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Old 02-28-2010, 03:18 PM   #92
Head2Wind's Avatar
Joined: Mar 2006
Location: NorthWet Washington
Oddometer: 2,606
Originally Posted by bkshovel
Ok fellas, fer us dumb ol' country boys that speak psi. instead of nm. What kind of pressure are you talking about? If I understand correctly the pump you're working with puts out 43gph at 45psi free flow. I gather that' not enough. Summit sells a pump that is 43gph at 85 psi free flow, part # sum-g3138. It's also cheaper, $81.95. I've had good luck with Summit's stuff as far a quality. It looks like a twin brother measures 1.87 x7.25. Probably comes out of the same factory. This with a bypass regulator and a return line to the tank to keep the fuel and pump cool? Am I out of line?
just so us other ol' country folk are not misunderstood, you cannot have "free flow" and 45psi of pressure.... in that if you have a open hose to atmosphere coming from the output of the pump I would call that "free flow" with no head pressure on the pump. In my understanding this is the pumps full on capability to move X number of Liter/Gallons of fuel per minute/hour. So, as described, the Summit pump will flow/pump 43 gallons per hour at a 85 pounds per square inch pressure. Which in this application, given the horse power rating of the engine, this pump would be able to deliver enough fuel to the injectors/engine to support the roughly 100 horse power that the LC8 produces. HOWEVER, we still need to REGULATE that pressure down to a usable level, in this case the stock pressure is 3.5 bar (50.7632082 pounds per square inch), so if we chose to use a fuel pressure regulator that is set at 3.0 bar (43.5113213 pounds per square inch) the fuel rail pressure would be reduced by roughly 7.2 PSI, a ~4.3% reduction in pressure, will result in a reduction of flow through the injectors.

So we either chose to create a system that bleeds the pressure off into the tank prior to the fuel rail or we do it at the end of the fuel rail, which in most cases for high performance (IMO) is best (end of rail pressure regulation/dump/drainback). The stock system dumps the fuel directly back into the tank at the pump assembly, and "dead heads" the fuel rails at the injectors. So the only fuel that flows is the fuel that is injected, which can lead to higher fuel temperatures at the point of injection and all the fun that comes along with that.... Again, in a high(er) performance application, cool(est) fuel and cool(est) air is best for maximum performance with current fuels and technologies. third beer for the day watching the hockey game so I might be off a bit.....
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