Why I did what I did
A few humble thoughts for you. The canopy frame comes down over the top/front edge of the panel so you'll need to be sure to leave space there especially around the top corners of the EFIS. Also, with the 496, you really don't need the other back up instruments. If you have an EFIS failure, the panel page in the 496 could be your back up. The compass is not necessary as you have heading in the TT and legally your magnetic heading is in the EFIS. Last thought for you is if you are going with the 430W and planning on IFR you may want an autopilot that does GPSS & GPSV especially in the -4 which can be pretty squirly in turbulence.
Thanks for the input. Tips like yours have saved me a ton of headaches over the course of this project.
I ended up with the layout as shown for several reasons, mostly driven by preference:
1) I always like mechanical backups for the pitot and static instruments. If the TT EFIS dies, the steam gauges are the only way to know my airspeed and pressure altitude. Oh, and I happen to have these instruments laying around anyway. Might as well get some use out of them. Also, there's some speculation that a DAR would require a TSO'd altimeter.
2) The TT EFIS is unique among EFIS systems, as it does not have a magnetometer (nor does it need one, but this is off-topic). To know magnetic heading, I either need another EFIS w/magnetometer, or a whiskey compass. I could probably get by without either, but I like having some way of knowing which way I'm going when the cards are down.
3) The TT EFIS AP IV has a crazy amount of capability for the price and size, including engine monitoring and a full 2-axis autopilot with GPSS and GPSV. Since the -4 is a handful in the clouds, the instrument to the left of the EFIS is a TruTrak ADI Pilot II, which serves as a backup attitude indicator and 2-axis autopilot. I figure 2 autopilots is better than one (though I still hope to be able to hand fly the -4 in the clouds). Actually, I thought long and hard about putting a Dynon D6 in this spot (backup attitude and air instruments, magnetometer, AOA all in one little box), but the autopilot won out after some input from a few pilots with much more experience and skill than I'll ever have.
4) I'm personally not a big fan of putting handheld GPSs in the panel. It just doesn't look right to me, and it seems like handheld GPS form factors change much more quickly than radios and instruments, so a special cutout for the 496 may not be useful in 5-10 years. I prefer a short RAM mount attached to the panel or nearby structure.
Prompted by other threads on this forum, I triple-checked the fit of everything under the canopy frame, and all is well. Definitely an important step!
Cheers,
Matthew