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Rear end gear choice

2K views 12 replies 7 participants last post by  gvasquez_81 
#1 ·
Hey guys I have a 7.5 gm 10 bolt with a saginaw 4 speed with 2.73 gears I wanna swap them out with something better i can't decide between 3.23 or 3.42 gears. I want good acceleration but I drive the car on the highway a lot. What do you recommend. And I'm not switching the trans lol thanks again
 
#4 ·
I had a 1980 Camaro 454 with 3.36 gears and didnt like it on the highway,,,,I also had a 1967 Camaro with a 350 with 4.11 gears and I didnt mind the odd trip on the highway.The 350 engine was quite happy at 2700 rpm,the 454 always felt like you were getting ready to race
 
#5 ·
You need to provide more information on your car before you will get a decent answer. However, 3.42 vs. 3.23 is such a small difference (about 150 rpm with 29" tires) that it probably does not really matter that much.

In general, a stock 350 will cruise and get decent fuel economy at about 2400-2800 rpm on the highway. However, you will get better economy if you can drop the rpm down to about 2100-2300.

You need to take one of the online calculators and enter your tire diameter, high gear ratio (sounds likes its 1:1), and the rear end ratio you are looking at. Then decide if you like the cruise rpm.

For example: If you currently have 29" tires, you should be running about 2214 rpm at 70 mph. 3.42 gears would bring that up to about 2760, which is still fairly reasonable.

Bruce
 
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