There are a few tricks that you can use to get better 1/4 mile times with an NA setup. I used to work for a company that raced the 350Z in the Speed Grand Am Cup series here in the US a few years ago, and we developed a lot of parts for the car that worked really well to increase overall performance.
intakes:
You can get VERY good gains from spacer kits such as Motordyne spacers www.motordyneengineering.com You will basically be able to gain power while also shifting the powerband to the left of the dyno, meaning more "useable" power. this is important for straight line performance.
Also, stay away from most intakes that are a cold air design that move the filter down into the fender and outside of the engine, these tend to heat soak quickly, and especially on hot days, will actually heat up worse than other designs of intakes.
I have used the Stillen cold air intake box on my Z for years now, but have tried a few different intakes to compare them all, and the airbox of the stillen really does help to reduce intake air temps. I'd highly recomend it.
Exhaust:
Anything nearly that you do the the exhaust of the car will help benefit performance, but you don't want too much high end power, you still want low end torque for 1/4 mile racing. I would recomend looking at the motordyne shockwave exhaust, or perhaps a light weight titanium setup from JIC. headers will help, but keep the cats stock or just use a high flow unit, straight pipes will shift the power output back into the high end.
Tranny:
upgrade the trans with a light weight clutch/flywheel this is the best possible thing you can do to the car for acceleration IMO.
Exedy has nice setups. ACT is fine as well and actually is very durable for constant launching etc... Nismo is not light enough, stay away from that flywheel....
Also, you can upgrade the final drive of your differential from the 3.5 that is stock in the 6mt to a 3.9 or a 4.1 ring and pinion (available out of many USA NISSAN oem vehicles). Lastly, upgrading to a 2-way differential will be killer as well, When I did this on my Z, I noticed a tremendous difference in how the car handles the launch, and how well the car stayed straight instead of fishtailing slightly off the line.
Spend more money not on power adders, but on the transmission, this is the key for any 1/4 racer with these cars.
If you have any questions, you can always just contact me, I've worked on these cars for 5 years now....
