# Torque hesitation at 4000 RPM on 330



## RKT BMR (Sep 7, 2002)

Over in this thread discussing torque, this dyno graph,










for a 330 was referenced.

I was immediately struck by the dip in both torque and HP around 4000 RPM. I never really noticed this until after I installed my ESS blower, which boosted peak torque to 300 ft-lbs and peak HP to 335 (calculated, based on 7psi boost pressure, and ESS claims from their own dyno measurements -- haven't dyno'd the car myself yet).

Due to the increase in power, this "pause" in acceleration right at 4000 RPM is much more noticable. I have been a bit worried that there was something wrong, until I saw this graph. Has anyone else with a 330 noticed this brief "blip" in power when passing through 4k? It is slightly reassuring to see it on that graph from someone else's motor; it would be immensely reassuring to find that it is ubiquitous on M54 motors in 330s.

I installed my Supercharger in July; I've been corresponding with Todd McWilliams from my330i while he went through his install, and mentioned this to him in September. He thought it might be the switchover in the intake resonance valve. It sounds plausible -- I think the valve opens in the 3800-4300 RPM range. Anyone have any other ideas?


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## Guest84 (Dec 21, 2001)

I don't feel a pause, but a boost at around 4300 rpm...:dunno:


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## webguy330i (Jan 9, 2002)

Ripsnort said:


> *I don't feel a pause, but a boost at around 4300 rpm...:dunno: *


That's precisely what I feel. It's more of a flatline feel between 3800-4300 or so, then it surges again.

Does the 330 have a secondary intake runner or something that opens for increased breathing once the peak torque has been made? Or maybe it's just something in the ECU management related to vanos?


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## TranceLvr (Feb 28, 2002)

Hmm, very interesting, this would coroborate what people where saying in the other thread about the hesitation.


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## RKT BMR (Sep 7, 2002)

webguy330i said:


> *That's precisely what I feel. It's more of a flatline feel between 3800-4300 or so, then it surges again.*


That's a very good description of what I experience, at exactly the same point in engine speed. With the Supercharger, it's 2x more noticable.


> *Does the 330 have a secondary intake runner or something that opens for increased breathing once the peak torque has been made?*


No, not in th sense that you are describing, such that there is an increase in the cross-sectional area for airflow.

What the E46 motors have is a resonance valve, that changes the effective distance between cylinders through the intake manifold at the RPM point we are discussing, in order to "tune" the resonance of the runners to the higher engine RPM. Basically, below ~4k rpm, the valve is closed isolating the first three runners from the second bank of three, in effect creating a longer path for resonance harmonics to get from cylinders 1-2-3 to 4-5-6 -- better matching the lower frequency pulsing of the air movement at lower rpm.

Around 4k, this valve opens, creating a bypass path across all six runners right at the point where they split off into individual paths. This effectively makes the pathlength between any pair of cylinders between the 1-2-3 and 4-5-6 banks shorter, which better matches the higher frequency pulsing of intake air at higher rpm.

Keep in mind that from the point of view of a single cylinder, intake airflow is not continuous, but rather pulses/surges with the opening and closing of the intake valves. Since air has mass, the momentum of the in-rushing air behind the valve when it closes causes a pressure wave to propagate backwards through the air in the runner (it's exactly the same as a sound pressure wave, so moves at the speed of sound). If the length between this cylinder and the next one opening is just right, that pulse arrives such that the extra pressure pushes in a little bit more air while the intake valves are open, increasing power and efficiency. However, since it is a pressure wave, there is also a trough (low pressure) segment as well, so if the length of the runners is incorrect, the exact opposite can occur.

So, the variable runner length design allows for optimizing the intake characteristics for power and efficiency. The M52/54 engine design is a simple approximation design in this respect -- a more sophisticated design would have much finer grain length variability, but would be much more expensive.

The effect is small, but not totally insignificant. It is small enough that NOT engineering for this doesn't result in a slug of a motor. But, like all the other various technology tunings that BMW builds in their engines (VANOS, etc.), it adds up.


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## webguy330i (Jan 9, 2002)

dwallersv, thanks for the information! Very detailed, I like that.

Do you think that perhaps the engine leans out a bit when this valve opens? The combination of the reverse pressure and the fact that the engine suddenly has more air to deal with could cause that I suppose. With Honda's VTEC for example, they've engineered the system to momentarily run rich right before the VTEC switchover, since the longer duration of valves opening/closing requires more fuel AND air.

