After reading about gear ratios on Wiki...I'm confused about why a 4.10:1 is more expensive than a 3.92:1. If I've read the wiki entry correctly, in the instance of a 4.10:1, the tires revolve once for every 4.1 revolutions of the transmission. Wouldn't a lower gear ration be better? What is desirable?

Thanks,
GillRilla

 

Wow, you've opened up a real can of worms here. The short answer is it depends on what you want out of the vehicle and how much power you can place to the ground.

The lower (numerically) the gear, the faster the car will go if the motor has the power to keep pushing the rpm's up. The higher (numerically) the quicker the car is if you can get the power to the ground without spinning the tires. There is a diminishing return to this however as if the gear gets to high (numerically), then you will turn your car into a rock crawler or a tractor.

Usually, 3.45 - 4.10's are good for the street. One of my old C3's had 4.56 gears and it was just a tire roasting pig!! Even in the 1/4 mile, the motor was completely out of rpm's before the end of the race, so I should have switched out the gears. Sometimes this will improve the time's and sometimes it will not, just depends on the power of the motor, but one thing is for sure, it will go faster (again depending on the torque of the motor).

I'm sure others can explain this much better than I just did.

 

Can of worms is right.

What do you mean by lower? In the world of cars, a 4.10 is lower than a 3.92, you realize that don't you? The higher the number, the lower the gear.

Ever ride a 10-speed bike? If you have, then you know the benefits of a lower gear, and the benefits of a higher gear. Your legs are just like an automobile engine....

Another way of demonstrating is this: the difference between a 4.10 gear and a 3.92 gear is very close to the difference between third and fourth in the gearbox. If you know when 3rd is desireable and when 4th is desireable, you know when the 3.92 or the 4.10 would be desireable.

Larry
code5coupe

___________
Often wrong, never in doubt....

 

Thanks very much guys. All makes sense now! And I'm guessing that getting what you desire is a matter of engine performance and gear ratio experimenting..all being tracked on a dyno...

GillRilla

 

Exactly. There was a real good article I read last week. It was in an older (june or july 2000) hot rod magazine that was sitting in the office of an alignment shop. What they did was take the same car and swapped out gears then ran the car down the 1/4 mile. In this instance the best performing gear for that car was around a 390:1 It ran within .002 of a second e.t. of the 410 gear, but gave a higher top end and better fuel economy around town. Sometimes lower isnt better. The higher 3.42:1 gear that was also tested ran about .2 slower et's. than the 390. And the 4.56:1 gear that they tried for grins was a waste of time and money.

 

This is putting it in layman's terms.

A 3.07 vehicle will be much slower than a 4.10. The downturn is the higher the number (4.10), the higher the RPM's. That means you're using more gas and the engine's life expectancy is less than a 3.07. It all depends on what you want out of the engine. The 4.10 will be faster off the line than a 3.07, but the 3.07 will have a higher top speed. The 4.10 just can't go as fast (top speed) as the lower numbered gears (3.07). I believe a good all around gear for speed off the line and top speed is a 3.73. It's like a middle of the road gear.

 

So 3.07 is not really a performance rear end?

 

It depends if you define performance as off the line acceleration or top speed. The 3.07 will perform better if you want to see 150+, but the 4:10 will accelerate right by the 3.07's until the motor run's out of rpm's. Nothing wrong with the 3.07's, but they will not accelerate as fast as an identical car with 4.10's.

 

Is there something on the differential that tells you what GR it is?

 

Good point here!!! Before you spend time and money on a rear end change, or buy a car first determine what you want the car to do and how your going to use it.

If you want the 4.10 for draggin' you have acceleration but sacrifice top end speed and fuel economy and perhaps reduced engine life because the engine has to work harder to maintain a given speed.

The 3.07 is a much more preferable ratio if you use the car for highway or high speed driving (think autobahn) or road course. Lower RPM means better fuel economy and higher potential top speed with the 3.07 gear, as well as less wear on the engine 'cause it's not working as hard.

Arguing about which rear end ratio is better is like carpenters arguing which tool is better, a hammer or a saw. Each has its place in the tool box and you use the right tool for the right job.

