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      02-16-2011, 06:54 PM   #1
jackka
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The advantages of a NA engine?

Hey there, fellas.

I've been lurking in the M3 forum for a while now eventhough I don't own an M3. I do think the M3 is one of the coolest cars on the planet and will most likely buy one someday before I get too old, haha. Would love to buy one now but that would delay my retirement too far back and I want to retire as early as possible.


Anyways, I always read that high revving NA engines are part of what M3s are all about.

Pardon my ignorance, but what exactly is the advantage of a NA engine?
Whether it be a turbo or a supercharger, isn't some sort of a Forced Induction always an upgrade?

I actually wouldn't mind if the M3 came with either, even at a bit higher price. Mainly because I can't think of what specific advantage I would have by having a naturally aspirated engine besides fuel mileage, if that.

Assuming that the rest of the car is exactly the same, isn't it a good thing from a performance perspective if the engine can make more horsepower and/or torque while revving less?

I always wondered why it was that the M division decided to go with a 414/295 engine when they could have easily made it much more. Especially the torque output. Why do you think that is?
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      02-16-2011, 07:05 PM   #2
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      02-16-2011, 07:09 PM   #3
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torque helps with straight line acceleration and only in the low rpm range. the m3 is built to perform on the circuit and therefore it does not need torque. all the umph of an m3 is in the high rpm range which makes total sense because out of every corner you come out of, you will be in either 2nd or 3rd gear revving very high, and thus putting your torque up high via a high revving NA motor, you are able to pull quickly out hte corner and on the the next one. that is why the M3 beat the C63, IS-F, and the RS5 on every circuit even though the cars mentioned all have more torque and horsepower. power isnt everything. there is more to life than holding down the gas peddle and going straight. a car purpose built for straight line speed and only straight line speed might as well not have a steering wheel. hope this helps.
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      02-16-2011, 07:11 PM   #4
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powerband/ area under the curve
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      02-16-2011, 07:37 PM   #5
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Quote:
Originally Posted by GhostRideTheWhip View Post
Turbo cars generally have loads of torque down low, but then die when you're up high in the rev range. On a track, this isn't what you want because you'll be in the higher RPM bands on a track coming out of corners. For day to day, tonice more torque down low is what it's all about. The M3 isn't a track car, but it can be tracked every once in awhile. You want a track car, get a Cayman S.
Throttle response/modulation of naturally aspirated motors is also better than forced induction.
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      02-16-2011, 07:46 PM   #6
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We have two strikes above.

Torque to the wheels rather than at the crank is what is vastly more important than torque at the crank. As it turns our peak hp is typically a way to account for the large torque multiplication provided by gearing that high revving cars typically have.

"Powerband" and area under the curve are in no way specific to to NA engines.


In short here are some of the basics:

NA

+'s

-Can achieve a very flat and broad torque curve which in turn provides flexible engine that feels very smooth in acceleration.
-NA has better throttle response than turbo, the benefits there are feel, performance and ease of modulation of traction (strip or track)
-A more simple engine system compared to turbo or supercharger

-'s:

-Fuel economy for a high revving/high performance NA engine (like the M3) is typically poor


Turbo:

+'s

-Achieves high power for a given displacement
-As a consequence of the typically gets better mpg for the same power level
-Great aftermarket tuning possibilities

-'s

-Throttle response is always slower due to turbo spooling/inertia ("lag" or "tubro lag")
-Complexity of a turbo system
-Concentrated thermal loading
-Current technology limits redline (this is mostly about the racy sound and feel of a high revving NA engine)
-Durability of turbo unit itself (the turbo often doesn't last as long as the engine itself)
-Complex lubrication systems


Supercharging:

+'s

-Great power gains at a given displacement
-Does not contribute to any throttle lag
-Preserves the basic torque/power curves of the base engine (if supercharger is aftermarket)
-Simpler lubrication compared to turbo
-Little to no thermal issues compared to turbo

-'s

-Poor fuel economy compared to turbo as supercharger is basically always running
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      02-16-2011, 08:04 PM   #7
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Often in production cars the weight of a FI system will be offset by a physically smaller (and therefore lighter) engine... but if you're talking in terms of aftermarket FI you're adding significant weight close to the polar extremes of the car, in addition to the increased heating the system adds.

