ok i just purchased a helix belmouth dp with the hks carbon ti exhaust for my 05 sti, and at the time only saw a couple threads about boost creep until after i ordered a catless dp. well we all see millions of post sayen they have boost creep, is this a for sure thing? if not someone please tell me they have a similiar set up and dont have boost creep!!!the catback and dp will be my only mods at this point....thankz in advance

 

If you have a catless ehaust you are almost certainly going to have boost creep..... and it will suck and make you angry when you hit fuel cut

 

does that mean this wont happen with a catted downpipe?

 

Cats seem to greatly reduce the risk for creep but it doesnt guarantee you wont get it...

 

im just going to install the catback to the stock dp for now until i have the ***** to port the wastegate =/ thankz for the info guys

 

You should just wait to put in the exhaust . You really won't get any significant power gain the stock dp will be trapping up alot of power . On the positive side your subbie will sound good . Speaking from experience here . To fight boost creep installed aps 725 fmic and perrin cat/delete tbe at same time . I didn't up grade my ecu yet and lesson #2 horrible boost spikes with flaming backfires . Got a ecu-tek reflash by I-speed problem solved . P.S. that 725 is over kill . It's only useful now with my gt-30r .

 

STis and boost creep with the factory turbo and a turbo-back exhaust system on an otherwise stock STi.

I would like to explain what we have seen with the factory boost control settings on the stock STis (2004-2005). The OEM ECU raises the Wastegate Duty Cycle (WGDC) % approximately 40% as RPM increases from 2400 to 5600 RPM. They do this in an effort to compensate for the restrictive exhaust system found on the stock vehicle. They are trying to maintain a level boost pressure at higher RPM while running with the restrictive stock exhaust system. If a less restrictive exhaust system is installed on the vehicle, then the increasing WGDC will make boost rise as RPM rises.

This does not mean that mechanical boost creep does not exist, or that a proper wastegate porting job is not possible. I am just trying to point out that if you install a turbo-back exhaust system that flows well on an otherwise stock STi you will most like see boost creep through your boost gauge. Although, this perceived boost creep is due to electronic manipulation of the mechanical wastegate using an efficient turbo-back exhaust system, not due to the wastegate on the stock turbo being too small.

I would highly recommend you verify that you have mechanical boost creep before you port your wastegate. My experience has been that you only introduce problems when you port wastegates.

Think about it this way; a wastegate's function is to re-direct exhaust energy past the turbine wheel into the downpipe so that the turbo shaft speed decreases or remains constant. With porting a wastegate, you are trying and make that function potentially work better which means that your turbo is going to lower boost super fast when the wastegate door/valve opens or not run as much boost as it was engineered to.

The MORE boost you run the LESS wastegate you need/use. So unless you want to run less boost than stock and/or have un-tunable boost problems, then I would leave your wastegate, the area around it, the turbine housing, etc. alone. If you make your wastegate react quicker then boost will be very difficult to stabilize and reach peak #s at an earlier RPM. If you make the wastegate flow better, then the exhaust energy your turbo needs to make and maintain boost will have less opportunity to flow across the turbine wheel. Generally speaking, air/pressure/exhaust gases will always flow along the path of least resistance. Not bashing, just trying to give you a different perspective.

Take care,
Christian.