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      09-06-2009, 04:51 PM   #1
bimmergoat
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What makes a high revving engine so special

I'm no mechanical engineer but I would like to know which is better. I know it's used in motorcycles, M cars, Ferrari's, etc. I loved my GTO and C5 but the M is exciting in a different way. Is the new X5 M engine a better design? Screw emissions, I just want to know which is a better and why?
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      09-06-2009, 05:16 PM   #2
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Originally Posted by bimmergoat View Post
I'm no mechanical engineer but I would like to know which is better. I know it's used in motorcycles, M cars, Ferrari's, etc. I loved my GTO and C5 but the M is exciting in a different way. Is the new X5 M engine a better design? Screw emissions, I just want to know which is a better and why?
Its not better in design many tend to argue that there is nothing better than a naturally inspired engine. I used to own a 335i with the first of the new reborn twin turbo design from BMW. NOT THE FIRST BMW TWIN TURBO but the first reborn one after long years. The 335i was a nice engine lots of low torque and 100hp for every litre of displacement. As the famous line says " There is no replacement for DISPLACEMENT" and that was BMW's answer. the 300hp 300 Torque engine proved to take small displacement to a new level. V8 engines and V10 engine level while reducing emission and fuel consumption. The new X5/X6 M engine is the same one used on the 7 Series. It's the 4.4L V8 Twin Turbo. another great engine making 555 HP. So 126HP for every litre of displacement. Another great achievement from BMW and of course another great torque curve starting at 1500 RPM. As you can see going from a 3.0 300HP to a 4.4 555HP meant that they improved HP to litre ratio while maintaining the same level of least turbo lag and improved throttle respond. A lot of cars before that were equipped with turbo's had a significant turbo lag and were not much liked by many people who have driven raw naturally powered V10 or even V12. A lot of other manufacturers in the same market are leaning towards this sort of turbo power. Example Nissan GTR and porsche. So to answer your question of which one is better it all depends. as you noticed people here complain about the M3 low RPM power saying its not there you have to hit over 5k RPM to feel the power. Drive the 335i and even though its just 300 HP you will feel the torque as low as 1500 RPM. So it depends on what you like a lot of people complain about turbo lag and from the 335i that I owned I can say that BMW reduced that lag to almost nothing. OH also another advantage of the turbo charged engines is that they produce the same power of a bigger engine but are compact and much lighter. For example the 335i 3.0 incline 6 is thought to produce the same power as bigger V8 engines but is more compact and can be as high as 80kg lighter. Which is good for weight saving. From what I see from BMW they seem to be changing the way they think of their cars, rather than putting bigger and stronger engines in next generations. And due to the Market in Europe and gas prices increasing, they want to make the engines smaller lighter improve on emissions and increase HP to Litre ratio.

I hope that helps you a little I'm not an expert but I try to read and learn. It's a very good question though. I wouldn't ask which one is better because you will get a million but rather what is the difference between the two.
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      09-06-2009, 05:21 PM   #3
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Quote:
Originally Posted by bimmergoat View Post
I'm no mechanical engineer but I would like to know which is better. I know it's used in motorcycles, M cars, Ferrari's, etc. I loved my GTO and C5 but the M is exciting in a different way. Is the new X5 M engine a better design? Screw emissions, I just want to know which is a better and why?
High revving engines allow you to make more top end horsepower with a smaller amount displacement. That's the primary reason motorcycles use high revving powerplants. You can extract good power output, but keep the engine size small. You can create a more effective (and very wide) power band, by setting the rev limit to 8400 rpms. (for a 4.0 liter engine) This can help keep the overall weight of the car down.

The X5M engine is a twin-turbo charged 4.4 liter V8 that will help move the much heavier sport utility vehicle around. (with gobs of low end torque on tap) And it can help the overall fuel economy of the vehicle...unless you drive the car like Mario Andretti all the time.

Which one is better?

