Firedome plus chimney - the challenge continues

See critical updates below:

Tonight I did a practice run with my Firedome this time with a chimney (water heater exhaust pipe) sitting over the top vent.  Pretty huge difference.  Fast to heat, and fast to ignite new wood.  Here's the temp data for the quick burn.

click on graph to see it enlarged

chimney mounted on top of vent

Update for the follower of this site
Jon in Albany demands details.  As a faithful reader, I am obliged to give more details, but thought I'd extend the post by answering here instead of in the comments.

The biggest problem with this thing has been the vigor of the flame.  Most of the time it's like a plasma furnace, but other times the fire burns like a girl scout fire, barely sending the inside past 500F.  The chimney, on this single run, seemed to take the fire and give it some updraft and a really good burn.  Still more testing to be done.

Fuel:  I start the fuel on the lower grate using just about 20 match light briquettes.  Once those are lit, it's all oak.  I use ca. 8" seasoned oak from year's past tree trims.  I split the logs, age tem about a year and  cut to a size that will fit beside the stone.  Half of the top grate has been removed to allow space to toss in wood.

The chimney is a piece of 4" dia. x 8" tall stainless pipe that just rests on top of the dome's top vent when open.  I also want to note I build the fire so it's offset from the cook surface.  The clay surface is on one side of the center volume and the flame is on the other.  This looked most like the configuration in pizza oven's I've seen.  So, that's it.  More testing and reporting to be done.  Stay tuned.

Update for 20-April-2012
This site is a fun way to share discoveries, mostly good.  But today, I hang my head in shame.  The furnace-like temps I got initially could not be duplicated twice since then.  

The Firedome project has been fun and addictive.  It lacks reproducibility regarding temperature.  For such a simple device, it's intriguing.  I live for this kind of problem.  At this point in the game, pizza is not about the dough recipe or the toppings, temperature is an ingredient.  The same dough topped in a 600 deg F oven is profoundly different than the same pie cooked at 900+ deg F.  Based on the last couple runs,  I don't think it's the chimney that launched the plasma beam initially discussed.  The current hypothesis is something suggested by my wife, moisture in the wood. 

Moisture content in wood is a great candidate because, to now, I've not checked it.  I started this project with briquettes.  Once those ash over, the heat drops considerably and  I began using oak or whatever the hell fell from my trees.  Using such a source is bound to be filled with all kinds of differences.  I still want to use wood because it burns hot and has low ash.  I ordered an inexpensive moisture meter for wood and will be scouting the city testing various lots of wood.  The measurement is non destructive and hopefully no supermarket managers will mind (if they catch me).  I will of course keep you all updated.