My modified '49 Trophy had 2 petcocks on the stock tank. The bottom of the left side of the tank was the reserve. At something over 110 MPH, (I was too busy hanging on to look) I could get a few more MPH out of it if I opened both. Didn't make any difference at sane speeds except that running out of gas with both open was a bad thing.
Come to think of it, it went about .2 or .3 seconds faster in 1/4 mile with both open.
