Chasing Response: Air-cooled Flat-Six with VGT Turbo Tech

[TopTuning]

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.

[TopTuning]

(continued. Why do we still have a 10 image limit here?)

For the exhaust, I didn’t just want to slap together a laser cut inlet flange and massaged to fit pipes. Instead, I designed a tight-fitting Y-pipe inlet with a bank divider to improve flow velocity and reduce turbulence. It took about 10 design iterations, plenty of fitment checks, and CFD simulations, but the final piece should work beautifully.

I'm using the the plastic 3D-printed prototype for fitment—final version will be 3D metal printed in GH3625 Inconel, a seriously impressive “super alloy.” Also the stock 718 turbine inlet as a comparison.





Stock 718 exhaust:




I chopped up my old setup and tacked in some new pipes from the headers (321 stainless). ER-347 rod welds it beautifully to GH3625. I’ll eventually build new headers, but my bargain-bin set has somehow held up to years of abuse, so they’ll do for now.

VGT Control

This is where things get really fun. As a MoTeC dealer, I have access to all the right info. MoTeC USA shared the actuator control details, pinouts, and connector part numbers. I also have full MoTec mapping for the engine and VGT system, so integrating it into my M150 ECU should be straightforward.

I’m also considering developing a standalone universal controller for these VGT actuators. Not every ECU can handle VGT control, but a simple programmable microcontroller (like Arduino) with some trim pots and supporting hardware could make it possible for nearly anyone.

Current Status & Goals

The turbo is mounted, and most of the puzzle pieces are in place. I’ll finish the exhaust once the engine goes back in—which should be in a couple of weeks.








Performance target:

Similar peak power to the EFR 7670 it’s replacing (around 414whp)

But with boost coming in as much as 1000rpm sooner

That change alone will completely transform the driving dynamics for the better.

More updates to come! Once everything is thoroughly tested, I’ll also make the adapters and components I’ve designed available to others who want to try this tech.

[Ryan_Cunningham]

This is awesome. Once life settles down we're definitely going to be talking!

[eastbay]

Super cool, that is some great work.

[75 911s]

Nice work. Following with interest.

[TopTuning]

Got bored last night and got my new back purging setup so I went ahead and welded the pipes up. 321 is hard (especially used, despite how much you clean it) Titanium isn't any easier (only my second time welding it!)

Results are decent cosmetically (maybe a bit too much heat), but full depth welds and back purged so they should be full strength. Back purging gives an equally smooth interior weld, which I smoothed out a little more with my bore sanding air tool attachments.

Just waiting on parts from my other big project (custom flywheels for the 996 gearbox swap) to put the engine back in now.

[TopTuning]

Got the custom Inconel hot side shield on today and, it fits beautifully!

Was built off a high resolution 3d scan I did on the turbo, directly to a 3d print to use as a templet.

This should also fit a factory 718S, so I will offer these as a product for those guys as well.

If you haven't experienced the FANTASTIC functionality of these units, it is SHOCKING how well they insulate. The radiant heat is effectively reduced by 90%+

I've run countless dyno tests with these, you can literally touch the shielding after. Try that with a uncovered housing - you'll be leaving skin behind! They also hold up to many, many thousands of miles of use without any issues or any signs of wear.

If you want one of these, and it's not currently available for the turbo you are using, feel free to reach out to me. They can also be made to cover exhaust manifolds, downpipes etc.

These are far superior to the soft fiberglass "blanket" style heat shields. They fit much more tightly, work equally well (or better), and are reusable (the soft ones generally fall apart if they are removed after a few thousand miles). They also wont promote a fire if they are contaminated with oil. This does come at a higher price, but I find it well worth it.

Here are some pictures for your viewing pleasure:

[TopTuning]

New part has arrived!

3d metal printed turbo inlet, Inconel alloy. Todays technology is very impressive, and surprisingly affordable for such a piece.

[David]

Very cool! Sure would like to see you post this on the turbo forum for those that don't go to the 911 tech forum too often.

[TopTuning]

Originally Posted by David

Very cool! Sure would like to see you post this on the turbo forum for those that don't go to the 911 tech forum too often.

Great suggestion - done!

