Decatting a standard system.

[Guest]

My rsk if you take the cats of will that put pressure on the Turbo. I have read that putting larger exhausts on it makes the primary over spool. Taking cats of make any difference?

[DRFVDR]

It will of course make a difference,how much I don't know as a cat would be the biggest restriction in a stock exhaust..

[Jord]

Yes its said removing the cat in the primary downpipe can severely reduce the lifespan of the primary, the one in the centre probably not so much.

[Guest]

Ok Mechanic didnt think it would be to bad? Any other opinions?

[Jord]

Get the mechanic to give you a warrenty on that...

Whats your reason for de-catting? Sound or performance?

[funkytown]

de catted my old BG5C (gtb) about 5 years ago - it'd done 140'xxx kms, i sold it but afaik it still goes beautifully at nearly 190k.

it does make a substantial difference but can decrease turbo lifespan - its one of those things where YMMV.

noise can increase depending on rear muffler / cannon and resonaters installed but so will performance (increase)

[Guest]

Ah Only if it increases performance.. Just told they go alot better without the cats

[ADIKT]

Just do it bro!

[Jakee]

 ADIKT said:

Just do it bro!

+ 1. Doing mine on Friday

[neodowd]

I got a full exhaust system on my gtb a couple of months ago, I too was worried about the primary turbo over spooling and a decreased lifespan with the cats removed. But I can tell you the pros far out weigh the cons. the worst that can happen is you might have to replace your primary turbo a bit sooner. Get er done!!

[drakon]

was wondering the same thing too. Had my middle and rear sections done for 6 months but just got the front pipes done this weekend.

Sounds nicer with free flowing pipes so pros outweigh cons

[rico]

Did you guys replace the factory exhaust parts with aftermarket cat-less ones or just gut the cats out of the factory mid/down pipes and re-fit?

[Jakee]

I cut them out and just weld some pipe in.

[neodowd]

I got rage 2.5 inch down pipes and 2.5 inch y piece going into a 3 inch exhaust, sounds good ;D. If your going to go catless you may as well do it properly and go with after market pipes.

[Guest]

Anyone recommend a place to do the cats in hamilton?

[Swindog]

Any exhaust shop will do but say your keeping the cat. Its full of expensive stuff that the scrapper will pay you good money for!

[Guest]

Yeah last cat I sold was for $50 bucks!

[drakon]

Replaced whole system with 2.5 inch turbos back.

Had the middle section back already done and then won a full one piece exhaust from turbos back of trade me for 1.50 ;D took it to pit stop and cost 260 to flange front part and minor tweak to fit.

Just looking for some extractors and uppipes to complete exhaust system

Sounds better now and boost is more responsive. One worry though is I hit over 15 psi coming home today and think i felt it over spin.

[Guest]

IMO, removing both cats is asking for trouble and more of a risk for your engine than the turbo. It only needs to overspool once to blow your engine. If your removing both cats, get the car tuned and you will make it a safer mod and it will pull some extra ponies as well. You will definitely need a high flow fuel pump as well. I have the middle cat changed to a high flow cat in my gtb.

[94 Leone]

If it's non-turbo; De-catting will just make it awesome, no overspooling to worry about haha

[neodowd]

Excuse my ignorance but how could a turbo over spooling blow an engine? I was under the impression the turbo would go before any thing else, and there are factory boost cuts in place to stop doing any serious damage.

[94 Leone]

Over-spool = too much boost = too much pressure = pistons out side of block, or melt or it all will just go boom.

But de-catting as being spoken about in this will increase the likelyhood of over-spooling, as will the various other mods being performed on these guys hotted up subies.

many of them run their own boost controllers, so it bypasses the factory boost control often to allow a higher boost, which is fine, If the cat is there, but de-catting creates more flow, therefore less ressistance on the turboo resulting in faster spooling, therefore increasing the likelihood of over-spooling. and without these factory boost-cuts in place engine go boom-boom. so if you have a standard system, you are less-likely to go blow, but with average boy-racer mods in place, chances are somethings gonna give, and it's not gonna be something cheap.

edit:amiright?

[Guest]

Mines completely stock. No boost controller or anything. My only mod was going to be decatting it

[Marky]

My logic goes the other way. You'll blow motors with excess knock, and especially in a high km motor having backpressure in the system from a blocked up cat converter is a sure fire way to increase the likelihood of det occuring.

If you reduce the restriction past the cylinder, you will then be able to make the same power, at possibly a lower boost pressure, and safer.

Ideally to make more power from a turbo car, you will just remove as much restriction as possible. Raising the boost on a restrictive setup will do more harm than just whipping the cat out. IF a car continues to overboost on "wastegate pressure" then the problem lies with the WG itself not flowing sufficiently - lancer evos being a prime example, just a decat and big exhaust is enough to need to bore out the WG a bit or they overboost up the top end.

The reason that people go on about it being such a dangerous thing on a legacy is that the factory sets these cars up with all the restrictions in place - having 1 or 2 cats post-turbo, big muffler to quiet it down etc, and sets up the boost control to suit this. It is not a closed loop system, it won't deviate from what it already works with, even if you take away all these bottlenecks. Hence people end up running big boost. Best solution then is to remove all the restriction you can, make things as efficient as possible - but if the boost is now too high, common sense says to take the factory boost control out of the loop and set it to a reasonable level yourself.

[WRXONP]

and just so u know hitting "boost cut" isnt exactly a very nice thing for ur motor either

boost cut is triggering the fuel cut - not exactly very good in any way shape or form