T25 Wastegate Porting
 

OK, I'm on the bandwagon, but I need a little more instruction and motivation.
FIRST: HAS ANYBODY DONE THIS BEFORE?
SECOND: HOW MUCH DO I PORT IT?
THIRD: WHO IS YOU DADDY?

You can see the ring around the edge of the hole where the flapper door sits. There really doesn't appear to be much metal to remove... maybe 2 millimeters. Will this really make that big of a difference in my boost overshoot problem? I still was some meat for it to seal against, right?
Based on the pic, can I remove about 50% of what's there? Should I take it right up to the edge of the flapper door or what?

And you can see there where I broke all of the bolts out of the housing... that's going to be fun!

I've never done this but I hear it makes a huge difference. Even if it looks like there's not much porting to be done, every little bit helps.

I googled it and saved a few very good writeups and even a few before/after dyno run stuff. If done properly, it seems to cure just about all boost control issues on T2 series internal wastegate turbos.
Since I don't want to get too crazy, I'm gonna take 50% of what's there to start with. I bought a couple Dremel carbide bits and we'll see where that gets me.

Sam, have you determined that the size of the flapper hole is the cause? I'm also thinking porting the inlet as to allow more efficient flow to the flapper might do the trick, but it's all theory. I'll look for a picture of what I'm talking about. I think the flapper port would be worthwhile either way.

I've done small porting jobs, although with a grinder. The carbide bits are money either way.

I'd also like to see the writeups if you have the links available.

+1...

It's only worth doing if you are getting boost creep, though I suppose it would also enhance closed loop boost control if you were getting weird spiking behavior. I've never run into this problem personally. I suspect it is more of a problem with smaller turbines or turbines that are being run closer to their HP limits. With the Link (and I suspect, most other EBCs) you can just increase the magnitude of the WG solenoid correction for closed loop, which is a decent bandaid up to a certain point.

I have ported out my new manifold WG from 20 to 26mm behind a 32mm flapper, in anticipation of more airflow. I'll let everyone know how it works once I get my EGT fitting from autometer and I can send it off for ceramic coating.

By the way, WG area and flow increases exponentially with diameter. Going from 20 to 26 is a 70% increase in area and a 185% increase in flow (due to drag from the walls of the passage).

http://www.aaroncake.net/rx-7/s4wastegate.htm
http://www.gnttype.org/techarea/turbo/turboport.html
http://fc3spro.com/TECH/HOWTO/ZWG/zwg.html

Finally got around to porting my RHB5 yesterday. No idea how effective the increases in area will be, I'll have to wait to find out.

I increased my wastegate hole diameter from 21mm to 23mm. While I was at it, I ground away at the turbine inlet to remove some roughness and hard casting lines leading up to the wastegate hole. Looking at a couple threads on boost creep on a DSM forum, it was suggested to increase the turbine inlet area and get rid of the casting roughness to allow efficient flow to the wastegate as well as slowing down the exhaust gases entering the turbine housing via a larger flow area (FLOW = AREA x VELOCITY^2). Both porting the wastegate and turbine inlet appeared to solve boost creep on 16G DSMs.

Assuming your flapper door has some wiggle room, pay attention to the amount of seating surface you have for the flapper to seal against. Example: if I was grinding on the flapper pivot side of the wastegate hole, I would bias the flapper door to the opposite side when judging how much material to remove. My flapper was not centered on the hole originally. Don't want to grind away part of your seat! ;)

Well said. I have pics of a DSM housing ported by forcedperformance, I have to find them.

The ring on the flapper as a guide?

I agree that's usually the reason for porting the flapper. I say give it a shot anyway. I do think the inlet (flow to the wastegate) should be ported as well, however.

Oh yeah. Good point :)

Yes, use the outside diameter of the flapper as a guide. Mine had enough play to move radially 1mm. That meant with all radial movement the flapper door would see, I couldn't remove so much material that the flapper seat on the turbine housing would create an inadequate seal (i.e. if light could be seen through it).

Also, just my personal preference, but in that S4 wastegate porting link, it shows how the author welded a washer to the flapper door. I'd steer clear of that...besides the fact that it looks shoddy, I can't imagine being fixed to the wastegate turnbuckle would create a good seal, flapper door to wastegate seat. That's probably why the flapper is allowed some play. You should be able to remove enough material from the wastegate and the turbine inlet that enlarging the wastegate hole diameter beyond the OD of the flapper door would not be necessary.

What's your boost setting? What are you creeping to?

Man Sam, that wastegate port looks large enough already. Are you sure it's not just a weak wastegate actuator?

For what its worth. Here's some pics of a T25 to T28 upgrade from a DSM shop that knows what they're doing. They did the following porting. I would compare the inlet to your turbo and see what material if any was removed.

Comparing the T25 flapper and the T28 flapper. Looks like they used a larger one. Hope that helps in some way.

if the port is a 1" hole, removing the 2mm (.080) from each side (.160 total) will give you a 15% increase in area which could be significant.