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Message: <blockquote data-quote="swampratt" data-source="post: 3594202" data-attributes="member: 15054">I drove a mid 70's 454 Dually  truck with 4.11 rear gears and granny 4 speed.This was a buddies and I towed cars with it as it was a tow truck with a winch on the steel bed.But get this it had a 350" in it and got an amazing 8 MPG and he said he stuck that 350" in it because he thought it would get better MPG than the 454 and it did .He said the 454 got 6 MPG.I was 21 at the time and pretty confident that I could stick that 454 back in and get better mpg with a few tweaks.He gave me the go ahead and i recurved the distributor ..all timing in by 2200 rpm and no more vacuum advance.18 initial timing and 38 total.I also took the Quadrajet apart and set the APT adjustment at 2.5 turns out.12 MPG!Winner.GM had a very lazy timing curve and tried to make up for it with a vacuum advance.Problem was if you got your foot into it the vacuum dropped and so did the timing and power.Most of the time the vacuum advance was not working anyway due to ruptured diaphragm or rotted vacuum hoses or other issues.</blockquote>