Downpipe question

[wrxbert]

Can anyone tell me the pro's/con's of an hks downpipe on an 06 wrx? i'm thinking it should prevent boost creep/spike with the flat plate over the internal wastegate, but i'm worried about problems with the stage 2 map....should i just wait until i can afford a better one (perrin/cobb)

[IMPREZvWRX]

The flat plate over the wastegate is a cause for creep, not a solution. If you are going to keep the internal wastegate, you should get a bellmouth or divorced downpipe.

[RyanG]

<--- been using an HKS for quite some time. as well as a few swaps I have done in GC's. no creep issues here although each car has some form of ems.
which should be the first thing you do anyway.

[TROLL]

but on the 06 with the 2.5L it has been a problem historically...
i'd also say go for a bellmouth, and if you're real concerned about boost creep and dont ever plan to go for huge power, think about a catted downpipe. if you're not making gobs of power then going catted isnt much of a restriction.

[CHAOS]

as long as u get some kind of tune it shouldnt be an issue... im running a 3" bellmouth with no issues.. and im ecutek tuned.

[Honest_Bob]

Your much less likley to get boost creep with a catted setup. I'd either go with a divorced waste gate or a bell mouth.

[TROLL]

the boost creep thing is weird, it happens on some cars and it doesnt on others... however one thing is definite: it is a mechanical issue and therefore your tune has no effect on it whatsoever.
the problem is that once you increase the efficiency of your exhaust by making it less restrictive, more air flows through the exhaust side of your turbo. the wastegate opens to bleed off a certain amount of air to keep boost from continuing to rise, but in this case even when the wastegate is fully open, it cannot keep up with all of the flow so more air gets around it and spins the turbo up even more, creating more boost.
its a mechanical issue that is basically a 'defect' of the wastegate design, but then again it works fine on a stock car so its not an issue as far as Subaru is concerned.
the problem usually only arises when people go catless on the 2.5L engine, whether its an STi or WRX. the guys going with catted downpipes dont have the problem since they arent quite as free flowing. from what i've seen, not everyone who goes catless has an issue though, not sure if its just hit or miss or it has to do with their catback section and how restrictive that is in the muffler, etc.
the fix on the stock turbo is to port the wastegate, and there is a good guide on nasioc about it for those who are daring enough. but learn from my mistake... more is not better. some minor and selective porting will go a long way, and if you do too much your turbo wont spool up properly any more.