Hi all, My 72 Buick GS has 3.73 gears in a 10 bolt Posi diff. Great for acceleration, but not so much for cruising/highway. Can I get opinions/advice on what ratio is best so as not too lose too much acceleration, but make it reasonable to drive on cruises/highway? Thanks, Jim G
3.42's should reduce RPM by about 10%. Could he get down to 3.23's without a carrier change? For some reason I seem to think so, but I'm not sure where the switch happens.
If you have a 3 series carrier, like I had with 3.08's, you can go all the way to 4.56's if you really want and don't mind a spacer. I ran that for years. Running 3.55's right now and I can run 65 at about 2800 rpm which is still a little high for me (26" tall tire) I don't want to go back to 3.08's, so I'm saving my pennies for a Gear Vendor Overdrive :TU:
The best change is a teanny swap. leave the gear you have and install a 200-4R trans. This gives you the acceleration and also a .67 OD which makes the final ratio like a 2.9-3.0 o No: o No: o No:
Don't be afraid of 2.56s! I just ran a 13.2 @ 107 (4100 pound car) two weeks ago, and I've been mid-11's on the nitrous. Then I drive home on the freeway at 75-80 MPH, comfortably along with the faster traffic and getting over 15 MPG. I stay in 1st gear until about 65 MPH, and I cross the line in 2nd gear. A 3.73 might beat me out of the hole, but then I stay in 1st gear that much longer and I catch back up. Same thing happens in 2nd- a 3.73 has to shift into 3rd to finish the run, but since i can run it out in 2nd I am making up for any advantage they had earlier on. (Yes, I've put a lot of "extras" into my engine, so you might not perform as well on all counts. However the point is that you shouldn't be afraid of tall gears.) If you do go to a tall gear, you should be careful about your transmission temperature if you have a high-stall torque converter. A lot of people who do highway driving go with a 3.08 ratio. -Bob C.
I went from 3:64 to 3:08 about 3 years ago. I really don't notice any difference in the acceleration. The car is so much nicer with the 3:08's. I will never go back to the 3:64's. Still blows the tires away from a start and has dropped my RPM's @ 60mph from about 3000 to about 23-2400 rmps @ 60. Do the change unless you are always doing the 1/4 mile with slicks. You won't ever regret it! Eric/ Oregon :3gears:
Thanks for all your replies. I am thinking of going to 3.08s. How will I know if I am able to install 3.08s in the diff's carrier? Thanks again, Jim
I like the trans swap also you will get close to 3-1 in 1st gear with a 200 or 700r4 and still have great hwy ratio. there is the cost though.
Going to a 4 speed auto would definitely be a good answer, but I have a great TH400 that is rebuilt and very stout, so I want to keep it. That being the case, my alternatives as I see them from the posts are either an overdrive unit (mega bucks, $2500+) or lower numerical ratio gears (lots cheaper). I don't go to the track, so I think the 3.08s are my best alterative for the buck. I looked at the rear end, it is a 8.5" rear. Is it simply a matter of installing 3.08 gears, or is there more to it? Jim
How do you figure that by holding in second gear longer you can out run a car that has shifted into third ? On my transmission there is NO delay on the shift so no disadvantage to the shift , keeps me in the power band longer . I am using 4.10 gears and drive the car as I need to , including the interstate , just runs the RPM's up some . We took 3.08 out and will NEVER go back below 3.73 .
just runs the RPM's up some . I guess the word "some" is the key...How much RPM's do you want to reduce @ 60mph. To me I'll gladly give up 6 to 700 rpm @ 60 for 1/10 of a second in the 1/4. If you look back at all the threads on rear end gears you find over and over again for street cars the majority of the responses are for 3:08's on the street. But to each his own! Eric/ Oregon :3gears:
I don't think you quite understood where I was going. Let's assume 500 ft-# of torque, in two similar cars. If my 2.56 car is in 2nd gear (1.48:1 ratio in 2nd gear) with 2.56s, and a similar car (same tire size, etc.) is in 3rd with 3.08s, the resultant torque to the drive axles is: 500*1.48*2.56 = 1894 ft-# 500*1.00*3.08 = 1540 ft-# ... therefore the 2.56 car will out accelerate the 3.08 car for as long as this condition exists. Even with a 3.73 rearend, he would get 500*1.00*3.73 = 1865 ft-# ...which is still less acceleration than the 2.56 car in 2nd gear. Of course the car with shorter gears will get a head start every time (assuming sufficient traction), and would theoretically win every time. In your case, however, which is even further in the extreme: 500*1.00*4.10 = 2050 ft-# ...so even in 3rd gear, a 4.10 car will have more acceleration than a 2.56 car in 2nd gear. But I don't consider a 4.10 car a "reasonable highway" driver (per the original question). Maybe you do, and everyone is different. Even with a 2.56, sometimes I wish I had an overdrive... Also, I did say "run out", not "out run" - meaning I could run out (i.e. finish) the whole quarter-mile in 2nd gear. In an acceleration contest from a dead stop, the shorter-geared car would theoretically win each time. -Bob C.
I know it is expensive, but the GV overdrive is simply awesome. I have 3.73's in an 8.5 10 bolt rear. At the track I use a 26" drag radial (275/50-15) which gives me a little more like 3.82's. On the street, I now have 28" drag radials (275/60-15), which makes the gear more like 3.55's. The GV brings that down to 2.76. 60MPH is about 2100 RPM. THe GV is pretty bulletproof and can be shifted at WOT at any speed. It's an awesome combo on the street with the switch pitch. On the highway with the GV engaged, it feels like the car could do 150 MPH. The ST400 will downshift giving you 2nd over and the car really goes.
If I am only interested in dropping 1/10 I will empty the trunk and not have a full tank of gas . figure in the 1/4 every 100 lbs. car weight is about 1/10 off ET . For the ET's I'm running I will be glad to turn the motor 6000 + .
