As a younger person who was under 10 years old when these cars came out. Could someone school me on what was different between the N code and P code cars.
Lets start with this... The P code is the engine desiginator in the VIN. They were usually marketed and sold as the HP (High Performance) just like any HP 360, 440 etc. They didn't call them High Output, because the bare engine on an engine dyno was (depending on the year) nearly the same. The difference in performance happened else ware down stream.
Both P and N are 4BBL 400. for 75 through 78 the P code got better bearings, a better timing chain, different emissions. Depending on the source you read 75 still got the famed 383 Roadrunner cam that was used in HP 400 and HP 383 prior to that. Cams were all the same for 76 and up. HP motors (not only P) were given more performance buy a factory change to the shift pressures/point in the trans (automatic of course) and a steeper geared rear end. Horse power ratings were measured at the wheel, so gear ration made a noticeable difference. Dual exhaust was part of the package but that went away, but could be and was often added. The same can be said for a Sure-Grip differential. Other ancillary options (towing package, HD cooling, Max A/C, etc) could be ordered with HP motors at a better price than with a "normal" motor. There are a very few options that were not normally available with out an HP; high speed A/C cut out, wide open throttle kick-down block, maybe a few others but those are the ones I know of. And those were usually on Police vehicles anyway.
There weren't too many people buying HP cars the way the did in the late 60's and early 70's, with just options for going fast. This era was saddled with government intervention so a HP car was a way to gain back some of what the government had taken away. Plus the nice things like A/C, fluffy interiors, better suspension, brakes, etc. all to make your commute easier were often added to the HP under the hood making it hard to tell if it was the engine option or something else that added things on the assembly line.
If you knew how to check the option list you could build a non-HP car that would perform as good or better than a HP version.
So in all reality there wasn't too much different when looking at components, but added all together as a package the difference was there.
