well you probably are not hearing pinging, probably it is the noisy lifters you are hearing. the 40w will provide more cushion and make the 4.0 run alot smoother
the exhaust well, i dont know specifically. but i remember i had a stock 4.0 and you could hear alot of well... engine noise on hard accel. nothing bad just noisy. I added a K&N cone conversion and a flowmaster delta 40 and it ran ALOT better and sounded alot better too. not much more HP but better throttle response.
this was on a 4,000 LB grand with an underpowered 4.0 too
