A lot of questions are redundant so I figured I would put the general questions into it's own thread. If you just got your QR powerd car and are not sure where to start, reading this may help you out a bit. Feel free to add on or to merge this with a another thread. Hopefully, this will help people get a better idea of what is available for their car and help avoid repeat questions and threads.
Performance Modifications that will help your engine gain power (these are almost all bolt on modifications):
-Intake-You can do this with a short ram, cold air or remove the stock airbox silencers and install a high flow box filter such as a K&N. For the sake of it being where most people go, we will discuss the cold air intake (AKA CAI).
.....Makers of quality CAIs: Injen; AEM; NISMO; HotShot; Place Racing
.....Notes: It is important to buy a good CAI. Lesser models can and probably will bounce around eventually destroying your MAF. This in the long run will cost more money than buying a quality intake. The good names have excellent mounting designs, better filters and are better researched hence they are built better. When installing a CAI, it is a good idea to put weatherstripping on the CAI where metal will touch metal. This will prevent vibration and a god awful noise. NPM dynoed 3.2 WHP, and 2.3 WTQ with an AEM. Keep in mind a CAI does not add as much power as many people claim.
-Header-This is the biggest modification for our car. The 4-1 design header will give more top end power and the 4-2-1 design will give more low end and mid range power. Depending on the model, you can gain close to 20 WHP with a header.
.....Makers: AEBS (down pipe included with high flow cat); HotShot; NISMO; Stillen (down pipe included); DC Sports (down pipe included); OBX; SS Autochrome; Kamikaze (I wouldnt reccomend this one at all lol)
.....Notes: Installing a header will throw a CEL (check engine light). Various ways of fixing this exist, with the most common being the installation of a sim.
-Downpipe-If your header does not have a downpipe, then getting one will add a few horse power. A downpipe without a cat will most likely mean you are running catless. This has pros (more power and less expensive) and cons (loud as heck and not a goood sound, somewhat stinky, not emissions legal, and almost 100% chance of throwing a CEL)
.....Makers: Stillen; VRS; HP Autoworks
-Exhaust-A million and one makers make exhausts for our cars but they sound very different. Resonators will help make the sound deeper and quieter. Mandral bent piping is much better than crush...especially for our cars. Muffler selection will also play a big role in the sound.
.....Makers: VRS; Stromung; Greddy; APEXi; Magnaflow; Megan Racing; NISMO
-Camshafts-This is also a big modification for our car. If they are installed correctly, not only will you not lose any low end power but you will gain about 8-10 WHP and it will show on top end big tyme!
.....Makers: NISMO; JWT (slightly more aggressive than NISMO)
-SAFC2 (Super Air Fuel Controller, made by APEXi)-The gains from this are higher on the 02-03 than the 04+. To see real gains, dyno tuning is needed. This is not something anyone can do and if done incorrectly, you could seriously damage your engine. On the 02-03, a gain of 7-9 WHP on a bolted QR is very possible.
-Grounding kit-This mod seems to help smooth the idle and help the electrical system more than anything else.
.....Makers: NISMO; Stillen; Vytor; a million and one custom companies
-Crank Pulley-While the dyno has only shown about 2-3 WHP, an aftermarket crank pully will be lighter than your stock one by over 3 pounds. Since they are the same size as the OE pulley, no new belts are needed and ammenities such as A/C will not be compromised.
.....Makers: Unorthodox Racing; Impulse Mechanisms
-Nitrous Oxide-A 50-75 shot has been proven to be safe. Having knowledge of what you are doing is important. Using spark plugs that are not platinum and one step colder is a must. I will not go into further detail as much information already exists.
-Balancer Shaft Removal Kit (made by Jim Wolf Technology)-This modification will be good for 8 WHP and only costs about 90 bucks. NPM has shown that it takes time for the ECU to ajust so you will not get the full benefit immediately. Your car will also hold over 1 QT more of oil. The big downside of this mod is it will prettymuch kill your warranty and your car will have some increased vibration.