That's up to the individual. There is no right or wrong answer to that particular question. Just opinions...
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      09-06-2009, 05:39 PM   #4
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Originally Posted by aelalfy1989 View Post
Its not better in design many tend to argue that there is nothing better than a naturally inspired engine. I used to own a 335i with the first of the new reborn twin turbo design from BMW. NOT THE FIRST BMW TWIN TURBO but the first reborn one after long years. The 335i was a nice engine lots of low torque and 100hp for every litre of displacement. As the famous line says " There is no replacement for DISPLACEMENT" and that was BMW's answer. the 300hp 300 Torque engine proved to take small displacement to a new level. V8 engines and V10 engine level while reducing emission and fuel consumption. The new X5/X6 M engine is the same one used on the 7 Series. It's the 4.4L V8 Twin Turbo. another great engine making 555 HP. So 126HP for every litre of displacement. Another great achievement from BMW and of course another great torque curve starting at 1500 RPM. As you can see going from a 3.0 300HP to a 4.4 555HP meant that they improved HP to litre ratio while maintaining the same level of least turbo lag and improved throttle respond. A lot of cars before that were equipped with turbo's had a significant turbo lag and were not much liked by many people who have driven raw naturally powered V10 or even V12. A lot of other manufacturers in the same market are leaning towards this sort of turbo power. Example Nissan GTR and porsche. So to answer your question of which one is better it all depends. as you noticed people here complain about the M3 low RPM power saying its not there you have to hit over 5k RPM to feel the power. Drive the 335i and even though its just 300 HP you will feel the torque as low as 1500 RPM. So it depends on what you like a lot of people complain about turbo lag and from the 335i that I owned I can say that BMW reduced that lag to almost nothing. OH also another advantage of the turbo charged engines is that they produce the same power of a bigger engine but are compact and much lighter. For example the 335i 3.0 incline 6 is thought to produce the same power as bigger V8 engines but is more compact and can be as high as 80kg lighter. Which is good for weight saving. From what I see from BMW they seem to be changing the way they think of their cars, rather than putting bigger and stronger engines in next generations. And due to the Market in Europe and gas prices increasing, they want to make the engines smaller lighter improve on emissions and increase HP to Litre ratio.

I hope that helps you a little I'm not an expert but I try to read and learn. It's a very good question though. I wouldn't ask which one is better because you will get a million but rather what is the difference between the two.
Paragraphs are your friend

Love the M3's high revving engine.
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      09-06-2009, 06:05 PM   #5
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I've also owned the 335 and you are right about your the low end torque. I'm thinking of buying another car to compliment my M, but I want something different but really fun and fast.
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      09-06-2009, 06:31 PM   #6
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I am no expert or anything..

but my view is it's more of a marvel to get rotation speeds that high consistently..
and I guess from not knowing anything, the faster is "goes up" the faster you will be going..

and yes, if anyone loves high RPM, get a superbike..
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      09-06-2009, 06:33 PM   #7
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One thing current turbocharged vehicles can't match with NA cars is throttle response - punch the throttle in the M3 and you get instant response. Punch it in a 335i and you it takes a noticeable period of time to get the car into motion. The new 4.4L turbo engine has patented technology that apparently addresses this issue, but we'll wait and see whether it does what it claims.

The other thing to note with an engine that has a wide powerband like the M3's, it allows for higher gear ratios without the penalty of reduced speed, therefore effective torque delivered to wheels over the same speed range can be higher.

For example, the 335i redlines at 7000RPM, whereas the M3 redlines at 8400RPM - in other words, the M3 has a 20% higher redline. This means BMW could gear the M3 20% higher in each gear and match the vehicle speed in gear of the 335i. This would effectively deliver 20% more engine torque in each gear.

