[Skyhigh]

I've been looking at the upcoming 2 Gran Coupe and more specifically at the 235i, and I was shocked to find out it is actually a 4-cylidner engine.

Comparing the specs, I can't help myself wondering what the extra volume and 2 extra cylinders of B58 actually bring or where the catch is!? What is the advantage of the B58 (except sound), from a purely technical point of view?

[Supr3me]

Originally Posted by Skyhigh

I've been looking at the upcoming 2 Gran Coupe and more specifically at the 235i, and I was shocked to find out it is actually a 4-cylidner engine.

Comparing the specs, I can't help myself wondering what the extra volume and 2 extra cylinders of B58 actually bring or where the catch is!? What is the advantage of the B58 (except sound), from a purely technical point of view?

Purely a guess on my part, but I'd say 'tuning headroom'. We've all discussed here how detuned the B58 seems to be coming out of the factory and how capable it is of so much more. My guess is that this variant of the B48 is tuned up to be making near B58 (stock) levels of power, and therefore would have less tuning headroom. If you don't plan to do any modding yourself, it might not matter to you.

[Skyhigh]

I thought about it too, but on the other hand manufacturers usually apply the same minimum Margin of Safety criteria... Which would mean the B48 is just more "ruggadised" to meet the power requirements even with lower volume and cylinders count...
In which case the question about the advantages of B58 still stands. Maybe reliability in the long run...

[enemigo13]

Originally Posted by Skyhigh

I thought about it too, but on the other hand manufacturers usually apply the same minimum Margin of Safety criteria... Which would mean the B48 is just more "ruggadised" to meet the power requirements even with lower volume and cylinders count...
In which case the question about the advantages of B58 still stands. Maybe reliability in the long run...

in b58 case it is not margin of safety. same engines have 340 and 360hp in stock form. even in 360hp tune boost is very low. while in new m235i case boost is quite high and I guess max you can get is extra 20-30hp

[marcthedark]

Originally Posted by enemigo13

in b58 case it is not margin of safety. same engines have 340 and 360hp in stock form. even in 360hp tune boost is very low. while in new m235i case boost is quite high and I guess max you can get is extra 20-30hp

For the B58 it is mostly marketing so that it doesn’t get too close to the M3 etc.
The B48 runs more boost > naturally more turbo lag etc. pretty sure you will find a big difference in daily driving vs WOT on the dyno

[G.Newt]

The B58, being a modern straight-6, will be more torquey down low, as it requires less boost and RPM to reach max torque. More headroom. There's some truth in the saying "there's no replacement for displacement" with all other things being equal.

The new M235i is taking the AMG CLA45 route: high-compression 4 pot 2.0T, with tons of boost.

[Skyhigh]

The compression rate of B48 is 9,5:1 ....
That is not much at all.
B58 is 11:1...

[cfm56d7b]

Originally Posted by G.Newt

The B58, being a modern straight-6, will be more torquey down low, as it requires less boost and RPM to reach max torque. More headroom. There's some truth in the saying "there's no replacement for displacement" with all other things being equal.

The new M235i is taking the AMG CLA45 route: high-compression 4 pot 2.0T, with tons of boost.

Totally agree. B58 will be silky smooth with a linear power delivery. Personally, I am not a big fan of over boosted 4 cylinder engines even with every balance shaft included in the design.

[G.Newt]

Originally Posted by Skyhigh

The compression rate of B48 is 9,5:1 ....
That is not much at all.
B58 is 11:1...

Everywhere I've seen says the B48 has 11:1 compression, same as the B58. They're supposed to be the same engine design/operation, just with +\- 2 cylinders.

[GenXer]

Larger displacement 6 cylinder would be less stressed than a smaller 4 cylinder making the same amount of power. Which could help with long term durability and maintenance.

"Six-cylinder designs have less pulsation in the power delivery than four-cylinder engines, due to the overlap in the power strokes of the six-cylinder engine. In a four-cylinder engine, only one piston is on a power stroke at any given time." (Wikipedia)

[Skyhigh]

Originally Posted by G.Newt

Everywhere I've seen says the B48 has 11:1 compression, same as the B58. They're supposed to be the same engine design/operation, just with +\- 2 cylinders.

You are partially correct. Used to be 11:1.

„225 kW version
This engine features a reinforced crankshaft with larger main bearings and new pistons with a lower 9.5:1 compression ratio. This allows the engine to take more boost pressure from a larger turbocharger, which blows compressed air through a reworked intake tract.
Revealed in May 2019, this engine is shared with the new MINI Countryman,Clubman JCW and MINI JCW GP models. Increasing from previous outputs by as much as 55kw/75hp and 100nm to 450nm."

[enemigo13]

lowest power versions of B48(B46) (e.g. 320i) has 1:11 compression ratio. mid power versions has 1:10.2 compression ratio (e.g. 330i), most powerful versions (M235i) has 1:9.5. B58/B58TU has 2 different compression ratios. first B58M0 is 1:11, B58M1 (supra, new g30 540i etc) is 1:11, B58O1 (M340i, new X3 M40i) is 10.2. hope now it is clear for everyone

Originally Posted by Skyhigh

You are partially correct. Used to be 11:1.

„225 kW version
This engine features a reinforced crankshaft with larger main bearings and new pistons with a lower 9.5:1 compression ratio. This allows the engine to take more boost pressure from a larger turbocharger, which blows compressed air through a reworked intake tract.
Revealed in May 2019, this engine is shared with the new MINI Countryman,Clubman JCW and MINI JCW GP models. Increasing from previous outputs by as much as 55kw/75hp and 100nm to 450nm."

[x5mad]

I saw a YouTube video comparing new m135i to m140i.

The m140i was quicker in every test. The biggest difference seen with the in gear / overtaking tests. The b58 would leave it for dust.

So in real world you would see at higher speeds and in overtaking this is where the b58 flexes it's muscles. Top end the b48 just runs out of puff.

[kern417]

Realistically you need to compare the B48TU to the B58TU. They won't be sold at the same time as our engines.

Also, I agree with they went the MB route. We used to have the same discussion on volkswagen forums because our 2.0T came with 200hp but the Focust ST came out with over 250. But a tune gaine 70hp on our cars, while their tunes gained about 20. So when rung out, the playing field is even. Some OEMs just deliver to a higher threshold for marketing purposes.

[G.Newt]

Originally Posted by enemigo13

lowest power versions of B48(B46) (e.g. 320i) has 1:11 compression ratio. mid power versions has 1:10.2 compression ratio (e.g. 330i), most powerful versions (M235i) has 1:9.5. B58/B58TU has 2 different compression ratios. first B58M0 is 1:11, B58M1 (supra, new g30 540i etc) is 1:11, B58O1 (M340i, new X3 M40i) is 10.2. hope now it is clear for everyone

Thanks for the info! Can you link a source? Much appreciated.

[sshao]

Four cyl is always four cyl even it has a M badge over there. I'd say B58 is perfect for dd if you have a lot of highway commute. It can reach 420+ HP easily with a tune while not sacrifice the ride quality and reliability. Perhaps the number from stock is close but 40i is like having a mild temper while the 35i is somehow feels very aggressive.

[hybris]

If you don't plan to tune you will be fine with the B48, otherwise you need the B58 - as the B48 is pretty much maxed from the factory unless you start replacing turbos etc.

[DrifterX]

Forget the motor specs because there are many 4 bangers out there making 350+hp/ft-lb... I'm more shocked to find an F44 (2'er GC) is ~3600lb! (1635kg) that's only 100lb lighter than my 340i

Edit: Damn, same with an M240i (xDrive), that has a curb weight of 3662lb... wow