[Nk993]

Very interesting. But now that tech is moving on...have you thought of instead of VGT instead retrofitting the new hybrid eturbos? I am not sure if enough have crashed yet to be able to find the spare parts but using one of the hybrid eturbos from the GTS would be incredibly interesting. I doubt there would be much of a weight penalty either as you might even be able to skip the alternator (unclear if possible though without the ISG on the gearbox) entirely

[TopTuning]

Originally Posted by Nk993

Very interesting. But now that tech is moving on...have you thought of instead of VGT instead retrofitting the new hybrid eturbos? I am not sure if enough have crashed yet to be able to find the spare parts but using one of the hybrid eturbos from the GTS would be incredibly interesting. I doubt there would be much of a weight penalty either as you might even be able to skip the alternator (unclear if possible though without the ISG on the gearbox) entirely

I have looked at those. Very cool tech, but much more complicated. That would require an entire 48v system, battery and management to be installed. Not very practical for most, and likely a significant weight penalty will all the parts together. It would let you run 48v electric AC though, which actually works well vs 12v systems.

[TopTuning]

UPDATE:

WOW. Setup works very well. Spool / response with the VGT unit is INSANE.

Something like 1600rpm faster response vs my previous turbo (EFR 7670 t4 twin scroll)

Above 3500 the boost response with the VGT unit is instantaneous. Basically as fast as you can put your foot down.


At 1.3 bar the peak power is similar to the EFR unit, but with a massive low end and torque advantage. Nearly 100ftlbs more peak.

Above 1.3 bar, the VGT unit basically runs out - no additional power to be gained. The EFR unit shines at the higher boost levels, and flows much more on the high end, but with a significant loss of low end and boost response.


The next steps will be to have the VGT turbo's compressor wheel upgraded. On the Boxster / Cayman this adds a little lag, but delivers far more flow up top - 600hp is possible (apparently)


Some notes on comparisons:

EFR 7670 dynos were on a 77 2.7 engine. The VGT dynos are on a 3.0 engine.

EFR 7670 dynos were done at sea level (Santa Cruz, CA). VGT dynos are at about 2600ft (North Idaho)

At sea level, the VGT unit would likely reach full power even faster, and deliver a bit more power.


At 1.3 bar. the VGT unit is clearly superior - even at higher boost the 7670's gains are small and only up top.


Overall, the stock VGT unit is absolutely fantastic for a street driven car. Porsche really knew what they were doing with this unit.

To get a little more power (400-450whp) a wheel upgrade is needed. I will test this next.


VGT 1.3 bar VS EFR 7670 1.3 bar:




VGT 1.3 bar VS EFR 7670 1.5-1.6 bar:





More to come soon.

[TopTuning]

TEST DRIVE IMPRESSIONS:

Good lord! It's been a while since a car made me say "holly ****!" out loud.

The turbo spools like any modern turbo car - nearly instant. Yet it pulls like a big turbo when it hits, and feels strong all the way to redline - which comes quickly!

This is leagues better than any turbo setup I've ever done, and I've done a lot, as in many dozens on my own and customer cars.

The fanciest setup with beautiful equal length headers, a super nice Borgwarner EFR turbo... CAN NOT TOUCH THIS. it's FAR better than I expected and hoped for.

It's hard to explain what this car pulls like now. It is similar to my fully upgraded 2013 audi s5 6 speed supercharged (daily), but maybe if that car lost 1000lbs. On first drive I completely unintentionally exceeded 130mph. Just feeling the power in the higher gears.

I will note test drive conditions were great for a turbo car, air temp about 40F, intake temps about the same, much cooler than I saw on the dyno. The engine is likely making 500ftlbs and 450hp to the wheel with the cool temperatures.


I used to build 900+ hp 959s at Canepa. This car would absolutely destroy one to about 80-100mph, unless you really launched the 959 (would likely break the torque tube couplers if you did!)


As a turbo guy (for decades) and "expert" in designing turbo systems - I will never build another setup not based around a VGT unit.

This turbo makes ANY traditional turbo feel just stupid and antiquated. Spool is crazy fast, boost response above 3000 rpm just matches your throttle position - zero lag!


I cannot recommend this unit enough. Absolutely shattered my decades worth of turbo experience and expatiations.

Compressor wheel upgrade will be next. I'm debating between the midrange upgrade or the maximum upgrade, as the car already feels so amazing. More to come.

[PeteKz]

I didn't see a reference to an intercooler. No intercooler?

