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E46 M3 (2001-2006) Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006.


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Old Wed, Mar-01-2017, 09:41:12 PM   #11
Joshe46
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

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Originally Posted by J05M3 View Post
This is contrary to the advice I have been given by respected members of this forum. I am sure one of them will chime in, but everything I have come across says going solid for subframe bushings is recommended to help PREVENT cracking due to the surface area of the solid bushing being greater against the RACP then the surface area of oem subframe bushings. Diff bushings are still recommended to go oem, but this putting greater strain on the diff does seem like it could be a concern.


+1 to this. That is also what I had heard from many many people. And people all seemed to agree. Im interested to hear more opinions. But for me Im running fresh oem subframe bushings and oem+ feel poly diff bushings and my diff is loud as ****. I regret it.
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Old Wed, Mar-01-2017, 10:09:14 PM   #12
ctres
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

Tons of cars don't even have subframe bushings and the subframe bolts directly to the unibody...then again most cars also don't rip out the subframe mounting points either so maybe that point is moot. I don't see how having aluminum subframe bushings would cause the diff to move around more though.
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Old Wed, Mar-01-2017, 10:15:41 PM   #13
J05M3
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

Maybe they are covering themselves for whatever reason because of some prior complaint.
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Old Wed, Mar-01-2017, 10:42:18 PM   #14
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

Solid will put a lot more stress on the mounting points. I personally would only do it with a half cage on top.

The torsional and impulsive loads from the driveline are converted to either tensile or compressive forces by the subframe (what the diff mounts to) into the rear axle carrier panel as the subframe is a rigid body.

A bushing vs solid will offer a rise and fall in force over a longer period of time as it's resultant pressure increases the more it deforms (like a spring). A solid mount is solid. There is no dampening on the forces applied.

It's simple impulsive forces. here's a basic google image to help explain below. The easiest way to imagine it is soft vs Hard suspension.

Some cars can probably take it, some are even designed with solid subframe mounts however, considering the chassis failure issues the cars currently suffer I don't believe it would be wise on an E46.
You'll notice on newer BMW's the subframe mounts are as wide as possible and directly mounted to the chassis rails unlike the E46. by increasing the perpandicular distance from the applied moment centre the force at the mount point is reduced. (T=F*d).


Last edited by AussieE46M3; Wed, Mar-01-2017 at 10:51:16 PM.
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Old Wed, Mar-01-2017, 11:23:17 PM   #15
SG/IRM3
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

Vorshlag Motorsports only recommends solid subframe bushings when used in conjunction with a cage.
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Old Wed, Mar-01-2017, 11:31:51 PM   #16
J05M3
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

Quote:
Originally Posted by AussieE46M3 View Post
Solid will put a lot more stress on the mounting points. I personally would only do it with a half cage on top.

The torsional and impulsive loads from the driveline are converted to either tensile or compressive forces by the subframe (what the diff mounts to) into the rear axle carrier panel as the subframe is a rigid body.

A bushing vs solid will offer a rise and fall in force over a longer period of time as it's resultant pressure increases the more it deforms (like a spring). A solid mount is solid. There is no dampening on the forces applied.

It's simple impulsive forces. here's a basic google image to help explain below. The easiest way to imagine it is soft vs Hard suspension.

Some cars can probably take it, some are even designed with solid subframe mounts however, considering the chassis failure issues the cars currently suffer I don't believe it would be wise on an E46.
You'll notice on newer BMW's the subframe mounts are as wide as possible and directly mounted to the chassis rails unlike the E46. by increasing the perpandicular distance from the applied moment centre the force at the mount point is reduced. (T=F*d).

Again this is contrary to what some, of what I consider experts on RACP damage, recommend. One of the most common cracks of the RACP originates from a pressure point caused by contact with the OE subframe bushing. Solid subframe or even poly subframe bushings help to alleviate this pressure because of the contact surface area with the RACP is greater and not concentrated over a spot weld where that crack originates.

Edit: Didn't realize you are the other new subframe mount solution person until I looked at your name after posting. What you are saying is different then what Vince is saying unless I am missing something

Last edited by J05M3; Wed, Mar-01-2017 at 11:44:47 PM. Reason: adding new info
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Old Wed, Mar-01-2017, 11:51:40 PM   #17
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

I'd agree with that statement about factory bushings on spot welds. My own car had a severe indent from the factory bushings on the underside of the FR subframe mount. I personally swapped to powerflex yellow when I did the repair.

