Internal or External wastegate

[BoostedTSI]

I was wondering what the advantages and disadvantages of running and external wastegate or internal would be when you are running a big turbo?

[npaulseth]

External gates tend to hold boost better. You normally don't see boost creep with external gates compared to internal gates. I don't think it's so much that it's an "external" gate or "internal" gate compared to the diameter of the wastegate port.

[Shane@DBPerformance]

Internal gates suck. Some have trouble with creep. Some have trouble holding high boost. Sometimes they make your boost wavier up and down. They start opening earlier than an external, so they are laggier. Internals normally only have one port on them, so you can't use boost to help hold them shut in higher boost applications. You could spend the same or more money in porting, fancy O2 housings, and the added cost of the internal gate itself to try to get it to work right instead of just mounting an external on the exhaust manifold collector.

[JET]

Yep, external gates are better in all ways except cost. Up to a 50 trim going internal is fine, I have done a few 56 trim turbo's too. Once you go bigger than that internal is pretty pointless. Even the 56 trim should have been external, but he didn't want to spend the cash.

[BoostedTSI]

what size wastegate should i get with an scm 61 ?

[dumb_ricer]

I would run a 38mm or 40mm for a SCM61.

[CDeutsch]

If you mostly drive your car on the street and you go external I'd recommend you factor in the price of routing the wastegate back into the exhaust or at the very least make sure it dumps way back out of the engine bay area. The sound of dumping to atmosphere is hidious and having exhaust in you engine bay just isn't a good thing IMO.

[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?

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.