What is the M3's biggest weakness?

[ersin]

Originally Posted by jfreisen1

Okay, everyone says louder, more power Scottie, Torgue, Tires, Cup holders, how about a real problem?
Power steering leaking. I track my car at 4 different tracks in Nasa TT3. I take care of my car extremely well. Clean, replace parts, fluid changes etc. I have had the dealer replace the power steering unit and hoses 3 times in 8,000 miles. After only 6 laps the Power steering is bubbling over through the lid. Anyone else have this problem???? I love everything about the car. Including the small, poorly designed cups holders.
John

I believe that if you track, it's gonna overflow on this car. Just be aware and check and refill the PS fluid after. But, in any case, I don't believe this is a problem if you don't track. However, for a car that is tacitly marketed at being suitable for the track, this is a shortcoming as many other cars on the track don't have this problem. But hey, if we're talking track there's a million things to fix. As far as street only, not too much other than nits.


Cheers.

[1MOREMOD]

mine has never leaked. early build 08s dont have hole in the cap so never has happened to me?

[klammer]

Mine doesn't leak either, but have taken the preventative measure of putting a wristband on the PS reservoir, but have never felt that it was wet...many track days, many different tracks... :

[BMRLVR]

Sorry it took so long to reply, here are my answers/rebuttals.

Originally Posted by bruce.augenstein@comcast.

A longer stroke by itself doesn't tend to affect peak torque at all

.

Yes this is correct, no substantial increase in peak torque is gained by a long stroke engine versus a short stroke engine.

Originally Posted by bruce.augenstein@comcast.

Can you explain to me how it decreases the rpm at which max torque occurs? From my point of view, there is no particular reason why that would be so

.

Lets compare two engines with the same displacement, one undersquare, one oversquare.

The undersquare engine has less room for in the combustion chamber for intake/exhaust valves so as a result their diameter and is smaller. Smaller intake vaves/ports/runners end up having higher velocity flow at lower RPM compared to larger ones, couple this with the higher piston velocity that is a trait of longer stroke engines and you have an engine that achieves peak VE at a low RPM. Since peak torque occurs at peak VE that puts peak torque at a low RPM.


In an oversquare engine the combustion chamber is large enough to house larger valves/ports/runners. These larger valves/ports/runners allow for the engine to breath at higher RPMs and make more peak power. Since an oversquare engine has lower piston velocity than an undersquare engine of the same displacement turning at the same RPM, the engine needs some RPM to achieve peak VE and peak torque. The plus to this is the fact that the oversquare engine is able to rev higher as a result of the reduced piston speeds and inertia. This mechanical ability of the rotating assembly to rev higher coupled with the better flow characteristics of the ports/valves/runners will make for an engine that can spin much faster and maintain torque at RPMs much higher than an undersquare engine.

Originally Posted by bruce.augenstein@comcast.

Sort of kind of agree, but as a nit, it's not the stroke length that dictates acceleration off TDC, but instead it's the ratio of rod length over stroke which dictates that characteristic. If you maintain that relationship, longer stroke won't matter

.

Yes, you were right on this one, I was a little bit off on what I was trying to convey. Piston acceleration/deceleration and dwell off of TDC/BDC is determined by the rod to stroke ratio. Overall piston velocity is a function of stroke length. Since all otto-cycle engines have 720 degrees to complete a cycle (four complete strokes of the piston; Intake, compression, power, exhaust) if two engines have the same displacement but one has a stroke that is 30% longer, it will have a 30% higher peak piston velocity at the same engine speed (RPM)

Originally Posted by bruce.augenstein@comcast.

I have personally flung flowery word bouquets at the S65 for its amazingly flat curve between 3900 and 8300 rpm - but in my opinion, while fun, a flat torque curve is not the ne plus ultra of automotive goodness. An S65 making 327.5 pound feet at 4900 (same rpm and torque per liter as E46 peak) and falling to 262 pound feet at 8300 (414 HP) would provide plenty of fun, and be noticeably quicker overall than the current car - especially off corners. Of course, it won't have as flat a torque curve, but this is mainly because it makes more torque while maintaining the same power

.

