Alright, I have asked this to a few guys here that I e-mail regularly with my firebird questions, but I wanted to get everyone's opinion.
Which posi rear end do yall think is the best compromise between highway driving and off the line 1/4 mile performance? When I mean highway, i mean like 120-130 mph. Not that I plan on doing this a lot or for extended periods of time, but just like to know i could. But at the same time, I would like it to jump off the line like hell and do well in the 1/4 mile. Am I asking too much? I just bought a 68 Firebird 350 4 spd and it has an open 3.08 out back. I wont be switching it out for sometime because of budget, but just want to get the research done. Thanks!
I dont think your asking too much but you'll have to fall somewhere in the middle. I know a guy that runs high 12's with a 3:08 rear but he does have a well built big block chevy in the car and the suspension is set up more for the 1/4. I would think that you could use somewhere betweem 3:31 to 3:55's to get where you want to go. Now you probably wont be lifting tires off the ground but at least it would be respectible. When it comes to 1/4 mile it's all about hooking up, If the car dont hook then it dosent matter what gears are in it. If you go towards the 355's you'll get better in the 1/4 and off the line (if it hooks), if you go towards the 331's you get more of a hwy racer. You'll have to make that choice. If you are going to flog this car from time to time just remember it's only as good as the weakest part, you may want to upgrade to a 12 bolt or ford 9" (i know the nasty ford word). From there is just gets more expensive LOL! Just my 2 cents, hope I helped a little, Nick
67 Convertible
67 vert 326,2 bl,3 spd,buckets,console,deluxe interior,manual top,3:23,open. Was factory Cameo Ivory but now Mercedes blue.
Hey guys...thanks for the input. Seems like most people like 3.55 out back. That is what I was kind of leaning towards. 3.31...I will have to look into. right now this car is numbers matching, but I plan on sticking a 400 or 428 in it and keeping the original 350 around in the ever so slight event I would sell the car. So I guess at some point I would have to step up to a 12 bolt or 9", but for the time being Q has let me know the 10 bolt is strong enough.
Hmmm, just thought about this...how about a 3.36 posi? I think that was an original gear in 68, code ZM. Do yall think that might be better than say a 3.55?
Steve, Do you have 14 or 15 inch rims on your 68. Do you notice much differance in the rpms with lets say a 3.55 gearing and using 14 compared to 15in rims. The reason I ask is that i plan on going with the 14 inch rims but not sure of the gears to go with to keep get the best all around performance out of the car. Thanks Joe
I was wondering the same thing I have a 3:55 posi w/a 4-speed,14" tires and 400 that I plan on building hopefully next year.I was wondering about maybe going to a 3:73 or should I stay with the 3:55.Doug
I replaced the 3.90 gears with 3.36 on my 69 400/4speed. I also went with 15" wheels. The car is much more freeway friendly and seems to be good compromise between 0-60 times and reasonable cruising comfort. The 3.36 gear was also as low as I could go with the posi unit.
225/70R14's on the back, 205/70R14's on the front. Didn't have a tach in the car when she was running, but could really feel the difference between the 2.56's before & the 3.55's after! I don't like the idea of running higher RPM's on the highway, would wear out your engine faster I would think.
its all a matter of what rpm range your engine is in its best power range, you want to keep most of your freeway speeds in that range so you will get the best fuel mileage as thats where the engine is most efficient. it dont matter if you run 14" or 15" wheels its a matter of the diameter of the tires. you can have two sets of tires mounted on wheels then when you are going to be running on the freeway. install the larger dia. tires then when you know your going to want to run it in the 1/4 mile install the smaller dia. tires. or you could add an overdrive to the back of your trans. its kinda hard to have the best of both worlds.
also if your planing on running at that high of speed make sure your tires are rated for it. nuthing will ruin you day faster than having a tire come apart at speed. and make sure your wheel bearings are in good shape.
I am running a 3.08 posi in mine. To compensate for the gear size I am running a 3,500 stall. With running some 26 inch Hoosier Quick Time Pro's I have made a 13.4 @ 97 with my first time out this year with my new set up. Found out that my factory fuel pump could not hold up to my new 400, so I had to pull back out of the gas at about the 1,000 foot mark. I'm installing a new fuel system this week and should have high 12 when I hit the track again in 3 weeks. So I would say you can get good speed out of a 3.08, just don't expect good 60 foot times.
Both my GTO and my 'Bird presetly run 3.55 gears. I will change the gears in my Bird for higher (numerical) gears when I install my T-56 (with the over drive.) I used to run 3.23s in the GTO. When I changed to 3.55s, the small change was very noticeable.
I love the 3.55's. At 80 MPH on the freeway, I am running just under 4000 RPM. I don't know how you feel about it, but I really LOVE the sound of my 455 at 4 grand. As for wearing out faster, how many of us do you think are going to put even 20,000 miles on our cars from here on out? In my very biased opinion, if you can keep the gears between 3.42 and 3.60, you will be very, very happy.
3.73 would be the absolute highest I would go without an overdrive for a daily driver/cruising car.
Q...I am still up in the air with between 3.23, 3.36, or 3.55. This Firebird I just bought will be my daily driver as it is my only car and feel comfortable with it probably breaking down from time to time since I live so close to my studio...so, engine wear is a slight concern of mine. Although I totally understand how individuals would want to baby their cars (especially after searching for so long for mine, or perhaps having a different car as a daily driver), I believe in the saying "drive it like you stole it." haha, also, "old enough to know better, too young to care!" Anyways, do you think that 3.55 and a regular highway a$$ hauling will wear that much on a 350, or even a 400?
Engine wear can be a funny thing. With today's modern synthetic oils, you will get much more life out of an olded engine. I wouldn't think wear should be a concern. My concern (for your case) would be never getting the car fully warmed up between home and the studio. I usually don't tromp on mine until I see the oil temperature above 200.
That works for me! My work is about 1-1/2 miles from my home. But ... for some reason ... whenever I drive my GTO or my 'Bird to work, I always end up going about 10 miles one way. There's a nice twisty-turny canyon road right behind my house. By the time I get to the top of the canyon and start to head down the other side, all the temps are just right.
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif"> There's a nice twisty-turny canyon road right behind my house. By the time I get to the top of the canyon and start to head down the other side, all the temps are just right. </font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">And He`s not kidding! its very nice road. ..you`d have a hard time finding one like that , even in Austin!
..you`d have a hard time finding one like that , even in Austin! 
