Newbizor wrote:

Cary wrote:Why do you want to eliminate the fuel pump? Mine has two, the engine driven one and the electric one. I only use the electric one on take offs and landings. Because it was standard equipment in the stock P172D which had a 175 hp Continental, the owners manual provides for using it whenever changing tanks at higher altitudes, but I pretty much forget to do that--usually "remember" when I see the fuel pressure light go on momentarily on my fuel flow gauge. But the point is that while gravity feed works fine on lower powered engines, force feeding with a fuel pump is more necessary when the power goes up.

Cary

I have the avcon 180hp conversion on my 175 and have no fuel pumps. The stock gravity system supplies in excess of 25gph to the carb right down to the last drop. The O-360 at sea level and 2700rpm is burning somewhere in the ballpark of 16gph. Removing the pumps also allows you to use the MoGas STC, athough some would argue the STC is not required since Lycoming published S.I. 1070A. For me just getting rid of the complexity of the extra components, electrical and plumbing is worth removing them. Less fittings to leak, less electrical load, no need for fuel pressure gauge, less cost and less maintenance. The only reason an electrical pump is even installed is in the event of the mechanical pump failing, the only reason the mechanical pump is there is because the O-360A1A/A1D engines used in the conversions came out of Mooney's which were low wing and needed the pump. Legend has it the guys developing the STC's were initially required to use the pumps because they were already on the engines. It wasn't until a little later they came out with the paperwork to remove them, but that document only covers 172's and omitted mention of any 175 S/N's.

The P172D like the 180hp conversions with a CSP, can require that extra (albiet small) amount of flow. The aircraft with the pumps removed increased the size of the fuel line from the selector valve fwd, meeting the minimum 150% flow requirement without pumps.