I can't say that you're wrong on this, but the more flat the torque curve, the more linear the power delivery! I am sure the engine you describe would be a great engine too.

Originally Posted by bruce.augenstein@comcast.

Not buying this at all. If there were limitations in airflow due to engine design limited by packaging concerns, then horsepower per liter would be much more directly affected - and the E46 and E9X engines are essentially equal in power per liter

.

It is not limitations in actual airflow that I was referring to but rather limitations in port design, runner length, airbox volume and exhaust header design.

The S65 has amazing breathing capabilities as shown by it's ability to maintain torque at a high RPM. To get this airflow required to make the engine breath at the high RPMs that it is capable of, large, free flowing ports, runners, throttle bodies and intake trumpets were required. The negative to these free flowing parts is the fact that large ports, runners, throttle bodies and intake trumpets do not lend themselves to good port velocities and cylinder filling at low RPM. The solution to this was to use the VANOS to independently adjust intake and exhaust camshaft timing, duration and valve overlap to allow the engine to take advantage of the resonance tuning effect over the entire power band. Although variable camshaft timing is not new, the VANOS system in the S65 had more adjustability at a faster rate than most of the other manufacturers were using at the time it was released. The key element to making this system work was that the MSS60 ECM which had the computing capacity to handle 200 000 000 calculations per second which at the time of release of the engine was the smartest ECM in a production vehicle. This ECM allowed the VANOS system to be able to be controlled at the speed and accuracy that was required for it to be effective in allowing the cam timing to always be at the optimum position for max power

I know that I am rambling a bit on this section, but I have to be adamant around the fact that the reasoning for the S65 not making more torque than it does is absolutely a result of the limitations caused by packaging. Given more space the engine could have made more torque (the bump in the hood wasn't for styling, it was put there to allow the intake plenum to fit). I am sure the final design that we got was a result of the best compromise they figured they could reach with the available space, styling constraints, cost and performance.

Originally Posted by bruce.augenstein@comcast.

Should've been more forthcoming in my 458 wording. I only brought this engine up to refute by example your point that long stroke adds torque. The 458 makes more torque per liter than any current smog legal NA engine I am aware of - and it's a short-stroke design.

Agreed, it is an amazing engine and the torque curve is quite impressive. Goes to show that amazing things are possible when there are no limits, the 458's engine had very few if any compromises! Yes BMW could have made the S65 have more power, but, it had to be a design that was cost effective to put into a passenger car at a $60-70K USD price point, not a super car at a 200-300K price point!

[Purple88Gold]

Weight.

[CrucialScott]

Had my car for 3 days and so far cannot find a single downfall other than my paranoia! To scared to leave or drive my car anywhere...haha...

[Envyscorpio]

That every generation of the M3 gets faster and you want to buy another one. It might end this time for me with the end of high revving N/A motor.

Torque of the M3 isn't really an issue for me. For lazy people that wants to stay in 6th or 7th to pass on a highway then that's a different story. I usually just down shift if I need more speed. I think when people say the M3 lacks torque is because of the flat torque curve BMW engines put out.

I do feel the E90's weight compare to the E46. But still own both so I should stop comparing LOL.

[Edjay]

Power steering leak. I believe it leakes cause the fluid gets hot when your driving hard. When it gets hot it expands so it over flows. The fluid cooler is directly behind the bumper suport. Remove it from the tabs, hang it lower so it is exposed. It might look getto but mine dont leak anymore. That or keep an eye on your fluid level. Suck some out so it doesnt over flow when drivinh hard. Just make sure to add when your done.

Do a search, Theres a thread about it here.

[Cortexiphan]

Shifter.

[1MOREMOD]

Originally Posted by Purple88Gold

Weight.

+1000000

[e36+e90+993]

Weight and need for an even stiffer suspension setting.

