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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 Tue, Oct-16-2018, 06:41:50 AM   #51
demolitionskunk
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Default Re: Learned something new (to me) about our subframes

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Originally Posted by Kdubski View Post
To support OP's experience. Two local and highly regarded race shops dealing almost exclusively with e46 and e36 M3's have both told me the bushing is a major cause to the mounting point failure. Both of these shops said plates and solid bushings would alleviate almost any chance of failure on a street car.

With that said, powerflex offers a "hybrid" harder front bushing on their street subframe bushing set. They do this because soft bushings allow too much movement that contributes to subframe failure.

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Good to know my shop wasn't the only one to say this. I'll definitely get the bushings upgraded in the near future.
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Old Tue, Oct-16-2018, 04:18:10 PM   #52
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Default Re: Learned something new (to me) about our subframes

I was wondering about the affect of the metal plates on their own vs the structural foam. The structural foam distributes the forces over the cavity and the I-beam type structure traversing from one rear mount to the other. (when you inject you can feel the heat of the reaction travels towards the centre of the car several inches). The plates alone would strengthen the lower sheet metal but wouldn't it then put more load on the upper metal structure where the tie in bolt meets the sheet metal, and wouldn't it allow for lateral shifts between the upper and lower sheet plates eventually leading to a tear in the trunk area above the mounts? The foam would not allow the lateral movement and forms a sandwich that forces the two layers to act as one. Is it not the plates leading to later problems within the trunk? I would think foam alone is the better solution if you don't have pre-existing cracks to the naked eye once the area is cleaned up.
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Old Tue, Oct-16-2018, 04:34:24 PM   #53
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Default Re: Learned something new (to me) about our subframes

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Originally Posted by m3streak View Post
I was wondering about the affect of the metal plates on their own vs the structural foam. The structural foam distributes the forces over the cavity and the I-beam type structure traversing from one rear mount to the other. (when you inject you can feel the heat of the reaction travels towards the centre of the car several inches). The plates alone would strengthen the lower sheet metal but wouldn't it then put more load on the upper metal structure where the tie in bolt meets the sheet metal, and wouldn't it allow for lateral shifts between the upper and lower sheet plates eventually leading to a tear in the trunk area above the mounts? The foam would not allow the lateral movement and forms a sandwich that forces the two layers to act as one. Is it not the plates leading to later problems within the trunk? I would think foam alone is the better solution if you don't have pre-existing cracks to the naked eye once the area is cleaned up.

For me the structural foam made a lot more sense. I measured the flex with an indicator and a camera on the trunk floor and it flexed like crazy during hard acceleration. This is on a car with no cracks. So to bond the RACP and the trunk floor together and create a thicker beam seems like a good way to strengthen the area. The plates just move the problem further out if you ask me. I'm sure it is a little better, but in the end will lead to the same result.


I can't back this up with numbers, but I have read of cars with plates still failing, but I have yet to hear about a car with structural foam injected (early in its life) do so.
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Old Tue, Oct-16-2018, 04:38:13 PM   #54
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Default Re: Learned something new (to me) about our subframes

I think foam + plates is a pretty good solution, but I was under the impression that the foam did not address the front mounts at all
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Old Tue, Oct-16-2018, 04:41:29 PM   #55
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Default Re: Learned something new (to me) about our subframes

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I think foam + plates is a pretty good solution, but I was under the impression that the foam did not address the front mounts at all
So maybe a good strategy could be to foam + add front reinforcement cups?
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Old Tue, Oct-16-2018, 04:44:35 PM   #56
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Default Re: Learned something new (to me) about our subframes

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Originally Posted by terraphantm View Post
I think foam + plates is a pretty good solution, but I was under the impression that the foam did not address the front mounts at all

True, but you can inject foam in that area also.


Just to add to my previous theory. I am not claiming that the foam with our without plates is as strong as the welded in bars, but I believe it reduces the flex to the point where there will be catastrophic metal fatigue.
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Old Tue, Oct-16-2018, 05:07:46 PM   #57
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Default Re: Learned something new (to me) about our subframes

Brace and plates >all
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Old Tue, Oct-16-2018, 06:28:54 PM   #58
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Default Re: Learned something new (to me) about our subframes

what sort of drilling is required to install the rear brace? I have the reddish plates but would like to add the brace to 'bulletproof' once and for all. Do I need to drop the subframe again to install the brace?
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Old Tue, Oct-16-2018, 06:32:18 PM   #59
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Default Re: Learned something new (to me) about our subframes

No, you drill up through the rear subframe mounts.
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Old Tue, Oct-16-2018, 06:36:30 PM   #60
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Default Re: Learned something new (to me) about our subframes

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Originally Posted by TboneM3 View Post
No, you drill up through the rear subframe mounts.
Up seems to imply from underneath, but you mean all that is needed is to drill down from inside the trunk/rear seat right? How does the brace attach to the mount? Is it threaded already or do I need to get underneath the car with a nut or something?
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Discussing Learned something new (to me) about our subframes 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)