Classic Mustangs (Tech)Technical discussions about the Mustangs of yester-year.
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I have a 68 coupe with a 302. Looking to upgrade to a traction loc differential. I am not sure what gear ratio I have, and not sure what would suite the car and my driving needs best.
I have a stock 302 with an 8" rear end. I have installed a line lock as well as I had to get some brake work done when I first got the car. I am wanting to have power at the lower end, but will be doing highway speeds a fair bit as well. What does everyone suggest?
Any suggestions would be appreciated.
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nobody makes a 3.73 for a 8" so the next one up is a 3.80, but most people do not like them on the freeway with a c-4.
I was considering the 3.25 or the 3.55, but don't know what sort of difference it would make, nor am I sure what I have currently. I am going to have to jack it up and spin the drive shaft to see. I also will have to check what the tire size is as well. It is loud as is, and with a wife and 2 kids who like to go on road trips in the car I don't want to be needing ear plugs on a 2 hour drive. Most driving would be shorter trips though.
You either have a 2.80 or a 3.00. A 3.55 is the best choice.You probably wont notice much of improvement with a 3.25. A 3.80 with a 25" tall tire will be very close to 3,000 rpm at about 70 ish on the highway.
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I went with 3.44s. On basically stock 302 I did not notice that much difference and was a little dissapointed. Now that I'm running my 347 glad I went with these gears plenty good down low and not screaming on highway. If you plan on staying close to stock I would go with 3.55 - anything taller will be reving high on +60 cruising.
What transmission are you running? An automatic will have a little slippage compared to a manual trans and will add a few more rpms to the tach on the highway.Tire size (diameter) will play into it as well. I would try to figure out what is the max rpm you can live with on the hwy and then do the math to figure out what gears will work for you.There are lots of online rpm calculators that can help you with this...The ultimate setup is an overdrive trans that will allow you to run a low rear end ratio for great acceleration and an overdrive gear for low highway rpms..For example my brother changed out his close ratio toploader 4 speed trans and a 3:1 rear end gear for a T-5 and a 4:11 rear gear..The car is much much quicker now yet runs the exact same rpms on the highway.
68 J code 408W topoader with 4:11 detroit locker 11.59 @120.95
As a guy in the same boat with the same setup I wouldnt bother till you do your transmission (exchange for AOD or 5 or 6 speed manual).
With a stock engine unless you go up to high gears you won't notice it that much. With high gears the highway stuff will suck (I do long distance on highways).
What I would and did do is find out the rpm range you like to be on the highway at cruising speed. The use the gear calculators to match that up to the MPH you would like to be going (65 70 75) and then use the AOD or T5 or T6 gearing to back into what rear gear you can get.
Be aware that your other shift points will change so spend some time on this otherwise you could end up in the wrong RPM range or gear other times.
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