The only definite positives to an NA engine is the smooth and progressive powerband, if you're starting an FI design from scratch you can design to account for everything else (weight gain, increased thermal stress, complexity etc.)

In reality from a purely logical point of view turbo motors are far superior to NA, especially considering the recent and rapid development of modern hardware & software and move to DCT & automatic gearboxes which dramatically reduce lag.
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      02-16-2011, 08:04 PM   #8
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Nice summation Swamp!
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      02-16-2011, 08:15 PM   #9
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Bottom line is throttle response for me. I have owned a few turbo cars and while they can be very fun I enjoy going the very instant I push with my right foot. 8300 rpm is just a bonus in this car. The VW vr6 motor is awesome in this respect max torque from near idle to redline.
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      02-16-2011, 08:36 PM   #10
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Quote:
Originally Posted by UNNATRAL View Post
torque helps with straight line acceleration and only in the low rpm range. the m3 is built to perform on the circuit and therefore it does not need torque. all the umph of an m3 is in the high rpm range which makes total sense because out of every corner you come out of, you will be in either 2nd or 3rd gear revving very high, and thus putting your torque up high via a high revving NA motor, you are able to pull quickly out hte corner and on the the next one. that is why the M3 beat the C63, IS-F, and the RS5 on every circuit even though the cars mentioned all have more torque and horsepower. power isnt everything. there is more to life than holding down the gas peddle and going straight. a car purpose built for straight line speed and only straight line speed might as well not have a steering wheel. hope this helps.
+1000 very well explained sir!
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      02-16-2011, 10:17 PM   #11
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Quote:
Originally Posted by UNNATRAL View Post
torque helps with straight line acceleration and only in the low rpm range. the m3 is built to perform on the circuit and therefore it does not need torque. all the umph of an m3 is in the high rpm range which makes total sense because out of every corner you come out of, you will be in either 2nd or 3rd gear revving very high, and thus putting your torque up high via a high revving NA motor, you are able to pull quickly out hte corner and on the the next one. that is why the M3 beat the C63, IS-F, and the RS5 on every circuit even though the cars mentioned all have more torque and horsepower. power isnt everything. there is more to life than holding down the gas peddle and going straight. a car purpose built for straight line speed and only straight line speed might as well not have a steering wheel. hope this helps.
This makes ZERO sense. Especially coming from someone who themselves upgraded their car to forced induction.

"Torque is only good for straight line acceleration", as it does not help out of a corner?

At corner exit you maybe at high RPM or at low. Just depends on the speed through the corner and gearing. Torque is always good!!!

Or "M3 does not need torque"? So why would anyone get a SC for it?
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      02-16-2011, 10:40 PM   #12
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Quote:
Originally Posted by 1MORELAP View Post
This makes ZERO sense. Especially coming from someone who themselves upgraded their car to forced induction.

"Torque is only good for straight line acceleration", as it does not help out of a corner?

At corner exit you maybe at high RPM or at low. Just depends on the speed through the corner and gearing. Torque is always good!!!

Or "M3 does not need torque"? So why would anyone get a SC for it?
He's confusing what most refer to as low-end grunt, calling that torque. Torque is important at all rpms, especially the higher rpms for racing conditions.
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      02-16-2011, 11:12 PM   #13
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I have both S65 & N55. I love to drive my M3 when there is not that much traffic around. The power of the NA is delivered more smooth and more direct. As a driver, it seems almost like you are having total control of it.

The N55 from 135i is fast and I enjoy the low-end rmp torque for sure. But it is just not as sophisticate as the M3 and its NA engine.
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      02-16-2011, 11:50 PM   #14
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Quote:
Originally Posted by 1MORELAP View Post
This makes ZERO sense. Especially coming from someone who themselves upgraded their car to forced induction.

