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nwilson44 05-12-2012 09:54 PM

550i motor
 
Why does the motor in the new 550i fall on its face after 5500 RPM's? Good tourqe before that, but why?

TahoeM3 05-12-2012 10:40 PM

The main reason is restricted airflow due to an air intake that is essentially a baffle. Supposedly Dinan has an intake in the works.

jjsC6 05-13-2012 04:24 AM

Quote:

Originally Posted by TahoeM3 (Post 6830871)
The main reason is restricted airflow due to an air intake that is essentially a baffle. Supposedly Dinan has an intake in the works.

That is clearly a simplification. I'm pretty sure BMW engineers are smart enough that they didn't wake up one morning and realize they put on an intake that was not right for the car.

I feel certain its all a balancing act to get the power, economy and drive-ability characteristics they wanted. All engines fall on their face at some RPM, what's the difference where it is if the car has the performance the manufacturer is shooting for?

Also, if you understand the relationship between torque and horsepower, you know that there are usually tradeoffs. In this case, with 450 lb ft of toque, to get the peak horsepower and RPM's up higher it is very likely that they would be dealing with cylinder pressures that could create problems. The car has an unusually high combination of turbo boost and compression ratio that helps give it more responsive acceleration and the 450 lb ft of torque.

Needsdecaf 05-13-2012 04:34 AM

Quote:

Originally Posted by jjsC6 (Post 6831038)
That is clearly a simplification. I'm pretty sure BMW engineers are smart enough that they didn't wake up one morning and realize they put on an intake that was not right for the car.

I feel certain its all a balancing act to get the power, economy and drive-ability characteristics they wanted. All engines fall on their face at some RPM, what's the difference where it is if the car has the performance the manufacturer is shooting for?

Also, if you understand the relationship between torque and horsepower, you know that there are usually tradeoffs. In this case, with 450 lb ft of toque, to get the peak horsepower and RPM's up higher it is very likely that they would be dealing with cylinder pressures that could create problems. The car has an unusually high combination of turbo boost and compression ratio that helps give it more responsive acceleration and the 450 lb ft of torque.

Don't forget, a lot of the intake design is due to sound absorption and baffling. WHich is not necessarily good for airflow.

Having two big turbos on top of the engine is prone to making a lot of noise. Not what most BMW customers want...

nwilson44 05-13-2012 07:08 AM

It's just not very BMW like to me. Drove an E60 M5 yesterday and probably going to buy it Monday. As the motor spins faster, the more and more power you get. A seriously awesome engine. Also has more low end than you would think.

sdg1871 05-13-2012 08:53 AM

Quote:

Originally Posted by nwilson44 (Post 6831191)
It's just not very BMW like to me. Drove an E60 M5 yesterday and probably going to buy it Monday. As the motor spins faster, the more and more power you get. A seriously awesome engine. Also has more low end than you would think.

The E60 M5's V10 essentially a Formula One motor in a sedan. The more you rev it the more power it produces. But it has little power around town and off the line and I often used to smoke that car in my E60 550 up to about 40 miles an hour from a Stoplight

TahoeM3 05-13-2012 10:16 AM

Quote:

Originally Posted by jjsC6 (Post 6831038)
That is clearly a simplification. I'm pretty sure BMW engineers are smart enough that they didn't wake up one morning and realize they put on an intake that was not right for the car.

Have you ever seen the intake on the 550i/X5 50i? In case you haven't, I can post pics, but in the mean time I'll give you the basics...it's a jumble of tubes. Air enters through two narrow channels off the grille and curves up and then down as it goes back to the back of the engine, diving underneath the airbox, changes directions 180 degrees and goes up through a restrictor plate with integrated air filter, then back forward to the front of the engine, where it changes directions 180 degrees again before entering the turbo inlets. The net result of that is that the air flow is slowed down and restricted. If you look at the M engine, the air pathway is wide open and goes straight off the grille into the airboxes at the front of the engine and then into the turbos.

I'm not saying BMW put on an intake "that was not right for the car." I'm saying that BMW purposely limited airflow for a couple of reasons...

1. To restrict max power so that the horsepower isn't close to the M engine. They are the same basic engine design after all. If you look at the dyno graphs, the power is very close until 4500 rpm when the 50i flattens of and the M keeps going up.

2. To decrease intake and turbo noise. This is supposed to be the more refined version, so less noise would be the goal.

If you understand the relationship between horsepower and torque, you will understand that horsepower is a function of torque. As revs go up, horsepower increases linearly with revs as long as torque is a constant...which it pretty much is in a turbo engine like this. The only way to prevent power from continuing to rise is through limiting airflow, which they did.

