IME I would not go too light on the flywheel.  You lose inertia when you step on the clutch making the car less fun to drive (constant rev matching).  I have an 11lb flywheel behind a 350 in my '86 IROC and regret it.  IMO the tiny performance advantage of a faster reving engine is more than offset by the chore of how the car has to be driven.  

Too light a flywheel can also lead to idle instability, mystery misfire codes, and stalling when the clutch is pushed in if you run EFI.  I had to adjust the idle compensation table in my Camaro to get it to stop stalling every time I pushed the clutch in when slowing down from a long pull.  I also found out when running a lightweight flywheel in my WRX that it couldn't be machined or it became too light and I had misfire codes and stalling issues.  

I know, I know, not directly "early Mustang" experience, but those experiences led me NOT to run a lightweight flywheel in my '67, or my '89 for that matter.  

TKO, the 363 will be carbureted so no issues related to fuel injection. The 347 with the 14 pound flywheel worked really well and the 363 produces approximately an 11% gain in both torque and horsepower. At 2500 rpm the 347 made rear wheel numbers of 140 hp and 280 ft lbs. The 363 will do better than that, so I may go with a flywheel lighter than 14 lbs.
 
BobE, in lighter cars I have always used lightweight flywheels. In a 2400 lb car with a built FE 427 and very large tires, the combination worked perfectly. Likewise, the 3200 lb Mustang, 347, with a 14 pound flywheel was a joy to drive. On a heavier car or truck I would definitely be looking at a heavier flywheel, but on this application, I am going to consider a flywheel 13 pounds or below. 
 
Important to note that in conjunction with the 14 pound flywheel, the 347 also had a light weight aluminum clutch pressure plate further reducing inertia. On my cars and motorcycles, within reason, I am always trying to reduce reciprocating and rotating weight. I view it as free horsepower.

I should also note that I cannot use the 347 flywheel as it is externally balanced whereas the 363 is internally balanced. 
 
Thanks for your input and hopefully I can attend a future bash and you can drive the car and comment.

Last edited by boss347convertible (7/01/2026 9:18 AM)

If it works for you, go for it.