I don't even want to go into all the problems leading up to my posting this question, so bear with me if it sounds kind of sketchy.

I had a LS6 swapped out for a 427 based on an RHS block and 6 bolt heads. I also have STS twin turbos on the car that have a single wastegate that were providing 6.5 psi of boost to that LS6.

I talked to my latest builder who is trying to clean up the mess from my original builder and he said that the wastegate apparently failed during the latest rounds of tuning. Now I don't have any real details, as the guy sounded worn out. But he said that he just happened to notice that the boost gauge was going up to 13 psi while on the dyno which meant the wastegate wasn't working. He's not sure how long that was going on, but only made a cryptic remark that it explained the high horsepower figures he was seeing. I'm guessing he made a few passes that way, but I don't know if he repeated it when he noticed the higher boost showing up to see if it was a CONSTANT peak of 13 psi.

So I then called the actual builder of the engine and he said that engine could safely handle 25 psi with a decent tune.

Then I called STS and asked them the price of a replacement wastegate and that conversation got diverted into the recommendation to have TWO wastegates installed. It did seem odd to me that other STS installs I have seen do have the two wastegates and mine only has the one, so I'm not sure what happened. Maybe their earlier kits only had one wastegate. But in any event, the price for the replacement wastegate along with the kit to add the second one was going to cost me $850. Ouch... Now if this was the only money coming out of my pocket lately, I wouldn't complain too much, but this is really a case of adding insult to injury...

So anyway, this got me to thinking. As far as I know, the purpose of a wastegate (or two) is to allow the pressure to be bled off of the turbos when it exceeds the setting of the spring instead of sending more boost than is safe to the engine. Sounds simple enough. But here's the thing. If that wastegate FAILED on my system, what's the chances that 13 psi was the max those turbos were going to provide? Now these are smaller optional turbos (Precision 60-1, .48 hotside) I have, since I wanted faster spool up instead of more power high up in the RPM range. So with the increased air intake needs of the larger engine, is it possible that the engine and turbos reach equilibrium at 13 psi? Or is it possible that the wastegate has just partially failed in such a way they it is still bleeding off boost, but now at the 13 psi level and there is still more oomph left on the table?

There is a reason for this question, obviously. If those turbos have maxed out at 13 psi and the engine is capable of handling 25 psi, what do I really need a wastegate for anyway? I was thinking I wanted the new engine to get 10 to 12 psi anyway, but heck if I can simply go to 13 psi and could bypass the need for those two wastegates (and keep that $850 firmly placed in my wallet) then I'm all for it.

So is this one of those kinds of thoughts that only looks good on paper (or in my head) and there's a real good reason to have the wastegates anyway?

Fragile minds want to know...

 

There's not much to a wastegate at all. A diaphragm, spring, valve and housing. That makes me wonder what's actually failed and what the logic is in adding another. If your boost is staying steady as opposed to creeping, your single wastegate seems to flow well enough. Has your tuner put a mityvac on the wastegate to test it or put a smoke machine on it to prove the continuity of the lines? It sounds more to me like the controller isn't working properly or something is causing you to run on the spring alone and that's all.
If the wastegate failed, your boost would be higher even on your engine IMO. With those small housings, it would create a feedback loop to the intake side and make more boost that wouldn't yield any more power.

I've followed your build for what seems like forever. What a journey man.

 

unless you have boost creep, my money would be on the controller.. If you are that concerned about the WG, take it apart, clean the shaft to ensure proper movement and test with a mighty vac.

 

hey rich, the base sts kits have only one 38mm wastegate. I would recommend adding a second gate. I installed the second gate on my car with the hot side still mounted on the car....It is easily done, same location but on the opposite side. I also followed your tough build..... Best of luck!