The JDM Honda Integra changed generation in early 1993. The new model, coded DB for 4-door and DC for 3-door received a body revision and quad-projector headlights. The most significant change however was the engine upgrade, from the 1.6l B16A to a longer stroke 1.8l DOHC VTEC B18C with a new intake manifold. The B18C engine red-lines at 8000rpm and generates 180ps at 7600rpm. Although only 10ps higher than the current B16A, its bigger displacement and the special intake manifold gave much better low-end and mid-range making it more driveable over the B16A especially with kerb-weight being only moderately increased.
The new B18C intake manifold uses two sets of intake runners. The cut-away diagram of this intake manifold on the right shows how the runners are arranged. A marks the plenum (which the throttle body attaches to). B is where the intake runners attaches to the cylinder head. C is used to give readers a sense of perspective, it marks the fuel injectors. The top set of runners are curved around the lower set making it longer. The lower set of runners have butterfly valves built into them (marked by D). During low and mid-rpm operations, the valves are closed and only the top set of runners are feeding air into the cylinders. After 5800rpm, the butterfly valves open and air will now be fed into the cylinders via both sets of intake runners. This new intake system works in conjunction with VTEC, which now switches at 4400rpm, to optimize air-flow into the cylinders at all rpms making the power/torque curve of the B18C extremely wide and flat. Peak torque of the B18C is 17.8kgm at 6200rpm but torque output of the B18C is already near or at 17.0kgm all the way from approx 2500rpm right until the 8000rpm, a smaller than 5% spread for practically all operating rpms !!
The DC2 Integra in this article is a JDM used-import. Manufactured in 1993, it is around 6 years old when the owner decided to upgrade its overall performance last year in 1999. The approach he took was the interesting question of using only drop-in/straight-fit mods. Drop-in/straight-fit mods are designed to give instant power increase with minimal work needed. Often it takes no more than an hour or so visit to the proper speedshop for dismantling and fitting. Straight-fit mods are designed so that they utilize the original mounting points and will not require any sawing or hacking for fitting.
Technically drop-in mods exploits the head-room and compromises built into a stock engine. Head-room is typically safety factor intentionally built-in, eg running the engine slightly rich to compensate for varying atmospheric conditions. Compromises are usually built-in for legal requirements or for domestic desirability : emissions, noise, fuel consumption, driveability, and sometimes even manufacturing cost. Drop-in mods - if properly designed - can exploit these two factors, eg by fine-tuning the air-fuel ratio, for instant power-gains without too much engine work. The down-side is that for well-designed engines - and Honda's DOHC VTEC engines are prime examples - the head-room is smaller and the compromises are more performance oriented, so power gains will almost always be only moderate. Also exploiting the compromises means some sacrifices for the driver, eg much louder exhaust, or in some cases the ethical issue of increasing emissions.
Prior to his product purchases, the owner did extensive research in the internet as well as consulted with friends & speedshops. For the engine, he decided on the complete filter-cat/back-header-a/f regulator combination. He also wanted to properly tune the a/f regulator device so a dyno session was deemed necessary. This combination was an almost complete straight bolt-on except for one minor detail which we will cover later. Careful planning was done so that the main hardware; headers and cat-back were installed first. These were bought from one shop. The remainder items, the air-filter, a/f regulator and dyno-tuning were from another shop which also supplied all the rest of his upgrades.
The first item that went in were Tanabe headers. This is a stainless steel design optimized for power delivery. The headers were for the B18C Spec-R since Tanabe doesn't make headers for the regular B18C. The Tanabe G-Medallion cat-back exhaust system was installed the following day. However the B18C Spec-R uses a shorter cat so the headers extended longer. When used with the longer cat of the B18C, the cat-back exhaust was pushed further back causing some of the mounting brackets to hit the under-carriage. This was resolved by replacing the cat with a custom made straight-through pipe. Though the owner was concerned about the increased emissions, the was unfortunately his only immediate solution.
During the weekend, the final parts were installed. This comprises the installation of a HKS Super-Power-Flow system, ie the Super-Power-Flow air-filter plus a custom designed HKS extension pipe and mounting brackets. This kit places the filter in the optimum position. Then the HKS AFR a/f regulator was installed. The AFR will allow the air-fuel ratio to be optimized for maximum power delivery. However the only proper method to set it is still through a dyno tuning session. Fortunately the AFR came packaged with dyno-tuning included so this nicely allowed the whole mods package to be optimized for maximum power delivery.
