I've been running E3 for six years and have over 60K on the same set initially installed. No problems. I have a rebuild, basically stock, different cam, same lift just different duration power band now comes in around 1500 and pulls all the way to rev limit, unlike the stock. Banks headers and cold air. I did onpen the throttle body up some; mostly removed the tapper. If I stay at 70 or less, I get 18-19 mpg. Above 70 - 85 drops to 16 and same with ac on. (FL summers suck) oh, I did replace stock fuel injectors with 23lbs Bosch and added a Gforce chip to simulate more air to get the fuel to run the injectors. Otherwise the ECM limits fuel to the injectors regardless.
An issue I am having are my banks headers keep cracking at the collector welds. I am on my 4th set, these are the "revolver" style and they sound much better...I just hope they don't crack. The cracking issues I found is due to the highway driving engine speed engine CHT temps (purposely runs extraordinarly lean for emmissions. Thus, the injectors and gforce. These last set of header did not show typical hightemp discoloration, so I am thinking I have checked that box. The headers are cracking at the weld line. Known as the weakest link in a weld...this still should not happen like it is.
But, the E3's are great in my opinion...I even run them in my 93 Harley Wide Glide.