"Torque is only good for straight line acceleration", as it does not help out of a corner?

At corner exit you maybe at high RPM or at low. Just depends on the speed through the corner and gearing. Torque is always good!!!

Or "M3 does not need torque"? So why would anyone get a SC for it?
re-read what i said before you get panties in a knot...I said with a high revving NA motor all the torque is in the higher rpm which is true, at least in our case..i said its good to have your torque up top for when u exit a corner, as it helps thrust u into the next one...

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      02-17-2011, 12:00 AM   #15
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Quote:
Originally Posted by MVF4Rrider View Post
He's confusing what most refer to as low-end grunt, calling that torque. Torque is important at all rpms, especially the higher rpms for racing conditions.
is that not what I just said? did i not say torque at higher rpms is important? did I not say torque is important, but for circuit racing it doesnt need low end?
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      02-17-2011, 12:05 AM   #16
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Quote:
Originally Posted by UNNATRAL View Post
re-read what i said before you get panties in a knot...I said with a high revving NA motor all the torque is in the higher rpm which is true, at least in our case.
Confusing. "All the torque is in the higher rpm?" What torque curve are you looking at? The S65 has good torque in the upper rev range, but it's diminishing toward redline. Not near as much as a typical BMW turbo, but diminishing nonetheless. Peak is at 3911 rpms. It holds near peak until 7K, then falls off considerably. I'd hardly say all the torque is in the higher rpms.
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      02-17-2011, 12:10 AM   #17
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Quote:
Originally Posted by UNNATRAL View Post
torque helps with straight line acceleration and only in the low rpm range.
This is what's fucked up in your words. It makes no sense. This is why I believed you meant to say grunt.
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      02-17-2011, 12:20 AM   #18
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dont forget the great sound that NA engines make
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      02-17-2011, 01:40 AM   #19
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Basically

NA is better at the track and FI is better for (spirited) daily driving imo

+ Power is linear in NA engines (torque is flat across rpm range) so a driver can control how much power is being cranked out of the engine better. Very important at a track.
+ FI power peaks and comes on in one surprising gob when the turbos spool, so you might have traction problems, but at least it will be exciting . You can train for FI power characteristics tho (like shifting at lower RPMs etc to stay on boost)
+High revving NA will lack torque (like Honda Vtecs in general)....Tq x RPM = HP...not always fun having to rev your engine to feel power from light to light.
+FI saves MPG by letting you have low end grunt and torque which saves you from having to rev for the same amount of HP. Lazy smooth surge of power.
+FI engines have more torque...more torque creates the impression of violent power which is more fun when driving around.
+Light to light street racing, high revs usually don't come to play (disadvantage for NA).
+at cruising speeds NA would need to downshift to pass a car, while a FI car can rely on lazy torque.

I own great (imo) examples of both NA (Flat 6) and FI (Twin Turbo I-6)...I don't track with either, but I know what I would use if I wanted to. Something to consider is that you can have lazy NA engines, they would just need higher displacements like Muscle cars for torque etc.
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      02-17-2011, 01:40 AM   #20
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Quote:
Originally Posted by swamp2 View Post
NA

+'s

-Can achieve a very flat and broad torque curve which in turn provides flexible engine that feels very smooth in acceleration.
-NA has better throttle response than turbo, the benefits there are feel, performance and ease of modulation of traction (strip or track)
-A more simple engine system compared to turbo or supercharger

-'s:

-Fuel economy for a high revving/high performance NA engine (like the M3) is typically poor
What are you talking about?



details are not important
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      02-17-2011, 01:44 AM   #21
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Quote:
Originally Posted by erhanh View Post
What are you talking about?



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last time my display showed "99.9MPG"
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      02-17-2011, 09:27 AM   #22
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TO ME, this entire issue boils down to throttle response. Turbo lag sucks...period! Turbos are the poor man's way to achieve more horsepower. If you want more horsepower, then add a supercharger or get a different car.
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