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Old 04-10-2011, 01:17 AM
 
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I have a 1970 Impala with a recently installed ZZ4 350 and Richmond T10 wide ratio 4 speed.

I need to get a stouter rear end so I was thinking about going to a 3:42 (currently 3:08).

Would I feel much of a difference in performance?

Gas milage difference is not a concern.
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Old 04-10-2011, 01:43 AM
 
Location: H-town, TX.
3,398 posts, read 5,461,822 times
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For the effort, just go right to 4.10s.
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Old 04-10-2011, 02:07 AM
 
52 posts, read 48,271 times
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I'm not a fan of 4.10s unless they're NEEDED for strength. Last year I swapped out the gears in my truck from 4.10s to 3.73s and was very happy with the result. That 11% change got my RPMs right where they needed to be and even though I "lost" some torque through the gears, I'm no longer riding on the governor and have twice as much "usable" power because I can run the engine at the peak of the torque curve without de-fueling at highway speeds.

As for what the OP should do, it depends on what your goals are. Taller gears are more "fun" in a car, but shorter gears will get more HP to the ground with less stress on the drivetrain. If all you want to do is the quarter mile, shorter gears will (usually) give you better times. It all depends on where you're currently running with RPMs at the speeds you want power and how much you'd like to change them.

As I see it, you have two choices; If you're happy with your current performance but need strength, you can put in a heavier rear end (like the difference between a 1/2 ton and 3/4 ton truck, or shorten up the gears. My seat of the pants experience is that taller gears are more fun on the street, but 3.42s wouldn't be a huge sacrifice if you had to go that route. They're a decent compromise, and will only increase your RMS by ~10%. They could be a good thing if 10% more RPMs would put you into the peak of your torque curve at the speeds you normally drive...like I said, it depends on a lot of factors.

If you really want an answer without having to commit to the change, borrow a set of rear tires/rims 10% smaller than your current set and take it for a drive. It'll feel the same as your current setup with 3.42s.

Last edited by missed; 04-10-2011 at 02:23 AM..
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Old 04-10-2011, 06:09 AM
 
1,735 posts, read 4,137,914 times
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Quote:
Originally Posted by doc1 View Post
I have a 1970 Impala with a recently installed ZZ4 350 and Richmond T10 wide ratio 4 speed.

I need to get a stouter rear end so I was thinking about going to a 3:42 (currently 3:08).

Would I feel much of a difference in performance?

Gas milage difference is not a concern.
Yes you would feel the difference with 3.42. 4.10 or 3.73 would get annoying at freeway speeds.
The best choice would be to go with 3.42 and a 5 speed. 1st gear is much lower than the T10 for the low end performance and with the OD you would be able to cruise at 70 and get better fuel mileage.
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Old 04-10-2011, 07:08 AM
PDD
 
Location: The Sand Hills of NC
8,776 posts, read 14,138,585 times
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Quote:
Originally Posted by RedNC View Post
Yes you would feel the difference with 3.42. 4.10 or 3.73 would get annoying at freeway speeds.
The best choice would be to go with 3.42 and a 5 speed. 1st gear is much lower than the T10 for the low end performance and with the OD you would be able to cruise at 70 and get better fuel mileage.
I sort of agree with this, go with a 5 speed like a Tremec with a 3. first gear but stay with the 3.08 rear.
A six speed would be even better.
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Old 04-10-2011, 04:41 PM
 
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Quote:
Originally Posted by RedNC View Post
Yes you would feel the difference with 3.42. 4.10 or 3.73 would get annoying at freeway speeds.
The best choice would be to go with 3.42 and a 5 speed. 1st gear is much lower than the T10 for the low end performance and with the OD you would be able to cruise at 70 and get better fuel mileage.
I'm already running the T10 so a trans change is out.

4:10s are way too low as I'm just driving on the street and some highway use, not the drag strip.

Thanks for the responses, guys.
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Old 04-10-2011, 04:52 PM
 
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3.42's sound like the best gears for what you are looking for and will no doubt give a big "seat of the pants" jump in performance.
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Old 04-10-2011, 06:08 PM
 
Location: South Jersey
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Id op for the 3.73's if this is a weekend cruiser and you want the best compromise. I really feel the 3.08 to 3.42 is not that big of a difference. Its the same cost to go to 73's and that will be quite a significant difference.
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Old 04-10-2011, 06:12 PM
 
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as long as you are not expecting to drive long distances, the 3.42 gears are a nice compromise for daily driving with a heavy car like the impala.
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Old 04-10-2011, 06:35 PM
 
Location: Earth
4,227 posts, read 20,285,035 times
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Yes you will feel a difference. You will have much better off the line acceleration.

And yes a 4.10 really isn't needed unless you're drag racing or if you have an overdrive trans.

You will also notice your speedometer will no longer read accurately unless you have it recalibrated.
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