The engine is tuned for good low-end power, but that's normal with a turbo engine. Torque peak always comes early when the turbos spool up. The boost levels on a stock N63 are actually quite low for a modern turbo engine...only around 9.8 psi (with a compression ratio of 10, which also isn't high). The M motor makes around 17 psi stock with only a slightly lower compression ratio (around 9.3, if I recall).

jjsC6 05-13-2012 10:17 AM

Quote:

Originally Posted by Needsdecaf (Post 6831043)
Don't forget, a lot of the intake design is due to sound absorption and baffling. WHich is not necessarily good for airflow.

Having two big turbos on top of the engine is prone to making a lot of noise. Not what most BMW customers want...

Good points.

Stealth.Pilot 05-13-2012 10:23 AM

The Dinan Stage 2 doesn't have the same drop-off. It's a more natural linear curve with a higher drop off.

That said, the engine has so much power I rarely see the need to rev it that high. That's what I love about this car is you can shift at 3500-4000 rpm and get superb acceleration without stressing the engine.

TahoeM3 05-13-2012 11:08 AM

Quote:

Originally Posted by Stealth.Pilot (Post 6831457)
The Dinan Stage 2 doesn't have the same drop-off. It's a more natural linear curve with a higher drop off.

That said, the engine has so much power I rarely see the need to rev it that high. That's what I love about this car is you can shift at 3500-4000 rpm and get superb acceleration without stressing the engine.

The Dinan tune on my X5 50i still has a drop off at higher rpms, especially compared to the M version. It's not as noticeable, but it's still there. An intake will make a lot of difference on this engine.

nwilson44 05-13-2012 11:20 AM

The E60 M5 has a soul though that's what i liked. For the same price I could get a 2012 550i, but the engine not only has no soul, it falls on its face at around 5500. The F1 derived V10 is simply amazing. I admire the low end torque, just not at the expense of a soul and the anti-BMW flat top end.

Stealth.Pilot 05-13-2012 11:28 AM

Quote:

Originally Posted by nwilson44 (Post 6831548)
The E60 M5 has a soul though that's what i liked. For the same price I could get a 2012 550i, but the engine not only has no soul, it falls on its face at around 5500. The F1 derived V10 is simply amazing. I admire the low end torque, just not at the expense of a soul and the anti-BMW flat top end.

This is complete garbage.

jjsC6 05-13-2012 11:56 AM

Quote:

Originally Posted by TahoeM3 (Post 6831444)
Have you ever seen the intake on the 550i/X5 50i? In case you haven't, I can post pics, but in the mean time I'll give you the basics...it's a jumble of tubes. Air enters through two narrow channels off the grille and curves up and then down as it goes back to the back of the engine, diving underneath the airbox, changes directions 180 degrees and goes up through a restrictor plate with integrated air filter, then back forward to the front of the engine, where it changes directions 180 degrees again before entering the turbo inlets. The net result of that is that the air flow is slowed down and restricted. If you look at the M engine, the air pathway is wide open and goes straight off the grille into the airboxes at the front of the engine and then into the turbos.

I'm not saying BMW put on an intake "that was not right for the car." I'm saying that BMW purposely limited airflow for a couple of reasons...

1. To restrict max power so that the horsepower isn't close to the M engine. They are the same basic engine design after all. If you look at the dyno graphs, the power is very close until 4500 rpm when the 50i flattens of and the M keeps going up.

2. To decrease intake and turbo noise. This is supposed to be the more refined version, so less noise would be the goal.

If you understand the relationship between horsepower and torque, you will understand that horsepower is a function of torque. As revs go up, horsepower increases linearly with revs as long as torque is a constant...which it pretty much is in a turbo engine like this. The only way to prevent power from continuing to rise is through limiting airflow, which they did.

The engine is tuned for good low-end power, but that's normal with a turbo engine. Torque peak always comes early when the turbos spool up. The boost levels on a stock N63 are actually quite low for a modern turbo engine...only around 9.8 psi (with a compression ratio of 10, which also isn't high). The M motor makes around 17 psi stock with only a slightly lower compression ratio (around 9.3, if I recall).

To your first point, of course they limited the horsepower to 400. That's the power they wanted for the car - doesn't matter why.

Of course I understand the relationship of hp and torque - that was my point. The more you increase the RPM's to make more horsepower, the more you have to contend with the cylinder pressures of a turbocharged engine with a 10-1 compression ratio.

I get everything you are saying, and you no doubt know something about engines. But to say the intake is the limiting factor doesn't really make sense. My point was that they designed the engine to meet the parameters they were looking for in the car and there are many ways to give or take power. The car runs the 1/4 mile in the very low 13's at up around 109mph. That's the part that counts - not how many RPM's it turns. Those are all tradeoffs to get the end result they were looking for.

As to the M engine, you know damn well that they also had to spend a lot of money to put components in the engine (and the rest of the drivetrain) that can hold up to the durability testing that nearly 600 hp (or whatever it really has) requires.

Steamer 05-13-2012 12:02 PM

I will keep my 550, with a dinan stage 2, there are few on the road that can keep up and can still get decent gas milage on long trips.

dunderhi 05-13-2012 12:49 PM

Quote:

Originally Posted by Steamer (Post 6831623)
I will keep my 550, with a dinan stage 2, there are few on the road that can keep up and can still get decent gas milage on long trips.

