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12V Delavan 7870 FATBOY 7gpm pump
http://www.pressurewasherproducts.com/

Performance

http://www.delavanagpumps.com/powerflo/fatboy.htm

http://www.dultmeier.com/pdfs/tech-library/02Water8.pdf

http://www.barens.com/cgi-bin/calc

Here's a list of information on the FATBOY picked from various threads that I thought should be all put together in one thread.

Click on the links above to read the FATBOY's performance chart, friction loss chart, and type in numbers on the nozzle calculator.

The new 12V Delavan FATBOY 7gpm pump
operates at peak performance using LARGE nozzles and hose.

#30 nozzles and 5/8" hose are too small, and are meant for the old 5gpm pump.

Using the #30 nozzle causes the 7gpm pump to max out at 29amps draw and will choke it, running at half speed. These nozzles will quickly kill your pump from excess amperage draw and overheating.

#40 works better but it is still overworking the pump out at 26.5amps, and chokes your flow running at only 2.5gpm.

Use at least #50 nozzles. This is the smallest nozzle you should use for the new FATBOY. Pump will run much smoother and shoot farther than the old 5gpm pump without maxing the pump out.
Pump performs at 80psi 4gpm drawing 23amps.

#60 nozzles also work well to give you more flow and good distance.

Pumps performs at 60psi 5gpm drawing 21amps.

#70 nozzles will give you more flow than the 60 nozzles and shoots surprisingly far

Pumps performs at 40psi 6gpm drawing 19amps.

All three nozzles perform well - good flow and distance
0050 nozzles shoot the furthest, 0070 gives the best flow, 0060 is in the middle
-experiment with the different sizes to see which ones you like the best

Use 3/4" output hose, 3/4" PVC ball valve for the 7gpm FATBOY or Flojet Pentaflex.  Use 1" intake hose for both pumps.

Use 10 gauge wire, 30+amp switch/fuses, and a BIG battery. 
I use a 770CCA/900CA battery

I buy my large nozzles from Lori with Pressure Washer Products.

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Here's a couple of threads of guys who have tried different size hoses, guns, nozzles and posted their results.

http://roof-cleaning-institute.activeboard.com/index.spark?forumID=123190&p=3&topicID=21015353

http://roof-cleaning-institute.activeboard.com/index.spark?forumID=123190&p=3&topicID=25879871

No arguing or debating simple physics. 

Small hose-small gun-small nozzles = Less flow, less distance
Large hose-large gun-large nozzles = More flow, more distance

Using the FATBOY with #40 nozzles you only get 2.55gpms drawing 26.5AMPS.� You can test this by filling up a 5 gallon bucket and time it.� You can also type in the numbers on this website. 

Pump flow GPM: 7

Pressure PSI: 122

Nozzle size: 40

http://www.barens.com/cgi-bin/calc

You also need .6 Horse power to push this much volume through a #40 nozzle to get 122psi.� The pumps maximum power output converting AMPS to Horsepower is only .4 Horse power.� So using #40 nozzles will cause the pump to be overworked and slow down by 33%, operating at only 66% of peak performance.

AMPS X VOLTS = WATTS
25Amps X 12 Volts = 300 Watts

WATTS X .00134 = HORSEPOWER
300 Watts X .00134 = .4 Horsepower


In other words, you are getting a considerable amount of flow loss using the #40 nozzles, defeating the purpose of buying a larger, high volume pump.� You are not getting your money's worth.

Using 1/2" hose on the FATBOY 7gpm pump, will also kill it's flow and pressure with a 50psi loss per 100 feet.�

This will quickly fry your pump, relay switch or fuses very fast from excess amperage draw.� The poor pump has to work it's a$$ off to try to compensate for such a small inside diameter hose.

Using the 12V Delavan 7870 FATBOY 7gpm pump the difference is even better going from 5/8" hose (20psi loss) to 3/4" hose (7psi loss) per 100 feet.