i'm looking in to chassis mod's to cope with 250+ bhp im about to be running in my MK2. i read an article in the golf + about the key to getting a mk4 to perform on the track was 4 days of custom fabrication on the rear beam. so got thinking about stiffening up my mk2 in the same way whilst the car is striped. i'm running a 25mm ebiach ARB ATM but have a welder and would like some pointers, if anyone has done anything like this in the past?
I would try to get hold of a mk3 plus axle tbh (the 5 stud one) they are very well built imo. Mk4 rear axles are a joke, the amount of them my mate changes at his work is scary, people fit big wheels to a mk4, give it some stick and the rear beam can't handle it. i bet my left testicle if you drive hard on big wheels on a mk4 your rear beam is bent to hell in 2 years time.
your mk2 rear beam should be fine. my old 20v (TT 225bhp motor) was fine for 3years til it met with a lorry. i ran a stock rear beam with an eibach ARB.. no problem at all.
i recon the stock beam would be fine but there has got to be a way of reducing the amout of flex (not adding to much weight) without using a 28mm rear ARB. for the amout it's going to cost me in welding gas etc and using stuff i have lying around, it got to be worth a go?
Ive seen a few race cars with a triangulated rear beams to stop to much flexing, i plan to do this to my mk1 over the winter. basically involves cross bracing the outer arms to the middle. if i remember correctly in needs a 6mm plate welded into the middle of the beam 40mm x 100mm ish, then 1 plate on each arm 40mm x50mm ish. holes drilled in each then connect the 2 with rose joints and some type of bar. A friend has this done on his mk3 race car i will have look at it in more detail before i do mine but i think its fairly straight forward tho. if your have over 250 bhp in the motor i wouldnt worry about adding a bit of extra weight, you will save loads more time in the handlig stakes
There was an article in CCC about one of the works rally kit cars, might have been a Seat. The rear beam on that was a work of art. I'll see if I can find and scan it.
Just generally on this topic, the mod is all very well for racing and trackday developments or some garage tinkering, but the benefits are generally on the margins. It's all about controlling toe out at the rear under high lateral loads, when the beam starts to flex, and gaining more stable geometry from it. Reams could be written, but the basic mod does have some inherent bump steer characteristics, but from the general racer feedback, it does work. See Mk3 Golf kitcar, Mk4 TDi (VW Cup), current Polo GTi in VW Cup, Frazero Mk4 1.8T (VW Cup), and various others eg New Beetles (VW Cup). That be this then! The Seat beam is complete re-engineer of the axle, which has a bearing in the middle and behaves like independent trailing arms. Anyway, enough waffle! Great to look at! Mk4 Golf Kitcar is broadly the same concept, with shorter bars and without the loop.
The Seat Ibiza Evo 2 & Mk4 Golf GTI are separate principles to the rest. Reeves one is based on Mk3 Golf Kitcar (which are also where the VW Cup ones originate).
thanks for all the peeps, most helpfull!! i think the Seat one is a little more involved than i want to get. seeing as it's going to be mainly a road car, but is a work of art! the one in the reeves thread looks a bit more do-able.
I'm no expert but I'd have thought you can add 'anti-roll' stiffness simply by using a thicker bar. If you stiffen the beam and add anti-roll stiffness in the process, you might add too much, and then it would be really awkward to take it off again (compare to unbolting an ARB). The other issue is beam distortion which introduces changes in camber during severe cornering. You could stiffen up or triangulate the longitudinal parts of the bar. Or, add a little bit of negative camber at the rear to compensate (wedge, or washers?) But I'm no expert, just theorising....
May not be very relevant but the 16V Astra tarmac rally/race cars used the Cavalier beam because it was stronger particularly around the axles. Might be worthwhile comparing the designs. I had one on mine and it made a big difference especially in the wet, but it's so long since I looked at one I can't remember what the differences were.
