For a 2.5 - a catless header is your best bolt on power adder. This is basically the equivalent to the Y-pipe in the 3.5 as far as "bang for the buck" bolt on performance. The Bully Dog Tuner can then be used to tune your ECU to optimize the performance gain found in any bolt ons you add. You will likely sacrifice some fuel economy in return using the Tuner, however. On the other hand, the BDT gives you the option to return to stock in the event you want to sip less gas.
sc20 wrote:How is 91 octane bad?? My car seems to run more quite. I do know that sometimes cars "don't like it" when you go from running higher octane for a while, and then switching back to lower octane.
detonation due to octane level
s*** like that.
also the part about how theres no real gain and wasting the extra couple bucks on something you dont even need..... the "quietness, smoothness, added performance" most of it is in your head...
Bottom line, end of story, especially in Nissan engines, it is better to run higher octane gas. It will NOT hurt your engine - it is better for it. There is a reason Nissan recommends it. I ran 93 octane in my Sentra Spec V (the same 2.5 used in the Altima Coupe 2.5) and I didn't run into any of the problems that were common in that car (precat deterioration due to post-detonation issues inside the precat area, leading to pieces of ceramic being sucked back into the engine and causing the engine to fail).
High octane gas will not give you a horsepower gain. It will give you an efficiency and a LONGEVITY gain for your engine. Keep it running smoother, longer, with less wear and tear on internal components. Not saying you HAVE to run premium fuel (unless you have a requirement in your vehicle, and the older 3.5s DO require premium), but it is never a bad idea to run it. You will eventually make up the extra cost in the long run saving on potential engine repairs further down the road - your vehicle will operate more efficiently and therefore last longer as long as all your maintenance practices are proper and in place consistently.