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      08-19-2013, 08:30 PM   #1
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Anything being done to address poor top-end?

It's no secret that these engines aren't big breathers. It's quite disappointing to see so many dyno charts where torque is on a downward slope after 4,000 RPM and fall completely off a cliff at 6,000. Yes, it's the nature of any turbocharged engine to have a torque-curve favoring low and mid-range torque, but these take it to the extreme. Have any of the tuners spent time focusing on preserving torque in the upper-RPM range, as in where it actually matters? What seems to be the main culprit for these engines running out of steam besides the obvious being a very small turbo? Wastegates not allowing boost to hold? Cams? We know it's not intake/exhaust restriction, otherwise we'd have 4" turbo-backs available showing impressive gains, so what gives?

Most out there believe a strong mid-range is what makes a car fast, but it's simply not true. Sure, it's good for passing in a given gear for a small burst of acceleration, but in actuality, it doesn't make for a fast car when time spent at WOT beyond one gear leads to decreasing HP. And since the majority of these cars are equipped with the 8-speed autos, this issue is exacerbated. I think this is what's holding these cars back from being faster given their impressive (on paper) peak HP/TQ figures.

Low-end TQ is good if you're towing something, though...
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      08-19-2013, 11:49 PM   #2
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Quote:
Originally Posted by F32 View Post
Yes, it's the nature of any turbocharged engine to have a torque-curve favoring low and mid-range torque.
Not true....

Quote:
Originally Posted by F32 View Post
Most out there believe a strong mid-range is what makes a car fast
Nope.

Quote:
Originally Posted by F32 View Post
Sure, it's good for passing in a given gear for a small burst of acceleration, but in actuality, it doesn't make for a fast car when time spent at WOT beyond one gear leads to decreasing HP. And since the majority of these cars are equipped with the 8-speed autos, this issue is exacerbated.
Do tell how the issue is exacerbated by the 8 speed auto.

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Low-end TQ is good if you're towing something, though...
Or for those of us who spend a lot of time city driving it's nice to have as well.
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      08-20-2013, 12:18 AM   #3
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Quote:
Originally Posted by verbs View Post
Not true....
Care to show me a dyno chart of a stock N54, N55, or pretty much any turbocharged car with a TQ curve like a naturally-aspirated engine? Really, I'll wait...

Quote:
Originally Posted by verbs View Post
Do tell how the issue is exacerbated by the 8 speed auto.
8 forward gears more tightly spaced than a car with 5 or 6 gears. Take one out to an open stretch of road and leave the throttle wide open from a dig or low speed for 15-20 seconds. Let me know how low the RPMs drop every time the car changes gear. Now take a look at the car's TQ curve. What is the slope of that curve in the entire RPM range the engine is spending its time.

Quote:
Originally Posted by verbs View Post
Or for those of us who spend a lot of time city driving it's nice to have as well.
Yes. It's nice to have a deep well of endless TQ accelerating casually from a light from 0 to 40 MPH at <50% throttle.

Thanks for your contribution.
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      08-20-2013, 01:52 AM   #4
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Dang f32...seems like you want an m3 or m4....or maybe a 911 Turbo S. Its an F30.. a 4 door sedan...Its pretty quick for what it is. Hell its as fast as my old 2000 vette. You want to solve the problem of TQ drop off? Why? It's damn skippy through 120 mph. More than enough for day to day...(its intended use)...I'm not getting the question, what were you expecting?
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      08-20-2013, 07:10 AM   #5
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Quote:
Originally Posted by F32 View Post
It's no secret that these engines aren't big breathers. It's quite disappointing to see so many dyno charts where torque is on a downward slope after 4,000 RPM and fall completely off a cliff at 6,000. Yes, it's the nature of any turbocharged engine to have a torque-curve favoring low and mid-range torque, but these take it to the extreme. Have any of the tuners spent time focusing on preserving torque in the upper-RPM range, as in where it actually matters? What seems to be the main culprit for these engines running out of steam besides the obvious being a very small turbo? Wastegates not allowing boost to hold? Cams? We know it's not intake/exhaust restriction, otherwise we'd have 4" turbo-backs available showing impressive gains, so what gives?

