So what exactly is the objective? Make more noise?
I'm not being critical, just trying to understand. I hope everyone understands that removing resos WILL NOT INCREASE POWER, but will increase boominess in the exhaust. The cat back part of our system is close to perfect from the factory and provides very little restriction. It's good for flow demands up to close to 350 rwhp. Each to his own, and if loud or boomy is what you want, go for it. The real purpose of those reso is to do what their name says: to remove resonations (specific frequency boominess) in the exhaust system occurring at certain engine rpms.
The problem is that the stock cat back system produces a very strong resonance and boominess at around 2500 rpm without the resos. The system is deliberately tuned to eliminate the boominess by using two tuned straight through resonators which tune out the boominess without decreasing power
I wanted more power, so I have deleted both the restrictive stock DP and highly restricive cats, replacing them with 3 inch DP and RP. Serious increase in power - dropped a whole second between 60-100 mph, but the stock resos would no longer handle the huge increase in resonation boominess at 2500 rpm, especially when decelerating. It seems the presence and effect of the cats was taken into account by Mazdaspeed engineers in selecting the frequencies those resos address.
This was amusing for a few days, but eventually was causing big headaches during my daily drive to and from work. So I actually ADDED A THIRD RESO where the second cat used to be and where the RP is now located. I had to cut the RP a couple inches inside each slange and weld the new Vibrant Ultraquiet reso inline between the two flanges. It's a 3 inch straight through design.
Presto: Power increase is unaffected and resonation cured. Exhaust is back to stock sound level, the booming and my headaches are now tamed, and I still have that big HP increase.
I've learned this from prior experience with turbo Saabs and turbo Volvos I have owned in the past when going for power gains with bigger and catless DP and RP combos. Of course, I'm in a state which does not have emission testing.
Sorry if I stepped on the intent of the thread. I'm just not sure what the objective of removing the resos would be. If it is to go for a certain sound yu are looking for and like, I understand. If it is to try to gain horsepower, I respectfully say it ain't gonna happen by removing resos.