Project Thirty Four: Chasing Power In A GT-R – Is It Really Worth It? – Speedhunters

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You know the kind of engine I’m talking about – one with a dustbin-sized turbo strapped to the side and a power band similar to the F1 Twitter feed during the Abu Dhabi GP. Nothing, nothing, noise building… absolute carnage two seconds later.

The car came from Japan with 650 horsepower, so it wasn’t exactly slow, but how much of a rocket ship would it feel like with another two hundred thrown on top…?


The quest for big power isn’t as simple as just winding up the boost; not on a 22-year-old Skyline whose history is documented entirely in kanji. Plus, I think we’ve all become slightly poisoned by modern car power outputs. 500bhp seems relatively normal now. 700bhp is an RS6 with an ECU flash, while 1,500bhp is the result of twin-turbocharging a Huracán with a few YouTube stickers down the side.


Maybe I’m glutton for punishment or just a bit envious, but a ‘build’ should require more than just software and a pair of downpipes. It should be approached in stages, growing both with your driving ability and urge to continually scare yourself. But I have to say that – I own a Skyline. Tuning in stages is the only way to avoid complete bankruptcy.

It’s all just part of the journey. Picking a power figure is well and good, but what about the power delivery? The drivability, and the engine’s characteristics? If a car is an extension of yourself, surely the engine needs to feel that way too.


I realise this is immensely contradictory having said several paragraphs back that I want 800bhp. But that does come with a disclaimer: 800bhp from a highly-strung RB that basically hates its own existence. Otherwise, I’d just swap in a supercharged LS motor and spend every spare minute telling strangers how superior it is.


But what kind of sadist actively wants pain? I’ve got my hand in the air, because I’ve bleated on countless times about the Skylines I obsessed over growing up – those that did top speed runs at Yatabe in the ’90s. They had boost levels to make you wince, tyres were an afterthought, and if the car stayed on the road that was cause for celebration.


Then you’d look at the engines. There would be an odd anticipation as each tuner popped open the bonnet revealing what turbo setup they’d gone for. Would it be a giant single, or the holy grail of top-mounted twins? Oh the irony that low-mounted GT2530s felt almost disappointing despite producing north of 600bhp.


There are many reasons why bigger doesn’t equal better. Lag is obvious, getting it to fit another. The response has never bothered me with RBs because shifting the power band a few hundred RPM lower doesn’t suddenly bring a load more drivability. However, if that big turbo is on full boost by 5,000rpm – and your engine has been built for 9,000rpm – now we’re in business.


These were the dilemmas being juggled around my brain while trying to choose a replacement for Project Thirty Four. The HKS T04Z fitted felt maxed out at 680bhp, and the obvious choice would be a T51R for maximum noise and JDM snobbery. But that’s 20+ year old tech now, so would it really be the best choice when everything else going into the engine is new?

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Step forward Xona Rotor. Actually, step back for a second, because prior to this latest rebuild, I’d never heard of Xona. I knew of TiAL Sport (who are behind the brand), but they otherwise sounded like something you’d find on an eBay search. That’s partly down to my own ignorance, and partly because Xona hadn’t explored much of the Japanese tuning scene (at the time).

Stuck in my ‘bigger is better’ mentality, I was ordering a giant 60mm wastegate when an e-mail came back from technical specialist Mike Franke at TiAL Sport asking what kind of application it was being used on. Mainly to check it wasn’t unnecessarily large, and also to introduce me to the world of Xona Rotor turbos.


I’d not seen any used on RBs so understandably had my reservations. But my knowledge here is dated and limited at best; I’ll always take time to listen to someone with much more experience. Mike was keen to run through the proposed engine specs and goals, not least the type of power delivery I was after too (worded slightly better than mad Japanese-spec). What he recommended made a lot of sense. Of course it would, he works for the company… so what’s the science behind it?

An easier way to look at it is bigger equals bigger,” Mike opened with. “As it applies to compressors, the inducer size doesn’t set a specific limit for the compressor flow rate, but it is possible to leverage the exducer size to provide either higher flow, higher efficiency or a combination of both.”

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“But with a larger exducer also comes a reduction in safe shaft speed, and this all ties into how the turbo can power that compressor most effectively. Where you’ll see the most benefits from modern turbo design is in the aerodynamics. Take for instance the move from cast compressors to fully-machined billet designs which allow blade shapes simply not possible when casting wheels. We’ve been able to leverage our own manufacturing capability to bring design changes to market rapidly, which is why you’ll see such a broad range of compressor and turbine housing designs from us.”


Back on the subject of intended use, my less-than-typical goal has always been to make the GT-R feel unhinged and a bit frantic. It’s just what I find entertaining, far beyond having the most responsive throttle or peak power lower down the rev range. For an engineering mind like Mike’s, that requires some deciphering. But again, he was quick to make sense of it all.

“The best indicator of peak power capability is always the actual compressor flow rate (at the required pressure ratio and efficiency percentage) so we encourage our customers to use that data rather than inducer size value.”


“For a road car, or road/track use, we often recommend a size smaller than what a customer typically has in mind since the majority of use will be focused on drivability and less on peak power. But for dedicated track vehicles, the focus becomes more about placing the power band where it can be used with response being less of a priority. In the case of your GT-R, we’re going to be looking at something which sits in the middle of those.”


We decided on a XR 105-68 which boasted a max compressor flow of 105lb/min with a turbine outlet of 68mm. This utilised Xona’s X3C frame which is surprisingly compact given its maximum power rating north of 1,000bhp. In other words, it looked about the same size as the T04Z which came off. My brain still assumed it’d run out of steam way too early despite Mike’s reassurance.