I actually think the Dinan's are getting better gas mileage than stock. That is, the one's with owners with some resemblance of self-control. ;)

As far as the high rpm performance fall-off I believe it is a combination of the air-intake and the single size turbos. This is where the straight sixes with the dual and tri-turbo designs have an advantage.

Steamer 05-13-2012 01:09 PM

Quote:

Originally Posted by dunderhi (Post 6831688)
I actually think the Dinan's are getting better gas mileage than stock. That is, the one's with owners with some resemblance of self-control. ;)

Self control, I have heard of this, I believe I saw it once but just can't remember were. :thumbup:

nwilson44 05-13-2012 02:04 PM

Maybe the new M5 is better with regards to high RPM pull.

nhs156 05-13-2012 02:52 PM

Quote:

Originally Posted by nwilson44 (Post 6831548)
The E60 M5 has a soul though that's what i liked. For the same price I could get a 2012 550i, but the engine not only has no soul, it falls on its face at around 5500. The F1 derived V10 is simply amazing. I admire the low end torque, just not at the expense of a soul and the anti-BMW flat top end.

I couldn't agree more. Really wanted to get the F10 550i, but ultimately it didn't put a smile on my face so ended up with an M5 with 6K miles for basically the same price as a new 550i. Drawbacks for the M5 are: clunky (and eventual maintenance cost) of SMG-equipped cars (though I didn't want the manual, as this car would be for commuting) and fuel consumption.

nwilson44 05-13-2012 03:26 PM

Yeah but open up the ten throttle bodies and damn lol the surge and sound is incomparable.

Sent from my PH44100 using Bimmer App

nhs156 05-13-2012 04:47 PM

Quote:

Originally Posted by nwilson44 (Post 6831893)
Yeah but open up the ten throttle bodies and damn lol the surge and sound is incomparable.

Sent from my PH44100 using Bimmer App

The sound is indeed great. Will say this in defense of the 550i: lower in the RPM range, and in everyday traffic, the 550i feels considerably faster. But the M wasn't really built for everyday traffic, so you could almost forgive it this shortcoming. Per Top Gear, the E60 M5 will do 204 mph - it pulls effortlessly at higher speeds, but is a little less impressive at everyday speeds. Still love it, though. It's a great deal of fun to drive - even though it sounds like a diesel when it starts up!

Stealth.Pilot 05-13-2012 05:18 PM

Quote:

Originally Posted by nhs156 (Post 6831851)
I couldn't agree more. Really wanted to get the F10 550i, but ultimately it didn't put a smile on my face so ended up with an M5 with 6K miles for basically the same price as a new 550i. Drawbacks for the M5 are: clunky (and eventual maintenance cost) of SMG-equipped cars (though I didn't want the manual, as this car would be for commuting) and fuel consumption.

The SMG is dead. The impressive thing about the new M5 is that it is actually smoother than the F10.

nwilson44 05-13-2012 06:42 PM

Yeah until you drive the M like its a manual transmission with a clutch, that happens to be computer controlled, then its jerky. But once you learn it It's great. Idk. I liked the new 550i until I hit it at 80 MPH. don't get me wrong it wasn't slow it just didn't pull like other BMW'S I've driven. Nice car though.

jjsC6 05-13-2012 06:49 PM

TahoeM3

I want to follow up to our earlier discussions. As I thought about this later in the day, I do think I took your original response out of context. I think what you were saying is that the intake manifold is the best source of easy hp and I took what you said to mean that the intake was the problem on the car.

I apologize if you and I were looking at it from two different angles.

Stealth.Pilot 05-13-2012 06:54 PM

Quote:

Originally Posted by nwilson44 (Post 6832246)
Yeah until you drive the M like its a manual transmission with a clutch, that happens to be computer controlled, then its jerky. But once you learn it It's great. Idk. I liked the new 550i until I hit it at 80 MPH. don't get me wrong it wasn't slow it just didn't pull like other BMW'S I've driven. Nice car though.

I still don't understand your issue about pulling. I am 100% my 550i could hammer your M5 in a drag race. I know because I have done it before.

nwilson44 05-13-2012 07:50 PM

With all do respect lol the new 550i is nice, however the precious M5 will kill that car in a drag race. It may start out close but the faster you go the bigger the gap will get. I don't even think the new M will hit 204 MPH. Could be wrong but the 550i won't. Got nothing against the new car, it just simply doesn't pull in the higher RPM range like the previous M5. The previous generation 550i and M5 had power bands that were very linear, the power just builds until redline. The new one hits you with a lot of torque throughout the range until, I think 5500, and then falls off dramatically enough to tell. With that said, there is no doubt that the new car is a better daily driver. I just like the soul, power delivery, and high RPM nature of the old one. Am I crazy or does someone hear where I'm coming from?


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