Solid subframe bushings with stock diff bushings?

[Mvez]

I know this subject has been beat to death, but as title states, anybody running solid subframe mounts with stock diff bushings? 6MT specifically. Seems like not many are doing this.

My car is heading in for a major overhaul, and while it will see track duty, it also will see street and highway driving. I know even the purple and black powerflex transmit a lot of whine. Wondering who has done just the subframe only, and how it is holding up on track?

I ran this exact setup on my E46 M3 for years on track with no issues, but the E92 does have a lot more power sent through the drivetrain. Me thinks the solid subframe would help stabilize the diff more, even with OE bushings. Didn't the GTS come with solid sub mounts and stock rubber diff mounts?

[dogbone]

I have a DCT. But I am running solid subframe bushings and stock diff bushings. The car is a dedicated track car. And it's supercharged. It's been fine for over a year.

[Ahmed Jimmy]

Originally Posted by Mvez

I know this subject has been beat to death, but as title states, anybody running solid subframe mounts with stock diff bushings? 6MT specifically. Seems like not many are doing this.

My car is heading in for a major overhaul, and while it will see track duty, it also will see street and highway driving. I know even the purple and black powerflex transmit a lot of whine. Wondering who has done just the subframe only, and how it is holding up on track?

I ran this exact setup on my E46 M3 for years on track with no issues, but the E92 does have a lot more power sent through the drivetrain. Me thinks the solid subframe would help stabilize the diff more, even with OE bushings. Didn't the GTS come with solid sub mounts and stock rubber diff mounts?

I've got DCT and ran solid subframe with stock bushings for a while, was fine. I then replaced to purple powerflex and I confirm the increased NVH is barely noticed, at least in my case with a loud exhaust. If your tracking your car more often and car is few years old, worthwhile changing your diff bushings (even get new OE) to avoid expensive fixes later on.

[///Mobbin]

I haven't gotten there yet but I am planning on the solid subframe and purple powerflex diff bushings. I have read many many posts on this and that seems to be the consensus for DCT cars that are either DD's or see some street and track time. I will also likely swap in the Hotchkis front/rear sway bars at the same time since the rear subframe is already coming down.

[Mvez]

Originally Posted by dogbone

I have a DCT. But I am running solid subframe bushings and stock diff bushings. The car is a dedicated track car. And it's supercharged. It's been fine for over a year.

That's encouraging, especially since you're blown.

I would think the 6MT inherently puts a bit more stress on the bushings than DCT though, but I could be wrong.

[Redd]

I have solid subframe with stock diff bushings on DCT. No increase in NVH, and car rides much better, chassis feels like it's one generation newer.

[roastbeef]

Originally Posted by dogbone

I have a DCT. But I am running solid subframe bushings and stock diff bushings. The car is a dedicated track car. And it's supercharged. It's been fine for over a year.

i'm kinda surprised you didn't do the differential bushings. i feel like you would get even more deflection by focusing those forces on the differential (as opposed to being shared by the differential and subframe bushings). any reason why you didn't? i have the turner derlin and the noise is noticeable, but very subtle. with the windows down, you can't hear it.

[roastbeef]

Originally Posted by Mvez

I know this subject has been beat to death, but as title states, anybody running solid subframe mounts with stock diff bushings? 6MT specifically. Seems like not many are doing this.

My car is heading in for a major overhaul, and while it will see track duty, it also will see street and highway driving. I know even the purple and black powerflex transmit a lot of whine. Wondering who has done just the subframe only, and how it is holding up on track?

I ran this exact setup on my E46 M3 for years on track with no issues, but the E92 does have a lot more power sent through the drivetrain. Me thinks the solid subframe would help stabilize the diff more, even with OE bushings. Didn't the GTS come with solid sub mounts and stock rubber diff mounts?

not many are doing this because it is costly and many see it as a minor improvement. for me, i'm really glad i did it. it really improves the feel of the car. the car feels very solid now, and is more communicative just driving around on the road. the noise is minimal, and doesn't bother me. i'm a big fan of small mods that "add up" and enhance each other. i have camber plates, tension arm monoballs, and solid subframe/derlin diff bushings. other than that, oem suspension. all of these mods were done separately with track days in between. although my track seat time/experience contributes, i'm very in-tune with how the car feels and i can say with a clear conscience that each of these mods contribute to a better feel and lower lap times. i also feel like these mods have a greater contribution to feel because they enhance the performance of each other.

here is a vid of subframe/diff deflection i took. this was before the swap. stuff moves a lot!

[aus]

We need an after vid!!
Thanks for that vid.

[roastbeef]

Originally Posted by aus

We need an after vid!!
Thanks for that vid.

thanks, i was going to take an "after" vid, but the way the car feels, i know its not moving around much. a little flexing (like the whole car) i'm sure, but not much). maybe one day when i get bored enough.

[///Mobbin]

That deflection is no joke! May have to move this up on my list.

[CorruptCommie]

In the video the subframe is moving, the diff bushings flex in the direction of the drive axle rotation. My line of thinking was that if you solid mount the diff to the subframe, you are now transferring that work to the subframe bushings, so you'll wear them out faster. I asked AKG about solid diff and poly subframe and they said do matching poly in both the diff and subframe.

