Why DON'T I Have Boost Creep?

[habitatguy187]

I've seen a lot of boost creep threads lately and it has me wondering why I'm not experiencing it.

I have a 14b with a 7cm unported turbine housing on it (from a evo3), a larger ebay o2 housing with external dump, and a 3" downpipe with a 3" in 3" out muffler on it. I'm running 19psi on my turbo. I get boost spikes if it's cold out, but no boost creep.

I posted this thread looking for some more insight as to why people with more restrictive exhausts than mine are getting creep.

BTW: I don't creep at 15psi either.

 

[gofer]

the external dumped o2 housing probably has something to do with it... and you are running the smallest of the tdo5 turbos, upgrade to a evo 3 16g and im almost sure you'll see some kind of boost creep if you don't port the turbine housing.

 

[7"exhaust_tip]

I would be happy that you aren't experiencing creep, rather than wondering why your not.

 

[airmail96]

It could be the fact that you are running 19psi on the 14b that makes it so it won't creep.

 

[MaNGiNa24]

Most likely the boost level combined with the external dump. I've seen quite a few 16g setups that swapped to external dumps to remedy their creep in the past.

 

[habitatguy187]

I would be happy that you aren't experiencing creep, rather than wondering why your not.

I'm glad I'm not, but curious as to why. I just want a better understanding of why.

It could be the fact that you are running 19psi on the 14b that makes it so it won't creep.

I can hold 15psi solid also, I haven't tried anything lower than that.

Most likely the boost level combined with the external dump. I've seen quite a few 16g setups that swapped to external dumps to remedy their creep in the past.

I've read lots of posts saying that o2 dumps won't help unless it's an actual external wastegate

 

[gofer]

im not an engineer but i drew up this picture as to why I THINK running an external dump helps with boost creep...

one word, turbulence

You must be logged in to view this image or video.

the stock o2 housing "recircs" the exhaust gases back into the system just before the downpipe creating turbulence in the exhaust. in turn exhaust gases have nowhere to go so they take the path of least resistance... right across the turbine wheel causing it to spool beyond what the wastegate can control.
*top picture*

the o2 dump housing gets rid of the excess gases to allow the exhaust coming across the turbine wheel to flow smooth out to the back of the car.
*bottom picture*

this is what i pictured happening when i was experiencing boost creep. again im no engineer and maybe a wisemen could verify... thats why i think youve got no boost creep though.

 

[Rob10_99]

That can be a cause of it, but the exhaust would have to be fairly restricted. What causes most creep is a bad path from the turbine housing. That's why people port them for better(smoother) flow.
Bigger flapper as well as one that opens further always helps as well.

 

[91-gsx]

I'm glad I'm not, but curious as to why. I just want a better understanding of why.



I can hold 15psi solid also, I haven't tried anything lower than that.



I've read lots of posts saying that o2 dumps won't help unless it's an actual external wastegate

A smaller volute like the 6cm stock housing has will make the turbo spool faster and allow less exhaust to be bypassed. Just swapping to the 7cm housing from the 16g will make it spool a bit slower, make more power, and also bypass more exhaust for a given RPM. This bypassing effect plays a big role on back pressure causing the turbine to spin faster because the stock wastegate and the stock turbine housing are too small. The external wastegate on its own will get rid of creep.. An o2 dump will help, but the dump tube is bigger then the ~31mm flapper that covers a ~25mm hole on the turbine housing... That is far cry from a 38mm hole and wastegate which has an opening about the same size or bigger then the dump tube.. The only way to control creep is to; (A): Port a bigger hole on the turbine housing to bypass exhaust and upgrade to a bigger flapper, or simply port the hole out more but do not exceed or go past the ~29-30mm so that the flapper still can close and not have gaps around it when it seals.. (B): Port the inlet of the turbo, but pay special attention to making the route to the wastegate hole easy. So that the exhaust does not have to make a hard 90 degree turn to come out the wastegate hole. You achieve this by removing material above the wastegate passage in the turbine housing inlet. (C): Go with an external wastegate.

I have ported my 14b as described above, a few years ago and still have it in my garage. I ported the step out of the inlet of the stock 6cm housing. I ported above the wastegate passage in the turbine housing inlet. And I ported the wastegate hole as far as I could, while still allowing the flapper to seal well. I was able to run 15psi to redline without creep on a ss o2 housing, 3" downpipe, and 3" catback with a straight through muffler and NO cat.. I might have been able to go lower, but I wanted more boost/power.

That was a long rant , but I hope it helps. Later.

 

[habitatguy187]

That was a long rant , but I hope it helps. Later.

I understand all that and how to get rid of creep, but I'm just curious as to why I'm NOT creeping.


Gofer, loved the pic Thanks.

 

[91-gsx]

I understand all that and how to get rid of creep, but I'm just curious as to why I'm NOT creeping.


Gofer, loved the pic Thanks.

Your not creeping because you have an external 38mm wastegate..

The external wastegate on its own will get rid of creep.. An o2 dump will help, but the dump tube is bigger then the ~31mm flapper that covers a ~25mm hole on the turbine housing... That is far cry from a 38mm hole and wastegate which has an opening about the same size or bigger then the dump tube..

 

[habitatguy187]

Your not creeping because you have an external 38mm wastegate..

No I don't. Sorry if I didn't explain my setup clearly. I have an ebay o2 housing with an external dump tube, not an actual external wastegate.

 

[gofer]

I'm telling you 100% it's that o2 housing... it takes 45min tops to put it back to stock, u should R&R your o2 and see if you can control boost.

glad u liked the pics

 

[91-gsx]

No I don't. Sorry if I didn't explain my setup clearly. I have an ebay o2 housing with an external dump tube, not an actual external wastegate.

My bad I totally misunderstood... Yes then, gofer is right in saying that it is your externally dumped o2 housing. If you did not do any creep relief porting, or have a external wastegate. Then I would imagine that the external dump o2 housing is the contributing factor.

 

[byebyev8]

you probably have a 34mm flapper. There good for low boost control but I couldn't get mine to go over 22psi. So i switced to a non ported non 34mm flapper e3 housing and 28psi+

 

[JusMX141]

I've read lots of posts saying that o2 dumps won't help unless it's an actual external wastegate

Size.

If you have a 31mm internal flapper, the hole beneath it (which actually transfers airflow) is smaller than the flapper size by a good 4mm so the flapper can seal on the housing.

External wastegates aren't available in anything smaller than 35mm, and most choose the 38mm gate as the flanges are the same size anyway. When discussing external wastegate size, you're talking about the actual size of the port in the valve....not the piston that seals it; hence a 38mm external gate is a good 10mm larger than a standard internal wastegate.

An externally-dumped internal gate is still an effective solution if you can put up with the noise as it allows the exhaust flow that is bypassing the turbine housing a short exit route with zero resistance.

Keep in mind the higher the boost pressure the more backpressure that will exist within the turbine housing. On a car that's creep-prone, it's much easier to control 20psi than 15psi just as it's easier to control 15psi than 10psi. Eventually you'll reach a point where boost creep becomes a thing of the past if you keep upping your boost level enough.


Wastegates are such a complicated item to understand. A good-functioning gate will open fully when your highest-desired boost level is achieved, then close almost entirely allowing the remainder of pressure to bleed off slowly through a tiny opening. If the gate stays wide open the whole time, your boost level will taper off as exhaust flow will continue to bypass the turbine housing, slowing the turbine speed drastically. A wastegate with too low of a spring pressure will operate in the same way as the spring pressure is too weak to force the gate shut again after opening fully. The result will be a sharp drop in boost pressure as the RPMs climb.