Some months back, I recall an article from a member whose feathers were all puffed up regarding various conversion improvements to his 3.0CS. I will report two particular warnings in conclusion, but I would like to add that I converted my 1975 BMW from a 3.0 CSA to an Aplina 3.5 motor plus 11:1 compression, triple side draft webers, port and polished matched to ceramic coated headers, free flow exhaust, 17" Alpina wheels and Bridgestone, full leather, titanium rods, aircraft quality flywheel, racing suspension, posi-track and on and on. I also got rid of the useless Borg Warner automatic and installed a 4 speed ZF. Horsepower and torque increased from 180 to 300. All of my conversion parts were sourced from Kormans. In conclusion, you need to be very attentive to two potential danger areas: 1) verify that the welds on the rear shock towers are at least a continuous weld and NOT spot welded for extra strength, and to inspect these welds regardless and 2) your differential is held to the underframe by ONE vertical bolt making it the weakest part of the car compared to two side bolts on the next generation 628, 630, 633, 635. The one vertical bolt is similar to the same problem as with the porsche 914 and is subject to failure. Why do I know about the differential bolt problem, simple, I dropped my differential laying rubber in third and which folded the rear wheels into the wheel wells and generally was not pretty,
Ouch. I had a 3.5 Motronic in mine. I had planned to put an E28 rear subframe in mine, but ended up selling it.
