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Discussion Starter #1
I recently picked up an 8.8 rear, to replace the 7.5 in my 80 T-Bird. The rear has a trac- lok with 2.73 gears installed. I want to set the rear up for daily driving, but also want the benefit of a hard fast launch. The old 7.5 rear has really poor gears, around 2.65, killing acceleration in a car around 4300lbs. I have have a warmed up 302 in the car with a C-4 transmission. The trans has a stock torque convertor for now, but the trans was rebuilt and a trans-go kit was installed, giving some decent feeling shifts. The 302 is built with an Edelbrock Performer package cam, intake and carb. I also ran a dual exhaust with headers and flowmaster mufflers. The ignition is all MSD. I currently run a compression of only about 8.4 due to the 77 smog era heads. I picked up a set of 65 289 heads with chambers about 54.4cc. This will be moving compression to about 9.9, I currently have a set of rear tires that are 235/60/14 with a height of about 25.1" tall. I plan to switch to a 15" rim and go to a rear tire between 27"-28" tall. With this combination what gear ratio should I install? I was thinking between 3.55-3.73-4.10. I understand that 3.73 is a very popular ratio with an auto trans, but is 3.73 the ideal gear to install or is it the final ratio that I should be shooting for? I understand that based on the increased height of the tire, the final ratio is reduced. So(just for example)lets say that 3.73 is the ratio that I shoud be shooting for, would I want to install a 4.10 set of gears? Is a ratio of 3.73 too much for a daily driver? What is the ideal finial ratio for what I am looking for? Any help is very appreciated.
 

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For a true daily driver without overdrive, and hitting highway alot, I think max would be 3.55, thats cruizing 60mph at 3000rpm, but awesome holeshots as well. You'd be hitting high rpm's on highway with 3.73's, but anywhere between 3.55 and 3.73 is good.
 

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Discussion Starter #3
Most of my driving is in the city..80% or so, back and forth to work. Most of my highway driving is done with my wifes 4 cylinder grocery getter. Would I notice a real difference in gas mileage between 3.55 and 3.73 gears. Also do heavier cars benefit from lower gears?
 

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Don't overlook the diameter of your rear tires. Going from 25 inch tires to 28 inch tires makes a big difference.With 25 in tires and in order 3.55s, 3.73s, 4.11s,at 60mph your rpms would be 2862,3008,3314 respectively.Changing to 28 inch tires would drop rpms in the same order of gear ratios at 60 mph to2557,2687,2960 so you can see cruisin at 60 with 4.11s and 28 inch tires your rpms are less than with 3.73s and 25 inch tires and not much more than the 3.55s.If you do mostly city driving and the odd stoplight grand-prix you might consider the 4.11s especially if you are considering a looser converter and the bigger tires.
 

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rolling tire diameter x 2.975 divided by gear ratio (direct top gear in trans) = mph per 1,000 rpm. Divide by od ratio if od trans.
 

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BBCFORD I got a T5 trans and 3.80 gears put in my 67 mustang about 1 month ago. Before it went 0-60 like 6.5 now it does 0-60 in about 4.8. I had a C4 in it before and 2.80 gears something like that. But the 3.80 gears work realy good on the punch. I would go with aleast 3.80 since you have a heavy car. It mainly depends if you want to have more mpg or have your T bird faster. Good luck
 

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Discussion Starter #8
I found that 3.55 gears would put me about 2606RPMs at 65mph and 3.73 gears would put me at about 2738RPMs. This is based on a 28" tire. The difference doesnt seem too extream based on the larger tire. I currently have a shorter tire thats only 25" tall. I know I can stuff at least 27" on the back, 28" max. Would I really notice a difference between 3.55 and 3.73...in terms of "seat of the pants"? Would 4.10 be a mistake for a daily driver, based on a 28" tire and auto trans? Putting in 4.10 gears would put me at about 3009 RPMs at 65 MPH. I would be looking at about1624RPMs at 35MPH city driving. Do the lower gears work well in heavier car? How would gears, say 3.73 and above effect cam selection? As I mentioned before I am running a performer package cam so does that limit my gear selection?
 

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Discussion Starter #9
One last question when it comes to rear gears...Who makes the best/toughest gears? Are there any preferences and are there any companies to steer away from? Should I stick with Ford parts? They all seem to run around the same price..around $190 or so. Thanks for the advice
 

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If you're trying to save some money and want to go with used gears there are a lot of Ford F150's out there with 3.55s. It should be easy to find a set at the wreckers.
 

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racerguy...I thought about picking up some that are "lightly" used. I noticed that used gears are on E-bay all the time for about half the price or less, of new gears(especially 3.55). I just dont know if its a waste of money to install used and somewhat worn gears. Anyone have experience with used gears? Thanks
 

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I've installed used gears before with good success. Take a close look at them though and make sure there aren't any bad wear patterns, chips off the teeth etc. I wouldn't pay more than about 1/2 price for a good set of used gears.
 

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Discussion Starter #13
I'll give consideration to a used gear set. I'm leaning twords 3.73. Maybe I can find a bargain on E-Bay if I'm patient...thanks
 

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Discussion Starter #15
racerguy..thanks for the info, I'll check the boneyards for 3.73 gears. With the money I save I can have the gears professionally set up. I would like to do it myself, but have heard that it really isnt a backyard mechanic job. Does anyone have an opinion on this? I only mention it since a basic tool set to install gears, runs about $100 or so, not to mention that I wouldnt have to haul it somewhere.
 
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