[roastbeef]

Originally Posted by CorruptCommie

In the video the subframe is moving, the diff bushings flex in the direction of the drive axle rotation. My line of thinking was that if you solid mount the diff to the subframe, you are now transferring that work to the subframe bushings, so you'll wear them out faster. I asked AKG about solid diff and poly subframe and they said do matching poly in both the diff and subframe.

Do solid subframe and poly or derlin diff bushings. Solid subframe bushings don't add any noise. Derlin diff bushings add a little noise.

[CorruptCommie]

Originally Posted by roastbeef

Do solid subframe and poly or derlin diff bushings. Solid subframe bushings don't add any noise. Derlin diff bushings add a little noise.

I went 75D on the whole drivetrain, would not recommend unless the car is track only

[Mvez]

I don't see it that way. Currently, when you accelerate, the diff pushes/pulls the subframe, and the subframe moves under suspension load too, so in reality you are asking the poor little diff bolts (which are connected to the subframe) to handle both the slop of the diff bushings and the subframe bushing, in multiple directions/axis.

By locking down the subframe, me thinks the diff bushings and bolts are better prepared to do the job they are intended to do, support the diff.

Maybe I'm wrong, but I'm fairly sure the M3 GTS used the same arrangement from the factory.

[roastbeef]

The nose of the pumpkin lifts on acceleration.

I would theorize the horizontal diff bolt doesn't see as much stress. It would take a ton of grip to get the pumpkin to rotate horizontally. You would have to have a ton of power and drag slicks. Just my theory. I could be wrong.

[SYT_Shadow]

Originally Posted by ///Mobbin

I haven't gotten there yet but I am planning on the solid subframe and purple powerflex diff bushings. I have read many many posts on this and that seems to be the consensus for DCT cars that are either DD's or see some street and track time. I will also likely swap in the Hotchkis front/rear sway bars at the same time since the rear subframe is already coming down.

I'm on the same path.

On the DCT 'track' car, it'll get solid subframe bushings, powerflex street diff bushings (not sure of the color) and the hotchins front and rear sways. Plus MCS 2WNR

[///Mobbin]

Originally Posted by SYT_Shadow

I'm on the same path.

On the DCT 'track' car, it'll get solid subframe bushings, powerflex street diff bushings (not sure of the color) and the hotchins front and rear sways. Plus MCS 2WNR

Very similar path, go go go!

I believe the order of Powerflex's bushing rigidity is yellow -> purple -> black [hardest] and I was originally thinking yellow for the diff bushings but saw they only make purple and black. Hence, purple it is as this car will still be my Friday/weekend car even after the next iteration of track mods.

[FrostyAZ]

I did solid subframe and black powerflex and the diff whine was pretty annoying. I was just driving to and from the track and it was pretty annoying, would not suggest that combo for dd. It did make the car feel better. I am now adding solid motor and transmission mounts but the car will be trailered now so don't really car about NVH.

[Mvez]

Originally Posted by FrostyAZ

I did solid subframe and black powerflex and the diff whine was pretty annoying. I was just driving to and from the track and it was pretty annoying, would not suggest that combo for dd. It did make the car feel better. I am now adding solid motor and transmission mounts but the car will be trailered now so don't really car about NVH.

The amount of diff whine you get from purple and black is probably very similar....which is what I was afraid of. That's what AKG also suggests. I'll probably just leave the diff stock and keep an eye on the bushings, as I can always go back and do it later. Maybe purple at most.

I'm adding Rogue rubber tranny mounts, because those are great, worked nicely on the e46 with very little extra NVH, no annoying noise, just slightly more direct shifting feel and better throttle response.

It's a lot of work trying to avoid NVH, but add performance. Almost makes me appreciate the work those factory engineers do.

[becausephilchow]

Originally Posted by Mvez

The amount of diff whine you get from purple and black is probably very similar....which is what I was afraid of. That's what AKG also suggests. I'll probably just leave the diff stock and keep an eye on the bushings, as I can always go back and do it later. Maybe purple at most.

I'm adding Rogue rubber tranny mounts, because those are great, worked nicely on the e46 with very little extra NVH, no annoying noise, just slightly more direct shifting feel and better throttle response.

It's a lot of work trying to avoid NVH, but add performance. Almost makes me appreciate the work those factory engineers do.

I have Purple Diff bushings and Solid Subframe being installed right now.

A local had that setup on his car, he said the whine was very subtle, turning on the radio would mute it already.

[///Mobbin]

Originally Posted by Mvez

The amount of diff whine you get from purple and black is probably very similar....which is what I was afraid of. That's what AKG also suggests. I'll probably just leave the diff stock and keep an eye on the bushings, as I can always go back and do it later. Maybe purple at most.

I'm adding Rogue rubber tranny mounts, because those are great, worked nicely on the e46 with very little extra NVH, no annoying noise, just slightly more direct shifting feel and better throttle response.

It's a lot of work trying to avoid NVH, but add performance. Almost makes me appreciate the work those factory engineers do.

I researched transmission mounts for awhile and found that on the e9x m3 the NVH complaints were significant. I was researching with DCT in mind though. Just advising caution on those. Perhaps the rubber is similar to OE though in which case the Rogue parts may be a good option. Anyone have these installed already?