Interested in gaining a minimum of 27% more power from your factory micra engine for around $1500!? I was too - so I did and its not just hype, you really can gain atleast that much power from your factory micra for only $1500, read on...
It's all about flow, both in and out. An engine is a combustion machine that requires air and fuel to feed it and in return it gives you a pile of gasses shot out the exhaust (not forgetting the power which is the real output you want it to produce!). Factory cars are made to a compromise, Nissan considered many factors such as noise and vibration supression, fuel consumption, compact design and more when they designed your little micra in the big Nissan factory. Most people wouldn't be buying a little micra to blow away much larger vehicles and I guess they were happy with the micra's conservatively rated 55kw factory output.
But the truth is that the micra's CG13DE engine is quite easily capable of a much greater output than its factory 55kw rating. It can easily out perform engine's like that of Suzuki's Gti twin cam 1.3 which makes 74kw due to its high flowing exhaust and higher than normal lift cams. The factory engine is quiet, smooth and well - very restricted. It can't breath and it can't expel exhaust anywhere near as much as it would like to. Nissan gave it a very skinny air intake, a pea shooter of an exhaust and a very ordinary exhaust manifold. The good news is that replacing these items represents some of the best-value power-up mods you can do to a factory engine. The skinny intake and pea-shooter exhaust surround a rock-solid and well designed twin cam engine just waiting to be unleashed.
Get yourself a decent set of 4-2-1 extractors - either custom made or something pre-made like Hurricane. Hurricane make really tidy 4-2-1 extractors for the CG13DE in Australia. 4-2-1 Extractors produce much greater mid-range torque than traditional 4-1 designs and that's what street driving is all about - drivability, acceleration, torque-weight. Sure top end power is nice, but if you don't get it until 6000rpm, a lot of car's with less top-end power will blow you away if they have better mid-range torque. There are plenty of micra owners with 4-2-1 extractors that are very happy with the results.
Install a high flow catalytic convertor after the extractors and connect that to a 2" exhaust system (mandrel bent if you like, but not neccesary at all if you don't need the extra cost). I used a single back box muffler and removed the factory hotdog resonator. This offered even less back pressure, however the car wasn't exactly quiet - if you don't want your car too loud you may want to consider sticking with 2 mufflers, the performance loss shouldn't be too great.
4-2-1 extractors, high flow cat and a high flow 2" exhaust should not cost you too much more than $1000 - shop around, you may need to pay a little more.
That's your exhaust taken care of. The engine should be able to expel exhaust almost as quick as it needs to. You should utilise this and redesign your micra's air intake system. Luckily for micra enthusiasts, Nissan placed the air flow meter right inside the throttle body, letting you remove the entire factory air-duct and air box without harm to the car's reliability or smoothness. I experimented with a whole range of different intake designs and by far the best was using a 3" flexible PVC pipe hanging over the top of the engine and connecting to a pod filter tidily sitting behind the car's front grill - right in the path of cold, fast-flowing air. You will need some kind of 90 degree steel bend to connect the throttle body to your flexible new air duct, and I used some coat hanger wire to properly suspend the filter end of the flexible duct so that it didn't bang and move around. The entire intake including pod filter shouldn't cost any more than say $100. The piping is very cheap and a pod filter should be around $50. See Cold Air Intake Design for more information.
Now you have a micra with exceptionally greater flow capabilities that still thinks its a factory engine and thus, will provide the factory fuel pressure even while your car is receiving much more air and expelling more exhaust gas faster. Here's where the $1500 power up comes in. If you want to stick under $1500 you can do like I did and trick the factory fuel pressure regulator to thinking it needs to supply more fuel. This is done by kinking its sensor pipe, which makes it more restricted. Then it goes "hey I'm not giving out as much fuel as I thought, I better supply even more". Note, this is no easy do-it-yourself home job, you will need to get this done by a professional and capable dyno-tuning shop. This is what makes up the remainder of the $1500. I think it cost me about $230 of tuning to get my car dyno'd and the fuel pressure regulator kinked perfectly to get the mixtures spot on. So for me it was more like a total of $1300 for the power up and my car was outputting about 80kw - a massive increase over the factory output even when considering the possible variations in different dyno readings. The other option is to go full steam ahead and install a re-burnt ECU. Something like uni-chip, power-chip etc, there are a few of them around - these chips don't do much at all unless you do improve the intake and exhaust of your engine as described above.
Don't think "I think this fuel pressure trick is a bit dodgy, and I don't want to spend $600 on a new engine computer either" - because its not quite that simple. When you install extractors and a 2" exhaust on a micra, the car immediately runs lean because the engine computer hasn't provided enough fuel to correct the mixtures. This will most likely leave you with a destroyed catalytic convertor if you don't get the car dyno-tuned quick enough - cats are very sensitive, poor mixtures can ruin them, and at around $240 each its a nasty lesson to learn. So make sure you arrange to have your car tuned as soon after the extractors and exhaust are fitted as possible.
Additionally and importantly, I found that my new exhaust and extractors were responsible for not even half of the power increase I received. The car felt like it had marginally more torque and sounded great, however it was only once I had the fuel pressure increased and my custom air intake fitted that I really felt the benefits of this mega-value power up. Just by installing extractors and the exhaust you are putting in place the "potential" to make good power, but you aren't utilising it yet. Its a myth that just installing extractors by themselves will give you a great power up: you need to use them: i.e. add more fuel and more air.
In summary, the breakdown of the gains I received were:-
The difference was amazing, my car was now more than zippy but almost "fast". It would beat a quad cam V6 camry in 0-100 springs repeatedly, a mate's SSS Pulsar was also a victim (although only very slightly) in 0-100 sprints. For a tiny micra, this 80 or so kw I found myself with made the car so much fun, but very much a sleeper. Noone expects a micra to keep up that well and it really turned heads and beat quite a few non-sluggish vehicles (4litre EF falcon, V6 camry, VT commodores, SSS pulsar). Using the factory ECU your car will hit the rev limiter at around 6900rpm - you will know it when you hit it too, I hit it all the time and my engine was unstoppable and ultra-reliable.