I Looked Under Neath My Car From The Passenger Side And Tooked A Good Look At My Factory Exhaust. I Noticed Toward The End- Before The Y Connect That The Pipe Is Flat About 15"
Long.i Mean It Goes From Being Fully Round To Flattened In Half.i Think This Gives A Lot Of Back Pressure And It Is Killing Horsepower. Has Anyone Else Noticed That?

 

Yes, I noticed that too.

 

I've noticed it too. I can't wait to strip out the entire exhaust system and replace it with some decent pipe. Well, once it all becomes available of course. IMO it doesn't do much good bolt on a cat-back without also replacing everything from the cat to the headers as well.

 

has anyone w/ after market exhaust felt the difference in horsepower? Is it worth to spend the money.

 

I have the Greddy SPII catback and yes there seems to be a good improovement. I definitely feel an improvement in my butt dyno and everyone that has ridden in my car premods and aftermods has noticed the difference too. Also had my car dynoed on a dynojet at Autotech Motorsports and the techs think that the exhaust combined with the intake are giving me an extra 5-8hp to the wheels. No real way of knowing for sure though because I didn't have my car dynoed before the mods

 

What are the numbers with the mods?

 

Numbers!!??

 

I'll have to look it up when I get home - left the papers there. I was like 1 hp short of the Injen intake numbers with my Stillen. Here's the Injen dyno info on a 04 Max. Dynojet techs say to add 20-25% to numbers due to drivetrain and other misc. loss. The 265hp numbers that Nissan advertise are a dyno straight from the motor - no running apps. Also forgot to mention my dyno guys didn't run my MAX at redline during testing - they stopped at 6K rpm, not 6.5Krpms. I asked why and they said they didn't wanna risk damaging the motor . Probably going to have it retested someday. Will post my numbers vs the injen later tonight. Hope this helps you brothers.
Peace

http://www.injen.com/webpages/testin...nal/RD1945.jpg