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fuel line ?

This very topic was discussed a while ago on the Yahoo Stinson board when discussing the the use of the improved Allen 6S122 fuel selector valve, along with a JPI Fuel Scan 450. Both neck down to 3/8" while the 165 HP Stinsons' have 1/2" fuel lines. Bob H., an A&P and retired engineer wrote:
One of the fundemental concepts in the study of viscous flow in pipes holds that: The resistance to flow caused by a restriction is proportional to the length of the restriction and inversly proportional to the cube of the diameter of the restriction. There is about 9 feet of fuel line in a Stinson 108 so changing the whole system from 3/8 in. to 1/2 in. tubing would reduce the resistance to flow by a factor of 2.4:1. Adding in 3 or 4 inches of 3/8 in. restriction only reduces the total improvement by about 4%. Hardly enough to get excited about.
I hope this helps clear things up a bit.
Merry Christmas!!
Stan
 
When you modify the fuel valve you use a 3/8" drill bit in the drill press. I am very picky and ream out all the ends I cut with a tubing cutter so they are not choked down. Any crimped tubing gets replaced. I would have to say it is pretty much 3/8" I.D. all the way through. The old Jensen STC required 1/2" tubing and looked like a real pain to work with. All of the fittings and ports in the gasolator are 3/8" anyway. The O-360 can't use that much more fuel then an O-320-B2B on take off so I don't see what the big deal is.

The O-360 is just an O-320-B2B with the pistons moving 5/8" further up and down the cylinders. Crash
 
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