A lot of people say EXP-119 and Thunderbolt all in the same breath, but they’re two separate things.
With the EXP-119 you primarily get the cold-air induction, the larger 200 mm airflow performance throttle body, and the option to delete the vacuum pump accessory pad….which I think is a bad idea. It takes away the ability to add a backup alternator.
With the Thunderbolt your engine is lovingly built by a one or two man team that takes special care during assembly. The engine is ported, polished, and balanced…it’s basically blueprinted. You can also choose the compression ratio (8.9 or 10:1) You also have your choice of ignition systems. I’m not one hundred percent sure, but I think you can also opt for the larger 200 mm airflow performance fuel injection that comes on the EXP-119. You also have your choice of engine colors.
If you’re planning on the SDS or EFII injection and ignition systems, other than the cold air induction, there’s really no reason to get the EXP-119.
If you decide to go with the “standard” 390….with or without the Thunderbolt treatment, I think you can still order your kit with the EXP-119 cowling and snorkel just as if it were an actual EXP-119. Don’t take my word for it though and confirm this with Vans. I actually don’t know what the differences are in the cowling?? I could be mistaken, but I think all of the kits come with the 4 into 2 exhaust pipes now. If the standard/non EXP-119 cowling is still designed for the 4 into 1 exhaust pipe, then you should be able to opt for the EXP-119 cowling and 4 into 2 exhaust pipe. But once again, you’d need to confirm these things with Vans.
I did a “home-brew” EXP-119. I got the Thunderbolt option, but I’m installing the Superior cold-air induction rather than going with the Lycoming cold air. I also had Clint build my exhaust pipe, which is a trombone design rather than the cross over. This pipe was required with the Superior cold air unit.
When ordering, I ordered everything (the cowling and snorkel) as if I were going with the EXP-119 even though “technically” it’s not.
Saying all of that, and making a long story longer, I’m sure you’ll be perfectly happy with the standard A3B6 and your airplane will still perform well.
Hopefully this will give you a little bit food for thought and help guide you through the maze.