Bracing floor pan, any pointers?

[K Simmonds]

Right my S2 project is nearing completion and I've been thinking about ways to stiffen the shell as much as possible with going down the cage route. Error404 has given me some good ideas for bracing the exhaust tunnel, a front lower chassis brace and I'm going to weld in some front strut brace mounts onto the rear turrets for a brace which I'm going to triangulate to the rear sub frame mounts.

It's occurred to me that as I have no sound insulation and very thin carpet then I have about an 3/4 inch of space across the inside of the floor pan to play with. I was thinking along the lines of welding box section steel to the full length of both sills and the floor, as well as the exhaust tunnel then triangulating the whole lot with more box section and have some of the the joints run into the same areas as where I brace the tunnel.

This will also mean my lighten front carpet will sit at the correct height for the pedals.

Any in put welcome.

[Error404]

Stich weld as much of the chassis as you can Kit, makes a real difference. The tunnel is the weak point, brace across between the transverse rails that the front seat mount is on. The difficult bit of bracing the tunnel is obviously clearance for the exhaust, its a PITA!

[K Simmonds]

Yeah I know stitch welding would be of real benefit, I'm pushed for time at the present due to work and stripping all the under seal off is a job I can't face at the moment. I may decide to do some of the easier seam's and tackle the others a later date.

Which areas have you done Alex?

[Error404]

yeah its not the quickest or the most pleasant job! I did everything I could inside and out as far forward as the firewall. Will do the front of the chassis at a later date when the engine and gearbox is out of the way - also planning on welding in some strengthening plates and some pick-ups so I can make some bolt-in braces between turrets and firewall just above the steering rack

[GazzaG60]

can you educate me on the reasoning behind the welding with the cage.

are you going rallying or are you trying to balance the chassis to the cage.

i know these dont have the best chassis its a bit flexy but it holds the power in ever so well. you can feel a subaru trying to rip itself apart near 400hp.

im interested

[Error404]

he doesn't want a cage Gaz - he's trying to stiffen the chassis as much as poss without
There are some good improvements to be had with a little work

[K Simmonds]

he doesn't want a cage Gaz - he's trying to stiffen the chassis as much as poss without
There are some good improvements to be had with a little work

Bang on there Alex, I don't want to cage this car as I want it to look as stock as poss inside and out. Going back too original 3B alloys as I don't think the lack of give provided by very low profile tyres does anything to help the situation apart from on perfect roads. IMO Audi didn't spend all their devlopment time for their hard work to be ruined by fitting bigger wheels. In all my experiance with modified cars they tend to handle best on stock wheels with the best tyres you can afford.

At the end of the day this car will be used for track days and the odd hill climb but will still be used on the road for day today use. And I want to be able to use the 350+ ponys I have without it being too scary. I can feel the limitations of my 2.3 FWD coupes chassis when I really push it so with 200+ more BHP, all be it with 4WD, I'd like to try and help the floppy old bus out a bit.

[GazzaG60]

seriously the chassis handles the 500 or so i have easily. it is very flexy though but ive uprated the all mounts and bushes along with suspension so it feels quite nice. i can still feel the tunnel flex on uneven roads moreso or in corners.

be interested to see what you think is a good way forward on this. not sur ei have room to brace the tunnel with the 3"

[Error404]

I have all but eliminated the squidge you get loading up the suspension on mine, stiffer chassis makes the suspension work harder too, so the ride is smoother.
Rear tower brace and front lower brace make a big difference in terms of cornering speed before you scrub wide, car also reacts to direction changes a lot more aggressively. Beefing up the stock tunnel braces has helped too but as above its difficult with exhaust, even more so obviously with a 3".

[Acidburn]

Stich weld as much of the chassis as you can Kit, makes a real difference. The tunnel is the weak point, brace across between the transverse rails that the front seat mount is on. The difficult bit of bracing the tunnel is obviously clearance for the exhaust, its a PITA!

I can agree 100% there, the tunnel is like paper as me and terrybullwon found out when we cut one apart the other day, his grinder went thru it well easily.

I have all but eliminated the squidge you get loading up the suspension on mine, stiffer chassis makes the suspension work harder too, so the ride is smoother.
Rear tower brace and front lower brace make a big difference in terms of cornering speed before you scrub wide, car also reacts to direction changes a lot more aggressively. Beefing up the stock tunnel braces has helped too but as above its difficult with exhaust, even more so obviously with a 3".

Hmmm i'll have to have a drive and see how it compares with my urq if I ever finish it

more goodies turned up for that yesterday.

[G60Rallye]

Its an interesting one this trying to strengthen it up without a roll cage. I would try to avoid welding the seams. I did this on mine and regreted doing so. Its a total nightmare of a job to do as you can get the seams cleaned up well enough and the welder hates it spitting and crackling. The flip side of that is that any paint protection there was between the seams gets burned off leaving it open to rust.

I would go with as much bracing as you can front and rear. I used to have a Golf Rallye which had an eibach front strut brace. It had the cross bar bolted in which I removed whilst the car was on its wheels. The car was then put up on axle stands to do some engine work, tried to bolt the brace back in whilst it was up in the air and the bolt was as least 5mm off going through the hole so it shows the flex you get even without any cornering load!

[K Simmonds]

Its an interesting one this trying to strengthen it up without a roll cage. I would try to avoid welding the seams. I did this on mine and regreted doing so. Its a total nightmare of a job to do as you can get the seams cleaned up well enough and the welder hates it spitting and crackling. The flip side of that is that any paint protection there was between the seams gets burned off leaving it open to rust.

That's one of the issues that realiy put me off seam welding, I have to do MOT welding at work and getting the surfaces clean enough to weld properly is a real PITA, and as you rightly point out some areas will be prone to corrosion. Also the amount of time it would take would drive me mad.

Over the next month I'll scratch my head over this one, definately going to be bracing the chassis as much as I can though.