Jeep Gearing for a CJ8

Hi, I am having trouble with my Jeep CJ8. I have completely rebuilt everything on the jeep (minus the transfer case). It has been converted from an inline 6 to a V8 AMC 360. The Jeep has an AMC 20 rear (273 gear ratio) and the T176 appears to have tree stump pulling ability. I am about to blow the engine up because it runs way too high (RPMs) in 4th gear. I am tacking at least 4,500 to 5,000 RPMs at 45 - 50 mph. Please help, the tech experts at Quadratec said I should just get bigger tires than 31s and that would cure my problem? Before I drop a ton of money on tires that I really don't need, the Jeep does have a 4.5 inch suspension lift with a 1" body lift, so the tires would actually look better than the small 31s. The experts said I should go with 35s or 38 inch tires and that would take care of the RPM issue. Please, help me out, I am sure many folks have already been thru this, and I could use their knowledge and wisdom. Thanks.
Todd

Welcome to Bulltear!!!!

Stock tach? If so, it's calibrated to a 6 cylinder (3 spark pulses per crank rotation), a V-8 has 4 pulses per crank rotation, so your tach would read 25% high. At 4500 RPMs, that's 1125 RPM high, so it would be turning about 3375 RPM.

If it's an aftermarket tach, there should be a setting inside for 4-6-8 cylinder.

That still doesn't sound right with 31" tires and 2.73 gears. My AMX with 26" tires and 3.73 gears turns about 3500 at 75 MPH. My CJ with 4.27 gears and 35" tires was 3200 at 75 MPH. Either you have much lower gears (high 4.xx or 5.xx) in your axles or you're in low range. 2.73s are considered "highway gears". Not much stump pulling power there.

If you do have low gears, then bigger tires is the only solution, unless you re-gear the axles or install an overdrive tranny.

The gear calculator here says you should only be turning about 1900 RPM at 65 MPH in 4th gear with 2.73 gears and 31" tires.

http://www.grimmjeeper.com/gears.html