Ron at RK Tuning shared a similar concern, but in typical Ron fashion he simply used words that were a bit easier to hear: “Well, at the very worst you’ll just have a really responsive 650bhp.” he said. The man speaks sense, and only sense.

I’m not a talented driver; I don’t need even half that power on the road, let alone 800+. Maybe I need to manage my own expectations and stop watching ’90s tuning videos. Right, dyno time.


Preparing myself for the worst – which wasn’t power related but total engine detonation – Stu at Rotor Torque called me around lunchtime with some news. “Right mate, we’re at 700bhp,” were his words. ‘That’s fair, to be honest I thought it’d be about that,’ I replied, masking first-world disappointment in the most obvious way possible. “What? No, we’re only at 1.3bar currently,” Stu quickly added. “I was phoning to see what kind of boost you wanted us to push too.”

‘Just keep going until you think it’s not safe,’ was my reply. You’ll likely all agree that it’s a good thing I don’t map cars for a living.


There’s a big gap between the finished engine build (late 2019) and the final mapping with Stu and Jaydee earlier this year. A global pandemic – and becoming a dad for the first time – will do that unsurprisingly. Throughout 2020, the GT-R just wasn’t a priority. Plenty was being done to it, including new fuel pumps, R35 coil packs and a crank trigger kit – but it sat down at Ron’s until life slowly resumed to some kind of normal.

I think the best delay of all was when Stu and Jaydee started doing the on-road mapping. Due to guidelines, they weren’t actually allowed to sit next to each other meaning it had to be finished later in the year. What a truly bizarre time we’re living through.

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Back to the actual mapping. 750bhp was dispatched at 1.5bar and by 1.8bar we’d now cracked through the magic 800bhp barrier. In the end, high boost was left at 1.9bar with a peak reading of 833bhp at the flywheel. That’s 706whp for the lets-not-dispute-transmission-losses dyno warriors.

Best of all, the Xona 105-68 still had more to give. My clutch on the other hand, not so much. Being rated to 850bhp I (wrongly) assumed it wouldn’t need replacing as the end figure wouldn’t reach that high. With 833bhp, anything beyond third gear now results in slipping. And it’s far from a two-minute job to rectify.


Not that it bothered Stu. “The power delivery is completely savage,” he laughed. “We just took it out with a mate’s 650bhp F80 M3 and even on low boost it left it for dead. At 1.9bar it’s a monster.”

That right there is music to my ears. Everything about this engine I wanted to feel savage. From its appearance with exposed pulleys and RB20 cam covers to the noise and power delivery. The only thing missing was a quiet Yokohama road to drag race down, although a similar thing did happen on the A14 just past Kettering followed by an undercover Audi S3 pulling me over. Probably not a story for here…


833bhp on the road, what’s it like? I’m aware this kind of power is far from outrageous in 2021, especially when you see the kind of builds Nitto Performance put together and the various ‘modern’ sports cars cracking four figures without their engines being opened.

But in a 22-year-old Skyline using a 32-year-old engine design it’s beyond brutal. The switch to a huge single throttle body makes it a pig to idle when cold. The cams shift the power band high up the rev range, and when it comes on boost the noise is deafening. But it’s pure theatre; it’s more power than you could ever use on the road properly, but that’s what makes it so entertaining.

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I was wrong about the Xona Rotor turbo, too. I assumed it’d build boost early and tail off by 7,000rpm. In reality, it comes in hard from 4,500rpm and then goes completely wild until the 8,500rpm limit. These words could be better described in say, an actual video. So, here’s a short clip of it going through the gears during mapping earlier in the year.

Was it all worth it? Now I’ve had the car back for a few months, absolutely. But it’s taken years to reach this point, multiple mapping sessions, several heated e-mails and Brexit levels of cash being spent in the process.


Would I do it all again? Absolutely not. And this isn’t even an ambitious build in the land of GT-Rs either. But it is for me; I take pictures for a living and this is the most I could achieve, and I’m pretty proud of that.

Ironically, in a point-to-point race, I’d put money on a mapped Golf R making a mockery of it – especially on track. But do 10 laps in each and I know which one I’d be fighting to get back into, even if the lap time was slower. Because this is my problem with aspects of modern performance cars; they’re ferociously fast but they’re not always engaging.

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If you’ve got £300 a month for some finance and £599 to flash the ECU, you can have a car faster than just about anything else on the road. And I’m not knocking that – that’s the most sensible way to go fast and if I had that option when I was younger, I’d have been all over it.

But what makes the GT-R entertaining is the complete sense of occasion it has. Yes, 833bhp will do that, but the way it delivers that is unlike any modern road or race car. The noise is deafening; but it’s a good noise, not a DSG fart. The tacho goes up to 10,000rpm because the engine wants to rev all the way there.

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It feels like it’s about to self-destruct because it probably is. But every noise is a by-product of the job each component is trying to do. Nothing feels artificial; it’s not been tuned for pops and bangs – those flames exist thanks to the volume of fuel being thrown in at full throttle. That alone makes (most of) the pain worthwhile.

And as every year goes by, I can’t help but think we’re a year closer to these cars being nothing but memories on YouTube. That’s not even a dig at EVs; how are we supposed to encourage the next generation of cars fans into Skylines and Supras when their current values put them beyond most supercars?


Racing brought Nissan Skyline GT-Rs into the mainstream, but the world of tuning cemented their popularity. The fact they’re now judged by mileage – rather than their potential – doesn’t seem very fair. Because fundamentally, they’re actually a bit crap when left standard. But everyone loves an underdog, and while an EV or modern supercar can reach this power with ease, very little will beat the sound of an RB screaming to 9000rpm with all the boost.

Mark Riccioni
Instagram: mark_scenemediaTwitter: markriccionimark@speedhunters.com

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