I have been meaning to share this for quite some time. I have seen ported turbos from Buschar, MAP, FP, CBRD, and even curt browns personall FP red. I have not seen anyone else do this. I have seen the back to back results of this porting and its absolutely monster on how well the turbine side works. its actually far more important than porting the inlets.

Some short tech on how the wastegate works. for one its important to understand if you set your boost controller to 20psi the wastegate doesnt suddeny fire open at 20psi. it will over come the spring pressure at maybe 12psi and slowly open farther and farther to the set 20psi. when the flapper lifts off the seat you loose torque as the twin scroll effect is lost. So when you raise the boost to say 30psi the torque rises dramatically. this is because of course you are running higher boost but masked inside this the flapper is staying on its seat longer. this is why you see higher boost pressures "spool" the turbo faster.

So to set the turbo up for fast spool and better high rpm power you want to run higher spring pre-loads on the gate. what this means is the flapper itself is simply opening less at crack pressure and wide open. problems with doing this is you can get a mean boost spike as excess boost building back pressure cant get out past the smaller opening.

So the simple trick is to port the wastegate so it flows well at small openings. rounding off the sharp corners works extremely well. ask any head porter how a one valve job flows and they will laugh at you. I have seen 4-5psi boost spikes reduced to nearly zero with doing this.

advatages:
eliminate spikes
allows flatter boost curves
lowers turbine back pressure and for more hp at less boost (more flow around turbine)
allows tighter pre loads for faster spool and better high rpm holding

 

Interesting. So what other porting would be needed on the hot side to enhance spool ( not allow more boost ) but bring it on faster.

Will the minor reduction in the separation on the flapper reduce in any way the twin scroll benefit ?

 

It will also help you reduce boost creep if that is a problem for you without messing with the inlet side. It's how I reduced the problem on my DSM because the flappers on 16g's don't open very far with the stock wastegate.

 

Interesting, thanks for posting. I'll have to check my hotside when I get home...

 

looks interesting. wouldn't it be preferable to leave the divider untouched to minimize crosstalk?

 

I wouldnt leave the divider untouched. I have done this many times and it works fantastic. The picture is funky. it accentuates the shiny spots. There is actually at least 2mm of seat retained everywhere. no loss of twin scroll effect when valve is seated. i should ad this is very difficult porting to do. this is done with a dremel, a small bit , and lots of patience. its very difficult to cut the edge without the bit walking off. ideally you cut at angles that allows bit to walk in direction that wont hurt the seat. but thats not possible unless you have a reverse cut bit and reversing grinder. you could also take the time to make little plates that protect the seat you dont want cut. in the end the marks left on the seat are not gonna effect seal enough to matter. they will fill with carbon when run just like deteriorating valve seats in the cylinder head.

here is another housing with ceramic coating I use. ready to go to work. better angle how much seat width I try to leave.

 

show us the porting job

 

Heres the one i did myself with a set of carbite burrs. Took awhile but a big difference from stock and worth the time.

 

Looks nice. Its tricky getting down that far on the inlet side. As I recall, there was a bump in one volute that I wanted to smooth as much as possible, but taking off too much would have put a hole in the housing.

 

Next time my turbo is off I think I'll give this a shot. Maybe practice porting the waste gate area on the busted housing that I have.