here's an interesting approach to an external wastegate
 

Modifying an ATR Turbo Wastegate
http://www.key-ideas.com/wastegate.JPG

I'm suddenly overboosting to 18psi when cool out.

This isn't really anything new. Us dsm guys have been doing this for quite a while because we used a 2 piece downpipe (think fm style) and a 38mm tial fit perfectly.

example:
http://stores.punishment-racing.com/...recircside.JPG

In fact, I talked to Corky when my down pipe was being built and asked him about doing the same thing so I could run a tial and use different springs to control my boost instead of a mbc, to which he replied " there isn't much of an advantage to doing this because in the end, you are still relying on the size of the internal wastegate hole to prevent boost creep." You can port it out a bit, but its risky business as it will eventually crack if you port it too much.

This is how Cjernigan's first setup was, he didn't have boost control issues.

The biggest disadvantage w/ this setup is flow quality at the turbine exit, probably doesn't amount to anything though.

I couldn't do this w/ mine, as the wastegate port can't be sealed to the housing (big cavity.)

My S5 manifold doesn't have boost control issues, yet.

Think space would permit something like this on a BEGi DP?

Is welding to cast more prone to cracking (ie BEGi's ex.manifold w/ ext wastegate)?

yes, it is more prone to cracking.

Right, but the flapper is gone too. That helps.

I love this design from ATP... clean and Vband.http://www.atpturbo.com/Merchant2/gr...cial%20t25.jpg

We (CAT) tried that on a few engines and it worked well until the weight started to "stretch" the casting/machined sealing surface of the WG flange.

suposedly those really screw-up spool-up.