G-Power transforms M8 into 820hp G8M Bi-Turbo

Electrification is one way to boost BMW's 4.4 V8 - another is an even bigger brace of turbochargers...

By Matt Bird / Thursday, 27 November 2025 / Loading comments

With the mixed reception afforded to the new BMW M5, perhaps the old M8 will receive more attention than it did when new. The F92, after all, boasts all that was so good about the old M5 - 625hp twin-turbo V8, smart xDrive chassis, classy interior - in an even better looking body. Don’t forget there was a four-door Gran Coupe, as well, and that was stunning. From less than £50k now, too.

Perhaps preempting a little more demand for its 8 Series wares with production having wound up, G-Power has now released its second project based on the big Beemer this year. Behold the G8M Bi-Turbo, G-Power’s ‘rocket in green and gold’. They aren’t exaggerating, either, with 820hp and 738lb ft now produced from the 4.4-litre S63 V8. That’s the sort of torque a hybrid M5 puts to very good use, only here with almost 600kg less to haul. So 'rocket' seems very appropriate.

Where BMW’s smaller S58 six seems to require nothing more than a cold air intake and some BP Ultimate for a million horsepower, gains for the V8 are harder earned. G-Power has its own set of turbos for this engine, the GP-900 package featuring larger compressor and turbine wheels for more air as well as sturdier seals for the additional boost. With both of those requirements ticked off, it’s easy to understand how the Bi-Turbo is soon well on its way to almost 200hp more than standard. The engine is managed by G-Power’s software, promising improvements ‘in engine efficiency, torque delivery, throttle response, and fuel consumption, while all OEM engine protection and diagnostic functions remain fully intact.’ More power for less fuel really would be some achievement.

While an exact power claim isn’t made for the G-Power exhaust, the beefier turbos will surely appreciate the freer flow. Also it’s suggested that reduced exhaust temps, with new cats included, will benefit turbo response and exhaust sound. Given the BMW V8 was never known for its acoustic sweetness, the new pipes are probably worth having.

The rest of the G8M Bi-Turbo overhaul is probably as divisive as most G-Power modifications tend to be. The Hurricane RR wheels are back, here 21-inch diameter all round, gold, and with Michelins almost as large at the front (285-section) as they are at the back (295). The carbon rear wing should improve downforce and therefore stability, which sounds wise with so much power, though it does rather compromise the M8’s restrained aesthetic. The vented bonnet is actually meant to keep underbonnet temperatures down, which does seem sensible given how hot those turbos are likely to get. But, well, it is carbon fibre, and the M8 arguably isn’t really a car that suits a carbon bonnet. Still, for the ultimate G-Power 8 Series experience - don’t forget that 900hp is possible - then it’s probably wise to have.

Naturally, this sort of performance from a turbo V8 doesn’t come cheap. Tot up the ECU work, the turbo upgrade, the uprated intercooler and the exhaust on G-Power’s website and you’re already staring at £23,000. Carbon never comes cheap, either. Nevertheless, with early ones cheaper than ever - this blue two-door is the same price as a new M135i - the appeal of unlocking the V8’s potential surely increases. And you only have to plug bigger turbos into the super unleaded pump, which is much easier than charging…