Here's a article by Carboy about it:

INTEGRA TYPE R

Honda's True "Tuner Car"

Original article written by Tamotsu Horikoshi, translated by Kaz Mori

Why does Honda choose to tune the R by hand?Japan's automobile makers are famous for using their experience and knowledge gained in the racing field and making use of it in their production lines for street cars. Well, the sad truth is that most of the time, such things are thrown around as hype -- most automobile makers will make a car "inspired" by racing, but they don't actually employ racing technology, and automobile makers never really "fully tune" their cars. However the Integra Type R is not so. Its racing spirit is not that of image, but is in its generous use of racing technology. The Type R is a car that comes fully tuned straight from the manufacturer.

Though the easiest way to increase horsepower is by increasing displacement or installing a turbo, Honda has made its reputation by sticking to its NA engines. The Integra's VTEC B18C type engine retained its stock displacement, but Honda increased its horsepower from 180 to 200. It's only *20* horses more, but those 20 horses were really tweaked out using Honda's formula 1 knowledge -- from an engine that was already getting 100 horsepower per liter. Fumiyasu Suga, Type R's assistant chief engineer, was kind enough to sit down with us. Currently, production line engines and engine parts are made by computer-guided NCR machines, and are of very high quality. However, Mr. Suga believes that in order to make a true race engine, some parts must be built/assembled by hand. In specific, the assembling of the engine, balancing parts, and porting and polishing need to be done by hand. Amazingly, all Type R engines are built this way.

Naturally, porting and polishing excessively won't yield good results -- it will only upset the balance between displacement and peak rpm's. Some basic physics explained... In any cylindrical enclosure/piping, the closer air is to the metal wall, it will flow slower, and the closer it is to the center of the cylinder, it will flow faster. As rpm's increase, slight variations in the enclosure will cause for serious air flow disturbances. Logically speaking, a straight, cylindrical port would prevent any problems of air-flow disturbance, but with street cars and their limited engine bay space, the port has to be bent. The stock port is built to within such precision that it can already withstand rpm's of up to 7,000 rpm without creating any unwanted air-flow disturbances, but once it reaches 8,500 rpm, the engine struggles to keep the air flowing smoothly. To augment this problem, two of the best mechanics at Honda were selected and assigned to manually port and polish the engine components. Though this limits production to 25 engines a day, this allows for the engine to reach 8,500 rpm, and respectively, 200 horsepower. For those of us who want to port and polish our GS-R engine parts, unfortunately, Honda would not disclose to us the details of this procedure.

Next, the valves and the valve springs needed to be upgraded in order to be able to withstand the high rpm's and the increased fuel injection. In order to increase air flow efficiency, the angle of the valve seat opening was tightened from 60 to 45 degrees. Also, bigger and lighter valves help to deliver more fuel. Instead of making the valve bigger, Honda engineers made the cone bigger and reduced the stem radius even further. In specific, the underside of the valve cone was shaved to its limit, and the valve shaft width was decreased from 5.5mm to 4.6mm -- making the valve 12% lighter than stock. Amazingly, the valves are made so precisely that their static balance differential is basically 0.0. We jokingly asked Mr. Suga what he would do if Honda's parts manufacturers sent over valves that had weight differences. His reply was quick and simple. "We would toss them out." Hm... very strict. Past 8,000 rpm, other valve-related problems occur. Such problems include surging, jumping, bouncing, etc... In order to prevent such problems, the valve springs are made by dual-bound springs. Furthermore, Honda used non-cylindrical, "flat" springs in order to keep the spring height near-stock, and still increase rebounding power.

The camshaft lift amount was changed for both intake and exhaust valves. The intake lift was increased from 10.6mm to 11.5mm, and the exhaust lift was increased from 9.4mm to 10.5mm. To compensate, the intake opening timing was increased from 10 to 15 degrees before piston apex, and closing timing was increased from 40 to 45 degrees after the piston reaching base. Likewise, the exhaust opening timing was increased from 40 to 45 degrees before the piston reaching base, and the closing timing was increased from 7 to 10 degrees after piston apex. By doing so, the valves remain open longer -- allowing for more air to enter the combustion chamber.

One of the keys to tuning a NA engine is the piston. In order to increase the compression ratio, aluminum, pent-roof-type pistons were used. In order to keep a good precision of mass, the aluminum pistons were forged. The piston ring was given more space to move around in, and to prevent piston "head" shake caused by the extra space, a molybdenum coating (also used in the NSX) was applied to lessen friction. The con rods are specially made for the Type R, and have a neat, little letter "R" molded onto it. The precision weight of these con rods are 2 levels above that of on-line production models. The weight differential between all four rods is so small that it is negligible, and all contacting surface areas are finished off with a race-car, mirror finish, and is connected to a fully balanced crankshaft. Furthermore, the assembly of the con rods and the crankshaft play an important role in attaining the high rpm's. In order to ensure perfect assembly, the engine is taken off-line and these parts are assembled by hand. A custom con rod micrometer gauge is used, and the stretching of the con rod bolt is taken into account for as the connections are tightened. This is something no machine can do, and this ensures that there aren't any unwanted vibrations at high rpm.

In order to prevent engine knocking at high rpm's, NGK's high-spark #7 platinums are used. Honda is so meticulous with its Type R production that it actually coats the spark plug tip with silicone so the spark plug doesn't collect any unwanted deposits during the stop-and-go of transportation. (Wow... does that help any?)

The intake port was simplified from a dual-port to a single-port -- in hopes of making high-speed air flow better. The stock exhaust piping that varied in width from 48.6mm~50.8mm was upgraded to a full piping with 57.2mm width all the way. Furthermore, the fully stainless-steel header a-pipe employs a 4-2-1 design, but with no sharp edges in the A-pipe when going from 2 to 1. This is a feature that is said to be impossible to do in mass-production.

In overview, over 60 engine-related parts were changed or entirely re-designed for the Type R. We asked Mr. Suga for any other advice on tuning the Type R any further. He replied, "I would prefer that people don't try to further tune the Type R. No, actually, they shouldn't try. Each upgraded part works in perfect harmony, and fiddling with the factory setting will only lead to a decrease in performance." It's probably safe to say that the Type R is a rare, "fully tuned" and "stock" automobile.