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

[TopTuning]

https://forums.pelicanparts.com/porsche-911-technical-forum/1183414-chasing-response-air-cooled-flat-six-vgt-turbo-tech.html

Linking to my thread in the 911 Technical forum, for turbo guys that might not visit there often.

This project is moving along. Hope to have it on the dyno within a couple weeks!

[David]

After reading your thread I got curious if Garrett has any VGT aftermarket turbos and unfortunately I couldn't find one. I'm curious to hear how the tuning goes and how you set up the VGT. Is it just RPM based?

[TopTuning]

Originally Posted by David

After reading your thread I got curious if Garrett has any VGT aftermarket turbos and unfortunately I couldn't find one. I'm curious to hear how the tuning goes and how you set up the VGT. Is it just RPM based?

VGT tuning is fully mapped on load and RPM, standard 3d table, with some functions like opening at cruise to reduce EGTS, closing at idle to quiet the exhaust etc.

[aschen]

cool project.

I always use it as an example of progress that my 4cyl cayman gts is so much faster than her older brother with 2 more cylinders.

[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.

[Tippy]

VGT is awesome for sure.

[Mocker]

For those of us not very far up the learning curve on the subject of variable geometry turbos, this photo shows how they alter the airflow on the hot side of the turbo to spool up more efficiently across the rev range. Pretty cool technology.

[TopTuning]

Originally Posted by Mocker

For those of us not very far up the learning curve on the subject of variable geometry turbos, this photo shows how they alter the airflow on the hot side of the turbo to spool up more efficiently across the rev range. Pretty cool technology.

It's also MUCH easier than I expected to control. Just a single PWM input (as well as 12v power, and chassis ground) runs the unit. The "feedback" wire I haven't quite deciphered, it seems to be a 12v pulse for error codes.

A stand alone control unit is definitely possible. I have my setup just run on a table, RPM and manifold pressure determine the PWM output.

[fourblades]

Originally Posted by Mocker

For those of us not very far up the learning curve on the subject of variable geometry turbos, this photo shows how they alter the airflow on the hot side of the turbo to spool up more efficiently across the rev range. Pretty cool technology.

Thanks for this, never understood how it worked before.

John

[Mocker]

Sorry for the giant photo...I swiped it off the intrawebs.

[spence88mph]

Originally Posted by TopTuning

TEST DRIVE IMPRESSIONS:

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

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.

[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.

[David]

I'll be following since I'm definitely interested. My car's making big hp but as a street car it's more of a party trick than useable power. I would like to see something less gangly than the Cayman turbo tho.

[TopTuning]

Originally Posted by David

I'll be following since I'm definitely interested. My car's making big hp but as a street car it's more of a party trick than useable power. I would like to see something less gangly than the Cayman turbo tho.

Less gangly?

[David]

Originally Posted by TopTuning

Less gangly?

My first thought at the start of the thread is there’s a bunch of hardware hanging on the VGT and how will all that fit in my engine bay. Now looking at it and how it would fit in place of my turbo, I guess it’s really not that much bigger than my Garrett and most of the extra components are under the tin and out of view.

[TopTuning]

Originally Posted by David

My first thought at the start of the thread is there’s a bunch of hardware hanging on the VGT and how will all that fit in my engine bay. Now looking at it and how it would fit in place of my turbo, I guess it’s really not that much bigger than my Garrett and most of the extra components are under the tin and out of view.

There is definitely some extra hardware, and a bit more restriction on clocking and mounting location. Well worth it though. For what it does, it's a compact and very well designed unit.

[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.

[MikeD930]

I sent an email to you, @ TopTuning, yesterday. Let me know whether you received it or not.

Thanks,
MikeD

[Porsche 935]

My first twin turbo Porsche set up used 2 small turbos which spun up so fast that full boost was achieved by 1800 rpm and it would pull the wheels off the ground in 1st gear under acceleration. I had to tame it down with slightly larger turbos that spooled just a bit later at 2500 rpm