I finally quit procrastinating and pulled my group apart today (big thanks to Jim King for the piston socket) and am quite impressed early on with the results. I'm kinda angry I hadn't done it sooner. Not only does it work a lot easier, the shots I'm seeing early on are a lot better in my opinion. Previously, with the almost 11 or so bar pressure exerted by the dual spring setup, there were two things I always disliked; the effort required to pull the shot made it slightly less fun to use than getting a root canal, and the power of the two springs snapping up often would result in an exploding portafilter out of the group unless I held the portafilter in my hand during the extraction. The amount of torque applied to the portafilter to seat into the group was more than enough to keep it locked in place, but the occasional surprise explosion and broken cups left me deciding to just hold on to it during the extraction as a fail-safe. Neither was very fun.
Second, and by far more important, is I'm already seeing better shot flavors and improved highlights in the coffee. Before, I had to grind finer for any given coffee, to tame the powerful two spring combo and that often led to flattening out the individual notes in the cup. Even with babysitting the extraction by retarding the spring wasn't always enough to improve the shot. Now (early on in the testing) it seems like I can just pull and release and focus on anything other than babysitting the portafilter and hoping nothing explodes off the group or that the shot's flow isn't ideal for that given dose. It's like having a classic Gaggia lever but a hell of a lot prettier to look at!
I'll rattle on some more as I go thru various coffees in the future, but for now I'm quite happy with the change. I pulled several shots this morning on the Linea on a coffee that I'm considering for a HB review and then switched to a quick dial in on the Leva and the Leva had the Linea beat hands down on the first attempt for flavor highlights and sweetness.
I measured a peak pressure of just over 6 bar using my homemade portafilter rig/pressure gauge. Previously, if memory serves me right, I was just over 10 bar on the dual spring.
One thing the Leva offers that other groups do not is this option to switch back and forth at will. It only took me about 20 minutes to do the job at a leisurely pace, and part of that was cleaning the piston and re-lubing the seal. I'm sure there's plenty of coffees that do better with the dual spring setup, but for now, I'm going to be happy using it as a single spring group.