Ok, I keep having threads with lots of questions about fuel and wastegates, and I get lots of beating around the bush about wastegate porting, and more fuel answers, so I decided to get one thread going and only ask one question.

If i'm getting a full RB Turbo Back exhaust for my S5 TII, how big should I get the wastegate ported to? From what people have been telling me, I should get it past the stock flapper, and as much as can be taken off. How much bigger of a flapper, and how big of a port should I get then? Whats the advantage/disadvantage of getting it REALLY big, or just big? Also, i'll be doing this BEFORE even buying the exhaust, so is there anything I should be concerned about it doing before even boosting more?

 

Dude.. email Brian at BNR Bryan@bnrsupercars.com he can give you a better idea of whats going on!!

BUT... you don't want to go bigger than the flapper.... that will lead to really bad lag..

 

Get the biggest flap you can fit, and port right to the edge of it. The more the wastegate can flow, the better boost control will be.

 

hmm....two conflicting responses....

 

No conflict; we're saying basically the same thing. Whatever the size of the flap is, you shouldn't port past the edge of it or you'll increase lag. The stock flap is very small so to get a really big port you also need a really big flap.

 

the s5 TII turbo with the larger flapper, if ported to the edge, then you should have plenty of boost control!

 

Oops, sorry. I didn't notice the S5 bit.

Upgrading the S5 flap would be tricky and not make a big difference. Just port the two holes as big as possible.

Read RETed's page on how much you can port the S5 wastegate.

 

I never intended to go actually past the stock flapper, I meant like go past the stock flapper, but add on a bigger one to handle it. So with an S5 wastegate, a port UP TO the stock S5 flap would handle an a'pexi intake, and full RB turbo back exhaust?

 

I have seen RETed's write up on the s5 wastegate porting many times but always wondered how boost would be affected IF the two passages were ported to the max and made into one large hole instead of 2. That is part of the twin scroll system correct? Would it help boost creep more if that small section dividing the 2 passages was ported as well?

If ported as one large passage would use of a boost controller be affected by one passage instead of two?

 

Correct.
No, there's still only one wastegate actuator.

I don't think it's possible to grind the two ports out to one big port since they're fed by two separate passages in the casting. You might be able to blend the exits closer together, but you can’t completely join them because each is fed by a different scroll (main exhaust passage). One of the wastegate passages actually wraps around the scroll that's vented by the other passage. Does that make sense? It's hard to describe.

 

Yea it makes sense. Thanks for explaining it. I didnt know that the passages were separate all the way down.

 

On the wastegate porting topic......theoretically..could a person port their wastegate with the turbo on the engine?
Could the wastegate be ported sufficiently, and could the metal shavings be cleaned up well enough to not damage the exhaust turbine?

 

Hey fellas.

There are a few ways to have better control over your boost. One port the wastegate, and two, clip the turbine wheel. The stock compressor wheel likes to overspeed quite a bit b/c it is so easy to turn. If you go with an upgraded compressor side, it actually makes boost more predictable.

Bryan
bnrsupercars@aol.com