Boost Creeping

[ARTSUPRA]

I am experiencing some boost creep my boost goes as follows 13-14PSI upto 4500RPM then rises slowly to 17-18PSI @ 6500RPM, this is more pressure then I need now, and it hesitates alittle when hits 18PSI so fuel is not there or timing is being pulled. I hit 18PSI 2-3 times for 1 second and let it off.

My mods are 3" catback from stock downpipe, no cats, 3" streight trough muffler, all the free mods except hacked AFM, hard pipes, HKS SSQV

Now, what can I do to get rid of it? I have yet to experience boost creep on Supra simply because WG is quite large on Ct-26, so it never creeps, so I am sort of in the dark here.

I am in proccess of building a O2 eliminator downpipe with non atmospheric WG, will that help? Or putting a silencer on the Muffler would lower it (I don't have a silencer, have to make one).


ART

 

[markGSX]

I had the same problem with a 3" exhaust and adding a cat fixed it.

 

[crazyboost]

sounds like you are hitting fuel cut. I would suggest porting the wastegate area and possibly adding a 34mm flapper so you can make the whole alot bigger, then the 02 eliminating dp would help out too. Search on vfaq for porting.

 

[TurBoGs-T]

Originally posted by markGSX
I had the same problem with a 3" exhaust and adding a cat fixed it.

Me also

 

[ECLIPSE4x4]

You running a boost controller? If so what kind?

 

[ARTSUPRA]

No boost controller, Altough I have a Greddy manual boost controller I've been reluctant installing mainly because not sure if it will make any difference.

maybe I should install it and then see..................yeah good idea

 

[coltboostin]

you dont need a 34 mm wastegate flapper, and the boost contoler wont do you much good (unless your going to run 18psi). What will work is enialating the lip above the wastegate. As much air as possible needs to get through their and the more you port, the better it will be. With my porting my friend can hold 14psi on his 93gsx, with and evoIII turbo, full 3ich including O2 eliminator, hard pipes, bla bla bla. He used to creep to 20psi :thumbdown

Port Port Port!

 

[Groomz]

Originally posted by ARTSUPRA
I am experiencing some boost creep my boost goes as follows 13-14PSI upto 4500RPM then rises slowly to 17-18PSI @ 6500RPM, this is more pressure then I need now, and it hesitates alittle when hits 18PSI so fuel is not there or timing is being pulled. I hit 18PSI 2-3 times for 1 second and let it off.

My mods are 3" catback from stock downpipe, no cats, 3" streight trough muffler, all the free mods except hacked AFM, hard pipes, HKS SSQV

Now, what can I do to get rid of it? I have yet to experience boost creep on Supra simply because WG is quite large on Ct-26, so it never creeps, so I am sort of in the dark here.

I am in proccess of building a O2 eliminator downpipe with non atmospheric WG, will that help? Or putting a silencer on the Muffler would lower it (I don't have a silencer, have to make one).


ART

Basically your exhaust is too large for your turbo. The exhaust is taking the easiest way out, which is through the 3 inch exhaust, not the tiny wastegate passage. Either get a larger turbo or start porting.

The number one cause of boost creep is an exhaust not properly sized to the current turbo.

 

[coltboostin]

I agree about the improper exaust sizeing, btu then again, who is going to buy a 2.5 inch exaust when later on they wil wnat to go 3 inch anyways?

 

[Groomz]

Originally posted by coltboostin
I agree about the improper exaust sizeing, btu then again, who is going to buy a 2.5 inch exaust when later on they wil wnat to go 3 inch anyways?

If you plan to use a 3 inch exhaust for a turbo capable of using a 3 inch, go ahead. Most DSMers bolt a 3 inch exhaust on a stock turbo and wonder why they have boost creep. Its better to have realistic goals and buy what you need, not what others say you need. In reality most DSMers could not max out a 3 inch exhaust, and typically buy parts out of order or which are not correct for each other. 16G and 3 inch turboback for example. Getting a 65lbs/min turbo? Go 3 inch for sure. 38lbs/min turbo's don't need a sewer system exhaust to operate correctly and to max efficiency. But no one listens, they just ask.

