Competition 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

 

[OPoole]

If your putting them on your 03 it's a tright fix. I have put the tial 38mm in the manifold before with no problems. On this 03-04 truck i had to put it in the manifold no room for a wastegate spacer. And had to lay it over to the valve cover also. Hope this helps!!

 

[AK RAM]

Thanks, they will be in my 03. Still much confusion and could use all the advice you can offer.



Most wastegates have two ports for feeding boost pressures to the actuator housing. From what I understand, the top port is used to fill the actuator housing with pressure that will affect when the valve opens, enabling you to tune the wastegate. Looking at diagrams from wastegate manufacturers, they show feeding pressure to both ports in the actuator housing from the same source. I understand the function of the top port, but not the bottom port. What is it's function?



Is limiting backpressure to 50lbs with 60lbs of boost realistic or should I be happy with a 1 to 1 ratio at 60lbs of boost? I understand that the least amount I can bleed off the better due to heat energy loss.



Thanks.



Brian

 

[OPoole]

If you get 1:1 you doing great. I use a heavy spring and add boost air to the bottom port on wastegate to help open it. Leave top port open.

 

[AK RAM]

Ahh. Excellent! So if I have this right, you have two options.



1. You can feed boost to the top and bottom of the actuator to keep equal pressure on both sides. Add, say a 15lb spring, and when the backpressure pushing on the valve reaches within 15lbs of boost, the valve will open. Is that correct?



or



2. Add big springs to put a lot of down force on the valve (I assume to minimize creep) and feed boost to the bottom of the actuator to help it open. This seems like it would be the most effective with creep in mind, but the hardest to tune as the springs for these only come in poundage up to about 25lbs. Seems you would have to use two springs, one fat and one skinny to fit inside of it, to provide enough force to resist opening to early. Is that it or do these springs not work quite like I'm thinking?



So, in picking a spring size while keeping unnecessary open time to a minimum, how efficient can I expect an external gate to be? Obviously the bigger the gate the more efficient and some road testing will have to occur, but in general terms. For instance, if I want backpressure limited to 60lbs, can I expect the backpressure rise to stop quickly enough if I have the gate open at 55lbs?…. or would I have better results if I have it open at 40lbs, giving it more time to stop the rise?

 

[BPonci]

When you feed boost to the top side of the w/g its like changing the spring rate. The more boost on top the more boost overall you are going to see. You can use a regulator to control inlet pressure to the top port for max control of boost creep.

 

[Huff N Puff]

Ive tried lots of different ways to control the externalwastegate. The best way to date for me was to use a 40 to 50lb spring to keep the waste gate shut. To open it I wired in a Hobbs switch set for 50psi which then operates a electronic pneumatic control valve which instantly blows 50psi & above into the bottom port of the wastegate. This achieves two things. It keeps the wastegate closed for low end spoolup then blows open the wastegate after 50psi to kickstart the bigcharger. Merv

 

[AK RAM]

Olee…. I'm finding out that getting a good weld to the cast iron ATS manifold will be tricky. What did you find provided the best stick for you?