BTW I heard of a person locally here who had the ESS unit put on his 330xi and apparently experienced TONS of electrical issues once it was on. How was your install (hours, cost if you wish to disclose it) and how do you like it?


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## RKT BMR (Sep 7, 2002)

webguy330i said:


> *Do you think that perhaps the engine leans out a bit when this valve opens? The combination of the reverse pressure and the fact that the engine suddenly has more air to deal with could cause that I suppose.*


Keep in mind that we're not talking about a large increase in air presure -- probably on the order of 1 psi or so (that's a pure WAG on my part). So, you're probably right -- the mixture leans briefly -- but the ECU will adjust to that very quickly, and get the mix back to stochiometric. This would be caught through MAF, fuel flow, and O2 sensor readings, which average these effects. I'd guess that within milliseconds the ECU has the mixture back in line at those engine speeds.


> *BTW I heard of a person locally here who had the ESS unit put on his 330xi and apparently experienced TONS of electrical issues once it was on. How was your install (hours, cost if you wish to disclose it) and how do you like it? *


Go here for a writeup of my experience. It isn't really a DIY writeup like Todd's, but there's plenty there to chew on. Make sure you click through the "Installation Notes" link near the top of the page for more meaty stuff -- it's easy to miss it.

Took me about 20 hours over 3 days. I've had no significant problems at all, and am very pleased with it. No electrical problems. The only issues I've had involve the fit of the tubing, but they were really adjustment issues, nothing serious.

I'll bet that fellow has spilled something on his alternator, causing his electrical failures. The oil breather hose connects to the Vortec intake elbow right above the alternator, so if it came off or wasn't tight enough, it could drip oil into the alternator windings. On the other hand, it is concievable that while doing the install he spilled some coolant, power steering fluid, or something like that on his alternator as well. All of these possibilities are not out of the question, given the steps to install the blower.

If you can install spark plugs and change a thermostat or water pump, you can install the ESS supercharger.

I now have 7k miles on mine, and it's running great!


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## RKT BMR (Sep 7, 2002)

TranceLvr said:


> *Hmm, very interesting, this would coroborate what people where saying in the other thread about the hesitation. *


Could you point to the thread?

Thanks!


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## webguy330i (Jan 9, 2002)

Wow very nice write up. You sound like an ME, am I wrong? 

Have you had a chance to hit a dyno yet? I'd be super interested in seeing your rwhp figures. Also some 1/4-mile times...  

Kudos to you for going with the ESS kit. And it's a 'vert, which makes it even more of a sleeper. Does the s/c have a nice whine to it?


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## RKT BMR (Sep 7, 2002)

webguy330i said:


> *Wow very nice write up. You sound like an ME, am I wrong? *


No, I've got a degree -- in science! 

Serioulsly, my background originally was in Electrical Engineering, with an emphasis in Circuits and Signal Processing. I minored in Physics. However, that was 20 years ago... Today, I'm an R&D Manager for a software lab. However, I've always loved mechanical stuff, hence my willingness to take on the SC install.


> *Have you had a chance to hit a dyno yet? I'd be super interested in seeing your rwhp figures. Also some 1/4-mile times...*


Dyno is on the to-do list. I'll definitely get it done before the next Bimmerfest in April. If I have time, I may go for it during the Christmas break.

Unofficial 0-60 using a stopwatch is around 5.3-5.5 seconds.


> *Kudos to you for going with the ESS kit. And it's a 'vert, which makes it even more of a sleeper. Does the s/c have a nice whine to it? *


The Vortec V2SQ is actually pretty quite when spun up. Paradoxically, it's noisiest at idle. It makes audible gear noise (it's direct drive) even with the hood closed at idle. As soon as you spin it up above 1200-1500 engine RPM, you can't hear it over the engine noise, except for a barely audible whine/whistle. The bypass is a bit noisy, which you can hear consistenly when going down hill in compression.


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## bimmer_w (Oct 12, 2003)

RKT BMR said:


> Over in this thread discussing torque, this dyno graph,
> 
> 
> 
> ...


this also happens on my 330i zhp. very noticeable around 4000rpm, sudden drop of power/torque.


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