My muffler man had a time & a half running TRUE duals under my '92 RC. Thing is, the factory 2 1/4" pipes proved to be the secret to our success!
The 318/360 - even in Magnum configuration - is NOT the monster MOPAR for HP or torque. Smaller pipes - ESPECIALY with true duals - is your secret to success, at keeping backpressure at nominal levels, and torque high: especially for a 4x4 application.
RELOCATING the cruise control to the top of the t-case skid, was the more interesting solution to our particular scenario. Unfortunately, the CC seems to be dead; thankfully, I
don't need CC on a trail runner!
Hi-Po JEGS cats were needed, so I could pass the visual part of the smog inspection - one one EACH pipe. Magnaflow glasspacks keep the exhaust flowing freely. Backpressure is good, the 318 Magnum breathes well, and torque is maintained, particularly in 1st gear.
Snaking 2 1/4" pipe through all the nooks & crannies of the underside was challenging, but even 2 1/2" pipe would've been MORE challenging - there are just spaces where it would not have fit.
http://vid212.photobucket.com/albums/cc305/The_War_Wagon/Ramcharger/100_8648_zpsfe1e2fa3.mp4