i have replaced the muffler too ... but never touched the headers tho ...
i think my gears are 5.12 and tires ran 215/75/15 + 31" and am getting the same speed... maybe 215s was a bit more ...thats all according to a gps speedo so its accurate
and maybe 50mph is not that bad... but it is when it takes 15+ secs to get there
am not that good of a fabricator but a shop in our area done swapping before for some kicks and he always fits Nissan Cedric v6 carb..
so i might try it... since i replaced/repaired 4 kicks engines ...am kinda tired of those lame engines always breaking up and letting me down almost every time i take a long trip "300+ miles"
A carbed motor should eliminate most matching electronics issues. Extra Hp is Great!! It is hard to stay out of it, so mpg will suffer for a while.
215x75x15 tires are not +31". 31+" tires will bog an 8 valve down, making it hard to run in 5th gear or even reach 50 mph (I know some are doing it, but it is normally hard). 215X75x15 are just .5" larger than stock, and should not have too much effect on performance.