Advice on External Wastegate on Twins

[AK RAM]

I have an opportunity to get a small set of towing twins really cheap, but if I do this I want to add an external gate before I put them on to keep backpressures in check. I don't think I want to consider these twins if I can't get an external gate to work. I have read through all the old posts and seen many pictures on external gate installs, but I'm still a little confused on a few things.

The biggest obstacle is fitting an external gate in there. Most are using a spacer between the manifold and the secondary and mounting the gate to that. Is there something wrong with mounting the gate directly to the top of the manifold? Reason I ask is it does not appear I would have enough room left in the engine compartment to use a spacer. The only way I can get a gate in there would be to drill a hole in the top of an ATS 3-piece manifold and weld on some pipe. I see Piers sells a manifold with an external gate already welded to it. I guess I'm just curious why more people don't do this…..something I should be aware of here? Seems like less work than fabbing up spacers. Is it just that most don't want to hack a perfectly good ATS manifold?

Second, where does the boost/backpressure reading come from that causes the gate to open? I have seen some with a tube running from the gate to a tapped manifold bolt to pick up a boost reading and others have no tube. Is that just the difference between models?….some picking up a reading from an external source and some picking it up internally?

Last, the models and sizes of external gates are never ending. Some of the brands I have seen recommended in old posts just don't look like the kind of gate you would use on twins, leaving me even more confused about how an external gate works. I see many with 5lb springs, 10lb springs, 20lb springs, etc.. The twins I am looking at are running close to 70lbs of backpressure at 60lbs of boost. My goal would probably be to try to limit backpressure to 50 or 55lbs if possible. From what I'm seeing, it leads me to believe that if you have 70lbs of backpressure and want 55lbs, you put in a gate with a 15lb spring??…is that correct or have I just not found the appropriate wastegate? I would think a gate set to open at 50lbs so it will have a chance to bleed off pressure before it hits the 55lb mark, but I have not been able to find a 50lb external gate yet.

Once I get this all figured out and if it will work, I'm looking at a Tial 38mm with v-band clamps. Any pros or cons to that particular model I should be aware of?

Any info you can provide would be greatly appreciated! Thanks. Brian