aftermarket subframe?

[Spike00513]

stock is heavy (steel, iron?) and rusts.
Any point in change?

Supposedly lighter,
stronger
stiffer, more responsive
customizable suspension geometry

Maybe it's not stock because OEM was easier/cheaper/faster?
stamped + spotwelded (robot) sheetmetal(?) vs aluminum, chromoly, etc.?
D3 A8 rear (4E0 505 235 H) looks the most similar, maybe it can be made to fit?
OEM B6 = 8E0 505 235 BP

as we know, a lot of VAG parts are interchangeable like legos, sharing the same parts bins, platforms, etc.
FWIW, D3 A8/S8 r.Diff looks the same as ours..Maybe the body connection points are too - if not, cut and weld?

vs. B6 diff:

Whats up guys! So I am in the process of building a race car using a B5 platform chassis. This car will be used for the NASA NE, NASA RALLY, and NASA AutoX series. Hoping to catch a few this upcoming season if it all comes together in time. I am well into this project and I am moving forward very quickly. I work at a fab shop that builds race cars, but not the kind of cars I'm into... so I decided to make my own. This whole processes is taking place at my personal garage and the fab shop. The plan is to get this thing at or under 2200lbs.

Bye bye rotted subframe!

Aluminum:
E39 M5:


C5 RS6:


Phaeton:


Passat 4motion:


Audi S2 (D M Developments, tubular)


MKIV VW, F M Fab (Canada, CAD vs. USD):

[sandspeed]

What exactly are you getting at, besides posting pictures of multiple subframes? Are you asking if replacing the subframe with a tubular steel one would be better for certain reasons, than yes.

[tchuck]

stock is heavy (steel, iron?) and rusts.
Any point in change?

Supposedly lighter,
stronger
stiffer, more responsive
customizable suspension geometry

Maybe it's not stock because OEM was easier/cheaper/faster?
stamped + spotwelded (robot) sheetmetal(?) vs aluminum, chromoly, etc.?
D3 A8 rear (4E0 505 235 H) looks the most similar, maybe it can be made to fit?
OEM B6 = 8E0 505 235 BP

as we know, a lot of VAG parts are interchangeable like legos, sharing the same parts bins, platforms, etc.
FWIW, D3 A8/S8 r.Diff looks the same as ours..Maybe the body connection points are too - if not, cut and weld?

vs. B6 diff:

Aluminum:
E39 M5:

C5 RS6:

Phaeton:

Passat 4motion:

Audi S2 (D M Developments, tubular)

MKIV VW, F M Fab (Canada, CAD vs. USD):

Is there some specific problem you're trying to fix?

[MikTip]

You have to remember the Audi B6 A4 is a "mass produced" vehicle that built and designed to sell to the general public.

Its not an off the shelf race car! Never was built or designed for such purpose.

Custom tubular chassis parts that are custom built are just that, and for specific reasons.

Also your OE sub-frame is "engineered" to hold up under "normal" use and in a crash. Is that custom subframe? Hmmmmm...

Race cars are subject to higher stress's than a normal road car.

If you want to see Audi Engineering for race cars...look at their DTM machines. Emphasis on safety! Safety for the driver! Cant have drivers dying driving race cars! Bad for business!

[MikTip]

Audi warns against cutting and welding on the OE subframes. Because you alter the metallurgy and the designed in safety.

You go out onto the streets...get in a wreck, and an investigation finds you altered the subframes/safety...you are liable.

Its actually against Federal laws(DOT) to tamper with any safety equipment on any road car. Its why "race" cars are not street legal.

[MikTip]

Here:



Install S4 aluminum bits and shave 5 pounds off each corner! Along with the light weight hub!

[MikTip]

The heavy rear subframe on the B6 balances the heavy engine up front!

[MikTip]

B7 A4 Brakes! All 4 corners!



Larger front and rear rotors!

Much improved braking power!

Heavier than OE.

You want better brakes? Or shave weight? Pro's and con's to both! But for me the improved braking is well worth the costs!

[MikTip]

Also notice the Audi S2 tubular frame...

Its a higher grade chromolly tubing...vise the mild steel looking one of the post by tinytimmy

[Audii-Dudii]

Is there some specific problem you're trying to fix?

For those of us who like to tinker with our cars and/or "race" them regardless of their pedigree (in my case, race = autocross ... haven't done the wheel-to-wheel thing for more than two decades), there's a lot of performance improvement to be had from tweaking the suspension geometry and also from stiffening the platform the suspension works against. If the SCCA's rules allowed me to do so, I wouldn't hesitate for a minute to replace the OEM subframe with a stronger/lighter/adjustable one.

Speaking of which, everybody here knows the B6 and B7 A4 Cabriolet front subframes come with solid aluminum bushings instead of rubber ones with metal sleeves, right? You can improve performance (at the expense of a slight increase in NVH, alas) and keep the car completely OEM!

[tchuck]

For those of us who like to tinker with our cars and/or "race" them regardless of their pedigree (in my case, race = autocross ... haven't done the wheel-to-wheel thing for more than two decades), there's a lot of performance improvement to be had from tweaking the suspension geometry and also from stiffening the platform the suspension works against. If the SCCA's rules allowed me to do so, I wouldn't hesitate for a minute to replace the OEM subframe with a stronger/lighter/adjustable one.

Clearly, but the assumption is that you know how strong or heavy your subframe really is in reality-land.

You have to have a goal in order to know that what you are doing is accomplishing that goal. Spending five minutes googling subframe pictures from a bunch of different cars doesn't tell you whether a random custom part will actually be stronger, lighter, or more corrosion resistant than the one on your car. Call me crazy but it seems like if you want a lighter part, step one would be weighing the thing. Once you have a weight you would have a goal (a lighter subframe). If you want a stronger one, you would identify the areas of weakness (like the b5 rear sway bar attachments that always break). If you want suspension settings outside the oem range (problem), then you need to find out how far outside the oem range your goal lies so you can build a part that solves your problem.

[Audii-Dudii]

Clearly, but the assumption is that you know how strong or heavy your subframe really is in reality-land.

For most the part, I do know roughly how heavy and strong parts are, actually.

You wouldn't have any reason to know this, but I am obsessive about tracking / reducing weight and weigh every part on the car whenever I have the opportunity.

You have to have a goal in order to know that what you are doing is accomplishing that goal. Spending five minutes googling subframe pictures from a bunch of different cars doesn't tell you whether a random custom part will actually be stronger, lighter, or more corrosion resistant than the one on your car. Call me crazy but it seems like if you want a lighter part, step one would be weighing the thing. Once you have a weight you would have a goal (a lighter subframe). If you want a stronger one, you would identify the areas of weakness (like the b5 rear sway bar attachments that always break). If you want suspension settings outside the oem range (problem), then you need to find out how far outside the oem range your goal lies so you can build a part that solves your problem.

I agree with you on all points.

[Spike00513]

Forgot about this, but saw a tubular ad today. Figured I'd post/add it on.

Looks like it's new..
But expensive.

Clicky

Same company that offers rear suspension Poly bushing kit.

Haven't seen this before. Poly subframe bushings, vs. solid metal:
Clicky

They just started advertising a rear one, but it's for the B5.
Clicky



I don't understand fitment though.
B6 6-speed manual uses a single center mount transmission bushing.
The picture shows two side mounts, like in the B5.

[Nollywood]

Spike, the car shown above is running an 01E.

Early B6 3.0 6-speed manual (2001-2003) were fitted with 01E gearboxes. These used normal side mounts and matching subframes, same as the B5.