linear power to redline

[8600RPM]

I for one am pleasently surprised with top end pull of this car.coming from an e92 m3, I saw the flat power curve up top and feared it would feel dead. However it feels like it pulls hard to 7500 rpm and frankly feels very similar to e92 only way more power. I am surprised frankly as I though constant power and flat power would feel subjectively like a drop in power but it doesn't so I'm not seeing how some reviews don't find it exciting to redline the car!

[chiplee]

Originally Posted by 8600RPM

I for one am pleasently surprised with top end pull of this car.coming from an e92 m3, I saw the flat power curve up top and feared it would feel dead. However it feels like it pulls hard to 7500 rpm and frankly feels very similar to e92 only way more power. I am surprised frankly as I though constant power and flat power would feel subjectively like a drop in power but it doesn't so I'm not seeing how some reviews don't find it exciting to redline the car!

I generally agree. I'd probably prefer a 7200rpm readline for auto shifts, but it's in the ballpark. There's such a lurch forward on shifts you know it's running out of breath a litlte at redline, but if it shifted sooner it might drop the RPM too far to keep the momentum going. Who knows? Not my expertise.

[8600RPM]

Lurch forward is dct shifting with no power interuption. Really doesn't run out of breath until 7600 which is redl8ne. 7500 is full power. 5500 to 7500 is essentially 420whp . Amazing force to me

[CanAutM3]

What is causing the "lurch" with DCT is the fact that the DCT does a "power shift", where the transmission recuperates the energy of the engine inertia from the drop in RPM and converts it in forward momentum of the car. The higher the RPM drop, the stronger the lurch.

Try a WOT high RPM shift in S1, there is no power interruption during the shift but also no lurch.

According to BMW, power plateau ends at 7300rpm, not 7500rpm.

[Black Gold]

Originally Posted by 8600RPM

I for one am pleasently surprised with top end pull of this car.coming from an e92 m3, I saw the flat power curve up top and feared it would feel dead. However it feels like it pulls hard to 7500 rpm and frankly feels very similar to e92 only way more power. I am surprised frankly as I though constant power and flat power would feel subjectively like a drop in power but it doesn't so I'm not seeing how some reviews don't find it exciting to redline the car!

Dude, thank you. I feel the same way, and have tracked the car (where I can actually experience redline).

The e92 also has a torque drop near redline which has the power curve flatten out a little too. Imo that was almost more noticeable because the car had less power to begin with.

I think the engine feels great, and I like the linear torque and power build at lower and mid rpm as well, as compared to the bigger early hit of power from the n54.

[quattr0]

thanks for this feeedback from e9x. I wonder why all tuners claim there isn't much after 5500 rpm

[teamwerx]

Yea I don't know, it feels like it pulls all the way up top to me.

[FC4]

What you guys are feeling is merely the pull of a faster car compared to an E9x M3.

There is a significant, undeniable difference in powerband characteristics and feel between most performance NA engines which make peak HP at or near redline and turbocharged engines. The S55 does not make additional power after 5500-6000 RPM which is the result of torque falling at a rate fast enough to keep HP flat to redline. This is exacerbated when modded where torque takes a nose-dive up top and peak power is made around 6000 RPM then is falling towards redline. Just because power is no longer longer climbing (or falling) doesn't mean the car isn't accelerating. The car has something called gears. It has more to do with the rate of change in acceleration. With a linear powerband, the rate at which speed is increasing remains more constant than if power was flat/falling and the rate of acceleration is slowing. This results in a sensation of being pushed back in the seat harder as revs climb.

[CanAutM3]

Originally Posted by FC4

What you guys are feeling is merely the pull of a faster car compared to an E9x M3.

There is a significant, undeniable difference in powerband characteristics and feel between most performance NA engines which make peak HP at or near redline and turbocharged engines. The S55 does not make additional power after 5500-6000 RPM which is the result of torque falling at a rate fast enough to keep HP flat to redline. This is exacerbated when modded where torque takes a nose-dive up top and peak power is made around 6000 RPM then is falling towards redline. Just because power is no longer longer climbing (or falling) doesn't mean the car isn't accelerating. The car has something called gears. It has more to do with the rate of change in acceleration. With a linear powerband, the rate at which speed is increasing remains more constant than if power was flat/falling and the rate of acceleration is slowing.

I don't think that is what anybody is saying here.

There were so many posts where folks speculated that the S55 woud fall flat on its face past 5500rpm, that the engine would need to be short shifted at 6000rpm etc...

I think the point being made here is that he car keeps pulling strongly at high RPM. In fact to extract maximum performance out of the F8X, redline or near redline (7300rpm) shifts are needed.

Originally Posted by FC4

This results in a sensation of being pushed back in the seat harder as revs climb.

To be able to achieve this, you would need a torque curve that keeps increasing in the power band (i.e. a torque peak achieve at/near redline). On the vast majority of cars (not to say all) the acceleration rate decrease as the revs increase in the power band, hence you are not getting pushed harder in your seat .

