Oldfeller--FSO
Serious Thumper ModSquad
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Hobby is now "concentrated neuropany"
Posts: 12639
Fayetteville, NC
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Dave, remember that Charon's tests had to do with refill rates from an empty fuel filter and empty fuel lines, the recovery period where air was flowing up the lines at the same time the trickle of fuel was flowing down. His discovery was that when the lines and fuel filter were full of air, recover to a full state was very slow.
During recovery, the flow volume of air going up the lines must be equal volume to the fuel going down and the line and fuel filter is a "two way street passing only 1/2 fuel volume" until the volume above the float needle is all solid fuel again. The volume of air that must vent up through the lines and the petcock nipple includes the line volume and the fuel filter volume.
While a quarter inch line/nipple may not be the restriction point of the entire system (I agree the float bowl/valve is) the recovery time is about doubled by using quarter inch hose/nipples. 5/16 is a better hose size as it recovers almost twice as fast as 1/4. 3/8" hose is better yet as it recovers fastest of all.
Remember, during the recovery period (the half fuel flow period) the 1/4" line could barely supply the float valve at normal low throttle. This is part of the reason people report such cobby running after a low bowl episode caused by the vac petcock.
Once the bowl is full and the fuel flow is sold fuel, all hoses and nipples can work OK for a stock engine, but since the vac petcock keeps running the bowl low and keeps putting air in the fuel filter and lines once again you are in a constant recovery state and the small hose size struggles to keep up or to make up the air volumes with the recovery two way flow.
End moral of the story was to get rid of your vac petcock and stay with 5/16 or larger hose sizes if you wanted to feed a high performance engine with no air in line hiccups.
Using this thinking, raptoring with a 1/4 nipple petcock kinda half defeats the purpose of raptorizing in the first place. When you raptor, you are seeking improved fuel flow to keep the bowl full at all times as you feed an engine that can demand half again more fuel flow at full throttle compared to a stock engine.
Intentionally selling a limited raptor that cannot properly support a modded engine is something a hop up shop shouldn't do. Especially when you sell ported heads and other hop up stuff and your name is SuperThumper. That kinda clashes a bit with the name, don't you think?
The guys that designed the OEM carburetor put the 5/16 nipple on it for flow reasons, putting anything smaller than that upstream is putting a restriction on the entire system flow (which is why the oem petcock matched the inlet on the carb and why we matched it with the Raptor sizing).
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