Got over 10,000 miles on my 340 with 3.91 gears. Motor runs great, no smoke at all. Compression was all even across when I checked it 2 years ago, haven't really drove it much since then. I rev that baby passed 6,000 rpms like every time I drove it and it goes 75 mph on the freeways. I have driven it for a hour each way at speeds of 75. Motor runs cool, tach hoovers around 4,000.
U do need a quiet exhaust system, it makes all the difference. With loud mufflers, it be a nightmare on the freeways. Instead, it feels like 2,500 on the freeways.
If i had to do it again, 4.10 or even 4.30 gears might worked better yet. And a solid cam, that is grounded on 114 lbc for a decent idle. But then the motor wants 11 to 1 compression or more.
So most people just stroke the motor and enjoy it around town and don't "fly" down the expressways for long distances. They "sit" in the far right lanes and do 60, maybe 65 or get OD but for automatics Mopar screwed us. There isn't much out there that simply bolts in and works great. U gotta program the trans and what you save in fuel costs goes out the window in trans costs unless you drive it 10,000 miles each year. Then maybe after 4-5 years you start saving money--if the OD trans doesn't break by then.
