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Hey guys, I have an 81 Firebird with a 305 and th350. Currently with a 2.41 open rear end. I get incredible mileage but no get up and go. I'd like to keep the original 305 in it so right now that isn't up for questioning, but want to beef up the rear end. Would a 3.42 be too much for that 305 or would the power transfer nicely through it? Deciding between 3.42, 3.23 or 3.08. Any opinions would be appreciated! Thanks.
 

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High Performance Rear Ends
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That's going to depend on what you are willing to put up with on the highway. For many people the 3.42 is too much with the 3 speed transmission. The 3.23 is a pretty good compromise. Any of these is going to require a 3 series differential because your 2.41 is on a 2 series and it won't work with these gears. I also recommend a good installation kit, like the Yukon or USA Standard kit. If you get an after market differential then you will need the kit with the special bearings for that differential. Stock bearings will not work.
 

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3.23 or 3.31/3.36 would be fine.
3.23s with a 27" tall tire will get you 2600rpm @ 65mph mathematically. 3.31 would be about 70rpms higher

Measure your tire height, if you have a 27.5 or 28" tall tire; your RPM will be slightly less. If the tire is SHORTER, your RPMs will be a little higher.

Now: Go out and find a deserted stretch of road. Go down the road at 2600-2700rpm. I dont care how fast you're going. LISTEN to the motor; are you okay with that? If so, then change to the 3.23/3.31/3.36.
If NOT: 3.08s is the best you can do for you, using the existing motor and trans.
If you said: "Im going to put a 700r4 in this tomorrow" I'd go 3.55s, but ONLY if you're dead serious about keeping the motor mild and putting a 700r4 in almost immediately.
 
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