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Discussion Starter · #1 ·
I just bought a 66 with a 454 and I am wanting to make some changes for gas mileage since I want to drive it a lot but I also want to take it to the track once in awhile. So I'm thinking a 5 speed maybe a 6 speed would be perfect for the job but I'm lost as to which would fit then I'm not sure which gear choice for the diff since it's got a 12 bolt but it needs a posi differential installed.

Any assistance would be appreciated.
 

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Does it already have a 4 speed in it? What is the current rear end gear ratio? If you don't know look at this video below and find out.


If your current ratio is a 3.08 or higher for example a 6 speed with a possible .5/1 in 6 gear would be useless in 6th gear because it would be a 1.6 final drive ratio! I have a 454 and a 4 speed also and they are not known for getting good gas mileage but higher rears will help.

Eric
 

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I installed a TKO 600 with the .64 overdrive into my 66 and put in a 373 gear. Seems just about perfect.

You will have to cut the tunnel for the TKOs. Not sure of any current od stick trans that don't require some cutting. Was not a big deal to me.
 
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