[kiloil]

Weakness=are probably the brakes and its amazing amount of dusting it does

Weakness#2 The auto start/stop mechanism is stupid, because the battery gets too low too quickly and shuts everything off.

Weakness #3. Its really not a weakness but always aware of when I park the car. I sometimes get a fealing that someone is going to key it just because its a nice car.


Nothing else comes to mind, its great vehicle and a great engine!!

[freeman727]

Originally Posted by Cortexiphan

Shifter.

Not so much a problem for those with DCT

[Lost]

Weight and mpg. When I read that for the new M4 are looking to have the e46 m 3 weight I was like - why they didn't start with that from the beginning????

[ScreaM]

We're gonna start ging backwards now..each generation will seek to be lighter weight..

[Da M3nace]

Horn! Cant honk unless car is On...wtf

[TurboBimmer]

Torque, fuel consumption, weight, brakes, stock exhaust.

[david @ eas]

Either weight or brakes imo.

[1MOREMOD]

Originally Posted by Da M3nace

Horn! Cant honk unless car is On...wtf

haha honestly never even thought about our car having one. never used it in over 4 years.

[bruce.augenstein@comcast.]

Originally Posted by BMRLVR

Yes this is correct, no substantial increase in peak torque is gained by a long stroke engine versus a short stroke engine.

My point is that there is NO intrinsic increase in torque from a longer stroke, period.

Originally Posted by BMRLVR

Lets compare two engines with the same displacement, one undersquare, one oversquare.

The undersquare engine has less room for in the combustion chamber for intake/exhaust valves so as a result their diameter and is smaller. Smaller intake vaves/ports/runners end up having higher velocity flow at lower RPM compared to larger ones, couple this with the higher piston velocity that is a trait of longer stroke engines and you have an engine that achieves peak VE at a low RPM. Since peak torque occurs at peak VE that puts peak torque at a low RPM.

In an oversquare engine the combustion chamber is large enough to house larger valves/ports/runners. These larger valves/ports/runners allow for the engine to breath at higher RPMs and make more peak power. Since an oversquare engine has lower piston velocity than an undersquare engine of the same displacement turning at the same RPM, the engine needs some RPM to achieve peak VE and peak torque. The plus to this is the fact that the oversquare engine is able to rev higher as a result of the reduced piston speeds and inertia. This mechanical ability of the rotating assembly to rev higher coupled with the better flow characteristics of the ports/valves/runners will make for an engine that can spin much faster and maintain torque at RPMs much higher than an undersquare engine.

Pretty much agree on all points. It looks as if I misinterpreted you in regard to earlier comments, wherein it seemed you were saying that a longer stroke automatically results in max torque occurring at a lower rpm. In fact, this current explanation points to indirect factors. Meaning: What tends to happen out here on the actual planet as opposed to the merely theoretical.

Originally Posted by BMRLVR

Yes, you were right on this one, I was a little bit off on what I was trying to convey. Piston acceleration/deceleration and dwell off of TDC/BDC is determined by the rod to stroke ratio. Overall piston velocity is a function of stroke length. Since all otto-cycle engines have 720 degrees to complete a cycle (four complete strokes of the piston; Intake, compression, power, exhaust) if two engines have the same displacement but one has a stroke that is 30% longer, it will have a 30% higher peak piston velocity at the same engine speed (RPM)

Since we're talking about what happens out here on the actual planet, the fact of the matter is that in actuality, what happens when you lengthen the stroke is that you reduce the rod-length-over-stroke ratio - unless you want to put aircraft warning lights on the deck height. Sure, you can raise the piston pin, or even go with offset pins, but those practices bring their own problems.

OK, reducing the rod length/stroke ratio is a mixed blessing. First (and as you've said), you pull the piston off top dead center more quickly, giving a stronger early signal to the intake, thus leading to better cylinder filling at low rpm. In addition, you mechanically take better advantage of the short-lived cylinder pressure spike, because due to increased rod angularity, you reach max energy conversion into torque by enabling a 90 degree angle between the rod and a line drawn from the crank throw to the crank centerline earlier in the powerstroke. Presto! More torque.

