Boost Creep!!!

[Raptor]

Eric, you are thinking of atmospheric dump. You can run an external gate without dumping it to atmosphere.

[MATCHBX]

Oh, OK. I didn't realize that. Thanks.

[Shane@DBPerformance]

Some of those tubular O2 housings with the internal dumps are even worse than an external because the internals start opening very early while an external doesn't open until you hit full boost.

[JET]

Originally posted by Raptor@Oct 25 2003, 04:27 PM

The wastegate hole diameter becomes a bottle neck in many systems with increased exhaust flow. You can make the entry into the wastegate as free and easy a transition as can be, if the wastegate itself is too small it is still a restriction and will still cause boost creep.
You have to remember that restriction in a tube is consistent with the length of the tube. A wastegate port is only a restriction for 1/2", so it is not that big of a restriction. The low pressure area created on the other side will help to suck the exhaust out of the wastegate hole. Just think of the stock TB on the high HP cars, they get away with it because it is not very long.

Anyway, after taking my turbo off and porting it 3 different times, I finally figured out how to eliminate the creep on my 16g. I had a full 3" from the turbo back, so that is a good boost creep test.

[slowbubblecar]

Originally posted by awd1dr@Oct 25 2003, 11:50 PM
I don't care too much for external because most of us already have larger exhausts and that's loud enough. You add the external and it's unbearable (IMO).
I have heard O2 dumps make the car much louder, but on my brothers car, it didn't seem to be that much louder. It just seemes to have more of an air whooshing noise. IMO

[Raptor]

Originally posted by JET+Oct 26 2003, 06:06 PM--></div><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (JET @ Oct 26 2003, 06:06 PM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin-Raptor@Oct 25 2003, 04:27 PM

The wastegate hole diameter becomes a bottle neck in many systems with increased exhaust flow. You can make the entry into the wastegate as free and easy a transition as can be, if the wastegate itself is too small it is still a restriction and will still cause boost creep.
You have to remember that restriction in a tube is consistent with the length of the tube. A wastegate port is only a restriction for 1/2", so it is not that big of a restriction. The low pressure area created on the other side will help to suck the exhaust out of the wastegate hole. Just think of the stock TB on the high HP cars, they get away with it because it is not very long.

Anyway, after taking my turbo off and porting it 3 different times, I finally figured out how to eliminate the creep on my 16g. I had a full 3" from the turbo back, so that is a good boost creep test. [/b][/quote]
So by that theory then, it wouldn't hurt to run a smaller turbo gasket that protruded into the exhaust flow by a centimeter or so because it is only .030" thick or so and couldn't be much of a restriction. Or weld a washer in your exhaust pipe and not worry because it isn't very thick. Also, if diameter of the gate doesn't matter, maybe people are wasting money going larger internal or external. I agree to some extent with your comment about the restriction being somewhat length dependant as well, but only in certain applications within specific velocity ranges. The higher the velocity of flow, the less it will require to create a significant restriction. Would you agree with that?

[JET]

Yes, I would agree with that. It also depends on the size of the opening on the other side. The larger the opening the bigger the pressure differential will be. On the outlet side of the internal gate has a very large area it gets dumped into, so it will have a large low pressure area. Because of that it will help to suck the air through the opening for the wastegate.

It would flow better if you opened it up, that is for sure. You should be able to get it to flow sufficiently without going to a larger flapper. That was my point. It would just help to prevent it blowing open at higher boost.

[Raptor]

I agree with that also, there is a point that just porting will solve creep issues. I have seen some sad attempts at porting to remove creep that actually hurt the flow of the turbine housing. In smaller cases where it is done correctly, that should not be a problem.