First time builder here, familiar with concepts but need help with implementation.

I'm planning a twin turbo build for a Porsche boxster. 2.7l h6, 207hp stock, 11.4:1 compression

So far I have gutted the intake and exhaust and now have catless 2.5" independent twin exhaust and a 3.5" short ram T intake.

Because of the layout I want to do a remote twin setup pushing a max pressure ratio of 1.5 moving about 15lbs/min with a goal of 300hp. Obviously smaller turbos are a must to minimize lag, so I am looking at t3/4 50 trim .48 ar. (I was thinking garrett 2860s w .57 ar but want to start cheap just to prove the setup works first)

Here's my problem - I can't find any of the t3/4 .48 turbos with an internal waste gate. I have little experience with external waste gates, but they seem like a headache in terms of plumbing - the simplest which I could see would be a single wastegate on an H pipe but I'm not sure that will work out due to flow dynamics in that setup.

So here's my question. Since I would be running on the ridiculously low end of the turbine chart, is it possible for me to run without a wastegate on the hot side? I know the question sounds crazy. My thinking here is that since I am so low on the compressor curve I won't stress the turbo (even at WOT), I can control boost pressure on the intake side (I was thinking an external wastegate mounted on the pre-MAF intake and controlled with an electronic controller), and the setup would be virtually lag free. I know this will be less efficient since I'm wasting charged air, but it seems like a small trade off for fast spool times and saving an assload of fabrication.

Anyway, feel free to rip this idea apart. I just wanted to get opinions from experienced builders.

Best, Ike

 

Wastegate in the H pipe won't have flow priority, and unless your exhaust pressure is really high is not likely to do anything.

No gate is a bad idea, remember as the turbo spools mass flow increases. You will end up with uncontrollable boost levels.

Search for a single turbo of the right size with an internal gate. It may end up being easier to package, especially if you cant find turbos small enough for twins with internal gates.

 

A 50 trim is a very bad turbo choice for twins. You may even want something smaller than a 2860 for 30 lb/min at 1.5. Like Ben said, a single will be a lot more cost effective, or look for import versions of a 2554 or 2860

 

Thanks guys. Im having a hell of a time finding import 2860s, every one I find is actually a 2871.

In terms of controlling boost pressure without a watergate in the usual position, I could position one on the T plenum just before my MAF. That way it could effectively regulate boost (through use of an electronic controller) and also serve as my BOV. I've never seen anyone do this before, but I didn't know if there's a hard reason why this won't work.

Why is a 50 trim bad for twin setups?

The problem with merging the exhausts for a single turbo is all space related - essentially the rear of the transaxle is in the way of a symmetric merge, and I would have to route the exhaust to one side or the other to merge the two and then back out toward the center to get the tips back to oem position.

Question - with remote setups, does symmetry of the exhausting piping before the turbos matter? It seems to me that unless the two sides were identical to the merge point, it would change flow characteristics and inherently hurt or help one side. Maybe that's over thinking it.

 

You can't control boost on the intake side, the turbo would overspeed, and eventually destroy itself. 50 trims are bad because they're just too large on the compressor side. They would most likely surge. It's much more important to size turbos correctly on a remote mount. As long as both sides are relatively equal in volume, and number of bends I wouldn't worry about it.

 

Thanks mlnx, I appreciate your input. I will keep up the search.

 

It's very common for the two banks to have unequal lengths feeding a single turbo. Many will have the turbo directly on one bank and the other side piping over to feed it.

 

Hey thanks disney, that's really valuable to know.

 

This is how my remote single turbo set up is, it works pretty well, and I made a Y pipe just before the turbo to mount the waste gate on to give it priority when its open. I'm using a single 44 mm tial gate.