[FC4]

Originally Posted by CanAutM3

I don't think that is what anybody is saying here.

There were so many posts where folks speculated that the S55 woud fall flat on its face past 5500rpm, that the engine would need to be short shifted at 6000rpm etc...

I think the point being made here is that he car keeps pulling strongly at high RPM. In fact to extract maximum performance out of the F8X, redline or near redline (7300rpm) shifts are needed.

Have you seen a dyno? Do you see the downward sloping torque curve? Of course the car "keeps pulling" to redline...it's not going to stop accelerating just because power is flat from 5500 RPM on.

Haven't timed acceleration or had the car at a drag strip, but based on the powerband, shifting at redline for max performance is likely only if completely stock. When modded, optimum shift point will certainly be much lower.

Originally Posted by CanAutM3

To be able to achieve this, you would need a torque curve that keeps increasing in the power band (i.e. a torque peak achieve at/near redline). On the vast majority of cars (not to say all) the acceleration rate decrease as the revs increase in the power band, hence you are not getting pushed harder in your seat .

Acceleration rate decreases as revs increase on the fast majority of cars? Really? Think about that for a second and imagine how a car's acceleration would feel once you went WOT if this were the case. Do you really think a [name any family-car] achieves faster acceleration in 1st gear from 2000 to 3000 RPM than from 5000 to 6000 RPM?

With a completely flat torque-curve, HP is upward-sloping and more power is made with each increasing revolution. Mated to gears which multiply torque, yes...the car's rate of acceleration remains close to constant in any given gear until air resistance becomes a greater factor.

Are you just arguing for the sake of it?

[CanAutM3]

Originally Posted by FC4

Have you seen a dyno? Do you see the downward sloping torque curve? Of course the car "keeps pulling" to redline...it's not going to stop accelerating just because power is flat from 5500 RPM on.

Haven't timed acceleration or had the car at a drag strip, but based on the powerband, shifting at redline for max performance is likely only if completely stock. When modded, optimum shift point will certainly be much lower.

Stock S55, redline shifts are needed in 1st and 2nd gear. All other gears can be shifted at 7300rpm for optimal acceleration.

I agree with you, tuned can be different depending on what the tune does to the torque/power curve. But the OP is discussing stock car, not tuned.

Originally Posted by FC4

Do you really think a [name any family-car] achieves faster acceleration in 1st gear from 2000 to 3000 RPM than from 5000 to 6000 RPM?

Not really sure what you want to imply here, but yes, it can be very possible if the engine in the [name of family-car] has higher torque in the 2000-3000rpm range than it does in the 5000-6000rpm range.

Originally Posted by FC4

Acceleration rate decreases as revs increase on the fast majority of cars? Really? Think about that for a second and imagine how a car's acceleration would feel once you went WOT if this were the case. With a completely flat torque-curve, HP is upward-sloping and more power is made with each increasing revolution. Mated to gears which multiply torque, yes...the car's rate of acceleration remains close to constant in any given gear until air resistance becomes a greater factor.

I did specify within the power band, the RPM range needed to achieve maximum acceleration across gears, not low RPM puttering around.

For instance, on the S65, when shifting at redline for maximum acceleration, the RPM always stays well above the 3900RPM torque peak and the torque drops from that point all the way to redline, hence reduced acceleration.

Further, even if the torque curve is perfectly flat, aero and rolling drag increase exponentially with speed and, as a result, acceleration will therefore decrease with increasing rpm.

My point is that even on NA cars, there is an acceleration drop off. It is not a FI car thing only; albeit it is usualy more pronounced with FI.

Originally Posted by FC4

Are you just arguing for the sake of it?

Isn't that the whole point of the forum

[Powerslide]

Having also come from an E9x M3 - I have to say that subjectively, the acceleration on the F8x from 6,000 to 7,600 rpm feels just as ferrocious as my E9x did up to redline (no more, and no less in that rpm range).

I am well aware of how different the hp/torque curves look for the S65 vs. the S55 engines. That being said, and given my experience - I also don't understand people taking the position that the S55 does not accelerate very hard all the way to redline - it clearly does!!!

[FC4]

Originally Posted by Powerslide

...the acceleration on the F8x from 6,000 to 7,600 rpm feels just as ferrocious as my E9x did up to redline (no more, and no less in that rpm range).

This speaks volumes given that the F8x makes ~50 RWHP more in that range than the E9x.

[Powerslide]

Originally Posted by FC4

This speaks volumes given that the F8x makes ~50 RWHP more in that range than the E9x.

Notwithstanding your sarcasm (again - this is why I pointed out that I'm well aware of the vastly different ways in which the S65 vs. the S55 engines make their power) I (and others on this post) are simply stating that the acceleration feels (i.e., subjectively) just as strong as the S65 in the last 1000 rpm up to redline.

You can sit there and point to graphs and objective data all day long (which nobody on here is disputing). All we are saying is that in no way is the S55 disappointing up to redline.