Cat positioning

[dark_02wrx]

I was curious bout cat positioning in the exhaust. I noticed most guys run it at the very back basicallynas a muffler. Is there a reason for this? When i was thinking bout it most back pressure is at the beginingbof the exhaust and you would want it at the less "pressured" part of the exhaust "tailpipe" but i wanted verification on this.

[dark_02wrx]

Sry if my words sound jumbled. I work in a fast paced factory and my only internet line is my iphone. And it takes forever to go back and correct grammar problems due to the phone. Thanks guys.

[Bubba02sti]

http://i806.photobucket.com/albums/yy345/Rally_Subie/Robs%20Toy/DSCF1619.jpg

Basicly there needs to be a "visible working cat" according to RA rules... they need to see the honey comb... the reason we did the angled tip is to help dispearce the sound across the ground to help with the DB (just in case we get a douche bag at tech) how ever we also run a resinator at the front of the exhaust to help with back pressure...

[mavric]

^ agreed, how do they know if you've gutted the cat if they can't see it. You'll see most peoples take the place of the muffler so you can see right into it.

[geekguy]

No cat required for open class vehicles in NASA FWIW.

[Ty Ty]

When they get hot enough...they'll spit fire when the engine goes rich, heh.

[Rallycat66]

Main reasons for putting at the very back of the exhaust...

Easy removal/replacement when it melts and/or clogs.
Less likely to melt/clog because of the cooler temps that far back in the exhaust.
Protection from rocks, banging, other physical abuse (which would help promote the first two).

Cars with antilag are especially hard on catalytic converters. And Mazda rotaries - life expectancy of a cat even at the back of the exhaust is less than one rally. :P

The fact that tech can "see" through the back of the pipe into the substrate is just an added benefit.

As for knowing if you've gutted it, they used to test the pipe temps before and after the cat - a working cat will cause a temperature variance, gutted will not. Now the rule is written that they will do a visible substrate test, so if your cat is in the up/down pipes, plan on being ready to pull them off and show them if you get protested.

Tim

[carl]

so if your cat is in the up/down pipes, plan on being ready to pull them off and show them if you get protested.

Tim
or weld a bung on so you can pull the plug and they can use the scope to look at it

[Rallycat66]

or weld a bung on so you can pull the plug and they can use the scope to look at it

That would work as well - I'm too used to the days before they started bringing the scope to all the events. :punch:

[Bubba02sti]

Main reasons for putting at the very back of the exhaust...

Easy removal/replacement when it melts and/or clogs.
Less likely to melt/clog because of the cooler temps that far back in the exhaust.
Protection from rocks, banging, other physical abuse (which would help promote the first two).



good points... but no mater what you do the cat can and will get beat up... its gonna melt down or clog no matter what when your running at high rpm... so out of your 3 very legit points... your first point is the best... no matter how far up you try to tuck it... the cat will get damaged from flying rocks... and its much easier to sawzaa off the end of the exhaust and slap a new one on...