Figured it was time to start a fresh thread for my latest “science project”
Background
About 15 years ago, I was one of the first to run a Holset VGT turbo on my MKIV Supra. I’ve always been fascinated by turbos and the gains they can bring. That project turned out decent—I used a simple pneumatic control setup and managed close to 450hp with very little lag compared to the single turbo I had before. My skills weren’t exactly up to the task back then, but sheer youthful determination made up for it.
Fast forward to today, and we now have VGT turbos designed specifically for gasoline engines. Even better, used units are becoming more common and surprisingly affordable.
I’ve wanted to experiment with these for a while. I even tried convincing Bruce Canepa to use them on the 959 SC builds, but he was happy with the performance from the twin EFR 6258s we were already running—and understandably didn’t want to restart development. Fair enough, but it left me itching to try it myself.
So, my development car is about to get a whole lot more “test mule” treatment.
The Turbo
This unit comes from the 718 Cayman/Boxster S. It’s compact, yet has relatively large housings. The factory CNC-machined compressor wheel is a nice bonus, though I’ll probably upgrade it.
And yes, there are upgrades! Several companies offer larger compressor wheels, with the biggest options capable of flowing around 64 lb/min—supporting up to 600hp.
Even the stock unit performs impressively. Here’s a comparison of a 718 2.5L 4-cylinder with just a reflash versus completely stock:
The most interesting part to me is the massive torque down low. While many chase peak numbers up top, enthusiasts who truly enjoy driving turbo cars value responsiveness and midrange punch. That’s where this shines. It transforms the overall driving experience, even if it’s not about outright straight-line speed—which, honestly, isn’t what a Porsche is really about anyway.
Making It Work
I picked mine up for about $1600, but there’s a catch: absolutely zero aftermarket support. No fittings, no flanges, no adapters—nothing. So I got to work and designed my own.
Here are a few of the custom pieces so far:
Oil feed adapter
Intake adapter
Coolant manifold fitting
Exhaust flange (titanium, of course)
Now we’ve got a universal oil inlet, a 3-inch intake adapter, and the start of an exhaust solution.
Challenges & Solutions
Clocking the turbo
The VGT mechanism is pinned, so the turbo isn’t easily clockable. The compressor housing must stay closely aligned to the CHRA for the actuator to function, unless the linkage is reworked. The solution: open the turbo and redrill the alignment dowel holes. This gives six possible turbine housing positions. Luckily, one of them was nearly ideal for a flat-six layout.
Wastegate actuator
From the factory, the actuator is a vacuum-operated pull-type. Not very convenient. I converted it to a more common push-type actuator. A universal bracket (with some mods and reinforcement) allowed me to clock it to match the new turbine position. The flapper arm needed reversing, so I grafted one in from a rebuild kit.
Mounting & Exhaust
Next, I designed a simple mounting bracket that ties into the original support bracket. SendCutSend makes this kind of fabrication painless and affordable.