The owner also wisely upgraded other crucial parts of the car. Eibach Sport-Line performance springs were installed to complement the GAB adjustable shocks that he already had. The Sport-Line drops the car by more than 2" and are tuned purely for performance so handling was improved by a large margin. Rather surprisingly however was the relatively good ride while the large amount of lowering did not cause a lot problems with undercarriage scraping.
The brake rotors were replaced by Powerslot slotted discs and the pads were later replaced with Endless brake pads, sourced from a third shop. The replacement of the pads were necessary because the upgrades allowed him to push the car so much harder that he experienced brake fade during spirited street driving. To improve the braking to the highest possible street level, the standard rubber-based brake hoses were replaced by steel-braided TEFLON hoses and HKS Super-DOT4 Racing brake fluid were used.
Earlier this year, a camber correction kit was installed for the front suspension because the owner didn't like the amount of camber change introduced by the Eibach Sport-Line's more than 2" drop (though apparently the absolute amount of deviation from factory recommended specs was really not a lot). Finally when the clutch was replaced, it was decided that the synchros in the gearbox were starting to fail so the transmission was replaced by a used-import unit from a specialist 'used-parts' shop. Rather fortunately for the owner, the replacement unit had the optional Honda viscous-coupling LSD fitted. The LSD made a significant improvement not only to handling but also to road-holding of the car. Dumping the clutch even on a wet road produced very little wheelspin which allowed the tyres to hook up very quickly enabling extremely rapid take-off. These final items completed the upgrade package to the car.
The owner did not do a benchmark dyno-test of his car prior to the project so we do not have a reference starting point for engine power.
However stock output of the B18C was rated at 180ps. With FWD, typical transmission loss was 11% to 15%. While 11% would be applicable to brand new engines/transmissions, a 15% loss would be more typical for a 1993 vintage engine/transmission. Using a 15% loss will give a power rating of around 150 - 153 ps at the wheels. This level would have been easily acheivable since the owner maintained his car very carefully. This is supported by a 148ps dyno-run of a fully stock 1996 DC2 and a listing of 149ps for a 1995 DC2 Integra SiR-G on the internet. Both these cars uses essentially the same engine. Therefore for this study, we should be able to safely use 148ps as the baseline power for this 1993 DC2.
The dyno-tune for the car actually started with a base of B18C with only the Tanabe header and exhaust system installed. This dyno'ed at 152.4ps at the wheels on a Dynojet. Peak power was generated around 7500 to 7600rpm, as per the spec, so this run also showed that the engine was in a good state of tune.
Next the HKS Super-Power-Flow air-filter system was installed. The stock air-filter box system was discarded since the HKS SPF is an open-element design. Addition of the SPF now allowed the engine to dyno at 155ps, again with essentially the same power curve profile. However a more important gain from the HKS Super-Power-Flow was the big increase in mid-range power, from 2500rpm to 6000rpm. Max power gain was close to 5ps at two points, below 4000rpm and again around 5000rpm. Thus the 2.5ps gain in peak power did not show the benefit of the open-element design of the HKS in full light - the gains in mid-range would have more impact to driveability than the peak power gain.
While the stock Honda ECU is more than capable of compensating for the increased air-flow from the filter-header-exhaust system, it is still tuned based on Japan's atmospheric conditions (the car being a JDM used-import). Thus the potential for fine-tuning the air-fuel ratio by the HKS AFR. This is the last item to be installed. Tuning of the AFR is relatively straight-forward but necessary, in order to realize the max power gains from mods. In this case, after properly setting it via a Dynoject tuning session, the AFR managed to up the power further to almost 158ps at the wheels, increasing the power by almost as much as what the Tanabe headers/cat-back system gave ! The AFR gave more increase at high rpms, from about 5500rpm till the 8000rpm red-line.
There are two basic methods to convert the 158ps at the wheels rating back to engine power. Using the 15% transmission loss will give us an engine flywheel rating of about 186ps, 6ps increase from stock. However, an alternate assessment would be to base it on our assumed stock wheels-power of 148ps. If we use this as the base, then 158ps will mean a 10ps increase on wheel power and will work backwards to about 192ps engine flywheel power. So we should be able to say that the whole engine tuning package gave it more than 10ps increase in engine flywheel power. It should also be noted that the Super-Power-Flow/AFR combination alone gave almost 6ps power increase to the wheels. The more than 10ps engine power increase represents an impressive increase which speaks well for the high spec nature of the B18C.
Equally important too is the balanced approach taken by the owner. When engine power is upgraded the other areas such as handling and braking should be upgraded in conjunction. After being able to go very fast, one should be able to stop very fast (and safe) as well ! It doesn't really matter which part is worked on first as long as one exercises sensibility during the whole implementation. This is the basic principle which the owner followed with this upgrade exercise.
September 2000