You’ve seen guides, you’ve heard conjecture, you’re mate is probably saying he is working on one as we speak. While it is fun to watch and observe, we have decided to jump in head first and build one ourselves!

The forced induction four cylinder scene has exploded in recent times and I can say without little doubt that the SR20 is the golden child of this scene. Wait a minute, you are probably thinking, there are definitely a few motors out there that can more than hold a candle to it. The SR20 does not deserve this title for being the best designed engine with a clear racing focus, because it isn’t; it isn’t the most deserving because it features awesome technology and clever tuning to achieve its goal, because it doesn’t. It does win the numbers game though.

The sheer bulk of SR20’s floating around in wreck yards is why it wins. The fact that it comes in rear wheel drive configuration making it the logical choice for all old school 4 cylinder conversions is also why it wins. Placing you bum in an SR20 car is also cheaper than placing your wide load in an EJ20 or 4G63 powered car. The all alloy design is another reason to enjoy the SR20, because it does not hurt the balance and poise of a car once it has been retro-fitted.

Having a bore and stroke of 86mm x 86mm makes the SR20 a relatively responsive engine considering its size and this is yet another reason why it is so popular. Finally, the fact that the aftermarket has noticed the SR’s popularity has compounded the issue, with so many tried and tested bolt on parts that anyone with a stock SR is living in sin and may possibly even go to hell for his lack of modification.

There are literally hundreds of aftermarket companies that cater for the SR20 and the choices are endless. Now that the SR20 has reached almost mythical status, we at Hot 4s decided it would be of interest for our readers and ourselves to head down the SR20 modification path and build an engine with some heavy duty hard core parts and techniques. That means no dodgy pod filters, oversized blow off valves, or 20 inch exhausts, just hardcore, power producing modifications.

The name SR Brawler was picked because the car will be built with a clear circuit focus and will have the numbers to back it up when it comes to a tussle. But it will be no show pony or dyno Queen. This build will be extremely comprehensive and with a performance slant steeper the Mt Everest. Make no mistake with this, once the SR20 is finished, the 180SX will love to get down and dirty and have a good brawl at any given opportunity. It will hit the circuit and drag strip and will be popping up at cruises so people can check out the handy work.

Each issue we will be doing something to the engine or car and showing you exactly how it was done and why it was done. This means there will be a heap of tech coming up for all you people who love the get their hands dirty, literally as well as figuratively.

Part I: Porting the Head

Traveling with us closely through the engine journey will be Indy So from IS Motor Racing. Indy was featured in the Player Profile in Issue 140, and he will be waving his magic wand over the engine, top and bottom. Bringing his numerous years of experience to the table, this engine is sure to be a ball tearer.

Saying that porting the heads of any engine is an involved job is an understatement. So why go to all that trouble and expense to port the heads? Porting expands on the limitations of the intake and exhaust ports. If you reduce the restriction, you can get more air into the engine faster. The more air you get in, the more fuel you let in, making way more power. Seeing there will be a dirty big turbo cramming as much air into the cylinder head already, imagine what kind of returns could be seen with even a simple porting job.

A good port job will generally leave the floors of the port untouched and instead focus on the roof of the port. This is because most of the flow activity occurs near the roof of the port. But porting isn’t as simple as getting in there grinding out a whole heap of the alloy. It takes subtle and pre-determined shaping to fix any flow problems in the initial engineering from the factory.

A basic port job essentially involves smoothing any imperfections out. As you can imagine with mass produced cars, there would be a certain level of inaccuracy and imperfection in the ports. A basic port job’s main goal is to clean these up and ensure that the stock design is working to the best of its abilities. One thing to take note of is that a basic port job will not attempt to rectify any engineering design flaws from the factory.

When getting a little more involved in the head porting, often the aim will be to round out the floor hump because it is the transition from the valve seat to the floor of the port. Stock engines generally have a sharp edge at this point which causes a non-laminar (turbulent) flow separation. Another thing to be aware of is that big ports have low velocity at low rpm. When porting the head, the mechanic will aim to increase flow as much as possible while keeping the port volume as low as possible to maintain a high flow velocity, particularly at low rpm.

Old push rod dinosaur engines with iron heads will experience the biggest gain from a good port job. There is probably no need to say it, and I will be preaching to the converted, but this is because the older engines with less technology have fairly poor head ports stock from the factory. Modern Japanese engines will more times than not see as big gains as those old engines will, but it is still definitely worth a look into for your application.

Another area that you can reap a nice percentage of flow rewards in the head is in a valve job. The best valve jobs are called multi-angled valve jobs and these will have three or more distinct angles. The significant angles are the throat cut, which will be a 60 to 70 degree cut that is to mould the port wall to the seating cut. The seating cut is the surface that the valve will be seated on. This is a very important cut and for a multi-valve engine such as the SR20 it should be 0.040-0.060 in width. Finally there is a top cut that blends the seating cut to the combustion chamber. The point of this cut is to allow the air to flow smoothly around the valve, especially when the valve is starting to open or close.

Some porters will put in an extra back cut just above the seating cut on the valve itself. This will further help air get around it, particularly at low lift. A five angle port job adds two extra cuts to the mix to help make this transition even smoother. Having a porting job that is accurate and even for every port is very important. The quality of the porting is also obviously very important in order to achieve the high level of flow gains that we are looking for.

Indy So is no stranger to bolting together a tough engine, having sorter a few big power GTR’s and having worked on countless competition race cars. He is also no stranger to the grinder and his hot dinners to port jobs ratio is exceptional. He will be putting in the hard yards with a mammoth 100 hours of work going into the SR20 Brawler cylinder head ports. This will be more than your regular ‘clean-the-imperfections-out’ porting job as you can imagine, and the flow gains Indy is looking for will be quite significant.

Porting styles vary country to country and seeing Indy has worked on primarily Japanese race cars, and having worked in Japan extensively, he will be bringing a distinct Japanese flavour to the porting job. Stay tuned to see what marvelous detail Indy manages to conjure with the SR20 Brawler port job.

Engine Builder:
Indy So
IS Motor Racing
Unit 5, 5-7 Bermill St
Rockdale 2216
NSW Australia Ph: (02) 9599 9918 Fax: (02) 9599 9981
www.ismotorracing.com