boost creep question

[jaredgsx]

I am planning on just running an open downpipe and i fully expect boost creep. i dont want to run over 18psi so i have a few questions. Does it always creep up to the same level or does it very depending upon conditions? should i just port the turbo to try to stop the creep, or is there any way to calculate boost creep + set amount of boost to equal what i am wanting..

 

[Quasimondo]

Depends on any number of factors, but in my personal experience, with an unported wastegate, I would creep up to 23 psi.

What you need to port is the exhaust housing on the turbo, both on the inside to allow more exhaust to be diverted to the wastegate opening, and around the wastegate opening itself.

 

[jaredgsx]

dang...ok so porting those two things are they only way around it?

 

[Quasimondo]

Either port them, or switch to an external wastegate.

 

[oldman]

dang...ok so porting those two things are they only way around it?

http://www.dsmtuners.com/forums/showthread.php?t=186525

or a manifold mounted external wastegate .

 

[Apeximprt2nr]

Hey guys, what exactly is an open downpipe, and why does it cause boost creep?

 

[jaredgsx]

an open downpipe is where you just say goodbye to the rest of your exhaust
like if you look at your exhaust it will go from your 02 sensor housing to your downpipe to your cat to another pipe, and to your muffler...mine will just go from o2 sensor housing to a downpipe.
it causes boost creep, correct me if i am wrong, because it allows the exhaust gas to flow out faster than wastegate on the 14b can compensate and so your boost starts to climb. i am like 70% sure of that...dont worry someone will come along and explain it better than i can.

 

[oldman]

it causes boost creep, correct me if i am wrong, because it allows the exhaust gas to flow out faster than wastegate on the 14b can compensate and so your boost starts to climb. i am like 70% sure of that...dont worry someone will come along and explain it better than i can.

Very close, about 70% close. Exhaust gas tend to choose the path with the least resistance, the less the restriction on the exhaust system, the more likely that exhaust gas will choose to flow through the turbine instead of the wastegate path therefore boost continues to rise after the flapper opens.

 

[jaredgsx]

and that is why you port it to make it the path of least resistance....YES, i am awesome!!

 

[oldman]

and that is why you port it to make it the path of least resistance....YES, i am awesome!!

Very close, about 90% close... The biggest problem, in most cases, concerning boost creep is not how much the wastegate path can flow, that is the small part. The biggest problem is the poorly design wastegate entrance in the turbine inlet, unported, it requires the exhaust flow to make a 90* turn in order to enter the wastegate, the solution is to remove materials on top of the wastegate entrance to GUIDE exhaust flow into the wastegate path. Obviously enlarging the path itself as well as the flapper exit without compromising proper sealing of the flapper goes without saying but the most crucial area remains at the entrance in the turbine inlet.

 

[jaredgsx]

well hell i am just going to shut up

 

[oldman]

well hell i am just going to shut up

No need for that, you were 90% awesome.

 

[tstkl]

well hell i am just going to shut up

finally hit 100% eh?

so does this mean bigger turbine'd turbo will have less problems with boost creep?

also, no one mentioned a dump, i would think that would make it less restrictive purly because the route is about 1/20 the length...

 

[oldman]

so does this mean bigger turbine'd turbo will have less problems with boost creep?

Bigger turbos usually means higher boost levels therefore boost creep becomes less of an issue. With that said, I have used the same technique on my GT12 and it holds 12psi to redline.

also, no one mentioned a dump, i would think that would make it less restrictive purly because the route is about 1/20 the length...

In my oppinion, an o2 dump plays a very small role and is not necessary at all in dealing with boost creep. Like I said before, the amount of flow of the wastegate path isn't really the problem, the entrance to the wastegate path is.

 

[cb3016]

Do you replace the flapper too or just port the hole but leave the flapper the same size?

 

[jessesgsx]

yeah i need to get external wastgate... i have a evo 3 big 16g with evo exhaust mani and rnr o2 houseing and 3" down pipe and r&d 3"exhaust all the way back... i still hit 25 psi if i punch it hard so i suggest external wastgate is the eassiest way to fix it..