Lighter is easy. Just move it forward as needed via motor mount design.
I don't know about instillation in a -10 but it sure sounds like a nice engine option for the RV-14. It is 13lb lighter and has 20 more HP than the I0-390.
I added 25 lbs of aux bat/wiring/contactor/fuse block at same station as main battery. Everything else per plans and stock. I love the balance solo, but I have to watch the aft limit. There is plenty of room in rear footwells to distribute the weight. Every flight since 25 hrs has been with a full load and it is fine. I would not want 100 lbs off the front and all of the additional modifications, less power and less climb rate. Yes, you could install firewall reinforcment for battery mount, main battery-PC925, contactor, #2 ga wire up front around the heat/vibration and balance would be very close. I also like having plenty of working room up front. If one likes to build more than fly, go for it.
With my aft full size battery and lighter MT 3 blade prop on the front the CG is perfect for almost all loads EXCEPT 4 adults and 100 lbs of luggage, which means that I have to be very careful when I get in the airplane or the tail will go down hard. I make sure that I am the last one on board so that I can do a last minute walk around and check everything before boarding.
My CG with 4 adults and 100 lbs of luggage is still within CG limits but absent moving the battery to the firewall reducing the weight of the engine by installing a 409 engine would take it out of the design CG limits.
At 75% power, I'm making around 182 HP on my IO-540 and running 200 MPH or better, so I'd think that the lesser horsepower may not be noticed much in cruise, but rather in takeoff and climb performance.
Best,
Is there anybody here that is willing to develop a firewall forward kit to suit the new 409 230bhp engine for the RV10. At 100lbs lighter, it might well be a good home for this package. If there is anybody out there, please contact me.
Andrew
AC KK