1998-11 CARBOY - Akira Nakai's Porsche Carrera Project - Roll Cage

Not only the exterior, but also the engine, suspension, and everything else follows Nakai’s philosophy.

This is where the origin of today’s RAUH-Welt mindset begins… (lol)

Last month, Nakai’s Porsche had its suspension system behavior checked.
But as expected—body reinforcement was unavoidable.

So work begins.

If you’re going to reinforce a car… it has to be a welded roll cage, right!?

“This wasn’t the plan…” — The Secret Pipe Bender

First step: buy steel tubing.

Off-the-shelf roll cages are way too expensive, and bolting on prefabricated bars with “quick fixes” is simply not acceptable to Nakai’s spirit.

So the pipe bender he had previously bought—anticipating a day like this—finally comes into action.

He ordered it from a mail-order ad in CARBOY.
It can bend pipes of various diameters and radii.

It had been sitting in a corner of his workspace for who knows how long… waiting for the day it would finally be used.

At a nearby materials supplier, he bought two 5-meter steel pipes for about 800 yen each. He also bought other steel plates at the same time, so the exact price is a bit unclear. The pipes were seam-welded type, not seamless. Ideally, seamless pipe would have been preferred, but the supplier confidently said:

“No problem. If you fill it properly with sand, it’ll bend just fine!”

So he took them.

The plan was simple:

Cut to length based on the stripped Porsche interior
Match curvature by eye
Bend everything by hand for a perfect fit

But reality was far harsher.

One end of the pipe was welded shut, filled with sand, then the other end was sealed the same way. Then it was mounted into the pipe bender… and slowly bent.

At first, it worked. But only up to a point. Beyond a certain radius, the inner side started to wrinkle and collapse.

He tried everything. Heating it with a burner made it bend more easily… but it became too soft and deformed uncontrollably. Was it because of the seam-welded pipe? He even tried seamless pipe. Same result.

Standing in front of the pipe bender, Nakai could only groan. Scrap pipes began piling up rapidly. The hardest part—the rear pillar section curve—simply could not be made. And without that piece, a full roll cage was impossible.

The stripped interior parts were now stacked everywhere, adding pressure. In the end, Nakai changed approach: He borrowed a roll bar originally used for an AE86 from a friend, and adapted it into the Porsche. The rest of the structure would be shaped using the bender and adjusted to fit.

“Real Men Reinforce with Welding”

Everything is welded.

Pipe-to-body joints → welded
Contact points on pillars and roof → welded
Rear cross bars → welded

No bolts. No shortcuts. Just raw welded reinforcement. That’s the Nakai philosophy.

Mid-Process Update

The large photo shows the project at the stage where the rear section connecting both sides is being finalized. But here’s the miscalculation: The last remaining pipe was supposed to connect the left and right sides…
but it was too short.

It’s actually a funny moment if you saw it in person. Even Nakai could only smile bitterly. Originally, the plan was to extend the cage all the way to the front. But due to time constraints (this is all done between work breaks), the project stops here for now.

Next Steps

Paint the interior and roll cage
Install additional reinforcement components at the front

Those include:

Porsche-specific A-arm bar
Strut tower bar

Together, they significantly improve front-end rigidity.

The rear is now solid thanks to the cage.
The front will be completed with these parts.

And if everything ties together properly… it might be finished.

The Pipe Bender Reality Check

The biggest miscalculation this month was the difficulty of pipe bending. People building drag machines manage to construct entire frames… so why is a roll cage so hard? That thought crossed his mind more than once. Still, the sections formed with careful trial-and-error produced some satisfying results, especially the custom curved areas.

A New Addition: The LSD

This month also brought a long-awaited upgrade: a limited-slip differential (LSD). Not a standard off-the-shelf part, and not a catalog item either. It was a one-off unit obtained through a contact.

The core uses GT-R internals, while the housing is a machined, Porsche-specific custom case. It was built by a metalworking craftsman near Haneda Airport. He normally manufactures aircraft components and ship propellers—but is such a Porsche enthusiast that he started making parts for his own car.

Nakai recalls meeting him:

“He’s an intense guy. Just talking to him gets you fired up.
You can feel the passion in the parts he makes.
It’s not something you can just buy with money.
And when you realize that… I feel lucky to have met people like this since getting into Porsche.”

Hot people attract other hot people.

Photo Captions

● Caption 1

Using the pipe bender purchased for this project, Nakai begins bending pipes.
But no matter what he tries, it doesn’t go smoothly.
Is it the sand? Or the pipe seam?

● Caption 2

A pile of failures.
It bends fine up to a point—but beyond that, it wrinkles or collapses.

● Caption 3

Nakai’s welded roll cage.
Pipes follow the door line and are solidly welded in place.
Spartan and aggressive—very much a “serious” setup.

● Caption 4

The custom LSD, made specifically through a contact.
Uses GT-R internals with a machined custom housing.
A “hot man’s differential” that hits hard.

● Caption 5

While building the roll cage, the interior was completely stripped.
The plan is to repaint everything inside in the same color as the cage for a unified look.

● Caption 6

Rear cross bars are fully welded, including lower mounting points.
The goal is maximum rigidity—completely different from a stock Porsche.

● Caption 7

The Porsche-specific A-arm bar from Technical Mate (Kanagawa).
Known as a highly effective part.
Price: 29,500 yen.
It locks both front A-arms firmly in place.

● Caption 8

A 4-point strut tower bar instead of a simple single bar.
Also from Technical Mate.
Price: 49,500 yen.
The staff are former mountain pass racers, so they bring serious passion.

A-arm bar + strut tower bar added
Rear reinforcement completed
Front chassis rigidity significantly increased