Hi MBT and Todd,
5 Lug conversion: This conversion uses GM rotor/hub combo with stock bearings and a spacer which comes with the bracket kit from CPP. The rotors, calipers, hoses and pads are specified in the CPP installation instructions and you purchase them from your local parts house. In contrast, with the 6 lug conversion, you have to use a pricey ($119.) custom bearing from the vendor as opposed to the $30. bearings for the 5 lug conversion. Being able to replace a bad wheel bearing without waiting on a mail-order vendor was a major influence on my 5 lug decision. The major downside of the 5 lug kit, is that you will be buying new rims with 3-5/8 to 4" Backspacing. The j-yards don't have them as I hit 3 big yards to come up with one beat-up rim for a spare mount. I was going to buy new rims so the 5 lug worked best and gave me a good selection of reasonably priced rims with the correct BS.
Todd, for your install, you're going to have to trim the bearing pilot regardless of the spacer thickness. If you cut your input shaft and pilot brg shaft, and just gently open up the bottom of the splines so your disc slides another 1/4-3/8" past the end, the clutch pack will fully release. You might be able to trim your disc flange a tad as added protection. As I pointed out in the pictures, the key is to make sure that the disc actually slides past the end of the factory splines to fully release.
Gearing: Based on my truck....basically a 261 grind cam, no HEI, 3.42, .72 OD and 28" rear tire diameter.
My goal was to have gearing so I could use my 5th gear without downshifting when slowing down to 45 mph (1330 rpm's) and to accelerate with normal traffic flow back up to cruise speed without lugging the engine. Keep in mind the 1330 rpm number as being close to the very bottom end of the useable torque curve. For cruising I run at 2000 rpms at 70 mph in 5th gear. In reality, this is a bit lower rpm than the true "sweet spot" on my engine. It really likes to run at 75 mph@2216 rpms. However, that's not really comfortable for me as a lawbiding driver, who isn't really in a big hurry to get anywhere!
IMHO...with a 3.08 R&P and a .86 5th gear you would fall right into the lower end of the torque band (45mph@1483 rpms) and be able to hit your gearing sweet spot at 65 mph@2143 rpms. You would still have plenty left if you wanted to cruise at 70-75 mph@2400 rpms. This would also let you run in 4th gear with a load or trailer at well under 3K.
As for the 2.73 with the .86 OD...it would stretch out your 1st-4th gears but you'd be really flat in 5th gear until you got up to 60 or 70 mph. That's what I faced when I installed the 3.08 diff with the .72. Worked great as a 4 speed, but was just too tall for normal driving without constant downshifting.
I hope this helps you guys with your decisions.
Dave