 

[crankbender]

The exhaust size isn't making you creap. It is the improper style used for the O2 housing. The problem is you are trying to bypass the compressor wheel with the waste gated exhaust but it gets backed up by the exhaust gasses still spinning comming out of the compressor.

If you want to fix the boost creep and you have a wastegate capable of not creeping then you need to fix this weak point.

I suggest in really bad boost creap you go with a dump tube. I posted a little while back stating what causes boost creep. If you have this problem I suggest you read it before just throwing parts at the problem. Its alot cheaper and you will have a faster car in the end...

Any turbo...and i mean any wants no exhaust at all!

 

[ARTSUPRA]

So what you saying is I need a ported elbow or custom made elbow from mandrel bents? If so I will get one tomorrow

 

[crankbender]

best thing you can do is to custom fab a j pipe that eliminiates teh o2 housing and doesn't dump the waste gated exhaust back into the main stream till after it is under the car.

 

[Groomz]

Originally posted by crankbender

Any turbo...and i mean any wants no exhaust at all!

Yes, if maximum efficiency is what is desired. Working with a relatively poor wastegate design of the MHI turbine housings, you have to make compromises to have it function correctly. A properly designed wastegate system would not be affected by the large exhaust.

 

[coltboostin]

Many people have played around with the idea of routing the wastegate into the exaust much farther down stream for better boost control, but does anyone know of someone who has actually doen this, and seen it work? If it did, im sure it would hold boost as well as an externaly dumped wastegate, without the rediculous noise

 

[TimG]

Originally posted by crankbender
The exhaust size isn't making you creap. It is the improper style used for the O2 housing. The problem is you are trying to bypass the compressor wheel with the waste gated exhaust but it gets backed up by the exhaust gasses still spinning comming out of the compressor.

If you want to fix the boost creep and you have a wastegate capable of not creeping then you need to fix this weak point.

I suggest in really bad boost creap you go with a dump tube. I posted a little while back stating what causes boost creep. If you have this problem I suggest you read it before just throwing parts at the problem. Its alot cheaper and you will have a faster car in the end...

Any turbo...and i mean any wants no exhaust at all!

Could not have said it better myself. Yet the exhaust does play a factor. If the exhaust were a little more restictive, full boost would be made much later in the rpm band and would not have the time to creep until the shift was already made.

Secondly, if you want the cheapest way out for now, here is an idea. Port the hell out of the hole on the O2 housing that the wastegate dumps into. Also port the downpipe side of the O2 sensor housing. This should allow less restriction from the wastegate to build up and you should be able to build a solid 14 pounds of boost.

If that fails, go with a larger flapper. If you try to free up the wastegate side of the O2 housing and that doesn't work, you know your problem is with the flapper size.

Goodluck.

 

[markGSX]

Everyone is saying to port the O2 housing and wastegate passage, but I went through all that. I had the O2 housing ported, the wastegate passage on the turbo ported, and the 34mm flapper installed. None of those fixed the creep, until I had a 3" cat installed.

 

[coltboostin]

Yeah, well who ported it, what did the port job look like? The port job I speak of is beyond a little dremel love, the port job I do, and what works, is a total enialation of the area above the gate exit. Exaust must move freely and be able to eaisaly exit the hole to control boost well. A cat solved your creep because it SLOWED EXAUST FLOW. Yuo know what else slowing the exaust flow does? Kills Power!!

