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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 Thu, May-14-2015, 08:05:36 PM   #11
m3 hal
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Default Re: Subframe: Front vs. Rear mount brace

If you are through bolting to that thing it is effective. If it is just attached to the floor pan and the factory connection to the floorpan is being used to bolt in the subframe it's hardly doing anything. If it's through bolted and you're still using stock subframe bushings, I suspect you will destroy them in short order due to the extra stiffness.

Something I've been thinking about to take care of the fronts is to use solid bushings along with a bracing element like the Mason bar in the rear subframe mounts, and poly bushings in the front mounts. The stiffness of the solid bushings and reinforcement bar will minimize deflection at the front mounts, and the front mounts being poly would give them some ability to deflect as the rear mounts are loaded.
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Old Thu, May-14-2015, 08:10:47 PM   #12
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Default Re: Subframe: Front vs. Rear mount brace

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Originally Posted by mgp333 View Post
Maybe I should have explained the bracing in the picture. There are two long bolts that run through the welded cylinder/tubes all the way down directly to the subframe bushing. You can see the head of the bolts if you look at the picture closely. They are nutted from underneath. As the rear subframe pulls down on the bolts, the force is distributed to the top of the cylinders and subsequently to the frame rails in the trunk area. In addition, the brace is directly welded to the box section between the sheet metal underneath the car and sheet metal in the trunk.



Can you elaborate on this, between the subframe and body? How does this differ from the typical reinforcement plates?
Aaah, okay. Yeah, as long as you're giving the subframe bolts/ carriers something to (directly) yank on up there, it sounds pretty good to me - that way you're distributing the force across that whole member up top rather than the sheet metal around the carrier. You just have to make sure there's a strong, direct link between the bolt carrier and the structural member.

For the front, I personally don't see a better way to do it other than plates - since you're just distributing the force, the best way to do that (IMO) is to use a plate of stronger metal between the two so that the Force/area is immediately reduced.
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Old Thu, May-14-2015, 08:13:20 PM   #13
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Default Re: Subframe: Front vs. Rear mount brace

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Originally Posted by nrubenstein View Post
Instead, you've basically just slapped that crap on top. It's hideous, unnecessary, and of dubious effectiveness.
Ssssshhh... Put the ego away for a sec, and read his post. He's actually going all the way through the subframe carriers to the "crap on top".
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Old Thu, May-14-2015, 08:20:32 PM   #14
Amadeus
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Default Re: Subframe: Front vs. Rear mount brace

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Originally Posted by nrubenstein View Post
All I needed to read was "900hp Turbo M3" to know that the link was largely irrelevant.
Clearly you did not care about the actual issue and instead are looking for reasons to give me grief. You can't even tell me why the brace is ineffective like you claim. I agree Randy's fix is ideal, but it is too much for me.

Anyway

Quote:
Originally Posted by m3 hal View Post
If you are through bolting to that thing it is effective. If it is just attached to the floor pan and the factory connection to the floorpan is being used to bolt in the subframe it's hardly doing anything. If it's through bolted and you're still using stock subframe bushings, I suspect you will destroy them in short order due to the extra stiffness.

Something I've been thinking about to take care of the fronts is to use solid bushings along with a bracing element like the Mason bar in the rear subframe mounts, and poly bushings in the front mounts. The stiffness of the solid bushings and reinforcement bar will minimize deflection at the front mounts, and the front mounts being poly would give them some ability to deflect as the rear mounts are loaded.
Yes definitely, the bolt goes through the brace down all the way to the subframe mount. Good point on the stock subframe bushings being destroyed. I already planned on upgrading to poly when I install the brace. Interesting. Are you saying you would put aluminum in the rear and poly in the front?
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Old Thu, May-14-2015, 08:27:25 PM   #15
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Default Re: Subframe: Front vs. Rear mount brace

Quote:
Originally Posted by Drewster View Post
Ssssshhh... Put the ego away for a sec, and read his post. He's actually going all the way through the subframe carriers to the "crap on top".
And:

1) It's installed in a hideously ugly manner that is difficult to undo.
2) It would be a lot more structurally sound if it were installed properly.
3) It's still welded to thin sheet metal in the rails. Mounting it remotely from the subframe just puts leverage on it.
4) Unless he has a giant turbo, all of this work is completely unnecessary and stupid.
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1999 323i KP/GTS2 Alpinweiß - Hood-in-the-windshield mod
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Old Thu, May-14-2015, 08:30:56 PM   #16
m3 hal
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Default Re: Subframe: Front vs. Rear mount brace

Yes, the idea is that if you can get most of the load going to the rear mounts (via stiff rear bushings connected to a brace, and a softer bushing up front that will allow the rear to get most of the loading), you don't need to worry about the front because it is now seeing less load that the stock setup, and it doesn't have the ability to deflect as much and push up into the sheet metal. I have not done this to my car, but it sounds good in theory, I think.
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Old Thu, May-14-2015, 08:44:36 PM   #17
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Default Re: Subframe: Front vs. Rear mount brace

I reinforced front and rear subframe mounts. I ran bolts up from the existing threaded inserts through the trunk floor. Then I used a 6 x 6 x 0.75" thick sheet metal and riveted
that to the existing 0.032" thick top sheet metal. I used 3/16 stainless rivets. In the front I had to make welded pockets in the sheet metal so the nuts could hold to flat material.
Underneath I made my own reinforcing plates and epoxied them in place and riveted them as well. Now the forces are being distributed in a much larger area and twisting will be difficult because of the top reinforcing. It does seem few people ever do the front mounts from the top.
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Old Thu, May-14-2015, 09:23:39 PM   #18
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Default Re: Subframe: Front vs. Rear mount brace

Here is what I'm doing with my fronts and rears (in addition to the Redish plates).

For me it's important to keep luggage space intact, and to preserve a OEM look.
Thats why I'm hiding the rear enforcement in between the boot floor and the RACP.




































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Old Thu, May-14-2015, 09:28:17 PM   #19
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Default Re: Subframe: Front vs. Rear mount brace

BTW, on the underside I had a small hairline crack left rear but no crack right front.
But as seen above, the top of the right front had cracked.






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Old Thu, May-14-2015, 09:31:46 PM   #20
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Default Re: Subframe: Front vs. Rear mount brace

While I still don't think that that level of reinforcement is necessary in a car that is even in the vicinity of stock, Vince's reinforcement is very much the way to go if you want massive overkill, IMHO.
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[B]2011 BMW M3 (E90) Alpinweiß/Cloth - Slicktop stripper, TCK D/A Konis, AS SSK
2006 GMC Sierra 2500HD 4WD - Duramax LBZ/Allison
2002 BMW M3 Alpinweiß/Black - Konis, AS SSK, JBL MS-62C, IDQ-12v3, JBL MS-8
1999 323i KP/GTS2 Alpinweiß - Hood-in-the-windshield mod
1995 M3 Dakargelb/Black - S50B32/S6S420G, Diffsonline 3.91, H&R/Bilstein, Hotchkis, AS SSK, etc...
1990 325is Brilliantrot/Tan - GC/Bilstein, Sway
1989 325is Alpinweiß/Black - Decontenting...
1989 M3 Alpinweiß/Black - S62B50 in progress...

Hers: 1996 Porsche 911 Turbo Black/Black - UMW LTW Flywheel, Bilstein
Hers: 1988 325iX Coupe Diamondschwartz/Black 5spd - Korman lengthened front driveshaft, 272 cam, H&R/Bilstein

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Discussing Subframe: Front vs. Rear mount brace 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)