Stock Exhaust is good for about 425 RWHP is what I hear?

I have stock exhasut manifolds, stock pre-cat, hi-flo magnaflo cats, dual dynomax mufflers...

can I put on a whipple with this? or does it need opened up a little more?

how much RWHP can i get out of this exhaust setup before i "NEED" to go headers and just 2 hi flo cats?

key word here is need... I don't want to put anything on if its only gonna net me 5 HP, or even if its gonna cost me 5 HP... I like thsound of my exhasut now and its not loud unless im on it.. I cannot stand Loud droning in the cab...

I hear complete stock exhasut is good for 425RWHP? I am at 375 on a mustang dyno.. I want to add the whipple, but not sure If i want the whole exhasut... can I get away with 500RWHP on my exhasut setup without hurting the motor?

 

Yes I ran well over 500 hp with stock manifolds , stock cats and a JDM catback for over a year before I upgraded to headers and Whipple.

 

99 Lightning, stock manifolds, stock factory exhaust, stock block and heads, K/B blower. 465/545 on Ca 91 octane pump gas.

 

I think Mike @ madenterprise is running close to 600 RWHP with the stock manifolds!And stock cats I believe.

Phil