Why does the WRX have 3 cats and the STI has only 2?

[Bryan Lee]

I have been posting on the club sites and so far no one knows? Is it just
to give the STI the performance advantage? You would think with the more
fuel, power and bigger motor it would run dirtier? Thanks for any info

 

[mulder]

The WRX is rated as a LEV (low emissions vehicle) while the STi is not.
The LEV status is acheived due to the uppipe pre-cat (before the turbo)
which heats up quickly on cold starts to lower cold engine emissions.

 

[FNO]

The WRX is rated as a LEV (low emissions vehicle) while the STi is not.
The LEV status is acheived due to the uppipe pre-cat (before the turbo)
which heats up quickly on cold starts to lower cold engine emissions.

Actually, Subaru claims the STi is LEV. However, it is a larger engine
using higher octane fuel and higher boost pressures. They claim a cleaner
and more efficient burn and don't need the third cat.

 

[mulder]

Hm, makes sense to a point. The octane requirement is not that
significant in practice since most everyone runs both cars on the
highest octane available. Boost pressure shouldn't have that much to do
with it either, since boost isn't an issue at cold start when the
pre-cat is most useful, and the max boost on a stock STi isn't that much
higher than a stock WRX anyway. But the STi may have larger down- and
mid-pipe cats and there are other engine differences that may allow for
cleaner cold running.

 

[BlueSTi]

Actually, Subaru claims the STi is LEV. However, it is a larger engine
using higher octane fuel and higher boost pressures. They claim a cleaner
and more efficient burn and don't need the third cat.

I was thinking I read that the STi is an, " Ultra Low Emissions
Vehicle" ULEV? I live in an area that doesn't even do emissions
testing. So, it is really a moot point for me. Seems like the cat is
the first thing a lot of folks like to take off.
BlueSTi
"Scary-Fast"

 

[Vince C]

Don't forget about noise, on the STI it's less of a concern.

 

[Bryan Lee]

most people do'nt buy the WRX because it's quiet.

 

[BlueSTi]

most people do'nt buy the WRX because it's quiet.

The STi has significantly more exhaust note than the STD WRX. Not
that I'm a fan of loud exhausts. I hate them! But, the exhaust note
on the the STi is not obnoxious or annoying. And it sounds nothing
like the local Honda boys who have the big fart cannons on the back of
their "hot-rods".
BlueSTi
"Scary-Fast"