My Wastegate Porting Idea.. Need input
 

So here is what im thinking.

The Car: 1991 Enfini GTX Turbo
The Mod: Porting the S5 wastegate
Related Mods: 3" full turbo back, intake, HKS sequential BOV
Turbo: Stock S5 Turbo
Boost Level: Stock boost (6.5psi i think)


The Idea:

Because the car will breath so good, i know that i have to watch for boost creep. I was planning on porting the waste gate obviously, i just want to make sure that the wastegate will be big enough for what i will be running(maybe even over kill). So after reading a lot of info, i had this idea.

http://i54.photobucket.com/albums/g1...wastegate1.jpg

The inner red portion is the removed material, the area between the inner and outer lines is were a lip would be created(1/8th inch). Also maybe rounding out the inlet for the exhaust gases (look on the diagram, it will be in blue box) so the exhaust gas be less turbulant going into the wastegate hole.

Here is a diagram.
http://i54.photobucket.com/albums/g1...egateport1.jpg


At first i was planning on doing this myself, but now i am thinking about getting it done on a CNC machine.. just so everything is precise and accurate. Also i would obviously be making a custom flapper door(welding new material) that would fit the ported wastegate, i think that leaving 1/8th of an inch or so extra around the perimeter of the wastegate hole (ie a lip) would help to seal the flapper so the turbo can spool up just as quick as stock configuration.

The Question:

1.Will a overly big wastegate have a negative affect on preformance?(ie. when the flapper opens, would it let out too much gas, hence having a sudden drop in boost, until the pneumatic actuator can adjust)
2.Will an overly big wastegate affect the structural integrety of the housing?
3.If there any issues i have over looked?


Thanks for the input, Cheers

You'll need some kind of boost controller. When the wastegate opens it may open to soon. As far as structural integrety, I don't think you'll have a problem. Cast Iron is pretty resilient stuff!

i thought the wastegate would open still at whatever psi the spring is rated for? Does the size of the wastegate door affect when it will open given the same spring is used?? How so??

I am getting my turbo upgraded by BNR and they will port wastegate to 30mm, but the wastegate will still operate as normal in that it will still open at 7lbs or so, though once open it will be able to flow way more exhaust gases, therefore eliminating boost creep. There should be no bad ramifications as long as the porting is done properly. that is my understanding on my S4.

Ya well i figure it should work good for what i need it to do. I just want expert opinion.

Any thoughts at all? I would really like to know what experianced people think.

Wastegates do not need to be *as* precise as lets say, a side housing, but it is good to have a nice seal on the flapper door. I ported mine to 31mm and weleded a washer on the flapper and smoothed things up. I was quoted by the few machine shops we have around town that it would be $200 and higher to have the thing machine. I said no and went with a $4 carbide bit from a car show. Those bits cut like mad by the way. :Kill1:

Im not worried about the actual process of doing the job, so much as how this mod will impact the rest of the system. I just want to know what affect an over sized wastegate will have on the boost level.

""BNR will port wastegate to 30mm, but the wastegate will still operate as normal in that it will still open at 7lbs or so, though once open it will be able to flow way more exhaust gases, therefore eliminating boost creep. There should be no bad ramifications as long as the porting is done properly""

bigger wastegate passage means less restriction on the exhaust gases exiting through wastegate, though the flapper will still open at same time due to same spring being used, once the flapper is open there will be less restriciton on the exhaust gases than stock, so that all of the exhaust that needs to bypass the turbo can exit through wastegate and not contribute to boost creep----> lean condtions---->detonation----->blown motor.

As I said, thats my understanding.

Bigger is better.........

try it!
im sure if it turned out bad you could always find another hotside here!
maybe do it to a spare one?

just make sure everything seals properly so you don't get more lag by inadvertantly bleeding exhaust gasses.