What is the best way to get some more horsepower out of an 03 Acura CLS6 minus adding a Supercharger and or an engine swap

 

headers

 

Headers is about it. Icebox will add a bit. Other than that, not much. Car doesn't respond the best to mods. Even with supercharger and headers, etc, it's not all that powerful.

 

The engine responds fine to mods. The issue is with the modders themselves or lack of aftermarket support which makes it harder to do.

If you like things easy with only off the shelf bolt on parts then this is not the car for you.

Do some searching and research then you wouldn't have to bombard the forum with all these questions that have already been answered 1 million times.

 

Nitrous

 

Search and you will find.

 

Disagree with you there Weezy... S/C with supporting mods puts down plenty of power for a 10+ year old car.

 

09 TL manifold is a start.

 

Problem is tuning. There's is any. At least not an easy low $ way.
Headers, & the manifold swap are your best bets.