Eliminate Secondary Cats!!!!

[986silverbullet]

Hey hows it going

i was wondering if i should Take off my Secondary Cats from what i hear there just there to quiet down the exhaust and if i do so my CE light shouldnt come on and it should Add quite a bit more HP

If any one has Eliminated there 2nd Cats Please Reply

Thanks......

[986Jim]

Second cats are not to decrease the noise level, they are to meet a specific emissions quota. You can eliminate them and still pass emissions and pick up some extra hp too.

Many new cars now have a precat thats right off the exhaust manifold and a secondary (normal) cat thats under the car part way like we are used it. Having the cat right off the manifold allows it to heat up faster and start to clean up the emissions more quickly from a cold start. It's all part of reaching ULEV standards. Not sure if the box is ULEV but with 2 cats I'll bet it close.

The current generation WRX has 222hp and meats ULEV with a precat and main cat.

[986silverbullet]

so what your saying is that It might not be able to Pass SMOG


and another question is have you ever found out more INFO about a RING AND PINION or any kinda gears? im not saying to LOOK just askin if you came across anything since the last post!!!

[Brucelee]

Originally Posted by 986silverbullet

Hey hows it going

i was wondering if i should Take off my Secondary Cats from what i hear there just there to quiet down the exhaust and if i do so my CE light shouldnt come on and it should Add quite a bit more HP

If any one has Eliminated there 2nd Cats Please Reply

Thanks......

Why do you believe that eliminating the second cat will release quite a bit of HP?

[986Jim]

Originally Posted by Brucelee

Why do you believe that eliminating the second cat will release quite a bit of HP?

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

[eslai]

Originally Posted by 986Jim

Any restriction in the exhaust system of a NA car robbs HP....

I highly doubt Bruce was looking for Backpressure 101, I think he was just questioning why anyone would think that removing the secondary cats would make a significant amount of power.

[986Jim]

Originally Posted by eslai

I highly doubt Bruce was looking for Backpressure 101, I think he was just questioning why anyone would think that removing the secondary cats would make a significant amount of power.

8hp is a significant amount of power. Because you get 8hp from headers and 8hp from exhaust and 8hp from intake etc.. So all the sudden you made say 20hp from the extras.

The thing is, you can feel that HP increase even when it's small, you will also have increased throttle response because the engine is now more efficient pumping air in and out with less restriction.

It's not Backpressure 101, however people seem to lose sight that any gain is a gain. When building a race car weight is a huge problem. We do everything to take weight out, and more than you think. Eventually we get into ounces of weight saved. We cut metal from the trunk and doors just to save 10 ounces of weight. Anything and everything you can do. Eventually all those ounces you pull add up to 10 lbs of extra weight you pulled, makeing the car better at it's job. So each HP even if it's only 1 is a increase, you just add it to the other small increase you work to get and they all add up.

Race a car for real with a track only car and you will understand what I'm talking about. Guys use different weight oil for different temperatures because a 0-20 will give 6 extra hp over a 10-30 if it's not very hot out.

[eslai]

I have raced many cars on real tracks and yes, what you say is true--for a race car.

On the street, simply removing the secondary cats is not going to make a car significantly faster. In my experience any increase under ten horsepower in a car that weighs a ton-and-a-half is not significant even to the butt dyno.

Now, if you replace the entire exhaust system and tune the ECU, sure you can get some noticeable gains, but that's not what we're talking about here and even so, I can't believe you're doing Mod Math.

Anyone chasing single-digit HP increases on a street car should really just learn how to drive better. You can't even accurately measure such small gains on a dyno--it's all within statistical error.

[spine911]

Originally Posted by 986silverbullet

Hey hows it going

i was wondering if i should Take off my Secondary Cats from what i hear there just there to quiet down the exhaust and if i do so my CE light shouldnt come on and it should Add quite a bit more HP

If any one has Eliminated there 2nd Cats Please Reply

Thanks......

What you are referring to is the Resonator, not a Cat. FYI, the 986 doesnt have the resonator. Typically, the Resonator is located in BETWEEN the Cat. converter and the Muffler...Yes, this is a simple mod. you can do this with other Euro cars(MB,BMW,etc...) that can pretty much increase the note of a stock exhaust system. There is NO HP gains associated with this mod. I already did this mod. on my 02 BMW M5 and 01 MB BRABUS E-Class. This is a cheap way to increase the exhaust note without spending too much $$$. The CE light wont get trigerred since the resonator is AFTER the Cat. converter, and it is still smog compliant.

[986Jim]

The 00-04 has two cats. One right off the manifold and one farther down the pipe.


http://www.pwr-tech.com/parts_exhaust.html They claim 8hp increase. It's technically against the law to remove a properly working cat converter from your car for any reason, so they say for off road use only. It has been said that you will pass emissions testing however you may not pass visual if you have one.

This is the bypass pipe he is refering to, I don't think those are resonators. The pre-cat is right off the manifold like this:


Thanks to 986online our great sponsor for that pic...

He wants to pull off the secondary cat with the pipe in the first picture.

[nastyboxster]

I did the Borla muffler and then the 2nd Cat bypass. It was pretty loud with the Borla muffler and even louder with then 2nd cat bypass. Definitely added punch especially at higher rpm's. I just dynoed the car and yelled 247.6rwhp with a few other mods (no chip yet) . You can check out my dyno here http://986forum.com/forums/performance-technical-chat/6040-dyno-results-mods-post45989.html#post45989

Have to do emissions test in the next few weeks to renew my insurance. I'm crossing my fingers.

I think eliminating the 2nd cats is a good way to get better sound and add some hp at the same time without spending a lot of $. Takes under 1 hour to install too.

[Brucelee]

I would bet my lunch money that here in CA, dropping the cat would make a Box fail smog. And as you may know, that is a capital offense here in LA LA land.

[nastyboxster]

Failed my emissions test, so I have to put the cats back and retest. Luckily, it's once every 2 years and it's an easy swap. Be prepare to do this if you are going to install the bypass pipes, but I think it's worth it for a bit more punch and a louder sound.