Internal or External wastegate

[Shane@DBPerformance]

The lower the boost you want to run, the bigger the wastegate you need.

[Pimpin Dsmstyle]

He's getting DSMlink, probably 1000cc injectors and an SCM61 within the next month or so. He has 3inch o2 elim ( almost straight piped) exhaust. What would the best way to fab up a dump tube and go externally gated? The car already has a 2g manifold as well. I've seen externally gated cars setup a couple different ways. I'm not sure what the smartest / simplest ways are.

He want's to try and drive this car daily even with the SCM61. The idea is to daily drive @ about 20psi on pump gas. He wants to have another tune setup for track and race gas.

Next question is how do you pick the correct size for the turbo? I saw alex mentioned 38mm or 40mm. What exactly are the advantages / disadvantages to going say 40mm instead of 38mm?

Originally Posted by ecoli

The lower the boost you want to run, the bigger the wastegate you need.

Did you mean the higher boost, bigger the wastegate? I wouldn't understand why you would want a bigger wastegate for lower boost levels.

[Speedfreak]

Because with a larger turbo, its harder for a smaller wastegate to bleed off enough air to keep the boost down. I have a scm61 on a Turbonetics manifold, and a Tial 40mm. I can't keep it from creeping on pump gas. I've ported the manifold as much as possible to get as much air to the wastegate, but with no avail. The placement of the wastegate on this particular manifold isn't the greatest, but in any case, the larger the turbo, the larger the wastegate needed to hold low boost levels.

[JET]

Originally Posted by Speedfreak

Because with a larger turbo, its harder for a smaller wastegate to bleed off enough air to keep the boost down. I have a scm61 on a Turbonetics manifold, and a Tial 40mm. I can't keep it from creeping on pump gas. I've ported the manifold as much as possible to get as much air to the wastegate, but with no avail. The placement of the wastegate on this particular manifold isn't the greatest, but in any case, the larger the turbo, the larger the wastegate needed to hold low boost levels.

I have a Tial 40mm off the O2 housing on my SCM61 and it is fine, runs 15 psi. Nash's was the same and didn't have an issue. It must be the placement.