-Hondata intake gasket-This is a high temp insulating intake gasket which claims to lower the intake temp. Gains on Honda engines have been proven but no dyno sheets to my knowledge exist for the QR.
-Throttle Body Bypass-I do not reccomend this modification but the idea of it is to have cooler coolant. The only possible way to see even the slightest gain with this mod would be to do this and the Hondata, which after a few hours and about 70 bucks may not give you more than 1-2 WHP, if that. Also, keep in mind people have had problems with this mod. See here http://www.b15sentra.net/forums/showthread.php?t=63742
-ECU-An aftermarket ECU for our engine does not exist, and probably never will. If someone claims to have one, they are probably lying. A few companies are claiming to develop a reflash for our ECUs, but currently, nothing exists except a piggyback ECU from Stillen called the QR pro. Considering gains from an SAFC2 are higher and the SAFC is a few hundred dollars less expensive, the QR Pro is not really worth the money, at least in my opinion.
-Wheels-said in a nutshell, you dyno higher with smaller and lighter wheels. This is a fact. If you want to dyno higher, drop those big wheels.
.....Makers: Too many.
-Knock Sensor-Many people will ground and or relocate this in the 02-03 due to oversensative knock sensors. Mind you those years will knock if they are not fed premium gas. The knock sensor is their for a reason, to retard timing so you dont screw up an engine. Using caution with this mod is always a good idea.
-Spark Plugs-The OE plugs are platinum, switching to irridium or copper is not a bad idea at all considering they are more performance oriented and platinum is more oriented toward long life. By all means, avoid Bosch and lean towards Denso or NGK. For every 50-75 extra horsepower, make your plug one step colder.
-Nology Hot Wires-While claims are made about higher HP, TQ and even top speed, I have never seen any dyno sheets to back this up. The idea is that Hot Wires creates a more powerful spark. I truely dont understand the logic for our cars because of the existing way the plugs are set up. For 200 dollars, I would personally spend it on something else.
-Turbochargers-FI-R and PTI make a kit. This has been discussed extensively.
-Superchargers-No production models exist currently. Any past supercharger attempts were either failures or simply a way of attracting attention to a company. Revolution Autoworks claims to be in development of a supercharger that will be released around the summer of 2005.
Other related items that will help your performance indirectly:
-Motor Mount Inserts-While these will not help your dyno gain, they lessen wheel hop and help smoother shifts on a transmission. If you launch hard, your stock mounts may be torn. You can install these even if your stock mounts are already torn. The downside of these is vibration is significantly increased at low RPMs. This is easy to install and uninstall.
.....Makers: Energy Suspension; Power Tech Imports; Place Racing
-Short Shifter-Self explanatory.
.....Makers: NISMO; B&M
-Stainless Steel Clutch Cable
.....Makers: Crown and many others
-Clutch Fluid (Redline MT-90 and MTL mix, 1 bottle MT-90, 1 bottle MTL and about 1/2 bottle of MT-90 or to where the proper level should be). This has helped people shift smoother.
-Pre Cat failure, most common in the 02-03 models although it has occasionally affected the 04+...see https://www.nissanforums.com/showthread.php?t=41855
-Transmission shifting problems-If you are experiencing tranny problems, you are not alone. Many threads exist on this problem and what can be done.
-ECM recall and floormat recall-this is well discussed as well.
-Butterfly Valve Screws-Recently, owners have been having screws being literally sucked up into their engine, sometimes even destroying it because of butterfly valve screws becomming loose and eventually completely dislodged. No recall to my knowlege has been issued yet, but many owners have removed the intake manifold, removed the screws and reinstalled them with loctite to ensure that this will not affect them. See here http://forums.thevboard.com/viewtopic.php?t=29162
As I said, add any info you have or correct me if I am wrong on anything. Hope this helps clear up what is and isnt available for our car and happy modding!