Okay, let’s get some things out on the table first. I want to try and keep this post informational. The last one got carried away with questions. Questions should either be researched or posted so you can get addressed and people don’t miss informational posts thinking it is all questions and answers now. Thank you for understanding. One more note: When I reference the SI I mean the 5th Generation Hatchback not the 1999-2000 Coupe.
First off I want to provide some information as to why Single Overhead Cam (SOHC). Because every almost every Civic out there has or had one to begin with and not everyone has the money (or patience) to buy a Dual Overhead Cam (DOHC) changeover. Sure, you may end up spending just as much money in the long run however, you will get to do things every now and then instead of just saving money. So, let’s get started shall we?

Intake: First things first. Allow the engine to breath, after all engines are nothing but big air pumps. To start off, we look at the filter and piping. AEM Cold Air Intake’s (CAI) are nice, common and even California smog legal. The great thing about the CAI’s is that they don’t suck in hot air from the engine bay. RSX’s have been dynometer (dyno for short) proven at +20 whp with CAI as apposed to the 5-8 wheel horsepower (whp) with a “short ram” design. There have been dyno sheets that show a 3" piping makes great power, the Integra Type R (ITR) CAI will fit on Civics and is 3” unlike the EX/SI CAI, which is 2.5”.
Next inline for the intake is the throttle body. This is more of a throttle response upgrade than a horsepower upgrade. They simply allow the engine to get its full breath of air faster because of the larger opening. Almost all Honda throttle bodies will bolt onto the D series intake manifolds, and will fit to the intake manifold with a little port matching. The VTEC B series and B20 (CRV) throttle bodies are all 60mm in size. Except for the ITR, which is 62mm. The H22 is also a 60mm throttle body. While the Civic, gets a puny 56mm.
Don’t forget about changing from electronic fuel injection (EFI) to carburetors. There are a few ways to do this, and it is a novel on it’s own. However, it takes makes fueling and ignition easier because carbs have been around for such a long time that there is an insane amount of knowledge about them.
Next, we come to the intake manifold. NOTE: This will not work for the D17's. Honda had the bright idea to make it a returnless fuel system. For that you want the D16Y8, often referred to as the Type R manifold for the D series. It has short, fat runners and a large chamber to allow the air to distribute to each cylinder properly. Also, for the non-vtec guys out there, it has the common horizontal throttle body, which will allow you to use the larger CAI's.
Lastly, don’t forget that heat here is a performance killer. In warmer climates you can remove your throttle body and Idle Air Control Valve (IACV) “coolant” lines to keep the heated coolant from them. Also, you can invest in a Hondata intake manifold gasket. It is designed (and proven) to protect the intake manifold heat soak.

Exhaust: Lets start off with the exhaust manifold (header). There is no OEM exhaust manifold out there that doesn't need work. The HF (all Civics other than the EX and SI) exhaust manifold can be modified to add a turbo. Then you don’t need to spend the extra money on a turbo manifold. But, for those of you who want to stay naturally aspirated (or don't have the money for a turbo) a used aftermarket manifold for the EX is where you want to go. There are a lot of people out there who by the time they can swap have already put a header on there D series and now need to sell it. You will have to relocate your catalytic converter under the car to use this header configuration (which happens to be illegal in some states). There is two different designs for a header. The 4-2-1 (or Tri-Y) and the 4-1. It is said that the 4-1 costs you low end torque to give you more power up top. However, if you follow this link http://www.automotiveperformanceengi...om/header.html you will see that some 4-1's have more low and mid then the 4-2-1's. Header desgins are so good that this is more a preference thing IMO. One advantage of the 4-2-1's is that you can remove the lower half when you need to pull the oil pan. Instead of pulling the entire header.
Following the exhaust stream out, we come to the Catalytic converter. Unless yours is old, don't worry about it. For those of you who can afford to upgrade the cat, tests have shown that a 3" free flowing cat has almost flown as much air as a 3" test pipe. In fact some people were shocked at how well a free flowing cat works (and it's legal). Or go with the 10.00 test pipe from Home Depot (NOTE: Test pipes are not smog legal and you face a $3,000 fine). That's right, people have even made there own test pipes with minimal effort.
After the catalytic converter, it’s the “Cat-back”. Most people recommend using a 2.25" sized exhaust for the little 1.6L. And a lot of the aftermarket exhausts are 60mm
or 2.3 inches. I agree that they should be at least 60mm. But, you also want to make sure you get mandrel bent piping and strait through designs on both the resonator (if you have one) and the muffler. If you don't get the strait through designs, you will loose power, it's that simple. However, with straight through designs also comes noise. A good compromise has been the Apexi World Sport (WS) cat-back.
Transmission/Flywheel/Clutch. Remember this, the shorter the gears the better. It is easier for the engine to push/pull the car. MistaBone's link. http://home.cinci.rr.com/mistab0ne/tranny.html</A> The VTEC engines have always had the shortest gears and it is a bolt on part. The 96-00 trannies will bolt on a 92-95 Civic. Also consider a ZC tranny with a SI final drive. For you cable tranny guys, there are the Hasport kits that convert your Cable to a Hydro. And, SRR offers a 4.7 and a 4.9 final drive for the D series transmissions. See <A HREF="http://www.aj-racing.com" TARGET="_blank">http://www.aj-racing.com about those. HX/VX/CX owners, upgrading the tranny should be the first thing you do. HUGE difference.
Once you get the shorter geared tranny or already have one, a limited slip differential is the second biggest thing to have on a D series. The performance improvement is profound. I recommend Quaife because it has gears, not a clutch and it comes with an unlimited lifetime warranty.
A lighter flywheel is also a recommendation. Not only do the increase throttle response, they “free up” horsepower by decreasing rotational mass. The aftermarket offers weights varying from 8.5 lbs to 15. You can shave your existing flywheel to no less than 13 lbs. However, this is a controversial issue and if you search will discover how everyone feels about it and the dangers that can come with it.
The clutch. Man, talk about a weak POS, the stock one simply sucks. With even stock tires your clutch will start to give out while doing a warm up burn out at the strip. There is no doubt, you have to upgrade this part or suffer the sliding shift every time you drive hard.

