Rear ends, how do they work? Options

[SlowCelica94]

Since I've been looking into ls1 FC's, a lot of talk has been about the streagth of rear ends. So how does a rear end work? What's it consist of? Thanks guys

[Ale_lock]

Automotive gear ratio is most easily explained as the number of turns of the drive wheels in relation to the number of turns of the engine.  Basically , if the engine is considered the input and the drive wheel is considered the output, then the input gear or pinion meshes with the output gear or ring gear to drive or rotate it. The number of teeth on each gear determines the ratio.  For example: A rear end pinion gear may have 15 teeth that mesh with a ring gear that has 45 teeth; mathematically (45/15) this yields 3.00 ratio. This means that the engine will turn 3.00 times for each turn of the drive wheels. Most manual transmission RX-7's came with a 4.10 rear ends, while most RX-7 automatics came with a 3.90 rear end.  A ratio of 4.10 means the engine turns 4.10 times as fast as the wheels.  A 4:10 rear end will help with low end torque which is great for a Rotary powered RX-7 because a Rotary engine does not produce a lot of torque.  However, a 4.10 rear end at high speeds means that  the engine RPM's will also be high because the engine is turning 4 times faster then the wheels.  Example:  A stock Rotary powered engine with a 4:10 rear end and stock tires going about 80 mph on a freeway would be cruising at about 3,500 RPM.  Since a Rotary engine redlines anywhere from 7,000-8,000 RPM's (depending on  the year) 3,500 is a comfortable cruising RPM for a Rotary engine.  Looking at the charts above, a GM Borg Warner (B/W) T-5 (5-speed) gearing is similar to the RX-7 5-speed gearing, so, at first,  it sounds like a good Hybrid RX-7 choice - but is it the best choice?  Since the B/W gearing is similar to the Rotary gearing, this means at 80 MPH you're still doing about 3,500 RPM's, but now you're doing 3,500 on a V8 engine that probably Redlines at about 5,500 RPM's.  This is why you want to choose a transmission with an overdrive,  let's say you install, a GM TH350 (Turbo 350) that has a 1.00 final gear and you have a  4.10 rear end, now at 80 MPH, you'll be spinning at about 4,500 RPM's (yikes!).

Borrowed off a site. It's starting to make sense after a few reads.

edit: I'll keep looking up more info.

This post has been edited by Meonspeed: Dec 1, 2004 - 3:15 PM