Cool man, you will be happy with a stock unit like that. Here's how I understand it all. You need 2 vents. 1 vent for filling your tank, the other vent is for driving and sitting, it's for heat expansion and such. Fill vent allows air to push out during filling so you can use the gas pump nozzle full throttle
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Here's the safety part. Small vent for heat expansion, for safety reasons, gets the rollover valve. Fill vent needs to be connected to your filler cap so the gas nozzle extends past it allowing air to escape back out through it, but seals it off with cap during operation. If you get into a wreck, rollover valve closes the small valve so fuel doesn't spill out and filler cap seals the filler vent. Safe.
I would say that's the general idea behind it all for safety and function. There are more sciences to it you can read about elsewhere
