12 replies to this topic

[TRQ-STR]

After the fitment of a 3 inch free flowing exhaust onto my vr4 engine the 16g turbo began showing symptoms of boost creep. After reading some threads on DSMtuners.com and watching a few videos on youtube. I decided to type up a little report on how I cured my boost creep. My aim is to help sufferers on team4g solve this problem. I found out the hard way and know it can be quite frustrating.

This is the thread which helped me out http://www.dsmtuners...ep-porting.html.


Before I begin hear is a little info for the newbie's. IF YOU WANT TO ONLY READ MY METHOD USED PLEASE SKIP TO SECOND POST


-Turbochargers and How They Operate:

Turbochargers are simply a high volume air pump which can be incorporated with an engine. Their main purpose is to increase fuel economy and power output.


Now, let's take a look at how a turbo works. The exhaust gas coming out of the engine exits through the exhaust manifold and into the turbine housing (rear of turbo) allowing it to spin the turbine wheel. The turbine wheel is connected via a shaft to the compressor wheel (front of turbo) and in effect it spins at the same rate. This allows the compressor wheel to produce boost (Boost is the amount of pressure above atmospheric which is being built up in the piping connected from the turbo to the intake). The more exhaust that comes through the manifold, the faster the turbine wheel will spin, therefore the more boost the turbo will create. A wastegate is a component used with a turbo to control the rate at which the turbine may spin in effect controlling the level of boost.


-Wastegate Actuators:
Wastegate actuators are an important part of a turbocharger systems which are often overlooked. They have a big influence on the amount of power an engine can make. The purpose of the wastegate is to regulate the amount of exhaust getting from the turbine housing to the turbine wheel threw a bypass, this controls the amount of boost. If we did not have a wastegate on a turbocharger, the turbine wheel would keep spinning the compressor wheel faster and faster as the engine RPM increased until either the turbo was over speed or the engine was over boosted to the point where damage would most likely occur.


This is a Turbo boost versus Engine RPM graph



Internal Actuators:
Actuators come in two different forms, one of them being internal and the other external. An internal actuator is what is found on a factory turbocharger application. With this design, the actuator is integrated to the turbo unit itself. There is an opening at the rear of the turbine housing (wastegate) just before the turbine wheel, which is covered by a flap. This flap is connected via a rod to the actuator. When a specified boost has reached the actuator, the diaphragm within the actuator pushes down onto the rod which opens the flap up and reveals the wastegate in effect controlling the boost. On factory boost and power levels, internal wastegates work fine as they are usually matched to the size of the turbocharger. But once the power is increased with modifications such as a free flowing exhaust, internal wastegates begin to show their flaws. Internal wastegates are generally small in terms of diameter which makes them slow to respond with pressure change causing problems such as boost spike and boost oscillation.

This is an example of boost spike. The red line identifies 10PSI, (pounds per square inch of pressure) this is set boost and should not be exceeded.

But as can be seen by the blue line, the pressure spikes above this when the turbo first comes on to boost, but then holds steady for the rest of the engine's rev (RPM) range.


This is not desired and can become an even bigger problem (boost oscillation) when combined with boost controllers. Here is an example.

As can be seen, there are fluctuations in boost levels as the actuator struggles to reach the desired 10PSI.


The wastegate being too small can also cause over boosting at high RPM, this occurs when the wastegate literally cannot flow out enough exhaust to slow down the turbine wheel. This is known as boost creep.



Turbochargers can also suffer from wastegate creep, this is when the exhaust gas forces the flap open before the desired boost pressure and makes the turbo lag.



-External wastegates:
The benefits of the external wastegate actuator is that they are much larger in design. This means they also have a larger diaphragm which makes them much faster to respond to pressure change.

Other benefits are that they are separate to the turbocharger and are plumbed into the exhaust manifold. This design results in the exhaust gas exiting from the manifold rather than from the turbine housing. Since the exhaust exits from the manifold there are fewer limitations to how large a wastegate hole can be in terms of diameter. As a result, you will see a flatter and smoother curve on the �boost versus RPM graph�.

This gas exiting from the wastegate can be plumbed back into the exhaust downstream as is with the internal design or it can be vented out to the atmosphere. However, venting to the atmosphere is highly illegal due to exhaust emissions.


Due to the mentioned features, external wastegate actuators do not suffer from the problems which are apparent in the internal wastegate systems.

Edited by trq-str, 26 October 2010 - 11:43 PM.

[TRQ-STR]

When I first noticed my boost creep I was unsure of what was going on with my turbo as all this was quite new to me. However, after some extensive research and a few road tests I realised my TD05 turbo suffered from boost creep. As boost creep occurs due to not enough exhaust gas flowing out of the wategate from before the turbine wheel, I was left with three options to solve my problem. 1 was to fit a more restrictive exhaust 2 was to simply port out the standard wastegate hole to a larger diameter and 3 was to completely block it off and modify the manifold to use a much larger external gate (this is the expensive option).


Since the fitment of my 3 inch exhaust was due to wanting more power, I wasn�t about to go fit restrictive mufflers onto my exhaust and since Australian legislations state that aftermarket external wastegates are not permitted for street use. I was left with no other option but to modify my standard internally gated setup to have a larger hole. The answer was to port.


