Internal or External wastegate
 

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

Re: Internal or External wastegate
 

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.

Re: Internal or External wastegate
 

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.

Re: Internal or External wastegate
 

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.

Re: Internal or External wastegate
 

what size wastegate should i get with an scm 61 ?

Re: Internal or External wastegate
 

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

Re: Internal or External wastegate
 

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.

Re: Internal or External wastegate
 

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

Re: Internal or External wastegate
 

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?

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

Re: Internal or External wastegate
 

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.

Re: Internal or External wastegate
 

Get the 44mm external wastegate

Re: Internal or External wastegate
 

It just comes down to packaging. We went with internally gated 50 trims on my stealth and I can get it to 15-16 psi no problem, and it doesn't creep. (heavy duty actuators).
The larger the wastegate, the lower boost you can run because you can bypass enough air.
I still perfer internally gated turbo's for street cars. Routing external wastegates is a pita and really adds to the cost of the build. Not to mention the room they take up. Granted, external wastegates are the way to go, but imho, you need to have a manifold designed for it. Just gafting a wastegate on a 1 exhaust runner is a piss-poor way of managing boost.

Re: Internal or External wastegate
 

The highest spring pressure is "HP 1.6 Bar (23.20psi).I plan to run over 30 PSI and don't understand exactly what spring pressure im looking for. O and that is on a tial 44mm

Re: Internal or External wastegate
 

The lowest boost level you can run with that specific spring is 23.20 psi.

Re: Internal or External wastegate
 

Yes but Swanny you have two wastegates for 50% more flow. Or in other words you have three cylinders your dealing with compared to four mighty 4G63 ones.:)

BTW, I have a 1 Bar spring, and I can run 30+ lbs just fine.

Re: Internal or External wastegate
 

Yeah I know.

We've put these 02 housings on scm61 cars w/o creep issues however.

Re: Internal or External wastegate
 

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.

Re: Internal or External wastegate
 

Mo, how do you run a tial 40 on a turbonetics manifold? aren't they flanged for 38s? doesn't it hit the hood?

Re: Internal or External wastegate
 

Yeah, I'm sure it's placement. I made a short curved conversion pipe, for lack of better words... 38 flange to 40 flange.. And the 38 flange is opened up larger then the 40.

Re: Internal or External wastegate
 

The spring psi is the lowest boost that the wastegate can run. The bigger the valve or flapper for a wastegate, the more likely it will be blown open by backpressure. So without any help, a smaller wastegate will be able to handle higher boost.

Most external wastegates have an extra port on them though that can be used to push boost pressure to the top side of the diaphragm to help hold the valve closed in high boost/high backpressure situations. I ran a 35mm Tial with my 67mm turbo and it was fine, but I didn't run extremely low boost and it picked up right from the collector.

There are tricks, not really the best for power, that can be done to help control boost on an internally gated turbo. You could run an O2 housing, that has a big open chamber that causes the exhauast flows from the internal gate and exhaust wheel to collide and mix together right as it leaves the turbo. You see this with a lot of OEM turbos on other kinds of cars, Mitsu kept the two exhaust channels seperate on our O2 housings stock. PTE tries to force the same thing to happen with most of their Mitsu internal gate turbos by cutting a channel in the divider wall. When the two channels of exhaust flow are allowed to collide right as they exit the turbo, you end up with a lot of turbulence and backpressure that helps to control boost and hurts your power.