340 Gets Terrible Gas Mileage

Jeremiah said

Years ago a friend of mine installled a 2800-3000rpm converter and it killed his low speed fuel economy. It did not lock up around town.

Probably your best course of action would be converting it to a 4-speed.

: D

Beautiful car btw!

I am an NGK man but have had success and failures with all of them. Like a friends brand new set of ngk r plugs that lost 100whp because of a bad plug in #7...new out of the box, installed by me. I was shocked.

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I have a cheap unknown-brand converter in my Duster that stalls around 2600 RPM and is pretty loose in street driving but I still average 14-16 MPG with a 450 HP 360 although I do have 2.94 gears. Still I think even if I had 3.55s it wouldn't be much worse. Loose converters definitely kill fuel economy though, engine is always spinning faster than it needs to to push the car around.

Good to know about the plugs too I'm about to get a set of 8 to put in my truck with a wider gap after installing a Pertronix Digital HP CD box and Flamethrower III coil, hopefully I don't get a bunk one.