The factory bushings had small protruding lips which have leaves a black stain directly atop spot welds where they had made contact with the body.

Consider that Pressure (P=F/A). Two approaches to reducing pressure is to either to increase area (A), or reduce force (F). The forces applied to the chassis are not static and constant. They are erratic and are applied as impulses.

Aftermarket bushings reduce the pressure applied as the surface area is generally greater. The same force over a larger area produce a smaller pressure.

The softness of the bushing is another consideration. A soften bushing will reduce the forces at the mount point. See how the red impulsive load achieved a higher peak force (Y-axis) than the Green? the area under the curve is equal however, by being softer and offering a more gradual rise and fall in resultant load over a longer period of time, the peak force is reduced exponentially.

As pressure has two variables there are two considerations. Something to consider is that even if the pressure is reduced, the force is still distributed throughout the structure. A lower peak force is less likely to pop spot welds.

Another simple analogy, imagine whacking something with a soft rubber mallet vs a forged hammer? Equal mass, equal velocity, (assume equal area).
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Old Wed, Mar-01-2017, 11:56:40 PM   #18
J05M3
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

I feel that this is a very important topic that needs to be sorted through. I am planing on doing extensive reinforcement work this summer and had always planned on doing solid subframe with oem diff bushings because of the advice I was given by more experienced e46 m owners. What I am reading from some of the people in this thread is what aligns more with a common sense or basic logic approach. However, that sort of approach does not always account for all variables in the equation.
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Old Thu, Mar-02-2017, 12:08:35 AM   #19
J05M3
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

After thinking about this a bit, if I were to use say the redish plates in addition to your or Vince's solution, then the surface area gain of solid subframe bushings would be negated because the load is already spread over a larger area on the RACP because of the plates. In that case it would be best to stick with OEM sub bushings because the pressure pts or load is no longer felt on the racp at the normal factory locations but rather the plates and their new distributed locations. This way, the overall force on the RACP would be dampened by oem rubber and the whole surface area argument of sold subframe bushings is null. Does this line up with what you are saying?

Quote:
Originally Posted by AussieE46M3 View Post
I'd agree with that statement about factory bushings on spot welds. My own car had a severe indent from the factory bushings on the underside of the FR subframe mount. I personally swapped to powerflex yellow when I did the repair.

The factory bushings had small protruding lips which have leaves a black stain directly atop spot welds where they had made contact with the body.

Consider that Pressure (P=F/A). Two approaches to reducing pressure is to either to increase area (A), or reduce force (F). The forces applied to the chassis are not static and constant. They are erratic and are applied as impulses.

Aftermarket bushings reduce the pressure applied as the surface area is generally greater. The same force over a larger area produce a smaller pressure.

The softness of the bushing is another consideration. A soften bushing will reduce the forces at the mount point. See how the red impulsive load achieved a higher peak force (Y-axis) than the Green? the area under the curve is equal however, by being softer and offering a more gradual rise and fall in resultant load over a longer period of time, the peak force is reduced exponentially.

As pressure has two variables there are two considerations. Something to consider is that even if the pressure is reduced, the force is still distributed throughout the structure. A lower peak force is less likely to pop spot welds.

Another simple analogy, imagine whacking something with a soft rubber mallet vs a forged hammer? Equal mass, equal velocity, (assume equal area).
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Old Thu, Mar-02-2017, 12:21:28 AM   #20
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Default Re: Ordered AKG solid subframe mounts and they emailed me back......

Popular combo on the E9x chassis, but they don't have subframe issues.

I went with AKG 95A for the subframe and differential. Totally happy for my weekend car. No vibration, just slightly "tightened up," imperceptible diff whine with my quiet Dinan exhaust. The 95A subframe bushings give the same protective advantage as the aluminum pieces.
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Discussing Ordered AKG solid subframe mounts and they emailed me back...... in the E46 M3 (2001-2006) Forum - Engine: S54 - Max Hp: 333 hp at 7,900 rpm / 262 lb/ft at 4,900 rpm
Total Produced: 45,000+ - Years Produced: 2001 to 2006. at BMW M3 Forum.com (E30 M3 | E36 M3 | E46 M3 | E92 M3 | F80/X)