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Selecting the right turbo for my car

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Good day all,

I am currently looking at doing a turbo upgrade and looking for recommendations.

First off this is a unique situation and not many information on these cars/engines.

The car is BMW 330e Hybrid.

The car is currently BM3 stage 2 tuned making 350whp 440wft-lbs (note electric motor is 88whp so the engine is pushing 262whp), with basically just a downpipe (stock 268whp 310wft-lbs).

The engine is B48 which is similar to the B58 (which is used on the new model supra with basically 2 cylinders less).

I am unsure the limits of this engine. I have seen Big Boost Turbo making 711whp on the b58 on stock engine internals and with upgraded pistons and rods over 900whp. I have also seen the b58 engines failed at 650+whp. Big Boost turbo also did a b48 on stock engine internals doing 422whp.

Considering I have B48, I can assume that at around 350whp (engine alone) I should be looking at upgrading pistons and rods for safety which I plan to do.

The b48 engine is 2.0l, 4 cylinder, 11:1 compression ratio.

The main goal is fastest quarter-mile time and also something within safe and reliable region for daily use.

Currently there is no transmission flash for the car and the car cannot rev beyond 3000rpm from stand still to launch. Hence spooling turbo may be slightly difficult, but being hybrid, the electric motor will provide instant torque at launch.

I would like a turbo that can be responsive throughout entire power band and yield fastest quarter mile times.

I was looking at G25-660, G30-660 or G30-770.

Thank you.

Regards,

Shane

Hi Shane,

intresting project.

the b48 isn’t quite a b58 with 2 cylinders removed, it’s been fitted to the JCW Mini range for 5-6years now so the b58 is likely to me a more developed b48. Regarding safe power limits I’d suggest researching tuning packages or common upgrades for the Mini Cooper JCW as JCW owners are more likely inclined to modify their cars than traditional BMW owners.

Lohan in the UK have a lot of experience building b48’s for competition so it might be worth dropping them an email https://www.lohen.co.uk/

Regarding turbo sizing, unfortunately there’s no shortcut to doing the maths to calculate the required airflow and referencing the compressor map, Garrett’s 101, 102 and 103 technical articles are pretty comprehensive. https://www.garrettmotion.com/turbocharger-technology/how-a-turbo-works/

If you do plan on further modifications in the future such as a built block, to save further expense I’d suggest going for something a little larger than you would for a stock bottom end and limiting boost levels until the rest of the power train/driveline can support it. As you say the emachine should be able to cover the spool phase providing you can get access to control the hybrid strategy. It’s also worth noting that the torque limit of the ZF 8hp in your car will be around 560Nm, beyond this the transmission will have a tendency to flare and pull power out unless clutch pressures can be recalibrated.

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