Seam Welded Front Subframes.
Discussion
In general the front sub-frame is over-engineered.
I always reckon you could save about 15% of its weight by cutting big lightening holes in the almost-vertical side webs, open out the turret side holes and generally lighten it a bit in other places.
However, for rallying I leave it alone as I am more concerned with handling and the weight I want to remove is the high-up weight, like the glass and seats.
I do seam weld the front frame a bit, but only in a couple of areas. The best modification is the addition of a 3mm steel triangular gusset plate onto each of the front tie-bar ears to prevent them bending back under any shock loads. It's vital on any rally car.
If I were intending to do very long and very rough events (I probably wouldn't use a Mini!) in a Mini I would weld a couple of additional 3mm steel gussets onto the spring towers from the rear sub-frame cross member, although I don't think this is really important.
On later cars, the rubber sub-frame mountings should always be changed to solid ones, but a real weakness is not the subframe itself, it's the front floor/bulkhead onto which the sub frame rear mountings attach. The mounting, unlike the earlier cars, is in the middle of a flat panel and the fore and aft loads cause the panel to work-harden and split. To cure this make up a 16 swg doubler plate about 10" x 6" and seam and plug weld this to the bulkhead when the sub-frame is out of the car. Also seam weld the seams inside the car in this area. Paint and protect after welding and fitting the solid mounts. You must fit solid mounts all round and all at the same time. I've met people who only fit them at the front and at the tower tops. This is, in theory, to keep the vibrations down, but it then puts the front sub-frame to body loads into the body only at top and front, which is not what is intended. The rear mounts must take their share of the applied loading.
I hope this helps and I'm sorry if it's a bit of a long post.
Peter
I always reckon you could save about 15% of its weight by cutting big lightening holes in the almost-vertical side webs, open out the turret side holes and generally lighten it a bit in other places.
However, for rallying I leave it alone as I am more concerned with handling and the weight I want to remove is the high-up weight, like the glass and seats.
I do seam weld the front frame a bit, but only in a couple of areas. The best modification is the addition of a 3mm steel triangular gusset plate onto each of the front tie-bar ears to prevent them bending back under any shock loads. It's vital on any rally car.
If I were intending to do very long and very rough events (I probably wouldn't use a Mini!) in a Mini I would weld a couple of additional 3mm steel gussets onto the spring towers from the rear sub-frame cross member, although I don't think this is really important.
On later cars, the rubber sub-frame mountings should always be changed to solid ones, but a real weakness is not the subframe itself, it's the front floor/bulkhead onto which the sub frame rear mountings attach. The mounting, unlike the earlier cars, is in the middle of a flat panel and the fore and aft loads cause the panel to work-harden and split. To cure this make up a 16 swg doubler plate about 10" x 6" and seam and plug weld this to the bulkhead when the sub-frame is out of the car. Also seam weld the seams inside the car in this area. Paint and protect after welding and fitting the solid mounts. You must fit solid mounts all round and all at the same time. I've met people who only fit them at the front and at the tower tops. This is, in theory, to keep the vibrations down, but it then puts the front sub-frame to body loads into the body only at top and front, which is not what is intended. The rear mounts must take their share of the applied loading.
I hope this helps and I'm sorry if it's a bit of a long post.
Peter
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