71 455 40 over forged pistons Ta 413 cam. The motor is currently down at TA now and I am being told this motor should make anywhere from 480 to 500 horsepower. I currently have a 71 olds 12 bolt cover 10 bolt ring gear that I can not find any parts for, but I have found a 71 cutlass rear end that I will be having built this week. I have a hughes 2500 stall converter built turbo 400, and I want to know what gear makes the most sense to put in the rear. I wanted to go 3.90, but Mike at TA said that is too high and that he would not recommend anything higher then a 3.55 gear. This is the exact same thing the shop that will be building the rear end stated. The car is a 69 GS, and it will be mostly street driven, but there will be a few track days as I have a few friends that have had a lot of trash talking going on. Any thoughts
For 1/4 mile duty, you want the engine to be making peak HP as you go through the traps. Spinning the engine significantly below or above the HP peak will diminish trap speed. Look at your dyno sheet when you get it. Note the RPM where peak HP is made. Then using the car weight, see if you can approximate the trap speed using rear wheel HP. Typical HP loss from crank to rear wheels is 20%. http://www.race-cars.net/calculators/et_calculator.html 336/tire diameter X rear gear X MPH = RPM (no converter slip) How efficient your torque converter is will infuence Trap RPM also. See if you can gear the car accordingly. As an example. If you think your trap speed will be 110 MPH, and you are using 28" tires, 3.73 gears will put the engine RPM at: 336/28 X 3.73 x 110 = 4924. Add 4-10% converter slip and you will be at 5100-5400 RPM.
Great post Larry! I think Mike at T.A. is steering you in the right direction, I have 373 gears in my buick, and I like it for short drives and 1/4 mile passes(Larrys post demonstrates its a good 1/4 mile gear) I have the 290-08 cam and 3500 stall. I think you would enjoy a 342, 355 or a 323 gear more on the street without hurting your 1/4 mile times much. If 1/4 mile times are the top priority than addd the 373 gear to concideration.
I agree with the low 3 ratio as Your Buicks always produce gobs of torque and burn out fun will not suffer. But if you truly spend more time DRIVING the car from place to place 3.08 3.23 3.42 3.55 will be the best bang for the buck in all around performance. Especially since we do not have as many gas stations as we use to and the price is going through the roof. JIm
I have 3.73's. Remember, tire size affects overall ratio. Stock tire size is about 26.6". I have 28" tires, P275/60R-15. That reduces the effective ratio to about 3.55.
I always liked 3.08 on a street car, 3.23 on a performance car, 3.42 on a race prepped street car. It's all based on the trans. If you swap in an overdrive than the 3.42, and 3.73 becomes the standard performance ratio. Can't comment on the 3.55 since I never had that ratio. I'd lump it in with the 3.42 though
For me if I was building a street car with the odd strip trip 355 would be my lowest choice without an overdive trans.I run 12 bolts so 331 342 355 with a 28' tall tire.I run 411 in my car with a 30' tire and 4500 stall but this is a pump gas strip car that I drive on the street. Jamie
for street driving without an overdrive i would go with a 3.08 my wildcat runs 24-2500 rpms at 70mph crusing on the highway and have ran 14.58 in the 1/4 with 2.78 gears if later you want an overdrive i would go 3.42 or higher just my 2 cents worth scott
I have a 20 inch rim with a 275-40 inch tire on the car now so what would that reduce the 355, or the 3.73 gear to. I believe the circumference is 29, or 29.5. Ill have to measure it when I get home.
Mine is 99% street driven, and my two cents are, for good highway speed driving, it's tough going much above 3.23's IMO unless you have an over drive. I ran 3.70's, 26" tall tire and a deep over drive (.64) and cruising at 2500rpm at 75 isn't much of an issue. I changed them out because first gear was too short and I was at redline about as fast as I could lay the pedal down. 3.08's I got for free, and certainly makes you feel the torque of the engine. I'll probably have 3.23-3.42's before the summer is out.
A P275/40R-20 is 28.66" tall. The gear on our cars will be based on a 26.6" tire. To figure the effective gearing with another size tire, use original tire height/ new tire height X gear. 26.6/28.6 X 3.73 = 3.47 26.6/28.6 X 3.55 = 3.30 That tire is a a full 2" taller than stock, so it will reduce the effective gearing. I would run the 3.73's. You could always run a shorter Drag Radial at the track to get the full gearing.
Thanks for the info Larry, the 3.73 is what i was thinking as well. Hopefully when she is all back together she will run pretty good. I am hoping to be somewhere in the low 13's realistically, and that should be good enough to take care of the minor issues i have with a couple cheevies, and one ford.
480-500 HP will put you solidly into the 12's, if you get good traction. That means Drag Radials. Don't even think you will get away at the track on street tires. It will be a frustrating exercise in Futility.:grin:
Quater mile times are important, but more so abusing a couple of Chevy guys and a ford lover. All three of the cars that I am shooting for are about 13.5 second cars, and I think I should be right there with my build if not a little faster. Mike(TA) believes the car should be about 480 -500 horse. and if that is the case with the 3.73 gear, any estimates of what I should expect in the quarter??
I thought as much too, so I bought a set of drag radials that I will pull out of the trunk at the track that I have on the stock rims. Im sure they will have a lot to say about that, as I have been keeping that a little secret. I may have to run them on the street tires once just to shut them up though. I have adjustable upper, and lower control arms in the rear now, are ther any other things I can do to keep her planted. The car with me in it is 4100 pounds.