Before I began I thought it threw and not long after a second turbine housing was purchased. This ensured my car would not be off the road for the whole period of the port job as It is very time consuming. After having a look at the newly purchased second hand housing it became very clear to me on what needed to be ported. Some measurements were taken and the standard waste hole was measuring in at approximately 20mm inner diameter and the flap to cover was 30mm, this left the flap with 10mm to seal around the hole. Since I wanted to make full use of the ability to port, the flapper needed to be modified or replaced the with a 34 mm exhaust grade washer as the new flap. Now this would leave 14mm to cover the hole, but since I only need about 3mm on either end in order to not leak exhaust gas, I would be left with 8mm to port (that being 4mm on each side of the hole). This being a 40% increase in diameter over that of standard.


After some further observations, I noticed that the path leading from the manifold to the wastegate was a near 90 degree turn. This being quite restrictive to flow I decided that once i began porting I would also concentrate on knocking off the wall leading to the wastegate entrance. This would make the exhaust flow much easier whilst not having to take such an abrupt turn.


Equipment needed:

- Safety glasses and gloves

- Metric spanner set

- Vice

- Rotary tool with carbide bits for grinding and other 80grit bits for smoothing.

- Solvent (to remove carbon build up)



Method:

Safety being priority, first thing is to dress appropriately, remembering to wear safety glasses and gloves as a bear minimum.

Before i began, this is what the o2 housing looked like. As can be noticed the wastegate hole can not yet be seen.





After some significant porting the progress began to look as such. You should notice the wall blocking the entrance slowly being removed.Dremels take forever! I found that music helped pass the time. At this point I was about 5 hours in.





Continuing to port, focusing on the wastegate entrance, just porting away with the rotary tool and some carbide attachments. After about five hours, the entrance was complete and my attention was now turned to the entire inlet as an oval shape was obtained from porting to one side. To reobtain the conical shape like from standard, I began focusing on the rest of the inlet. It can be seen that the wastegate is now easily accessible with far less effort. Here is a picture for comparison.





After completing the inlet my focus went onto the wastegate hole. So I began porting to achieve the calculated 28mm which I was after. This step took about 4 hours as I was using a dremel and being quite cautious, remembering to continually check the size of the wastegate. By comparison, the difference can be seen.





Now that the 28mm was finally achived, progression took place to the final stages of my project. A new 34mm flapper was purchased and shortly after it was installed. Fitment took about 2 hours and here is the end result.





The porting and fitment on the 34mm flap is now complete and the o2 housing is ready to be fitted onto the turbo.


To remove the turbo the following steps were taken:


1. I drained the engine oil and coolant from the engine to prevent major spillage which could occur when removing the coolant and lubrication lines from the turbo.

2. Disconnected the dump pipe (beginning of exhaust system) from the turbine housing (also known as o2 housing), and oil and coolant lines from the turbo.

3. Removed the bolts which connect the turbo to the manifold to release it then pulled it out from the engine, there are four bolts in total.

4. Once removed from the motor the band clamp from the turbo was removed. This separated the o2 housing from the rest of the turbo.

5. Now that the o2 housing was out, fitting the modified one was a simple reversal of the steps above.




Conclusion



Porting the turbine housing solved my boost creep completely. The car now has the ability to hold set boost to redline (peak RPM). This project was simple and cost effective however very time consuming. Enjoy

Edited by trq-str, 26 October 2010 - 11:35 PM.

[3zercrowd]

Cool info dude.

We have covered it a few times before.

People just forget to search unfortunately.

http://4gtuner.com/s...porting housing

I know ive spent hours porting mine out:lol:

[bazeng]

We should sticky this guys in the database!

Good write up!

[JiMi]

are there any other considerations? more prone to cracking need a stiffer wastegate spring?

looks awesome though

[DOUGMO]

I did the same too mine also made a massive difference
but mine isnt quite 100% yet so Im having another go at it soon.

[TRQ-STR]

Hey Jimi, a stiffer spring will only increases boost. If for example your boost crept to 18PSI and you had a 20 Psi spring you would no longer have creep.

Fitment of smaller exhaust or restrictions such as non hi flow cats and mufflers will help. The theory behind this is that Pressure is indirectly proportional to flow. Therefore, the more restriction you have, the higher the pressure in the exhaust will be. In effect the turbine wheel will be spinning at a slower rate to begin with. This pretty much means you can get away with a smaller diameter wasegate hole. This is why they are small from standard.

[milkandoj]

Yeah that true but what would you spend time and money restricting your exhaust?
When you can port your exhaust housing or get one of those ones form gt pumps with the larger 34mm flap and all.

Spend your effort solving the proiblem no going backwards:lol:

[evopwr]

maybe a silly question, but where can i get a 34mm diameter flapper from??

[TRQ-STR]

Turbo repair shops.

Easy way out is to weld an exhaust grade washer

[Dean]

maybe a silly question, but where can i get a 34mm diameter flapper from??

GTPumps

[evopwr]

sweet, thanks guys.

[Liberoz]

I went down the road of a E3 GTPumps 34mm dump, was a great base to start with and spent around 28 hours over a week porting it out and the result = what boost creep
definitely worth every minute on the die grinder covered on filings and cast dust and more than a few Crownies