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ButtDyno

WRX Exhaust points question

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ButtDyno

My WRX has the following exhaust mods:

 

uppipe (deletes factory cat)

turboback with high flow cat (deletes one factory cat, replaces one factory cat with a high flow)

axleback

header

 

I want to make sure I understand this:

The uppipe removes a cat: +1 - rule 31

The turboback +2 - rule 29

Turboback removes another cat +1 - rule 31

Turboback includes high-flow which "upgrades" factory cat +1 - rule 31

header + 2 - rule 28

 

Total: 1 + 2 + 1 + 1 + 2 = 7?

 

Or, does the downpipe's +2 take into account the two cat changes, so it's only a total of 5?

 

Is the axleback "included" in the turboback or do I need to list it separately?

 

Here's a diagram

http://us.st11.yimg.com/us.st.yimg.com/I/fastwrx_1928_69880998

 

I've also got an intake and a remapped ECU, FWIW.

 

thanks,

John

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Greg G.

Just take +5 for the exhaust system. Headers +2, Complete exhaust +2, Cat delete/mod +1. Nice diagram BTW.

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subachad

Greg, out of curiosity, how would the up pipe cat work? In 2001-2004 the WRX has a 2.0 with a catted up pipe. (I have a few in my garage). In 2005, it's still a 2.0 liter motor, but Subaru no longer put a CAT in the up pipe?

 

As for the difference, there is not really any HP gain peak, but you get quicker spool up by about 400 RPM. Makes the motor feel less "turbo-ee"

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Greg G.

I don't know what the engineers were thinking when they put a pre-cat in the up-pipe. Clearly you can meet (even CA) emission standards without it.

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Shawn M.
I don't know what the engineers were thinking when they put a pre-cat in the up-pipe. Clearly you can meet (even CA) emission standards without it.

 

 

They were thinking it would warm up faster, work hotter and be a good thing for the environmentalists....

Cats are only good for.... running over in the streets.

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Valhakar
I don't know what the engineers were thinking when they put a pre-cat in the up-pipe. Clearly you can meet (even CA) emission standards without it.

 

I passed VA emissions with a sniffer using only one cat, the last one. Not only did it pass, but it still qualified as an LEV.

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subachad

I should have reworded the question. What I meant was for points. If an 02-04 WRX gutted the up pipe or replaced it with an aftermarket piece would they have to take a point for modifying the catalytic converter? As for how they work...

 

Most modern cars are equipped with three-way catalytic converters. "Three-way" refers to the three regulated emissions it helps to reduce - carbon monoxide, unburnt hydrocarbons and nitrogen oxide molecules. The converter uses two different types of catalysts, a reduction catalyst and an oxidization catalyst. Both types consist of a ceramic structure coated with a metal catalyst, usually platinum, rhodium and/or palladium. The idea is to create a structure that exposes the maximum surface area of the catalyst to the exhaust stream, while also minimising the amount of catalyst required (they are very expensive).

There are three main types of structures used in catalytic converters - ceramic honeycomb, metal plate and ceramic beads (now almost obsolete) - the Scorpio like most cars today use a ceramic honeycomb structure.

 

The Reduction Catalyst

The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the nitrogen oxide emissions. When such molecules come in contact with the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2.

 

The Oxidization Catalyst

The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas.

 

The Control System

The third stage is a control system that monitors the exhaust stream, and uses this information to control the fuel injection system. There is a heated oxygen sensor (also called a Lambda Sensor) mounted upstream of the catalytic converter, meaning it is closer to the engine than the converter. This sensor tells the EEC-V PCM how much oxygen is in the exhaust. The EEC-V can increase or decrease the amount of oxygen in the exhaust by adjusting the air-to-fuel ratio. This control scheme allows the EEC-V to ensure that the engine is running at close to the stoichiometric point, while also making sure that there is enough oxygen in the exhaust to allow the oxidization catalyst to burn the unburned hydrocarbons and carbon monoxide.

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