[TopTuning]

Originally Posted by PeteKz

I didn't see a reference to an intercooler. No intercooler?

It has my full WTA intercoolers setup

[quattrorunner]

Impressive

[TopTuning]

Originally Posted by spence88mph

This is incredible, you have about 330 as apposed to 120hp at 3500rpm, would be wildly fast out of corners if you can get traction.

My 996 six speed swap and wavetrac made good work of that

It's so responsive that it's much easier to drive hard. The power comes on much sooner much much more predictably, and throttles easily. Above 3500 the torque / boost literally comes on about as fast as you can put your foot down. It's unbelievably good.


I will be releasing / selling a FULL support / product line for these turbos.

Most of the products are already listed on my eBay account and webstore.


My personal car - I decided to tear the engine down and upgrade the internals, while the turbo is out for upgrade. Pushing more power than this on stock 3.0 internals would be extremely risky, even on e85.

So it will go back together with forged pistons, rods, new cylinders and probably a cam change. With the upgraded VGT turbo, we'll see what it can really do!


If I can make about the same torque and just hold it a bit longer up top, it will be absolutely perfect.

I'll tell you guys, I had a toyota 1jz powered fd rx7 making 750+ whp before. This is far more fun. Peak power is for fan boys and dyno queens. We (generally) aren't racing these cars at the drag strip or from a 80mph roll. This is coming from someone that used to chase big power and had a few MKIV supras, the fd mentioned, and built / designed the 900 hp 959SCs at Canepa.

An engine with BIG low-end torque and good peak power is FAR, FAR more fun on the street, and actually much faster in basically every real world driving situation.

[quattrorunner]

So you're making this vrt kit as well as the 996 trans swap kit? When will you be selling this one? And with what headers?

[TopTuning]

Originally Posted by RarlyL8

Nice that you are looking at VNTs! Will you have the opportunity to directly compare with a conventional turbo by swapping one in place of the VNT? The typical modified CIS 3.3L 930 engine can hit 375whp with 1.0bar all in by 3000rpm, I don't know what that would look like on a 2.7L engine or what a VNT would look like on the 3.3L low C/R 930 engine. I played around with the old school VNTs 20+ years ago (no computer aids or EFI) and while they did improve drivability full boost didn't come any earlier. EFI and computerized engine management alone helps performance and reduces turbo lag which muddies the waters when trying to compare.

VNT / VGT (Basically the same tech) turbos require careful calibration to realize all the performance. This means AT LEAST a 3D control map, though factory style calibration has a multitude of 4d mapping.

If you look at my dynos, there is a somewhat direct comparison to a EFR 7670 WITH a quick spool valve. I don't know why I forgot to mention that part of the old setup - I'll go back and edit it!

Spool is basically irrelevant on it's own - what matters is the torque band! What's much harder to show / prove is the boost response in important areas.

The VGT turbo in this setup absolutely DESTROYS the response of the EFR 7670 - a turbo that already responds MUCH faster than a "traditional turbo"



Example, from my experience having driving 100s of turbo Porsches:


4000 rpm - decel to full throttle:

Stock style turbo (tuned and bolt-on upgrades etc): About 1-1.5 seconds to full power. Old school turbo tech, but still pretty fun and fast!

Modern ball bearing turbo (EFR 7670 or similar, properly sized performance turbo): About 0.4- 0.6 seconds to full power response. Huge upgrade over an older style unit. Cars feel awesome like this!

VGT turbo: the power comes on as fast as you can put your foot down. There is essentially ZERO perceptible lag. 1/4 second to full power, or less. The engine feels like it's triple is actual displacement, or like a very healthy supercharged setup.


I hope that helps explain just what these things can do! It's not just about the quicker spool and low end gain (though that's a primary benefit!) - the boost response is one of the most noticeable changes. Complete transformation over a normal turbocharger.


I'm not a "keep everything secret" guy. Here's my data for control on the Porsche VGT unit. Please note this could use a bit more work, and will change with different engine and exhaust setups etc:







Please note - running other duty cycle frequencies or duty cycle below 20% or above 80% results in the controller going to to fault mode. The fault will not reset until power has been cycled to the controller. (this was fun to learn)


I still plan on making a stand alone controller for the VGT turbos, for guys with less advanced ECUs or that just don't have the available outputs.