Most out there believe a strong mid-range is what makes a car fast, but it's simply not true. Sure, it's good for passing in a given gear for a small burst of acceleration, but in actuality, it doesn't make for a fast car when time spent at WOT beyond one gear leads to decreasing HP. And since the majority of these cars are equipped with the 8-speed autos, this issue is exacerbated. I think this is what's holding these cars back from being faster given their impressive (on paper) peak HP/TQ figures.

Low-end TQ is good if you're towing something, though...
N55 runs out of steam at about 5500 so shift then and u'll be fine
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      08-20-2013, 09:03 AM   #6
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Quote:
Originally Posted by verbs View Post
Not true....

Nope.

Do tell how the issue is exacerbated by the 8 speed auto.

Or for those of us who spend a lot of time city driving it's nice to have as well.
Quite nice for those who want punch out of a corner on a nice windy road, and aren't all that excited by a straight road and seeing how fast we can go.
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      08-20-2013, 09:42 AM   #7
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http://www.n54tech.com/forums/showth...=14974&page=14
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      08-20-2013, 09:52 AM   #8
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The turbocharger itself determines where you're going to get that peak. You could optimize the top end if you're willing to throw on a big turbo and accept a lot of turbo lag and no low end by swapping out the turbo.

Makes for a great drag/track car but a crappy daily driver.

So if you want more top end, look into a new turbo. The tune and cranking up the boost will only get you so far.
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      08-20-2013, 07:53 PM   #9
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Quote:
Originally Posted by F32 View Post
Care to show me a dyno chart of a stock N54, N55, or pretty much any turbocharged car with a TQ curve like a naturally-aspirated engine? Really, I'll wait...



8 forward gears more tightly spaced than a car with 5 or 6 gears. Take one out to an open stretch of road and leave the throttle wide open from a dig or low speed for 15-20 seconds. Let me know how low the RPMs drop every time the car changes gear. Now take a look at the car's TQ curve. What is the slope of that curve in the entire RPM range the engine is spending its time.



Yes. It's nice to have a deep well of endless TQ accelerating casually from a light from 0 to 40 MPH at <50% throttle.

Thanks for your contribution.
single turbo n54


11 mustang


Pretty close (well if you don't count the turbo lag)
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      08-20-2013, 07:55 PM   #10
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Quote:
Originally Posted by shockin330i View Post

Pretty close (well if you don't count the turbo lag)
How can you not count the turbo lag? That's kind of the whole point.
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      08-20-2013, 08:04 PM   #11
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Quote:
Originally Posted by F32 View Post
It's no secret that these engines aren't big breathers. It's quite disappointing to see so many dyno charts where torque is on a downward slope after 4,000 RPM and fall completely off a cliff at 6,000. Yes, it's the nature of any turbocharged engine to have a torque-curve favoring low and mid-range torque, but these take it to the extreme. Have any of the tuners spent time focusing on preserving torque in the upper-RPM range, as in where it actually matters? What seems to be the main culprit for these engines running out of steam besides the obvious being a very small turbo? Wastegates not allowing boost to hold? Cams? We know it's not intake/exhaust restriction, otherwise we'd have 4" turbo-backs available showing impressive gains, so what gives?

Most out there believe a strong mid-range is what makes a car fast, but it's simply not true. Sure, it's good for passing in a given gear for a small burst of acceleration, but in actuality, it doesn't make for a fast car when time spent at WOT beyond one gear leads to decreasing HP. And since the majority of these cars are equipped with the 8-speed autos, this issue is exacerbated. I think this is what's holding these cars back from being faster given their impressive (on paper) peak HP/TQ figures.

