Hello All, I'm thinking of dropping in a 8.50 10 bolt posi with 2.73 gear in my '72 Stage one. I've 3.73 gear now and want something better for daily driver status. I don't want to disturb the 12 bolt in there now, rather was thinking to freshen up the rearend that's been on the shelf for 15 years and set it up for hiway cruising. car has nicely built 455 with ported iron heads, b4b, 750 speed demon carb and T/A cam with 230/240 duration-can't remember exact grind but got it from JW last year. turbo 400 with tight 10" converter. What would happen with those hiway gears?? I was thinking of dropping the headers for Gessler ported manifolds as well. I put stock type 2.5" mufflers and that helped quiet it down some. Will it even run right with those gears? I'm thinking it would scream from 60 to 120 mph or so?? Any thoughts on this, MPG savings? Would I be able to smoke the tires still?? Was thinking of 225/70/15 narrow whitewalls to add to the sleeper stock look at the same time. :idea2: o No: Jerry
I wouldnt change from a 3,73 to 2,73. I run my Centurion with a 2.92 But its a standard 455 with a crane cam and performer intake and 800CFM Q-Jet. This apliction runs fine with the 2.92 I can cruise the car on the highway with about 90 mph. When Im going with about 80 mph the car runs about 13 - 14 mpg. But like I said: this is a Centurion with 4000 pounds.
It will work fine.There will be more than enough torque to break tires loose.I would not go too tall with the tires though.I have a 3.08 12 bolt with a 240* duration cam and it still works great.Getting 15+mpg (US gallon) with 28" tall tires.Sure makes for nicer cruising and still get respectable acceleration. Rod
Of course it will work, and quite nicely too. That is if your daily driving takes you on the highway. My commute is mostly highway, and with 2.56 gears my 455 will cruise right along with traffic at 75-80. And 2nd gear will go to about 110, so if I happen across the occasional Mustang, I just downshift and lay waste. The biggest problem I see is your 10" converter. The new rearend will bring your revs way down, and your converter will be slipping more, which might increase your tranny temperature. So it depends how "tight" your converter actually is. If your stall speed is 3000 and you are cruising at 2200 RPM, your converter will be slipping like crazy. -BC
Jerry, your build sounds like it's perfect to suit a 3:73 gear, so I'd be reluctant to change to gear any lower than a 3:31 or 3:08 (numerically). JMHO
I have a 2:56 gear, 26 inch tire , a slightly longer duration cam 288 and a Coan 10" ~`2200 ....with the bbb you will easily roast the tires as mine does...J.
Why don't you try a 3.23-3.42 gear? Maybe run a taller tire on the street to get your RPM down. I'm using a 3.42 with my Skylark and I've been running a 235/75-15 (about 29"). My car cruises well with it. I keep up with rural road traffic without going over 2500RPM. For racing I put my 26" slicks and I get decent 60' times.
See the attached link of a mild 455 in a Regal and I believe that in this video he had the stock 2.41 10 bolt 7.5 rear with a 3400-3500 converter. Not your most common combo out there. Great cruiser but that converter isn't the best for highway driving even with a good trans cooler. http://www.youtube.com/watch?v=lvsC4ZPBn6c I say that with mega Buick torque you can run a taller gear for better cruising yet still leave the line fairly hard when needed.
What size tires are you running? Although it wouldn't give you the sleeper look, TA makes the Radial TA in a 255/70/15 that is 28.9" tall. That may take enough gear out of it to make you happy without bothering with a swap. And, they're meaty enough to (possibly) hook while fitting on a 15x7 factory rim (could always go dog-dishes). Another option is to look into a Gear Vendors overdrive unit to attach to your trans. It will give you the overdrive for the highway, while also allowing you to have the lower gearing combination for launch at the track. The biggest detriment to your gas mileage is attached to the bottom of your right leg. When it comes in contact with the tall, skinny pedal - the mileage goes down.
I had a similar engine build in my car a few years back. It was my first engine upgrade and I hadn't changed the rearend yet. The rear was a 2:73 at the time. The car would really run! People were amazed at how well it did with that high gear in it. At 25mph it would break loose under full throttle. Sometimes I wished I had it back now.
http://v8buick.com/showthread.php?t=90121 Note how D Berry only lost 0.04 in the quarter using 2.56 gear over the 3.42 he had before.
Thanks for pulling up that link sean Buick 76. Like already stated, Buick torque can work wonders with tall gears.
Actually GM did this with Olds. They put together a package with tall gears, 455, suspension etc. It will work with the correct tune and a non locked converter. My setup will work fine in 4th lockup down to around 1300-1400 rpm. This is with a TA413. Below that I have to switch off the lockup. When the lockup is off there is no real problem except is not good for the transmission. When I get my next converter I am going to work on lockup in 3rd and see how that works. I would not expect miracles on fuel millage without building things specifically for that purpose. I love my overdrive just because it allows me to cruise the highway at reasonable rpm's. But with its big street cam and a Holley there is no free lunch.
True, but not valid while just cruising down the highway at a constant speed. Then it is the fact that our cars have the aerodynamic Coef. of a brick compared to modern cars that affects mileage considerably. Do you have a front spoiler on your car ? Larry (aka The Wizard) put a gear vendors behind his TH400 / 3.73 10-bolt and hasn't done much better than 15 mpg. His motor is singing baratone instead of soprano though ... Cam and Carb need to be optimized for low rpm chugging to really see some gains
No spoiler on mine (or my old 71 GS455 or the 72 GS350 I had in high school). But then again mileage was never a concern with mine and my new one which should be putting out over 500hp once finished will be measured for mile gaseage instead of gas mileage. It has a 2.56 rear in it currently, and when I drove it to the track the day I hurt the motor a few years ago, it felt really nice when held in 2nd. But in Drive, it cruise around 1600 rpm with a stall about 1000 more than that. I'd start climbing a hill and watch the rpm's go up as I slowed down... until the converter finally caught up.
Thanks guys for all of the responses and great input. I'm really impressed on how strong some people are running with "Hi-way" gears! I really like the gear vender idea. Even though they aren't cheap, I wouldn't have mess up the original 3.42 rear on the shelf and just keep my 3.73 12 bolt in there now. I would probably end up spending a grand or more to bulid up a strong 10 bolt with all new stuff, so it really isn't much more to step up to the gear vender. I'll have to reread some on Larry's posts on his swap. I keep going back and fourth. Now I'm thinking to keep the headers and bolt on the Offy dual quad with two 750 Carters on top just for summertime kicks!:TU: Are we ever really done with these things?ou: Thanks all-great disscusion Jerry
