New 128i owner

[racerhawk]

I think I figured out why it feels like it winds slowly up to 2000 rpm and then surges. The engine does accelerate faster above 2000 rpm with fixed throttle and it might be the way the valvetronic works, maybe increasing cam duration by RPM and not throttle demand.

It's really noticeable in sport mode and manual mode but I think it surges when above 2000 rpm in normal mode and even in neutral. It's just harder to tell because the trans shifts around 2000 rpm in normal mode.

So I think the converter is a little too low stall speed and needs to be about 400-800 rpm higher stall. Then the valvetronic is non linear and surges above 2k rpm and the trans is programmed to not freely unlock the converter when cruising around.40 moh in high gear and a little acceleration is called on making acceleration laggy until it downshifts.

[racerhawk]

But what I wonder is if much faster engine acceleration above 2000 RPM under steady light throttle is normal operation or not, or maybe the vanos solenoids and valvetronic motor isn't working properly. Do other members' 128i auto operate similarly.

[asbrr]

I don't have an auto, so it's hard to compare but I can tell you in stock trim the 128i seems to be tuned to be "happiest" 2krpm to 4krpm, that's where it really feels like it's "on-cam".

After I added the 3 stage intake manifold, I feel 3 very distinct "zones" in the rpm range, corresponding to the 3 different intake stages. The first one up to about 3krpm, second one up to about 4.2krpm, and then a third beyond that.

It's possible that's what you're feeling...

[racerhawk]

Originally Posted by asbrr

I don't have an auto, so it's hard to compare but I can tell you in stock trim the 128i seems to be tuned to be "happiest" 2krpm to 4krpm, that's where it really feels like it's "on-cam".

After I added the 3 stage intake manifold, I feel 3 very distinct "zones" in the rpm range, corresponding to the 3 different intake stages. The first one up to about 3krpm, second one up to about 4.2krpm, and then a third beyond that.

It's possible that's what you're feeling...

Hm, you think the surge in engine acceleration and engine power above 2k rpm even under light steady throttle is normal for the 128i. It feels like slow normal engine/vehicle acceleration for the amount of light steady throttle, then surges at 2k rpm in acceleration and power as if the accelerator pedal was being pressed about half way down.

It's as if the valvetronic is giving it more valve timing/"throttle" above 2k rpm. I wonder when the engine transitions from throttle valve to valve timing throttling above idle?

[asbrr]

Originally Posted by racerhawk

Hm, you think the surge in engine acceleration and engine power above 2k rpm even under light steady throttle is normal for the 128i. It feels like slow normal engine/vehicle acceleration for the amount of light steady throttle, then surges at 2k rpm in acceleration and power as if the accelerator pedal was being pressed about half way down.

It's as if the valvetronic is giving it more valve timing/"throttle" above 2k rpm. I wonder when the engine transitions from throttle valve to valve timing throttling above idle?

Pretty sure the throttle valve doesn't do anything unless there's a failure, it's always "wide open" and valvetronic is in play for the most part (someone correct me if I'm wrong). To give you another analogy, if say I am in 2nd gear at 2krpm and give 30% throttle - without me changing throttle position (meaning hold it at 30%) I can VERY distinctly feel the 3 "humps" in the torque curve corresponding to the 3 stage intake manifold switching the intake runner lengths. I wonder if all you're feeling is the initial ramp up of torque at 2krpm?

I think you may really just need to drive another (well functioning) car to compare - could be just a quirk of how the engine is mapped + tuned and that's what you're feeling.

[racerhawk]

Originally Posted by asbrr

.. if say I am in 2nd gear at 2krpm and give 30% throttle - without me changing throttle position (meaning hold it at 30%) I can VERY distinctly feel the 3 "humps" in the torque curve corresponding to the 3 stage intake manifold switching the intake runner lengths. I wonder if all you're feeling is the initial ramp up of torque at 2krpm?

Yeah I understood what you meant. There is a ramp up, more like a jump, in torque and power suddenly at 2,000 rpm. But the thing is, if you're at light and constant throttle, normally most engine would not surge and would rev and deliver power linearly. If you were commanding near wide open throttle it would be acceptable, but this is such a sudden and huge jump and at part throttle.

I think you may really just need to drive another (well functioning) car to compare - could be just a quirk of how the engine is mapped + tuned and that's what you're feeling.

Agree and ask others on here how there's drives. This car is all stock and original and is not modified.

[blackberryq10android]

The throttle response is completely normal. The transmission does this in drive to save gas and to prevent engine damage until the engine has been driven a few miles. Then you will notice normal throttle acceleration. If you want it faster than before it warms up. Drive in sport or more preferably manual mode so it warms up faster just don't go above 4k rpm until a few miles after driving. One owner auto 128i here.

As someone mentioned you can get a ecu tune to fix the throttle lag from when the car turns on.

Also, this engine is known to have low torque in the low rpm ranges so this effects your throttle as well

[racerhawk]

Originally Posted by blackberryq10android

The throttle response is completely normal. The transmission does this in drive to save gas and to prevent engine damage until the engine has been driven a few miles. Then you will notice normal throttle acceleration. If you want it faster than before it warms up. Drive in sport or more preferably manual mode so it warms up faster just don't go above 4k rpm until a few miles after driving. One owner auto 128i here.

