Featured: Jae Lee Drives A 1973 Porsche 911 With A Massive Air-Cooled And Naturally-Aspirated 4.4-Liter Flat-Six That He Built

Jae Lee Drives A 1973 Porsche 911 With A Massive Air-Cooled And Naturally-Aspirated 4.4-Liter Flat-Six That He Built

By Patrick Stevenson
April 8, 2019

The sound is still ringing in my ears and it’s been well over a week. Approaching its 7,500-rpm redline, the 4.4L flat-six in the back of this car demonstrates just how worth it all the hard work was. Being a Porsche enthusiast and 911 owner myself, this is nothing short of a dream engine build. It is 440 horsepower of pure air-cooled magic; no turbochargers, just naturally-aspirated operatic screams.

At Chuckwalla Valley Raceway, after my pulse has settled after the ride we’ve just had, I sit down with the car’s engine designer Jae Lee. He owns Mirage International, a Porsche race and service facility in San Diego, CA. After a bit of catching up, we talked about the five-year development of what is at the moment the world’s largest air-cooled Porsche flat-six.

Jae’s passion for Porsche started with the 1973 911T pictured here, which he purchased in 1990 when it looked quite different. Mirage International was exporting Porsches to Japan at the time, as the country was having a huge economic boom and gobbling up all the clean 911s Jae could find.

As many Porsche owners do, Jae started taking his personal 911 to the track with his friends, and he became obsessed with tuning the suspension on his car. On his humble track day beginnings, he says, “I was driving out at Willow Springs on the big track, and I was just not confident in the car. The balance was not right, so I kept messing with it. I knew it could lap faster, but I wasn’t comfortable with how it felt. Finally I got it dialed and started beating all my friends. Soon after, they were all asking me to set up their cars. So, the business kind of just evolved into a Porsche race shop.”

With personal and professional pursuits aligning, Jae always made time to develop his own car, and soon enough his trusty ’73 911T was modified with RSR wide fenders in the front and rear, the stock torsion bar suspension was removed and springs were added, larger wheels were introduced to fit larger brakes and they wore wide racing slicks. Of course, in this pursuit of speed power is eventually needed after the chassis work, and Jae found a new obsession in the engine room.

Being a racer and race shop owner, Jae has seen his share of blown engines. Racing is the most stress anyone can put on a motor without the intent to brick it. The sustained high revs and corner G-forces will put any engine to the test, and he certainly tested a few. The 911 ended up with a 3.6L engine out of an early ’90s 964 back in 1995, which was then built out to a 3.8L.

As he started to break more and more of these motors over time, he learned which components failed and why, and constantly looked for improvements to implement into his next mechanical heart. His drive for perfection in the engine bay led to him landing on the right combination of parts to make reliable race-ready motors.

Eager to learn more about what that really means, I asked Jae expand on the process: “It is all in the details. I spend 40-50 hours just measuring everything. These engine cases are old and the main bearings are not all the same. The crankshaft dimensions need to be addressed along with con rod dimensions. This makes a difference in how balanced and smooth the engine runs. I have also found it makes them much more durable on track.” Jae has earned a reputation in the Porsche racing community for his high quality engine builds, and the degree of thoroughness combined with the countless hours of empirical research and development makes a strong argument as to why that’s the case.

In fact, when Singer Vehicle Design was building its first cars, Jae was brought in to design and build the 3.8L engines, bringing his expertise to the now-famed high-end modification brand. He personally built most of the early engines for Singer’s projects, although all of these engines wore the Cosworth badge instead of Mirage International.

Jae’s focus in his own car could not stop at a 3.8L though, and Jae’s 4.4L Porsche is an absolute monster. The thrust of the torque from this motor pins you in the seat like something modern and all-wheel drive might, and it doesn’t let up until you shift gears, after which it slaps you right back into place. Coaxing 440 horsepower out of an air-cooled flat-six is no easy task, and Jae told me a little bit about the difficulties of going so big: “These Porsche motors suffer from harmonic imbalances when you build them beyond four liters. I have personally seen the vibration on the dyno and watched as it explodes the GT3 oil pumps and other internals without notice. This was a serious hurdle to overcome in developing this engine.” This is also the reason Jae’s 4.4L is so unique, and at the time of writing, the only one of its kind.

He had to design a custom crankshaft, connecting rods, rods and pistons and cylinders to make it all work properly. Much like Porsche itself, Jae put his engine through the crucible in motorsport to vet its abilities to do more than make a one-hit wonder dyno printout. The process has taken over half a decade and countless hours on track to get to this point. The 4.4L in this once-humble ’73 911 has over two years of track use on it since completion without failing. In fact, right before this shoot, he took home second place in a PCA (Porsche Club of America) time trial at Chuckwalla Valley Raceway in Desert Center, CA.

Track days and countless hours of testing means she’s no beauty queen today, but this Porsche platform has made it all possible for Jae, and it’s lived a far more interesting life than most in the process.

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Jasmine Thompson
Jasmine Thompson
5 years ago

I have read your post. It solved some aspects of the problem. I think you need to make the problem clearer http://run3.run

5 years ago


new here .
here is an old dyno run from about 2015 or so…..

and another one running 2 laps on the track…. (sorry, old tires, a little sloppy)…..



Son of stig
Son of stig
5 years ago

great article, but patrick we need some videos of this beast

Chris Fisher
Chris Fisher
5 years ago
Reply to  Son of stig

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