Project Rough: Achieving ‘Perfect’ Sound

Waiting for the call that Project Rough was ready to pick up from R31 House, where I’d left it to be given some very special modifications, has been akin to when I was a kid, counting down the days til Santa Claus came sliding down the chimney with some gifts in tow.

But unlike December 25, there wasn’t a scheduled day that I could count down to. As with everything Shibata-san at R31 House puts his name to, only absolutely perfection would do, and there’s no minimum or maximum time limit for that. And of course, I definitely wasn’t going to try and rush the process.

But, I think that not knowing when the car would be done, actually made the time pass by quicker. Because before I knew it, I was headed back to Gifu to pick up my Skyline and, for the very first time, experience what Shibata-san calls the “perfect” RB25 sound.

The 70/10/10/10 Rule

Even though the R31 House team had kept me up to date with photos as the build progressed, I still hadn’t heard what Project Rough sounded like. No surprise then that I was dying to hear it.

When I arrived at R31 House, I found my car up in air alongside Shibata-san’s own R31 (stay tuned for a feature on this) so I could see exactly what had been changed to achieve the perfect sound. To explain the order of importance with the parts, Shibata has what he calls the ’70/10/10/10 rule’.

To achieve 70% perfection, the takoashi manifold is required. It’s not surprising to hear that the bulk of the heavy lifting comes from this part alone.

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We talked a little bit about the importance of the turbocharger when it comes to sound in the last Project Rough update, but I was a little surprised to learn that its importance only came in at 10%.

Sound aside though, the smaller-sized turbo now fitted means Project Rough has more power down low and in the middle of the rev range, which is right where I need it for the sort of driving I generally do.

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The remaining 10% plus 10% comes from a less-restrictive sports catalytic converter and a custom cat-back exhaust. The Kakimoto Racing and R31 House collaboration exhaust adds that final percentage that Shibata-san deems necessary for perfection.

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Another added bonus was the massive weight savings found with the new exhaust system. The old setup was Japanese aftermarket but of an unknown origin (like many things that have been changed out in the car over the years) and weighed in at a hefty 35kg (77lb). I forgot to ask Shibata-san to weigh the new system, but a conservative figure would put it at around 15kg (33lb).

The Results

So what does it all add up to?

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Something like this – hit play above.

Although I perhaps went a little over the top in the video to demonstrate how beautiful Project Rough now sounds, to truly appreciate everything requires you to experience it from within.

With the boost now kicking in almost 2,000rpm sooner than it previously did thanks to the smaller turbocharger, the acceleration forces harmonize with the combined sound of the RB straight-six and turbocharger, creating an experience that continues to produce a mile-wild smile across my face every time I drive the car.

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I’ve always said Project Rough is a fun car to drive, but something always felt like it was missing. Now I know that that ‘something’ was the complete R31 House Premium Sound exhaust.

Best of all, my two-year-old son now runs around the house screaming “Dadda’s car go baawWAAAAA! I’m dadda’s Skyline in a tunnel!” So that means Project Rough is the best car in the world.

Nevertheless, there are still many ideas in my head for Project Rough…

Ron Celestine
Instagram: celestinephotography
www.labcuriosity.com