LS400 - recomendations for new exhaust

[lemonhead401]

I have a 1990 LS400 and I am looking to get a new exhaust system. What would guys recommend as far as pipe size, mufflers, cats and resonators in order to get a nice low rumble but still be practical. Right now I am thinking 2.5" to two flowmaster 50 series, any recommendations?

 

[stevechumo]

I have a 1990 LS400 and I am looking to get a new exhaust system. What would guys recommend as far as pipe size, mufflers, cats and resonators in order to get a nice low rumble but still be practical. Right now I am thinking 2.5" to two flowmaster 50 series, any recommendations?

The stock exhaust system only has 1.75" of inner diameter. So a custom 2.5" thin wall will be good. 2.25" is also ok. With an increase of .5", you'll have a lot of free flow. Too large of the pipes will make you lose low end hp. However, you'll gain it back at high end. Track cars use really large pipes because they don't have stop lights. You'll gain approximately 5 hp with 2.5" pipes. Someone already gained 10 hp with headers and complete exhaust system.