When your left the showroom or forecourt, engineers and mechanics had set it up perfectly for the average driver who wanted an efficient, reliable and economical car. There are however, a few of us who want a little more from our cars and see them as a platform for creating something unique and special by modifications. This can be as simple or as complicated as your wallet can stand, but there are a few rules that need to be followed first. Before starting any sort of modifications you need to ensure that your car is mechanically sound. There is little point in fitting a carbon fibre wide arch body kit to a rusted chassis, or tuning an engine that is about to die.
If you choose to work on your own (or anybody else's) car please take care and work safely using good common sense. If something seems unsafe, it probably is, so don't do it.
The scope of this document is aimed at 'bolt-on' modifications that can be easily be done by a mechanically minded individual without specialised tools. This is by no means a complete guide on Honda modifications and I am by no means responsible for information that may be incorrect or inconsistent. This information is provided for reference only!
Basic engine tuning is all about 3 simple concepts:
- Getting as much clean, cold air into the cylinders as possible. - Induction
- Burning the fuel at the optimum time, as effectively as possible. - Ignition Timing
- Removing exhaust from the cylinder as efficiently as possible. - Exhaust
Engine power is directly related to the rate of incoming and outgoing airflow, and many factory intake systems are highly restrictive, thus limiting engine horsepower and torque. Replacing the intake system is one of the most common and easiest upgrades that can be done to a stock engine. It consists of replacing the factory air box to an aftermarket filter and tubing. There is a huge market for air filters, each with different designs and as always they have their good points and bad points. They range from a replacement panel filter that fits in the factory air box, to short ram and cold air intakes, each type has different styles and materials for the filter.
The panel filter can be fitted in only a few minutes. They are a direct replacement for the factory filter and can be made of paper, mesh or foam.
They still suffer from the restrictive piping and boxes that the factory setup uses.
The cone filter is probably the most popular filter, with manufacturers such as K&N and AEM using them in their induction kits. They have a large surface area allowing more air to be sucked into the engine.
Pictured here is a blue cotton gauze filter.
The Mushroom filter was designed by HKS.
The unique design of the Super Mega Flow combats the propensity of airflow to move towards surface areas which generate turbulence and reduces airflow capacity, typically a weak point of box-type designs. HKS patented super-funnel design, with its vacuum-inducing inner lip, draws air from the filters outer edge and directs air away from inlet throat surface areas.HKS
Short Ram Intake places a cone or mushroom filter at the end of a short tube inside the engine bay. This can slightly boost performance levels in a vehicle by increasing air volume intake, at the expense of increased intake noise. The high temperature of air near the engine can reduce performance in some cases, but this is often made up for by the increased volume of air.
Cold Air Intakes are similar to short ram, but they use longer pipes to relocate the intake outside of the engine bay (usually in the front bumper or wing. They benefit from colder air, but due to the length of the piping, throttle response is lessened.
After the intake, the next bottleneck is the throttle body. A larger throttle body will help increase the volume of air travelling to the engine. But keep in mind, bigger may be better, but biggest is not the best. Too large of a throttle body and you will loose the velocity of the intake charge and the throttle may be over sensitive. A good size for most naturally aspirated B16's is 62mm. 65mm is good if the IM is modified and some head work. 70mm is for all out raging fun. It is highly recommended to port-match the intake plenum to the TB for excellent results.
After the throttle body, the air is moved through the intake manifold. This is where the air and fuel are delivered to the cylinders. Air flows like water, to the path of least resistance. Straight, rounded passageways allow for a faster flow of air. A square shape passageway will allow a greater amount of air to flow. But if either of those passageways has to have a bend in it, the air flow begins to tumble, creating turbulence and causing restriction. The manifold can be Extrude-Honed, which is a process of forcing a heavy liquid with a cutting compound in it. The liquid will form passageways to allow ideal flowing conditions without removing too much material. An intake manifold from an Integra Type R bolts directly up to a B16 and offers a mild polish. There are a handful of other companies out there that make manifolds, basically what you are looking for are a larger plenum and straight runners.
Once we have air and fuel in the cylinder, it needs to be ignited slightly before the point of maximum compression to allow a small time for the flame front of the burning fuel to expand throughout the mixture, so that maximum pressure occurs at the optimum point. If the fuel is ignited too early the piston cannot effectively transfer the load to the crankshaft or is forced to act in opposition to the motion of the crankshaft, causing a massive shock to the bottom end. This can be heard as a metallic 'pinging' sound known as detonation (or pinking or pinging). Changes to the ignition timing should be left to qualified professionals with proper equipment.
We can, however, help provide the engine with a good strong spark by using quality high tension leads (HT) and using quality spark plugs. There is much controversy as to how much an improvement aftermarket HT leads, such as Nology Hotwires, provide over stock, especially on Honda engines, but one thing that is clear though is that old, worn leads will not be as effective as new leads. They should be replaced along with spark plugs in accordance with the manufacturer specifications.
Another area we can look at is electrical earth. While this will not have a net gain on horsepower, it will help to smooth out the running of the engine by providing a more stable, high-quality electrical earth. Factory earth leads are usually a very stiff iron alloy, usually cheap and will corrode over time. There are many grounding kits available which use an oxygen-free gold cable, similar to that used in high definition audio equipment, which provide very good earthing. Alternatively, you can use 8 gauge speaker wire and make your own.
After combustion, the engine needs to get rid of the burnt waste, or exhaust, as efficiently as possible. This is one of the biggest bottlenecks on engines and it is also the most competitive area in the market, with anyone who is anyone making different products. There are different four components in the exhaust system which can be looked at.
The most popular exhaust modification is to change the muffler or an 'axle back' system. This has two results: sound and looks. The muffler is the main contributor to the tone of the exhaust, from quiet to raspy, racy to all out loud! They also serve as a visual mod - nobody likes a pea shooter when you can have a 5" exhaust tip. Fitting axle-back systems generally will not have any affect on performance.
The next progression from here is from the 'cat-back' which replaces the exhaust piping from the catalyst at the front of the car, underneath to the muffler. This is where you can free up some power that is lost on the restrictive stock system. Remember the stock system is designed to be efficient, reliable, economical and most importantly quiet.
The third area is the exhaust manifold. This is the collection of pipes that collect the exhaust from each cylinder and combine it into one pipe. There are two ways of doing this: 4-2-1 and 4-1. Again each has a positive and negative.
4-2-1 manifolds collect exhaust from the 4 cylinders, and pair them together forming 2 pipes which then merge into 1 pipe.
This setup is better for low to mid range power, but not so good for top end.
The 4-1 setup collects exhaust from the 4 cylinders and combines them all together at once.
This results in a higher top end power band, but sacrifices low end.
The final component is the catalyst converter. This device is used to clean up the emissions from the engine, but they do sacrifice a lot of power. When the car was built by the manufacture, they were very conscious of the cost of production, so they fit cheap, reliable parts that do the job. Typically they have around 500-600 cells per square inch. These parts can be replaced with 'high flow' catalysts which can cost up to five times more than the factory unit. They will provide less restriction as they have 100-200 cells per square inch (freeing up horsepower) whilst still offering the same levels of emissions cleaning.
And it does not end there! Although not in the scope of this page, there are many more upgrades that can be done to your engine - head work, cams, pistons, stroker kits, turbos, superchargers.. the list is endless.
That is by no means a conclusive list of modifications, I have only covered the most basic intake/manifold/exhaust combinations. There are a literally hundreds of different components to choose from within this and there are plenty of reviews on the internet for each product.