Transmission Upgrade - Impala Tech
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post #1 of 2 (permalink) Old 09-05-2016, 10:20 PM Thread Starter
Join Date: Nov 2015
Location: North Carolina
Posts: 8
Transmission Upgrade

I have a 1963 Impala SS with a 355 engine and TH350 transmission. Looking to upgrade to 700r4. Transmission shop is recommending that I change rear gears to 4.10 to get the best performance from the transmission. Car currently has 3.42 gear. Looking to drive the car in highway from time to time. Currently the TH350 is pushing rpm`s to 3000 when I hit 70 on the highway which is why I want to go with the 700r4. What are your thoughts about going with the 4.10 gear and 700r4?
Uncle61 is offline  
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post #2 of 2 (permalink) Old 09-05-2016, 11:42 PM
Join Date: Jan 2006
Posts: 12,222
A 4.10 gear is reduced to a 2.87 final ratio rear gear by the 0.3 over drive. The lock up converter gives another 5% improvement (acts as a tiny gear 0f 0.05 which gives a 2.72 final effective gear). That should improve mileage by lowering your effective gear ratio while at the same time improving acceleration due to a steeper rear gear and a steeper first gear ratio in the tranny. So an OD tranny is the best of both worlds.

I used to run a 4.56 gear on the street with my BBC and a 4L80e transmission that has the same 0.30 OD ratio.

Big Dave
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