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Discussion Starter · #1 ·
I've looked around some and have not seen any discussion of rear axle ratios. I am ordering a C7 Z51 M7 with magnetic ride and performance exhaust that will likely be one of the lightest driven vettes in the history of man (at least until I get used to driving a $65,000 vehicle), so i am imagining that the stock rear end ratio will be fine. I've seen that the A6 is thrashing the dragstrip pretty well bone stock.

SO...what might be the advantage of ordering a different ratio? Who is or has done this and with what results or for what reason?
 

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I don't believe you have the option to specify the rear ratio. You get the following depending on what you order

A6 - 2.56
A6 w/Z51 - 2.73
M7 - 3.42
 
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"SO...what might be the advantage of ordering a different ratio?"

The advantage of changing the rear end gear to a numerically higher (like going to a 3.42 from the stock 2.56 ) ratio will increase the torque multiplication of the motor, resulting in more rear wheel torque.

Engine Torque x Transmission Gear Ratio x Rear Differential Gear Ratio

The trade off is some lost of gas mileage and you have to shift sooner and some lost of top end speed.

But you'll have better 1/4 mile times for example.
 

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SO...what might be the advantage of ordering a different ratio? Who is or has done this and with what results or for what reason?
At a given speed (MPH) and in a given transmission gear, a higher ratio means the RPMs your engine must turn to achieve that MPH in that transmission gear is higher.

So, for what you indicated your use case will be, don't worry about it. Choose the transmission you want, the Z51 (or not) option you want, and take the rear end ratio which has been chosen for that setup by the Corvette engineers. I am sure you will be very happy.
 

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"SO...what might be the advantage of ordering a different ratio?"

The advantage of changing the rear end gear to a numerically higher (like going to a 3.42 from the stock 2.56 ) ratio will increase the torque multiplication of the motor, resulting in more rear wheel torque.

Engine Torque x Transmission Gear Ratio x Rear Differential Gear Ratio

The trade off is some lost of gas mileage and you have to shift sooner and some lost of top end speed.

But you'll have better 1/4 mile times for example.
That is backward. To have more torque you would need a ratio like 4.11:1. i.e. it takes 4.11 engine revolutions to have the wheels turn once. However you would also need slicks to get the traction to handle the higher torque off the line! If you went to a 2.56:1(if were an option, which it is not) I’m not sure it would be helpful even at 70 mph considering the low rpm already in 7th gear which is a 0.48:1 overdrive. That makes the 3:42 already like a 1.64:1 if the transmission top gear were 1:1 like the old 4 speeds! The engine has enough torque to use 7th gear at highway speeds but not that useful around town.
 

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Sorry you're right had it backwards, higher gearset you will have less torque in any given gear, but will have a higher speed at any given engine RPM vs the lower geared set.
 

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Nope, I don't think so. Higher NUMBER:1 gearset--> more engine turns to turn wheels once -->at same RPM will go slower with higher gearset.

I think you had it right the first time: higher gearset means lost gas mileage and lost high-end speed.

However, with the higher gearset, at a given speed, your RPMs are higher, and, depending on the shape of your torque versus RPM curve for your engine (dyno graph, anyone?) you may be in an engine torque range with more or less torque depending on all the factors that play into how that torque versus RPM curve looks. Again, this is engine torque, not wheel torque.

I think I got this right. Hopefully some of you guys can confirm.
 

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It's all moot guys, the engineers calculate the rations and with the 6, 7 and now 8 speed boxed the old days of selecting an optional rear ratio are long gone. Unless you are buying a truck, where the ration determines the tow capacity, you get the ratio they spec for your model and options combos, period.
 

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It's all moot guys, the engineers calculate the rations and with the 6, 7 and now 8 speed boxed the old days of selecting an optional rear ratio are long gone. Unless you are buying a truck, where the ration determines the tow capacity, you get the ratio they spec for your model and options combos, period.
True, true. I agree. See post #4 above. However, at this point, I think we have turned the discussion from the OP intent into a general discussion about gear ratios. Gear ratios for gear heads. Well, I am not really a gear head, but I do like the discussion, and I like to learn.
 

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I don't believe you have the option to specify the rear ratio. You get the following depending on what you order

A6 - 2.56
A6 w/Z51 - 2.73
M7 - 3.42
The only way to get a different gear set on a manual is to go aftermarket. Most folks who have done this on a C5 or C6 have gone to either a 3.90 or a 4.11. I think in all the 12 or so years I have been on online corvette forums, I've only seen 1 or 2 folks go for higher mileage, and they went for a 3.15 rear end. I don't know if the C7 uses different gear sets from the C6, but even if it does, sooner or later, someone will come out with different gear sets for the C7.


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Discussion Starter · #11 ·
Thanks for the input. I thought I had read an article somewhere that you could order a different ratio.

Just checked the order guide and found that it is not possible to order a different ratio. They are forced as MJW930 said.

For the record, My Dodge truck has 4:88 rears, the higher the number, the more engine rotations per axle rotation resulting in higher torque, lower speeds. I do know that much.

I was just wondering if it were possible to change it up with the vette, which it apparently is not. Sorry, answered my own question with a bit more research. :-(
 

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Nope, I don't think so. Higher NUMBER:1 gearset--> more engine turns to turn wheels once -->at same RPM will go slower with higher gearset.

I think you had it right the first time: higher gearset means lost gas mileage and lost high-end speed.

However, with the higher gearset, at a given speed, your RPMs are higher, and, depending on the shape of your torque versus RPM curve for your engine (dyno graph, anyone?) you may be in an engine torque range with more or less torque depending on all the factors that play into how that torque versus RPM curve looks. Again, this is engine torque, not wheel torque.

I think I got this right. Hopefully some of you guys can confirm.
Believe you said it correctly. I’ve been a gearhead for over 50 years! My 1st car, a 41 Ford opera coupe had 4.11:1 gears because it came with a small Ford 60 V8 and needed those gears with a 1:1 top transmission gear to get up hills. (Put a ’51 olds engine in and bored it an 1/8 inch for ’55 pistons. Blew 1st gear first time I got on it! No problem through it would light up the tires in 2nd until I lifted!) The confusing point is what is higher and lower, for whatever reason a lower gear refers to the higher number! Best to say what it is, in that case it takes 4.11 turns of the engine to get the rear wheels to turn one revolution. Torque is multiplied 4.11 times. Top speed is reduced and gas mileage - - at $0.25/gallon-who cared!!
However in a Z51 Vette with a 7 speed, 7th gear has an overdrive ratio of 0.48:1 meaning before the engine revs get to the rear they are increased by 1/0.48 or 2.08 times. So you can multiply the 3.42 rear end by 0.48 and get an effective total ratio of 1.64:1. Of interest, the none Z51 has the same 3.42:1 rear and a 7th gear overdrive ratio of 0.42:1. Then the effective total gear ratio is 1.44:1. Hope I did not confuse it further! It’s below freezing today so have time to write this dribble! It will 50+ over the weekend and 65 on Monday; be out in the Vette!
 
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