Unfortunately BMW geared the M3 MT taller than the x35i MT, so the M3 MT doesn't get the full benefit of its wider power band. The DCT addresses this in 3rd gear onwards, but I do think could have been geared shorter in 1st and 2nd gears to give it more explosive acceleration off the line.
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      09-06-2009, 07:01 PM   #8
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I am a mechanical engineer and the issue is stress on components and quality of machining. I think the other thing to note is the necessity for very high quality machining leading to tight tolerances and very precise weighting of components. That is really what makes a high revving motor special. The airflow management in the head design to keep the motor breathing at the high rpm is also a pretty difficult task. Something simple like bearing and crank balancing becomes so much more precise at the high speeds. At 8300 rpm each piston is going up an down over 138 times per SECOND! The load on a connecting rod at that speed is incredible, not to mention the load on the crank and the bearing surfaces. All of the dynamics are more complicated. I have a 3.8 liter turbo motor in a Grand National that makes over 600HP at the crank but never revs over 5,500 rpm, I would drive over the crank at 7,000rpm. It really comes down to the precision and accuracy of construction. It is difficult and expensive to create.
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      09-06-2009, 07:06 PM   #9
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Quote:
Originally Posted by Bob86GN View Post
I am a mechanical engineer and the issue is stress on components and quality of machining. I think the other thing to note is the necessity for very high quality machining leading to tight tolerances and very precise weighting of components. That is really what makes a high revving motor special. The airflow management in the head design to keep the motor breathing at the high rpm is also a pretty difficult task. Something simple like bearing and crank balancing becomes so much more precise at the high speeds. At 8300 rpm each piston is going up an down over 138 times per SECOND! The load on a connecting rod at that speed is incredible, not to mention the load on the crank and the bearing surfaces. All of the dynamics are more complicated. I have a 3.8 liter turbo motor in a Grand National that makes over 600HP at the crank but never revs over 5,500 rpm, I would drive over the crank at 7,000rpm. It really comes down to the precision and accuracy of construction. It is difficult and expensive to create.


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      09-07-2009, 08:30 AM   #10
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One key aspect of high rev engines is lower weight. The engine is smaller and also all the drivetrain is lighter because the lower torque of the engine makes it possible (ie. the 335 makes the same torque as the M3).
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      09-07-2009, 08:45 AM   #11
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Quote:
Originally Posted by DevJ View Post
Paragraphs are your friend

Love the M3's high revving engine.
hahahaha

Quote:
Originally Posted by Bob86GN View Post
I am a mechanical engineer and the issue is stress on components and quality of machining. I think the other thing to note is the necessity for very high quality machining leading to tight tolerances and very precise weighting of components. That is really what makes a high revving motor special. The airflow management in the head design to keep the motor breathing at the high rpm is also a pretty difficult task. Something simple like bearing and crank balancing becomes so much more precise at the high speeds. At 8300 rpm each piston is going up an down over 138 times per SECOND! The load on a connecting rod at that speed is incredible, not to mention the load on the crank and the bearing surfaces. All of the dynamics are more complicated. I have a 3.8 liter turbo motor in a Grand National that makes over 600HP at the crank but never revs over 5,500 rpm, I would drive over the crank at 7,000rpm. It really comes down to the precision and accuracy of construction. It is difficult and expensive to create.
But I already knew all that....hahahaha jk
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      09-10-2009, 10:10 PM   #12
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A high-reving engine is more efficient at turning air/fuel into power. An engine can't rev high without having internals made of strong, lightweight, quality materials, and tight machining tolerances. The idea is to be able to drive continuously at or near the point at which power and torque are at their peak, hence the reason race car's run around at much higher RPMs than street cars (more emphasis on thermal efficiency and power delivery than fuel economy). If it weren't for restrictive intakes and exhausts, heavy flywheels, etc., our engines could probably run at 9K rpm all day long, especially with the dry sump oiling system.

Big block, big bore engines make good power and torque at lower RPMs, however, their design prohibtis reving high and possibly making more power and torque (long strokes and connecting rods tend to break).

There's a lot more to all this than has been mentioned so far. There are other technologies that high-reving engines use that make them better and more reliable, such as hydaulic or pnuematic valve lifters instead of solid lifters, multiple overhead cams with variable timing for intake and exhaust valves, variable intake runners, dry-sump oiling, multiple throttle bodies, multiple high-energy ignition coils, sensors galore feeding mini super computers, etc.

By the way, it's "naturally aspirated", not "naturally inspired".
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