Toyspeed.org.nz Message Board

by **dnalunchie** » Fri May 17, 2013 7:51 pm

A mate of mine up north just brought a new car (V8 sti), I know what a bastard right.

Anyway he is getting its ecu remapped for more power but was also suggesting removing the catalytic converters in the exhaust and replacing them with steel sections of pipe. Reason for this over a full exhaust is that he doesn't want to make it more noisy if possible.

Do you guys reckon this would liberate more power or not?

by **Stott69** » Fri May 17, 2013 8:27 pm

Not unless they have colapsed or blocked. Been covered a few times on here I think?

by **dnalunchie** » Fri May 17, 2013 8:32 pm

Stott69 wrote:Not unless they have colapsed or blocked. Been covered a few times on here I think?

oh? wouldn't have thought that, would have thought they are quite restrictive

by **Makaveli** » Fri May 17, 2013 8:49 pm

Cat Converter restricts exhaust gas flow. It's not a huge difference. But it does make a difference. Maybe 20-30hp? Maybe with stock turbo the difference is slightly less.

by **ee904age** » Fri May 17, 2013 8:52 pm

Makaveli wrote: It's not a huge difference. But it does make a difference. Maybe 20-30hp? .

So around 10% !?!?! Seems a fairly big difference to me...

by **dnalunchie** » Fri May 17, 2013 8:58 pm

at first I would have told him just to do the whole exhaust but after living with my flatmates stock v6 RA for the last year I was surprised by how loud a stock sti exhaust really is

by **Lloyd** » Fri May 17, 2013 9:57 pm

A cat restricts flow. A muffler restricts flow. Every exhaust bend restricts flow.
By how much is what matters. And in reality, it's very little.

by **rollaholic** » Fri May 17, 2013 10:42 pm

dnalunchie wrote:at first I would have told him just to do the whole exhaust but after living with my flatmates stock v6 RA for the last year I was surprised by how loud a stock sti exhaust really is

exhaust on our v5 is completely stock apart from deleted cat (not me)

its quiet as $&#$%. (i like that)

get them to dyno before and after cat for final say imo

by **RomanV** » Sat May 18, 2013 12:30 am

rollaholic wrote:get them to dyno before and after cat for final say imo

Yep I did that (on an NA car though) for zero difference. Obviously depends on case by case basis however.

Just leave it as is.

by **dnalunchie** » Sat May 18, 2013 12:34 am

rollaholic wrote:
dnalunchie wrote:at first I would have told him just to do the whole exhaust but after living with my flatmates stock v6 RA for the last year I was surprised by how loud a stock sti exhaust really is

exhaust on our v5 is completely stock apart from deleted cat (not me)

its quiet as $&#$%. (i like that)

get them to dyno before and after cat for final say imo

Maybe his is louder since it is an RA. Bigger pipes maybe

by **stoffa** » Sat May 18, 2013 8:20 am

having come from WRX ownership it definately makes a difference, but worth replacing the whole downpipe with a Rage one on those twin scroll turbo's.

by **rollaholic** » Sat May 18, 2013 3:01 pm

RA doesnt get more power, just less weight AFAIK. plus tricks like DCCD or w/e

by **tiny2009** » Sun May 19, 2013 10:15 am

Replaced cat in the Runx with a resonator, felt ever sop slightly slightly better in lower RPM, also resonator made it sound the same. No proof that its actually better however it was removed due to smelling like Rotorua so was possibly blocked? Kept the cat and sold it to scrappies, so cost to get it replaced wasn't much.

Did the same with the JZX110, the 1JZ felt much better in mid range after.
EDIT: Dyno shows before (red) and after cat removed (blue):

by **Mr Revhead** » Sun May 19, 2013 10:42 am

What year is a V 8 and what are the applicable cat laws for it?

by **thegreatestben** » Sun May 19, 2013 12:16 pm

Also have to consider that none of these cars are what would be considered as "new" and as such the Cat would be far from it too. Might be a very little in it if you dyno'd them before and after out of the showroom.

by **Heylin** » Tue May 21, 2013 1:27 pm

Not sure how they vary to the 2004 Legacy GT, but the order of gains for the Legacy are

- dump pipe \ front pipe which includes cats
- mid cat
- mufflers

Complimented by a remap \ tune at the end.

by **dnalunchie** » Tue May 21, 2013 2:38 pm

Mr Revhead wrote:What year is a V 8 and what are the applicable cat laws for it?

2003

by **rollaholic** » Tue May 21, 2013 6:38 pm

Heylin wrote:Not sure how they vary to the 2004 Legacy GT, but the order of gains for the Legacy are

- dump pipe \ front pipe which includes cats
- mid cat
- mufflers

Complimented by a remap \ tune at the end.

i'd imagine the cats are mainly included here cos they are part of the front pipe, and its cheaper not to re-use / fit new ones.

but i might be wrong?

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