what's wrong with my coil?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Robert by way of Terry Fritz <twftesla-at-qwest-dot-net>" <obiwan1186-at-sunflower-dot-com>

I don't think i'm getting the performance i should out of my coil. here 
are the specs
Primary - flat spiral with x number of turns where x depends on what 
topload i'm using, 8.5" ID, quarter inch copper tubing spaced a quarter 
inch between turns.
secondary - 4.5" diameter, 23 inches high, 22 gauge wire on a pvc form 
sealed with polyurethane (smooth as glass)
spark gap. RQ/TCBOR gap hooked up to my shop vac.
capacitor - LTR geek mmc bank.
topload - 4" dryer ducting bent around 2-10" pie pans and covered in 
aluminum tape.
secondary is grounded in my garage to a large array of aluminum foil 
sheets.
coupling is pretty good, since the base of the secondary is about 2 
inches underneath the primary with no racing sparks, any farther under 
and i get racing sparks, so it's just about as coupled as it can get.
input power is 1.35kva (9/150) and the spark length is only about 2.5 to 
3 feet at most. the arcs aren't even that hot either. i've seen coils 
that get 4 foot arcs using just a 12/60. is there anything i can do to 
improve spark length (besides upgrading to Marc's trigger gap, which I 
am currently working on). thanks a lot,
Robert