4000 watts + 20 plants = 32 Oz. slightly under 1/4 gram per watt.

This time next year I will see how much improvement I have made.

any pictures of your set up ..

I tried to take phone pics when I first started up, but I kept getting horizontal stripes over my pics, so I haven't bothered with trying since then.
I have four 1000's in cool tubes over my plants.
I have a heavy duty Timer board to feed 120 and 240 into the room.
My pots are too small, will step them up from 2 gal to 3 gal next cycle.
I use AN 3 part, Promix, and a pump and watering wand.
I am going by AN guidelines for feeding, I don't have a TDS pen as of yet. I measure, mix, feed, and aim for 10-20% runoff.
8 inch exhaust fan, 8 inch intake fan, 8 inch cool tube fan, all on speed controls and a Temp control.
Plants are on a grate over a catch bed I built so when I water, I siphon the overflow out of the bed and dispose of it.

The horizontal stripes are from the frequency of the lamps you use. Turn off lamps and use FLASH for the best pics. Or use Normal warm CFLS to take pics. HPS and MH just make the plants look odd, coloring and tend to wash out details.

I have found over the years lack of yield is usually genetics, PH out of wack, or just to many additives.

Check your PH, apply KISS(keep it simple stupid) to your feeding solution and try another strain, once you find a strain that works well with you, GPW(grams per watt) will come up.

Peace...Buddha

PS. This is a good read for PH, I learned a few things in this thread.
http://forums.cannabisculture.com/forums/ubbthreads.php?ubb=showflat&Number=1728995#Post1728995

Hehe....GPW

I thought that one and a half oz per plant was decent.
They are all falling over due to their weight in the last two weeks, hard to imagine heavier buds.
I have no idea what my PH is. I will put that on my list of things to do. My room runs a little warm at times, I have adequate to more than adequate airflow. The cool tubes cut down some of my yield, and my laziness of not wiping down the inside of them probably costs me a little more.

With 4k and only 32oz, there is plenty of room for improvement. You have come to one of the best places to get tips/info. With 20 plants and 2 gal pots, you should aim for the same outcome with one of those lights. Good luck and happy growing!

the mystical goal everyone wants to attain is 1 gram per watt which would put you at 4000 grams rather than 896 grams. What is being said is that you did good and keep going because you can attain greatness in future grows.

I would reduce your light until you get your room dialed in and you do a little more reading.
At this point, at only 32oz for 4000w, your just tossing money away.
If you can ditch 2000w you can save money while you learn, and you should easily be able to beat your last weigh in.
4000w is a little ambitious for somone who has no idea what the pH is.
Best of luck!