I had a perfectly running (at least) twice rebuilt '77 AMC 401. Most recently rebuilt by me (because I let a bolt fall into the intake on a test drive...), so I know all the juicy numbers and exactly what is in it now.
Dyno'd at 250hp (SAE corrected) at the 33" mud tires. Oddly, after adding fiberglass wrapped short tube headers, Holley Sniper EFI and HyperSpark ignition control with a professional tune, crossover x pipe on the exhaust, best dyno run was 249hp... go figure. The late 70s heads just do not flow air past 43-4500 rpm.
After getting maybe 14mpg on highway at best and you can bet more on 11mpg especially if holding 75mph, this didn't sit well with me. I want big power if I have to deal with all the cons of a big ('small block' based) V8. It certainly felt like plenty of power on the road but 250 to the tires just wasn't enough to tickle my pickle and brag about.
I also had issues in the summer, with a bed full of camping gear and a cab full of 2 humans or less, the truck would really struggle up mountain passes in terms of coolant temperature and apparently, fuel temperature.
There was a horrible clunking noise last time it was crawling in Moab. Made others uncomfortable. I didn't like it either.
So the shenanigans list was as follows:
- Mo powa baby (happy at any improvement to tires, very happy with 300, hoping for more like 315)
- Lower coolant temps in summer baby
- No more fuel pumps crapping out on me on the trail, making Karens in late model 4Runners mad that they were delayed by 2 minutes while I rub an ice cube on my external pump
- No more clunkity clunk on trail