 

[myblack98gst]

PORT!!!!


okay I was a mis-believer too.. I would be at 14 then @ 4k it would climb past 20 psi (big 16g)

while I had the motor apart recently I ported everything on the turbo..

the manifold exit turbine entrance are a perfect matched 2.5"
the wastgate hole was enlarged to barely smaller than the flapper.
the turbine entrance was ported so that looking straight in you could see into the wastegate hole.
the wastegate on the other side of the flapper was ported out to match the 2g o2 housing and then some more..
the o2 housing was matched to the new porting on the turbo
the wastegate runner on the o2 was opened up and the divider wall at the bottom opened up more..
from the divider opening to the o2 exit it was openend to 2.5"


I just got the car running yesterday.. and have not broke it in yet but heres the results.. with the wastgate flapper un-hookd it builds 1psi at 5k.. with it hooked up it sticks to 10psi at 5k.. VERY satisfied with the results

 

[markGSX]

Originally posted by coltboostin
Yeah, well who ported it, what did the port job look like? The port job I speak of is beyond a little dremel love, the port job I do, and what works, is a total enialation of the area above the gate exit. Exaust must move freely and be able to eaisaly exit the hole to control boost well. A cat solved your creep because it SLOWED EXAUST FLOW. Yuo know what else slowing the exaust flow does? Kills Power!!

All the porting was done by Slowboy Racing. I do realize that the cat fixed the creep by reducing flow, but for me the trade off was worth it.

 

[coltboostin]

That is not the first time I heard of a slow boy racing port job creeping. A few local guys have slow boy "ported" turbos, and they all creep.
Myblack98 described the port job I speak of perfectly by saying "when your looking straight in, you can see the wastegate hole. That will solve all your boost creep wowes. Do that, and get the cat off the car!!!

 

[markGSX]

Originally posted by coltboostin
That is not the first time I heard of a slow boy racing port job creeping. A few local guys have slow boy "ported" turbos, and they all creep.
Myblack98 described the port job I speak of perfectly by saying "when your looking straight in, you can see the wastegate hole. That will solve all your boost creep wowes.

I attached a picture of the port job.

Do that, and get the cat off the car!!!

Nah, I like it much better with the cat.
1. no creep
2. car doesn't stink
3. no brown stain on bumper
4. no $1000+ fine for getting caught
5. I honestly notice no performance hit after installing a cat. If it's there, its negligible.

 

[coltboostin]

That picture does not show me anything, and that wastegate exit looks pretty untouched. A pic on the turno inlet is what I am interested in because that is where porting needs to be done to eliminate creep. Understand what I am saying? Hey, if you want to run a cat, then run a cat. As with everything, ti has pluses and minuses, I cant dog that.

 

[LessIsMore]

I ordered a 16g from slowboy over the summer, I had them install a 34mm flapper and give it their $50 port job. Well you get what you pay for. The port job is pretty much a removal of the inlet step and a nice shiney polish. It creeped to 18psi by 6K where I let off. Well I pulled the turbo and removed a ton of material from above the wastegate. No more creep, 15psi to redline.

http://www.twingles.com/ideck/rebuild2/green2.jpg

This is a good example of the correct way eliminate boost creep through porting. Remove material from above the wastegate passage to allow for better exhaust flow through the wastegate. Its that simple.

 

[myblack98gst]

here you see that you can look down in there and see into the wastgate hole.. also not how much larger this is than a standard housing now

if you have ever seen this part yo know how much I opened it up. and I opened the wastegate hole so just barely smaller than the flapper and the hole is cut at a slight angle so that the exhaust flows better out

here you can see how I cut the housing & o2 to match each other almost exactly. the exhaust flow will primarily hit the bottom left edge of the gate porting.. because of the angle it sits ( this would be the bottom when mounted), factory this is MUCH smaller and no where near matches the o2 housing

here is the bottom side of the o2 housing. I opened the port up where the wastegate exhaust enters the main chamber then opened the rest of the opening to 2.5" from the entrance to the bottom.

here is the manifold, this metal is HARD it took awhile using the right tools to do this. I dont know what the stock size is but it is now 2.5" and I also smoothed the runner path out and thinned the divider wall.

like i said previously this cut out all boostcreep and it went from a 14 psi base boost (that crept past 20) to a 10 psi base boost ( that holds)