As revs rise, however, and the engine moves toward max VE (and above), rod angularity starts to hurt you, because you are generating more friction due to increased side loads on the piston. In addition, those low-rpm benefits erode, because you begin to take advantage of the intake and exhaust resonances along with more optimum cam timing. At high rpm, "short" rods (in relation to stroke) just hurt you powerwise, eating up those low-rpm torque babies, and more.

Originally Posted by BMRLVR

I can't say that you're wrong on this, but the more flat the torque curve, the more linear the power delivery! I am sure the engine you describe would be a great engine too.

At a guess, 99 out of 100 M3 owners would be pleased by having peak torque upped by 11% while leaving peak power alone. Not theoretically pleased, but from behind the wheel.

Originally Posted by BMRLVR

It is not limitations in actual airflow that I was referring to but rather limitations in port design, runner length, airbox volume and exhaust header design.

The S65 has amazing breathing capabilities as shown by it's ability to maintain torque at a high RPM. To get this airflow required to make the engine breath at the high RPMs that it is capable of, large, free flowing ports, runners, throttle bodies and intake trumpets were required. The negative to these free flowing parts is the fact that large ports, runners, throttle bodies and intake trumpets do not lend themselves to good port velocities and cylinder filling at low RPM. The solution to this was to use the VANOS to independently adjust intake and exhaust camshaft timing, duration and valve overlap to allow the engine to take advantage of the resonance tuning effect over the entire power band. Although variable camshaft timing is not new, the VANOS system in the S65 had more adjustability at a faster rate than most of the other manufacturers were using at the time it was released. The key element to making this system work was that the MSS60 ECM which had the computing capacity to handle 200 000 000 calculations per second which at the time of release of the engine was the smartest ECM in a production vehicle. This ECM allowed the VANOS system to be able to be controlled at the speed and accuracy that was required for it to be effective in allowing the cam timing to always be at the optimum position for max power

I know that I am rambling a bit on this section, but I have to be adamant around the fact that the reasoning for the S65 not making more torque than it does is absolutely a result of the limitations caused by packaging. Given more space the engine could have made more torque (the bump in the hood wasn't for styling, it was put there to allow the intake plenum to fit). I am sure the final design that we got was a result of the best compromise they figured they could reach with the available space, styling constraints, cost and performance.

Again, completely disagree.

Have you checked out the exhaust headers on the S65? They are not only works of art, but IMO they are the primary reason why the torque peak is at an artificially low 3900 rpm on this engine. Those long runners are optimum for low-rpm exhaust tuning, while the rest of the engine seems to be designed for high-rpm greatness. If they tuned those runners for a higher-rpm resonance, you'd need even less underhood space, while gaining torque because the exhaust tuning benefits occur at a more "natural" rpm, dictated by the rest of the design.

Originally Posted by BMRLVR

Agreed, it is an amazing engine and the torque curve is quite impressive. Goes to show that amazing things are possible when there are no limits, the 458's engine had very few if any compromises! Yes BMW could have made the S65 have more power, but, it had to be a design that was cost effective to put into a passenger car at a $60-70K USD price point, not a super car at a 200-300K price point!

Again, we're talking about torque per liter, not power, and I began some of this back-and-forth by stating that if BMW had only matched the S54 torque-per-liter output, they'd have an even better engine, making for an even finer eye-popping drive.

Be honest, now. Are you insisting that raising the torque by 11% on this engine while keeping the same peak power at 8300 would somehow make for a less capable and exciting offering?

Bruce

[phrozen06]

Aren't we driving bmw's last NA V8?

[wooderson]

Originally Posted by Envyscorpio

Torque of the M3 isn't really an issue for me. For lazy people that wants to stay in 6th or 7th to pass on a highway then that's a different story. I usually just down shift if I need more speed.

I'm gonna go out on a limb here and speak for the lack of torque crew in this thread and say that the lack of torque we are refering to is NOT in reference to passing a mini van on the highway.