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Originally Posted by Brucelee
Why do you believe that eliminating the second cat will release quite a bit of HP?
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Any restriction in the exhaust system of a NA car robbs HP. You may loose on the bottom end, but overall in the peak where HP matters to go fast, the best exhaust system is a totally open one.
This has been proven on the dyno over and over. Many all motor cars that race in that class benefit from funny looking headers that dump right behind the motor with no cat or exhaust system. They produce 15 more peak hp than the best exhaust system can. Mid range may be affected, but for racing it all about peak HP.
In thoery eliminating the secondary cats will eliminate restriction in the exhaust and give more hp around the HP curves peak (where ever that is on a boxster). Best woudl be to eliminate both, and have a straight through muffler for the most peak HP possible. That however would be really loud and probablly negatively effect mid range which is nice for the street, but would be better for top end power.
This is a popular race header for the B-Series honda motor. many have gone 300whp all motor with a header like this. They could never do it with a cat and exhaust system. They suffer from no mid range, but make crazy top end power.
Here is our All motor drag car,
It made 278whp and 199ft/lbs of torque at 9900rpm lol. Yeah great for racing but no good for daily driving obviously. See the header? The old school thinking was we needed back pressure, but this is simply not true ever no matter how you slice it. Back pressure is ALWASY bad under every circumstance on any motor ever built. This used to be the train of thought until header started to be tested on cars at the dyno and showed that the best NA exhaust system is just like a turbo car, which is no exhaust system, just a straight pipe with a nicely designed merge collector and nothin else.
All motor power is one of my specialties because coazing 278whp from 2.2L is not easy as you can imagine but 10,000rpm redline sure helps.
[edit] BTW, the car runs 10.74 @ 123mph incase your wondering