You use the 4.10 or similar ratios for draggin, the others for road course or high speed work. Thats why a lot of race cars have quick change rear ends. If your on a track with long staights you would use a ratio closer to the 3.07 end of the spectrum to get higher top speeds, if the track is chopped up with lots of turns and short straights you go towards the 4.10 end so you get good punch coming out of the curves. The quick change rear end is one of the tools that allow you to tune the car to the track.

If you got wads of money, and are mechanicaly inclined, you could put one in your car and use a 3.07 for normal, everyday driving and if your into draggin swap out to a 4.10 on race day, or if your runnin' stoplight to stoplight on the street go for something like a 4.56 for tire smokin acceleration for short runs where maximum acceleration is more important than top speed.

All it takes is money!

Time for a brewski

 

It was a performance rear end on the A4 car. Because the stock ratio was I believe 2.59:1 or thereabouts (may have been different for different engines).

Speed in gears is a factor when picking a rear. If you put something like a 4.10:1 on an A4 car, the four gears may not be enough to go 130mph or something. That's a guess number, but you could compute the speed in gear.

I.e. on a ZF6 car with a 3.45:1, 4th gear is good to about 150 mph. If you go to a 4.10:1 rear, that drops to about 127mph or so. If you only had 4 gears, you'd be gaining acceleration at the expense of speed. The ZF6 of course has two more gears so you can make more of a tradeoff in rear gear while still being able to go fast on the big end.

The A4, especially on something like the L98 with its limited RPM range, probably needed these taller gears like the 2.59:1 in order to achieve any sort of decent top speed. That's the situation around which the 3.07:1 was considered a "performance" gear upgrade from the factory.

 

The original ratio is etched on the bottom of the case (at least in '89) but it's not very deep or long lasting. Check the Service Parts ID label on the bottom of the console lid or on the bottom of one of the storage compartment lids. You want the Gxx codes-one of them will be the ratio.

 

The L98's came stock with a 3.07 rear when you have a manual. If you have an auto, you've got the 2.59 (unless of course you've got the car modded).

 

Thats right, I forgot about the Service Parts ID...I'll look for it in the morning.

 

What about the 89-91 manual L98 cars did they too have 3.07 gears? Did all auto cars have only the 2.59 rear, what about the G92 cars?

 

Unless you have a Z51 or Z52 A4 car, in which case you have the 3.07

 

I spoke too soon. I was referring to a simple stock L98. Thanks for the clarification.

The websites below can help you calculate your rear end ratio and a whole lot more.

http://www.idavette.net/tech/ratioc.htm

http://www.idavette.net/facts.htm

 

since i've got 3.33 gears, 6 speed, now i get to say GM f'd me on that too, another item where i'll have to say "stock sucks"..

 

Wasn't there a performance option for autos? Something like a 3.23 or something? I think the LT1 auto fbodies had something similiar, 2.73 was normal and there was a 3.23 or 3.42 optional.

I have a '93 C4 with the 2.59s, I know one thing, the SUCK! Sure, gas mileage is good, but for the amount of torque the car makes, the car feels slow and non-responsive, especially from a stop. Unless you keep it in "D" (third gear), the motor is never in it's power range in normal driving situations. Basically, compared to other LT1s I've driven, my car feels like it's hooked to a 60 foot horsetrailer unless I hold it in a lower gear that lets me cruise at 3000rpm.

Once I get off the highway and hit the backroads coming home, I even put it in "2" lots of times. This still has me at only about 3000 rpms just cruising the backroads. My Corvette is bone stock, but if I ever mod it, the diff or at least the final drive gears are going to be my FIRST mod, before exhaust, headers, or anything. My plan is probably go for something between 3.07 and 3.73. From one of the gear ratio discussions a while back on this board, it sounded like for a relatively stock LT1 or L98, even 3.73 may be a little too high (numerically speaking). I bet the responsiveness would be greatly improved however, even if 1/4 times suffer.

 

My 94 was a 2.59 car. The car couldn't get out of its own way let alone against another car. Swapped to 3.73 and the car is respectable. As stated many times, it all depends on what you want to use the car for. Even with the 3.73 gear the mileage on the highway is around 18mpg, city around 16mpg. The other thing to consider is a torque converter swap to help the engine get up into its powerband. You have to decide what your after. Lastly, with the Dana 36 the 3.73 gear is a bit noisy (whines some) and may not be something that makes you happy. I have a stereo for that. Good Luck with your decision.