I read a post on the "old forum" regarding the Rotec 2800 used on a CB-1. There was issue raised by some that the Rotec 2800 on a CB-1 would have the accessories close to or just through the firewall.
I come to a different conclusion (calculation). If I am in error I'd appreciate some help with my math. If I'm correct I think the forum needs this info in it so as not to deter someone erroneously from the Rotec 2800. So here it is:
Using only the data on P. 27 of the plans and the manufacturer of the Rotec's stated dry weight of 224 pounds.
1. The battery weight for the change from an O-200 to an O-290 as depicted on p. 27 would calculate to be about 35 pounds if moving the battery from its fwd position shown with the O-200 (using 35" forward of A/C CG) to its aft depicted location for use with the O-290 (using 50" aft of A/C CG) to result in no net empty CG change in the engine/battery swap. - Probably a realistic battery weight when drawing was made. This is if I am interpreting it correctly that the O-200 has the battery in front and the O-290 in the rear.
2. Taking an aircraft such as depicted on p. 27 with an O-290 installed and the empty CG falling 8" forward of station #10 and changing nothing but the O-290 to the Rotec 2800 would result in placing the Rotec CG 23" fwd of the bottom of the firewall to cause no CG change. This would put the aft face of the engine mounting plate (according to Rotec drawings)at 18" fwd of the bottom of the firewall and the back of the accessories at 8.75 forward of the lower firewall.
3. Changing the same 35 lb battery to a 25 lb battery (available now) but leaving it 50" aft of A/C CG (42" aft of Station 10) would mean moving the engine CG back about 2.25" still leaving plenty of firewall clearance.
4. Removing the 35 lb. battery from the rear and installing a 25 lb battery 35" forward of the A/C CG would require moving the engine CG aft 11.75 inches from its original position (scenario #2) which would put the aft face of the engine mount plate 6.25 inches forward of the lower firewall and the aft end of the accessories about 3" aft of the lower firewall. This would be pretty close to interference with the aft sloping firewall.
With an aft mounted battery I don't see a problem with the Rotec 2800 on a CB-1.
Of course there are other minor factors: The Rotec likely holds more oil which would move the A/C CG forward. The prop would be moved aft with the Rotec moving the CG aft. The cowling change would likely move the A/C CG aft (especially if you did not cowl the cylinders, only the accessories).
Does anyone have contrary information? or have I misinterpreted the conditions depicted on p. 27??