Welcome to the forum, and congrats on the new 400E.
1) Before you start messing with modifications and lowering, I'd STRONGLY recommend going through the entire suspension and seeing what needs replacement. Unless it came with a stack of records and/or was maintained open-chequebook by the PO, there's a strong possibility it may need new steering linkages, some bushings, almost certainly the rear wheel carrier joints, and dampers (struts/shocks, strut mounts/buffers/boots).
2) Lowering will require a dealer alignment, most all alignment shops won't do it properly, unless (maybe) they specialize in Mercedes. You want to fix everything on the chassis first, then pay for ONE dealer alignment (~$180 or so). Ride height affects alignment, and you may need to change the spring pads to tweak the height front & rear... requires driving a bit after each change, measuring again, etc. Do all this BEFORE the alignment and also before you buy new tires.
3) Remember that H&R springs are one-size-fits-most. There are factory Sportline springs which allow more fine tuning, but will cost a bit more.
@a777fan is working on a full Sportline conversion for his E420 and might be able to chime in. Blue Ridge MB has custom sway bars available if you want to reduce body roll. Dampers are a personal preference thing but if lowered, you'll probably want OE Sportline, Bilstein Sport, or KONI yellows (in order from least to most firm).
4) The wheels shown above are an aggressive fitment, specifically the 8.5 ET30 rears. You WILL need to roll the fender lips and use fender spacers are shown in the AMG wheel install docs at the link below (scroll to the bottom):
http://www.w124performance.com/docs/mb/W124/
5) Tire size selection is critical, note that Gator used a 225 rear tire on the 8.5 wheel. Be very very careful with tire sizes. The ABS and cruise control will have problems if the difference in diameter/circumference is more than about 2%, and Gator's setup is at 1.6% difference. If your car has optional ASR make sure the rears are slightly larger than the front, or you'll also have ASR issues.
6) The exhaust on these cars is quiet. Ask
@kegmankipp about that. The factory catalysts flow extremely well (near zero power loss) but also reduce most of the growl. If the resonator delete wasn't enough, all you can do is try an aftermarket muffler as well. If the factory cats are in good condition, DO NOT modify or replace them. If you insist on changing them, remove the factory cats & crossover pipe, and install custom parts (like the Leistung exhaust). The factory parts are NLA and nearly impossible to find used.
7) Don't forget to check condition of the upper & lower wire harnesses, datecode on the ETA (especially if the car has ASR), all ignition system components, and verify spark plugs are NON-resistor. Search the forum for details on all of the above.
8) I always recommend dropping the lower oil pan at your first oil change to inspect for chain rail debris. If you find any, you MUST pull both valve covers for inspection, and may need to replace all the upper chain rails/guides. If the oil pan is clean, replace the O-ring for the oil level sensor while the pan is off, and if the sump pickup boot is the old/small version, replace with the new/large version. Cost of parts is low, and this is a once-per-ownership job.
9) I don't know how familiar you are with part vendors for MB's but there's more and more garbage on the market the last ±5 years or so. If you buy based on price, it will bite you. Follow the recommendations at the list below. For certain items you'll be forced to buy OE/Genuine parts from a dealer as there are no quality aftermarket equivalents anymore. There are a bunch of different MB dealers that sell online at a discount using the Revolution Parts platform, find one near you with good pricing to save on ship costs.
Click here for info on one of them.
Many folks wonder as to which brands (OEM and aftermarket) are good quality and are worthy of purchasing. Here is a listing (subject to change and modification over time) as to which vendors are "safe" to buy from and which ones have "caution" and "do not buy" flags. This list is based on the...
www.500eboard.co
10) If there's no record of the ignition tumbler having been replaced, order one from the dealer (VIN-coded) and replace it proactively. Cost will be near $100 but it comes with a new steel key, use the new key only. The tumblers can seize without warning and trust me, you do not want that to happen. When I get a new 124, the very first part I order is the tumbler (p/n 126-460-02-04).
11) Almost everything you need to know has been covered repeatedly on the forum. Search first, or
@xfadmin won't be happy.
And finally...
Thanks!
Now I only need to do full rear subframe rebuild.
