Did you not do the wind tunnel tests on your car before optimizing the weights?
Then there are the bearing surfaces. Did you not wear in your axles and bearings with graphite?
Then to check did you not apply at least 7 coats of hand applied lacquer sanding between each with final sanding with 2000 grit paper before before wax polishing?
Don't forget to sand off the edges of the wheels where the plastic mold contact spot is too.
As to weight, it's best put over the front axle.
Just helped by son build one last year, in fact.
Have to spin the axles at about 10000 rpm to see if they are straight. We were allowed to select as many axles as we wanted so we did reject a few as out of line.
Then you need to polish the axles. Abrasive powder for final stone polishing put in a rag and then spin the axles again in the polish.
Then its time to apply the graphite.