What do the numbers (3.08 or 4.56) 10 bolt mean? Do these numbers designate performance and what is the best? Thanks for the help.

Ratio of # of teeth on the ring gear to # of teeth on the pinion (as well as the ratio of their diameters)

Effect is, # of times the drive shaft turns per one revolution of the wheels

Higher ratio = higher engine speed for any given car speed, in the same gear; better acceleration as long as the engine can operate within its optimum power RPM range (it's possible to "over-gear" a car and force the engine RPMs so high that it can't cope); poorer gas mileage usually, though not always (again, related to engine efficiency at the different RPMs)

Generally, higher ratios go with higher-perfomance setups, as all the things that you would do to make an engine produce more power, increase its RPM capability

What do the numbers (3.08 or 4.56) 10 bolt mean? Do these numbers designate performance and what is the best? Thanks for the help.What they represent literally is the ratio of drive shaft revolutions to each turn of the axle. Yes, it's the number of teeth of the ring gear versus the pinion gear inside the rear end which will determine that ratio, but the number designations such as "3.08" or "4.56" is in fact a designation of how fast your axles and drive shafts will turn as compared to each other.

For instance: if you have 3.08 ring and pinion gears in the rear end of your vehicle, that means that the drive shaft will turn exactly 3.08 revolutions for every one revolution of the axles and wheels. In other words, if you raised both rear tires of the vehicle off the ground with the transmission in neutral, and you placed a white chalk mark on the drive shaft where you can easily see it, and then you turned the rear wheel by hand one full revolution while keeping your eye on that area of the drive shaft where you placed the chalk mark at, you would find that the drive shaft will turn just a hair over 3 full revolutions ( or 3.08 turns).

And if you did the same thing with a vehicle that has "4.56" gears in the rear, then you would find that the drive shaft in that vehicle turns just a hair over 4 1/2 turns (or 4.56 turns) for every one turn of the wheel. The numerically higher the number, the "lower" the gear ratio is said to be, since it will give your vehicle greater acceleration at lower speeds.

For instance, 2.56, and 2.73 ratio ring and pinion rear end gears are considered to be "highway" gears because although they will cause the vehicle to reach higher top end speeds, they will not provide the best acceleration rate from 0-80 MPH. In contrast, at the other extreme end of the scale, 4.88 ratio ring and pinion gears are considered to be "low" gears because they will provide intense acceleration off the starting line (or wheel spin if the suspension cannot handle the torque of the engine) and great acceleration from 0-60 MPH, but less top end MPH speed.

Now as far as the "10 bolt" or "12 bolt" designations, those terms refer to the number of bolts on GM rear end covers and therefore different types of rear ends. The 12 bolt rear ends have a cover with 12 bolts on it, but more importantly, the internals of that rear end are stronger and more durable than the GM 10 bolt rears are.

However, the number of bolts on the cover of GM rear ends as well as some others, are merely an indication of what type of rear end it is that you're looking at. It isn't the number of bolts itself;f that makes a rear end stronger or weaker. It's the internals as well as the design differences of the housing itself which determine durability.

For instance... the Dana 60 rear end that I've installed in my 70 Chevelle, only had 10 bolts on the rear end cover. however, it's a well known fact that Dana 60 rear ends are more durable and can endure more torture and handle more torque than GM 12 bolt rear ends can. So it isn't the bigger quantity of bolts on the cover of a 12 bolt GM rear end that makes it more durable than a GM 10 bolt rear end is. It's the design and the dimensions of the internal parts that does. It just so happens that the stronger and superior GM rear ends have 2 more bolts on the covers than the weaker 10 bolt rear ends have on their covers. But the cover itself is not a major factor of where the strength of any given is.

BTW, a decent compromise of street driveability and decent off the starting line and 0-60 MPH accelearation can be obtained with 3.73 ratio rear end gears, or 3.55 ratio gears with vehicles that have transmissions that do NOT have an overdrive. With vehicles that do have an O/D (overdrive) then you can easily have a daily driver with 4.11 ratio rear gears, or even like I had in mine, 4.56 ratio gears and have the best of both worlds. I hope that this explanation helps you to have a better understanding about rear end gear ratios, and rear ends in general. ;)

Billie has basically described the workings. There a couple of more things in relation to the G.M. rear ends. The one with the ten bolts around the cover will also have ten bolts holding the ring gear to the carrier and the twelve bolt has twelve bolts attaching the ring gear. The ten bolt can either be 8.2" in diameter or 8.5". The car twelve bolt ring gear is 8.875" in diameter while Billy's Dana has 10 bolts and is 9.75" in diameter and is quite a bit stronger than the Chevy, but a fair amount heavier too. I wish the magazines would do a test to see how efficient all these rear ends are so we could compare them. It is said the the Dana is 95% efficient, the Chevy 12 bolt 92% and the Ford about 90%. I'd still like to know for sure just how much is lost because nobody has ever done a direct comparison of these three rear end types. One was done comparing a Dana 60 to a Mopar 8 3/4" rear that is similar to a Ford 9" in a "Dodge Hemi Dart" and both turned the same kind of times. The Dana was quite a bit heavier.