The E55 is basically a E550 with a supercharger fastened on top (Please, no cheap shots from the peanut gallery about SBC, auxiliary battery, etc). Adds complexity and makes some maintenance more labor intensive. The E55 fuel delivery electrical system sucks; I've replaced melted relays, sockets, connectors multiple times. Plus the filter and fuel pumps will run you ~$1000 every 60,000 miles. Supercharger clutch dog bone springs can fail resulting in cut oil lines and destroyed thermostat housing (remedied with clutch scatter shield). Rebuild the supercharger idler pulley versus purchasing a new one; again, every 60,000 miles. EDIT: if you ever have to go into the supercharger because the rear bearings' grease dried (front bearings are oil bath), be advised there is a six-month to one-year lead time on a run of custom bearings out of Japan unless you can find someone with a pair in stock (Australia should/might have the bearings in stock). Note the rear bearings are a non-standard, custom bearing. You might consider going to the Whipple 2.9 liter supercharger in lieu of rebuilding the stock supercharger.
If you lean towards reliability, go for the E550. If you want the thrill of feeling the supercharger engage and rock your world, go with the E55. Just recognize the E55 is going to cost you a lot more money and time to maintain. And I do not recommend "dyno mode" on the street unless you are looking to submit an insurance claim for totaling your E55...
Last edited by bbirdwell; May 7, 2022 at 10:00 PM.