Engine: Well, where the hell do we start? The motor mounts all have gaps in them. Filling them with window cement is a poor mans way to get some “solid” mounts. Okay, now that you got that sucker still, lets increase some power.
On a naturally aspirated engine there are # things you can do. 1. Up the compression. 2. Increase the displacement. And 3. Add more aggressive cams.
One way to up the compression is to mill the head. It is very important for you to not remove more than .30. If you do, you risk timing issues because the timing belt is going to be shortened and you will risk jumping teeth. You can also get thinner head gaskets, the Y8 is cheap and is the thinnest metal OEM head gasket that you can get.
Now that we have covered some inexpensive increases, lets go to pistons. The 1988-1989 D16A1 Engine came with some really high dome pistons. They cost around 30 dollars each from the Acura dealer as well, and will increase your compression ratio as follows:
d16a1 pistons (stock bore) in the following with a y8/z6 metal headgasket(no mill):
d16a6= 11.08: 1 compression
d16z6= 12.03: 1 compression
d16y8= 12.61: 1 compression

Obviously high compression and you 91 octane folks should consider a thicker headgasket.
Since you have decided to open that sucker and upgrade the pistons you should also consider upgrading your rods. Whether you decide to shot-peen your stock rods or upgrade to some LS rods, it’s up to you. Better yet, shot-peen the LS rods! When upgrading these, you should consider some ACL bearings and ARP rod bolts. Strength is always a comfort, right?
The head is what traps all of the power in any style engine. Be it naturally aspirated (N/A), nitrous injected, supercharged, turbocharged or all three. It has the valves that allow the air in and out of the combustion chamber and the cam (J) that opens and closes the valves. Porting is the process of removing material to make the holes for the valves larger to allow more air even if you use the stock cam. But, within the head you have all of these moving parts that rub against each other, even with oil there is friction. To reduce friction, you can get bronze valve guides, coated valves, and roller rockers. Roller rockers are cam followers that have wheels instead of a contact point. They greatly reduce friction and, the HX has them! Unfortunately, it only has a standard 2-lobe cam instead of a 3-lobe cam. Again another crazy topic that has been discussed a few times. Still with a custom cam, This “VTEC-E” head could theoretically produce more power than the VTEC head ever could. Since the rollers would allow for a cam lobe so aggressive that the regular followers would fail. Adjusting the cam with a cam gear can also change your power band to what best suits your driving, some drive easy, some drive hard every now and then, and some (like me) visit 7200 with every stop light and every shift. Well, almost.
Remember, an engine is an air pump, the more air it moves the stronger it is. And the best way to move air is to open the valves really high for a long time. Some good quality camshaft makers are Crower, Zex, Hondasaver, and Skunk2.

Cooling: Hey, if you don’t know this, heat kills. Keeping your engine cool is not just the radiators job though. The water pump, thermostat, your coolant/water mix, and even the radiator cap affect your ability to cool the engine. If you change one you affect the whole system. Radiator caps pressurize the coolant to up the boiling point (good) but, if you over-pressurize, the radiator could fail at the tanks.
There are two radiators that you can use for the Civic; there is the Del Sol, which is a dual core. Or it has two cooling cores, one in front of the other. And the other is the Integra. You have to make custom mounts but you will have your needed cooling for sure. Or, spend stupid amounts of money ($400) on an aftermarket radiator that is very efficient.

For you track guys, since antifreeze isn't allowed, there is a product called water wetter. You mix this and water, no coolant. It is discussed in the racing forum if you haven't been over there. DON'T use this on the street. Antifreeze does exactly that, when water freezes, it expands and will crack your block. You've been warned.

Fuel/Spark/ECU: Fuel isn’t as easy as we all would wish; a fuel pressure regulator (FPR) isn’t necessarily a good thing. Too much fuel can cost power, and forcing your injectors to flow more than what they were made for can hurt them as well. I personally believe that you should upgrade the system as a whole, injectors, fuel pump and regulator. And same with the DOHC ECU’s, they feed more fuel than needed as well. The best way to figure the needed fuel out is to “tune” on a dyno. Whether is be with a FPR or a fuel controller. Apexi makes a VAFC or VTEC Air Fuel Controller. Which allows you to adjust your fuel amounts in the RPM range. These are good but there is better, Hondata. Yup, Honda is in Hondata, and they are making great amounts of power on the SOHC’s. http://www.hondata.com
Supplying fuel is just one part though. You have to ignite it J. To do this, NGK’s, why because Honda sends there cars to the dealer with these inside. And then MSD, with only an intake or exhaust these will only add a little power however; they will get a cleaner burn and better mileage. With more air and fuel comes the need for a more powerful spark to burn the extra fuel. MSD has many different models out there to control the spark and increase it’s strength.
The stock Civic (other than 99-00SI) and Integra LS fuel pumps only flow 79lph and the SI, GSR, Type R flow 135lph.

Well, that just about sums it up for now; feel free to add any knowledge. However, if you have a question about something, please use the search or call attention to yourself and post a new thread. Thank you for reading. I will update this often to not only add pictures but to add things that I have learned or found out the hard way.

Oh one more thing, the SOHC’s weight in roughly 75lbs less than the DOHC’s. That should speak a lot for you tar removing junkies.

Originally posted by ComatoseSedan
if it was done with a single cam, it MOST DEFFINATLEY can be done on a dual cam...