I currently have a axle back w/ resonator delete and I'm looking into getting a catless midpipe. Someone told me if I got that I'd need to re-tune my car? Something about the computer not reading the "power" exhaust so I wouldn't get max hp?

 

I would probably not be listening to "someone" any more.
If this was a motorcycle and you put a complete exhaust on...then yes, the computer would need reprogramming.
With your IS, even with an axle back and resonator delete, you won't need any tuning.

 

Even if I were to get the catless midpipe I wouldn't have to retune it? In conjunction with my axle back?

 

Nope. Reality is the car will only sound different...it will make little to no horsepower more. With a full exhaust and intake, you'd probably get 10hp more...maybe.

 

Thanks for your help!

 

BUT!

With an intake and exhaust + a tune you could make a bunch more horses. The RR-Tuning flash gets you like 30whp with just intake and exhaust.

 

^^^^ +1 That is absolutely correct...crack open that piggy bank Lveyolfe

 

Please keep in mind that the +30 wHP is with a full exhaust. With your current set-up, it's around +10 wHP.

 

i think the best choose it to research what bolt-ons will give you what horsepower gains. If the bolt-on part really gives you any gains, the manufacturers will want to promote that...usually with Dyno results to back their claims.
Personally, for an axle back, with or without the resonator delete, +10whp (wheel horsepower) is unrealistically optimistic.
Keeping in mind that horsepower is going to be lost through the drivetrain, so to get +10whp, the engine would roughly need to make +12hp...and the 1-2hp difference will be the driveline loss.
RWD vehicles have more driveline hp loss than FWD vehicles...and to get +12hp from an axle back exhaust just isn't going to happen.
If you got +2whp from it, that would be more realistic.
A +30hp gain is possible with a tune, full exhaust, and intake...but really the vast majority of the hp is coming from the tune.
Looking at cost, the tune is way cheaper than the exhaust and intake, and will give you more hp gain...but the car will sound the same.

But like i said in my opening sentence, do the research for yourself, definitely don't take my word for it...what do I know?!?!