Should I swap the 3.91's for 3.55 or 3.23

Post#9
and, I vote 3.23s. Heres why;
1) You have an M/T. If you need more torque on take off, its easy to find.
2) the 268 cam will be at its highest vacuum around 1800 or thereabouts, so for best fuel economy, you will want to cruise a little above that, and lean her out on the low-speedcircuit, and tune the timing to the nuts,The 323s run(see post#4), 44mph at 1800. So you are good to go.
3) The 323s wil let you cruise 8% faster with the same engine noise,vibration, and harshness, than what you could with the 355s.
4) Depending on your exhaust, conversating with 355s, at 70mph, is not really fun. Cruising with 323s will be 10% or better, less frustrating.
5)That VOODOO cam is not very fuel-friendly. The 323s will get the best economy of the listed rears.