Low-end TQ is good if you're towing something, though...
The reason the n55 doesn't make much power up top is due to the twin scroll design.
This should help
Quote:
Twin-scroll
housings are becoming very popular for performance use, and for good
reason. By dividing the manifold and turbine housing into two flow
paths, the engine firing order can be made to “alternate” the flow all the
way to the turbine wheel inlet. The engine blow-down pulse is generated when the exhaust valve opens. During the blow-down, the engine power cylinder is still at very high pressure as a residual of combustion and the power stroke. This initial “pop” of energy travels at very high speed down the manifold runner, through the volute, and impacts the wheel. For this reason, the stream is very much a “pulsed flow” and the divided nature of the system simply amplifies and arranges those pulses. The engine firing order creates a “one-two” (alternating) punch on the wheel, keeping the pulses evenly spaced and in rapid succession. As the engine speed increases
, this becomes a blur and the alternating nature loses its value. Hence,
twin-scroll housings only benefit the low and medium speed operation of
an engine. Within this range, it is a very effective way to improve turbine effectiveness. The wheel loves the high velocity evenly-spaced pulses of gas, and as long as they are “slow” enough in succession and duration, the wheelcan make good reaction usage of the energy. What results is an
improvement in “effective” efficiency, and at lowerengine speeds more
turbine power can be generated. The obvious result is quicker spool
and better low-end boost response. As mentioned, the top-end operation is not improved, everything else being equal. Put into practice, a single-scroll housing of sufficiently large size is the recipe for a user that is seeking only top-end power optimization. That said, a very potent combination is a twin-scroll divided system that works to retain good low speed boost response, while sizing
it large (aerodynamically) for the best top-end power. It’s the best of both
worlds, in many cases.
Good read if you ever really want to learn about turbos...
http://www.full-race.com/articles/efrturbotechbrief.pdf
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      08-20-2013, 08:16 PM   #12
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Quote:
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How can you not count the turbo lag? That's kind of the whole point.
LOL. And he goes and cites one of the most highly modified N54 cars around. Cool.
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      08-20-2013, 09:04 PM   #13
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Quote:
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LOL. And he goes and cites one of the most highly modified N54 cars around. Cool.
Or, you can go ahead and read the post above you.
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      08-20-2013, 09:05 PM   #14
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Any way you look at it, this car is a daily driver, not a track car, so who cares? Run a few laps with your modified 335 at a track and your engine will go into a slump...if you want high end power, buy a high end car!
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      08-20-2013, 09:54 PM   #15
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Internal combustion engines aren't new or rocket science. Air + fuel = bang.

The engine runs out of air, less bang. You want more bang, add more air. Intakes don't do much when your bottleneck is at the turbo.

Remember that turbos are just one of many compromises that can go into an engine. You won't ever get the smooth linear torque of a high revving low torque engine like the M3 and the low end grunt of a big displacement V8.

Unless of course you boost an LSx engine. Then yeah, that's pretty much perfect.
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      08-21-2013, 04:11 AM   #16
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Quote:
Originally Posted by F32 View Post
Care to show me a dyno chart of a stock N54, N55, or pretty much any turbocharged car with a TQ curve like a naturally-aspirated engine? Really, I'll wait...
You said it's the nature of any turbocharged engine to have a torque-curve favoring low and mid-range torque. That's false, and it doesn't have to look like a naturally aspirated dyno to be false. Here's a Porsche GT2 dyno that doesn't favor low end torque.



http://www.edmunds.com/car-reviews/t...no-tested.html


Quote:
Originally Posted by F32 View Post
8 forward gears more tightly spaced than a car with 5 or 6 gears. Take one out to an open stretch of road and leave the throttle wide open from a dig or low speed for 15-20 seconds. Let me know how low the RPMs drop every time the car changes gear. Now take a look at the car's TQ curve. What is the slope of that curve in the entire RPM range the engine is spending its time.
My 8 speed auto has paddles; I can shift wherever I want, so again you made a blanket statement that's not correct.

