger valve springs, better valve guides and better valve seals. You must work the whole head as a process and know what you want. If you enhance one aspect then all others must be enhanced as well or you could actually loose power.
There is absolutely NOTHING in this or any other article of this subject that isn't debated. You will find people who believe the exact opposite of everything I write. So you the reader are kind of screwed, it is up to you to figure out which one of us is more accurate/correct. Do remember that everything varies from engine to engine.
The Valve Train
Lets start off with the valve train upgrades. First thing first, if you have a 20R pull out your steel rocker arms, throw them on the ground and jump on them several times for good measure. These were a mistake by Toyota, which they realized and changed in the later 22R models. These steel rockers were replaced with aluminum rockers with hardened pads. These aluminum rocker arms are a huge improvement over the steel because they are lighter and the last longer. The steel ones also have been reported to have a habit of ruining a camshaft. I recommend genuine Toyota rocker arms all the way. You can get them from your local Toyota dealership or Cyberspace Automotive Performance.
That taken care of you will want bigger valves. Oversize valves are a great improvement over the stock size valves.
Stock 20R intake/exhaust: 43.0mm/35.0mm
Stock 22R intake/exhaust: 44.5mm/36.5mm
But don't just go out and buy the biggest valves you can find. You have to consider what you are going to be using the engine for. As with everything a gear head has to deal with, it is a trade off. The bigger the valve the less velocity the air will have, the smaller the valve will have more air velocity, but the valve itself proves to be a restriction. You make up for velocity loss by running the engine faster. If you go and buy huge valves you wont experience the top gains until you hit ~6,000RPM. For most daily drivers an increase of around 1mm will be perfect. If you actually plan to hit and use the higher RPM levels (5,000+) you may want more. There are too many brands to list. If I had to pick one I would go with Ferrea because they best suit my needs and they have an excellent reputation. You can get Ferrea valves from Cyberspace Automotive Performance
No matter what valve set you get you will want stainless steel (or better). Stainless steel is stronger and helps prevent carbon buildups. You will also need new valve seats. The best valve guides I have found are Manganese Bronze. These are much better than the stock valve guides in that they are stronger and will take a high lift cam. To complement these Manganese Bronze valve guides you should get Viton valve seals. These are more durable than standard seals, and that is all you should need to know. A good source for Manganese Bronze valve guides and Viton oil seals is LC Engineering, though they are over priced.
Stronger valve springs help to control the valves on high lift or high RPM setups. You can get dual valve springs prefashioned or you can get aftermarket inner springs to complement the standard outer springs. LC Engineering makes great dual valve springs. Isky makes great inner springs. The LC Engineering setup is softer than the Isky setup. You probably don't want Isky's unless you have an extreme camshaft. You can get Isky inner springs and standard outer springs from Cyberspace Automotive Performance.
You will want a more aggressive camshaft. This is an entire article in itself. At this point I will just tell you that you need a better grind to get the potential out of the engine. For a mildly upgraded head/valvetrain I would recommend the TRD stage 1 camshaft. You can get these from TRD.
Like I said earlier, you should generally leave the head work to an expert. But unfortunately you have to know what you want, and even more challenging you have to figure out WHO is an expert. Never trust a machinist you don't know and don't have any experience with. It is up to you to interrogate them from knowledge. Remember EVERY machinist will tell you he is an expert, and chances are after reading this article you will know more than three quarters of the 'experts' out there.
Shop around, go to every machinist you can find, bring your head (the one on you shoulders and the one from you engine), and ask questions, lots of questions. It is your money remember. A poor machinist will likely do more harm than good. Bring your head in and ask them what experience they have with this engine and what they would do to it, also ask about price. Be wary of too cheap a price. I know that is important but it seems to be a regular truth that you get what you pay for. Though this is not always true. The machinist should be willing to work with you and want to know what the engine is going to do. Once you have told him (or the rare her) of the engines future job they should be able to list a few personal tricks and name off everything I list below.
The first and most obvious thing to take care of is porting. Porting is opening up the ports, both intake and exhaust, to allow better air flow. You do not want to simply carve away everything in the port, that would ruin the head. You want to think like the air. There should be a smooth transition in every aspect. As close to strait in and strait out as it can get. No ridges or lumps where vortexes can occur, vortexes will make it more difficult for the air to enter and leave the combustion chamber. You do not want a mega porting job on a daily driver. As with valves, bigger will reduce air velocity, and you have to make up for that with higher RPM. Most daily drivers want a power band from 1,500RPM to around 4,000RPM. The more aggressive the porting and valves the higher up the power band will go. This is good if you race the car regularly. Super heavy porting with giant valves will give you greater peak power, at the higher RPM level. Lets say around 7,500RPM. This is great for an autocrosser, because shifting is bad. If your peak power is at 7,500RPM then you will probably only have to shift once to get to 60MPH (depending on your gearing). Now the problem with this setup is that you have no power until ~2,500RPM. City driving would be nothing less than a bitch! You have to start the clutch out at 2,500RPM every time you take off. That will greatly reduce the life of the clutch.
Another part of porting is port matching. Port matching is simply matching the size and shape of the manifold and head ports. Usually you match everything to the gasket, hence the term 'gasket matching'. You want the intake manifold to be perfectly matched so there is no ridge at all. It should be a perfect transition from manifold to head. The exhaust manifold is a little different. It is generally accepted that you want a little ridge, that is the exhaust port on the manifold flange should be a tiny bit bigger than the port on the head. It is believed that this will help to reduce the pressure wave that occurs when the exhaust valve closes. Yet another example of 'thinking like the air'. This ridge should be as close to the exact shape as the manifold port as it can get.
A fairly misunderstood process is CCing. This is measuring the exact volume of each combustion chamber in cubic centimeters (CCs). Then the idea is to make every combustion chamber the exact same size. Thus evening out the compression in all four cylinders. This is done by removing tiny amounts of material from each combustion chamber until it reads the same volume as the largest combustion chamber. When you remove any material from a combustion chamber there will be a loss in compression and therefore power. The idea is to take as little as possible. This is a very optional step. Many people skip this one.
Polishing is just that, polishing the metal to a mirror (like) finish. The combustion chamber and exhaust ports should be polished as smooth and perfect as possible. This prevents carbon buildups and allows better air flow. It is generally agreed that the intake side should not be polished. The rough grain is believed to aid is smooth regular air flow.
Milling is trimming the seating surfaces, like the head-to-block surface or the manifold surfaces. Milling, has two uses. One is it returns the surfaces to a perfectly flat plane so that the gaskets will seat properly. The other is that if you mill the bottom of the head, where it meets the block, a reduction in combustion chamber volume will occur. This is usually called shaving. This reduction will increase compression. A very tiny bit. If you want higher compression this is not the way to get it, go out and buy a set of higher compression pistons. You don't want to shave too much because when the next rebuild comes by and the head has warped some, there won't be enough material to mill it true again. The head then becomes a very expensive paper weight. Something to consider is that any time you shave the head there will be a decrease in distance from the crankshaft to the camshaft. This will alter the cam timing, in a bad way. In order to return the cam timing to normal (or better than normal) you will need an adjustable camshaft sprocket. If you want a good adjustable camshaft sprocket I would recommend OldMage.