As someone mentioned you can get a ecu tune to fix the throttle lag from when the car turns on.

The throttle response may be normal operation but it's not good or acceptable. I don't think your reply relates to the issue I'm talking about or that it would save fuel or prevent engine damage. The throttle surge at 2000 rpm doesn't change after warm up. It's more noticeable in sport or manual mode. The car actually drives better when engine is very cold and there's no torque converter lock up.

The issue is the engine acceleration and power surges suddenly at 2000 rpm with constant light throttle even after it's warmed up and been driven some miles. It doesn't serve any useful purpose and it's not something engines normally do. It seems to be how the valvetronic maybe works and is non linear. It might be possible to reprogram so it's more linear at part throttle but if it was seems BMW would've done so and I'm not inclined to alter the programming with some ify tune.

The issue is at light, constant throttle application that would rev the engine to about 3k rpm, the engine/car accelerates from idle to 2k rpm at a rate that seems appropriate for the amount of throttle, but suddenly surges at 2k rpm onward as if it was put at half throttle. So the car will drive smoothly putting along and keeping the engine below 2k rpm but if you pick up the pace a little it is surgy and faster than called for. I wonder if this is how others' 128i operate.

[racerhawk]

I noticed something else about this car's odd throttle control. With light, steady throttle that will only rev the engine to 2k-3k rpm in neutral, in M1 or M2 the engine/car will accelerate very slowly up to 1500 rpm then starts accelerating increasingly faster and all the way to redline like a runaway freight train lol.

Does other members throttle operate like that?

[racerhawk]

Does anyone else's engine increase throttle substantially itself at 1500-2000 rpm under light steady throttle most noticeable in M1, M2 and Sport?

I might try videoing it. I need to find a hosting site.

[asbrr]

Originally Posted by racerhawk

Does anyone else's engine increase throttle substantially itself at 1500-2000 rpm under light steady throttle most noticeable in M1, M2 and Sport?

I might try videoing it. I need to find a hosting site.

I know I have a manual + the 3SIM, but what you describe seems very familiar to me. Even before I had the 3SIM, pretty sure the car would behave this way.

Never did any logging to look at "throttle %" or whatever the valvetronic equivalent is, but this could just be a quirk of that system (valvetronic).

[racerhawk]

Originally Posted by asbrr

I know I have a manual + the 3SIM, but what you describe seems very familiar to me. Even before I had the 3SIM, pretty sure the car would behave this way.

Never did any logging to look at "throttle %" or whatever the valvetronic equivalent is, but this could just be a quirk of that system (valvetronic).

I think you are probably right that this valvetronic throttling just isn't as linear and consistent as throttle by butterfly. I notice in neutral and vehicle stopped the throttle isn't as aggressive with the same gas pedal amount as in neutral and rolling. Also in any drive range M, DS, D under steady light throttle the engine begins to accelerate faster above 1500 rpm. Although if you back off the gas pedal slightly it will hold a steady rpm. I think I have some video and I'll try to post it.

[racerhawk]

<iframe width="560" height="315" src="https://www.youtube.com/embed/3HzSH2V8NVU" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Here's video accelerating with light steady throttle and backing off at 3k rpm. You can see the car slowly winds up to 1500 rpm then accelerates faster above 1500-2000k. It looks subtle in the video but is quite noticable riding in the car.

[nevetstoj]

Originally Posted by racerhawk

https://youtu.be/3HzSH2V8NVU

Here's video accelerating with light steady throttle and backing off at 3k rpm. You can see the car slowly winds up to 1500 rpm then accelerates faster above 1500-2000k. It looks subtle in the video but is quite noticable riding in the car.

These n52 engines make peak torque at around 2700 rpm and hold it to almost redline. You can look up graphs from bmw press.

[racerhawk]

Originally Posted by nevetstoj

These n52 engines make peak torque at around 2700 rpm and hold it to almost redline. You can look up graphs from bmw press.

I understand every engine has a torque/power curve at WOT, but at light and part throttle a throttled engine shouldn't have any surges in power when accelerating especially not abruptly with stock, mild cam timing. This a throttling issue rather than a power curve one. But maybe throttling by valve timing rather than a butterfly throttle even with steady valve timing will cause power to surge as rpm rises in accordance with the engines power curve, but not really sure what the valvetronic mapping is doing.

[nevetstoj]

https://www.e90post.com/forums/showthread.php?t=478363

This post shows a 330i dyno in post 19. I know there are differences in our cars, but are similar. Coming from a e46 the torque in these cars are much improved and is given much quicker. Nice push feeling in the seat.

[racerhawk]

Originally Posted by nevetstoj

https://www.e90post.com/forums/showthread.php?t=478363

This post shows a 330i dyno in post 19. I know there are differences in our cars, but are similar. Coming from a e46 the torque in these cars are much improved and is given much quicker. Nice push feeling in the seat.

I don't doubt valvetronic increased lower rpm torque. It's the apparent non-linearity and surging at light and part throttle I don't like.

I noticed the sort of successor to the N52 the N53 in 3-series and 5-series dropped the valvetronic for direct injection. I wonder if they and other non-valvetronic BMW engines have a smoother throttle operation.