You're also not understanding how torque multiplier/gears/rpms work. Assuming full traction, an 8 speed BMW is going to have a gearing advantage over a 5 or 6 speed car. Not to mention, horsepower is a function of torque and rpm....I don't care that my torque is dropping at higher rpms vs. in the mid range so long as my car is getting the most power to the ground via gear multiplier+average horsepower throughout the RPM range I'm using. I'd rather be making 220rwhp at say 6600rpms in say 3rd gear than say 230rwhp at say 4600rpms in 4th gear.





Quote:
Originally Posted by F32 View Post
Yes. It's nice to have a deep well of endless TQ accelerating casually from a light from 0 to 40 MPH at <50% throttle.
And it's great for freeway passing power.

Quote:
Originally Posted by F32 View Post
Thanks for your contribution.
I'm glad you learned something.
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      08-21-2013, 09:54 AM   #17
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slightly larger turbos do wonders for the n54s, they sustain the potent levels of midrange torque while pushing out a higher rpm horsepower curve.

Vargas and RB are working on the N55 turbo upgrade and from what I've read it should be compatible with the f30/2
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      08-21-2013, 11:17 AM   #18
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Since you want to compare apples to apples take the universally loved Toyota 2JZ-GTE. It's basically spec for spec identical. 3.0L Straight 6, single or sequential turbos, and modded heavily for the past 20 years.

Go out and look at some of the Supra forums and you can get an idea what different turbos will do for an engine. You'll very quickly see the impact of the sequential turbos, single turbo, or giant turbo.

At the end of the day you have to decide do you want to maximize the top end at the exchange of absolutely no power in the normal driving range and crazy turbo lag?

Turbos make up for displacement, but they can't do it across the rev range so you have to pick where you want it.

If you want a torque curve like this, buy a V8. ;-)

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      08-21-2013, 01:27 PM   #19
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This iteration of the N55 is all about BMW's "Efficient Dynamics", and not designed for tracking or racing. That falls to the "M"-engined cars, either NA (E46/E90 M3, E39/E60 M5 and M6, etc.). If you're really looking for a "top-end" high-revving engine, those are the cars to look at. This N55 provides more than adequate power with great fuel economy (especially with the 8AT and its top-2 overdrive gears), but in sport mode is also great for spirited driving (non-track). The low- and mid-range torque provides a great driving experience on streets and roads, but it's by no means a top-end high-rev racing powerplant.
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      08-21-2013, 02:05 PM   #20
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Quote:
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This iteration of the N55 is all about BMW's "Efficient Dynamics", and not designed for tracking or racing. That falls to the "M"-engined cars, either NA (E46/E90 M3, E39/E60 M5 and M6, etc.). If you're really looking for a "top-end" high-revving engine, those are the cars to look at. This N55 provides more than adequate power with great fuel economy (especially with the 8AT and its top-2 overdrive gears), but in sport mode is also great for spirited driving (non-track). The low- and mid-range torque provides a great driving experience on streets and roads, but it's by no means a top-end high-rev racing powerplant.
Well said.

I loved my M Performance Power Kit-tuned F30 M Sport 335i. The N55 is truly an outstanding little turbocharged motor. However, as has been pointed out in this thread, the N55, tuned or not, does start to run out of steam as the revs climb and speed increases.

The 6.2L V8 in my new C63, however, pulls and pulls relentlessly. The way it reels in on the highway on 80-140 pulls is on another level. That's what you get with a large-discplacement, free revving, naturally aspirated engine.
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      08-21-2013, 02:19 PM   #21
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I think this is what attracts me to the stock N55 setup. I don't have to tickle the rpms near redline to feel that strong seat of the pants acceleration. I enjoy being able to shift around 4k and still having max tq. I don't want to redline my car every day to get the last drip of power and tq out of it.

But at the end of the day there really is no replacement for displacement. I too have quite a bit of seat time in C63s and I really don't think a turboed motor will ever feel that good. If I could have a 6.2l beast and still get 35 mpg on the hgihway I'd be all over that but it's jut not a reality at this time.
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      08-21-2013, 02:41 PM   #22
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I believe Rob Beck is working on an N55 Turbo upgrade for E9x's. Not sure how different fitment is compared to the F30's. I know the factory intakes are in different spots.
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