Let the numbers speak, no debate, but it seems tail heavy
I don't want to step in it, because several have expressed strong opinions and I am going to disagree, sorry in advance. But a nose "light" RV-7 will have limited baggage capability and Acro CG will always be exceeded with two-UP. Sorry the numbers don't lie. Granted I picked the worse one, this is From Dan C's web site a W&B data base. This RV-7 has a 320/wood and has a very aft empty CG. I am going to say the 320/wood works but not ideal CG wise for a RV-7. Baggage will be limited and it may even be a single place Acro plane, at least in these examples.
Weight and Balance for Van's RV-7 N203CR
Owner: cary rhodes
Engine: Lycoming O-360 (180 hp)
Propeller: 68" Other 2-blade Wood Fixed Pitch
Number of Seats: 2
Fuel Capacity: 42 gallons
Empty Weight: 1058 pounds
Empty CG: 83.14" aft of the datum
Max Gross Weight: 1800 pounds
Useful Load: 742 pounds
Full Fuel Payload: 490 pounds
Normal: ....CG Range: 78.7" to 86.82" aft of the datum @ 1,800 lbs
Acrobatic: CG Range: 78.80" - 84.50" aft of the datum @ 1,600 lbs
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Sample Scenario 1: Normal Pilot & Pass, Full Fuel, *Max Baggage*
* Note: RV-7's has 100 lb max bag limit normally, but this builder arbitrarily made 60 lbs max, but is still is too much in most loading scenario's.
Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 252 / 80 / 20160
Pilot 210 / 97.48 / 20470.8
Passenger 160 / 97.48 / 15596.8
Baggage 60 / 126.78 / 7606.8
Total 1740 / 87.24 / 151796.52
CG is 0.42" aft of the aft normal limit. No go
CG is 2.72" aft of the aft acro limit. No go
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Sample Scenario 1A: Normal Pilot & Pass, Full Fuel, No Baggage
Weight / ArmCG / Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 252 / 80 / 20160
Pilot 210 / 97.48 / 20470.8
Passenger 160 / 97.48 / 15596.8
Baggage 0 / 126./ 78 0
Total 1680 / 85.83 / 144189.72
CG is 0.99" with in normal limit OK
CG is 1.33" aft of the aft acro limit (80 lbs over wt) No go
(Even with lighter pilots or less fuel its impossible to do dual Acro. If solo and a big boy you will be at or aft the Acro CG.)
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Sample Scenario 2: Heavy Passenger, *Max Baggage, Minimum Fuel
(* 100 lbs is normal, 60 lbs is this planes bag limit)
Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 30 / 80 / 2400
Pilot 210 / 97.48 / 20470.8
Passenger 300 / 97.48 / 29244
Baggage 60 / 126.78 / 7606.8
Total 1658 / 89.07 / 147683.72
CG is 2.25" aft of the aft limit. No go
CG is 4.57" aft of the aft acro limit (58lbs over wt) No go
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Sample Scenario 3: Standard Pilot Weight, No Baggage, Full Fuel
Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 252 / 80 / 20160
Pilot 170 / 97.48 / 16571.6
Passenger 0 / 97.48 / 0
Baggage 0 / 126.78 / 0
Total 1480 / 84.25 / 124693.72
CG is 2.57" with in normal aft limit OK
CG is 0.25" with in acro aft limit OK
(Full fuel helps move CG fwd. 170lbs is max pilot weight with 28 gal of gas or more.)
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Sample Scenario 4: Lightweight Pilot, No Baggage, Full Fuel
Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 252 / 80 / 20160
Pilot 100 / 97.48 / 9748
Passenger 0 / 97 /.48 0
Baggage 0 / 126 /.78 0
Total 1410 / 83.6 / 117870.12
CG is 3.72" with in normal limit OK
CG is 1.40" with in acro limit OK
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Sample Scenario 5: Very Heavy Passenger, *Max Baggage, Half Fuel
(* 100 lbs is normal, 60 lbs is this planes bag limit)
Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 126 / 80 / 10080
Pilot 210 / 97.48 / 20470.8
Passenger 310 / 97.48 / 30218.8
Baggage 60 / 126.78 / 7606.8
Total 1764 / 88.63 / 156338.52
CG is 1.81" aft of the normal aft limit. No Go
CG is 4.13" aft of the acro aft limit (167 lbs over wt) No Go
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Sample Scenario 6: Very Heavy Passenger, *Max Baggage, Minimum Fuel
(* 100 lbs is normal, 60 lbs is this planes bag limit)
Weight / ArmCG /Moment
Aircraft 1058 / 83.14 / 87962.12
Fuel 30 / 80 / 2400
Pilot 210 / 97.48 / 20470.8
Passenger 310 / 97.48 / 30218.8
Baggage 60 / 126.78 / 7606.8
Total 1668 / 89.12 / 148658.52
CG is 2.3" aft of the normal aft limit No Go
CG is 4.62" aft of the acro aft limit (68 lbs over wt) No Go
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You could add one of those weighted harmonic balancers for fixed props to add engine rotational inertia (better idle). Also you could use a heavier battery, starter & alternator.
I think a metal prop (Sensenich) is the obvious choice. Expressing my opinion only, I would go with a Sensenich, its has better performance, prop pitch can be changed in the future and has better product support. Even better its GOING to be faster, in my opinion than a wood prop. A metal prop is a no brainer, especially if you are going to build a RV-7 with a O320/Fix.
Paint makes CG go aft (more surface area aft of CG than fwd). I dare mention priming internally, that will also add more weight aft as well. If going with a real light engine/prop combo, you need to do everything you can to add weight fwd of the spar and as little aft, where possible. You could put some lead ballast on the front of the engine. It does change the "moment of inertia" of the plane in the yaw axis (spin) but its only making up for the light engine/prop.
The ideal make weight and aft CG from a practical stand point for a RV-7 is 1095 lbs and CG of 80" or more fwd. Lighter is fine but CG of 80" or less (fwd) is kind of critical to carry the full 100 lbs in the aft bag area and to stay in Acro CG with two pilots. Fuel helps move CG fwd, but with full tanks you may run into weight restriction, especially Acro wt of 1,600.