Ok yes Im new and have a lot of questions that I have posted but I want the car done right.

I have a 10 bolt open diff(peg leg) with 322s in it now. I want to get a new 12 bolt posi.(new or used dont matter) Im not sure what gears to put into it. I have been told by one guy(who im having trust issues with) with telling me put 390s 410s or 456s in it(car is NOT tubbed). Originally I wanted 373s in it. My friends dad tells me either 322s, 355s, or 373s highest. So before I spend the money I would like to know what to get

The car will have the regular sized tires, and its only driven localy really, due to insurance reasons. If its going far away then I trailer it.

I bought a complete rear end out of a 67 firebird. It was the same as my 67. I have kept the original with factory 256 geared non posi in storage. The one I bought I changed to 355 gears with a auburn posi unit, and new axles. For what my original 326 engine slighly modified, it does great on the street, but going down the highway, it's another story. rpms are up there at 60 mph. It all depends on alot of major factors. First off what do you plan on doing? Srip car? street cruiser? maybe the all elusive best of both worlds? What ever you choose, you need to consider the total package of what you want to do. do some research first before you jump into the mix. You will be ahead of the game and a little lighter in the pocket

i went with a 3:55 posi with a 200-4r overdrive tranny. BOP bolt pattern , same lenghth as a th-350 same drive shaft.just had to add the shift pressure cable and move my trans member back 1 hole. best of both worlds. (yet to be proven)

I have a 12 bolt in my 69 with 3:73 gears.
I don't like it at all. Driving on the highway sucks.
If you plan to drive on the highway or at speeds above 60,
I would go with 3:55 or 3:08. I don't think there is anything
between them for a 12 bolt.

The car will be driven on the highway at times for local car shows. If it goes long distant then it gets trailered. Should've mentioned that before

I am running 3.23'as with my 461 and M20 4-speed right now. The acceleration is awesome and I don't rev above 3K doing 65 MPH. I would like to maybe put in some 3.08's but that is as high as I would go. A pontiac engine is known for it's low end torque and doesn't need the 3.73's or lower gears a Small block Chevy does for performance. There is a guy here on FGF that is running 2.56's with his 400 and he smokes the tires ALL of the time leaving a parking lot or just driving down the road.

'a guy'....lol

You need to look at what the end project is going to be. Are you going to put an overdrive in it? If so which one? ARe you going to run a turbo 350,400 or 4 speed? If so I would not go any more than 3:55's. If running a overdrive transmission you will need to do more homework.

I'm not liking my 3:73's at all. I'm thinking about 3:08, or holding off for a while and going with an OD tranny.

Yeah, you might recognize him, in the mirror!

That is true, forgot pontiac engines like dont like to rev high.

Still deciding and doing some more research on what to get

I am running a 4 spd manual tranny in it, would like to keep it a 4 speed as well

Like I said, Im looking for the nice launches for the 1/4 mile and all. Its very rare the car goes onto the highway, mostly driven just in town for fun. Fuel is not a problem for the use of the car(even though gas is ridiculous) so I am not looking for it to be fuel economy friendly

My 68 has a m22w and 3:55's with stock wheels. Drove it to NY two weeks ago, 1200 mile round trip. I was at a constant 3200 rpm doing 65 with no issues, I did pull over a couple times when temp reached 220 but it was around 97 degrees outside (felt like 450 degrees inside). Still got 14 mpg. Not a trip I would do every week but it is doable.

I have 3.73 in my 68 and even a short trip to the local car show is agony in fourth gear. If your using it mostly on the track they'd be great, if your driving to the track they suck. I'm looking to change to 3.55 or lower.

huh, 'whos this guy'?...looks familiar though....some old jerk

lol

after you have a lot of fun 'racing' it , you might want more fun on the roads too....once you get in to a nice group , if you do...as we have, you might want to go with them on cruises?? we do several every year...to Corpus for a weekend (200 mi ea way) and somether...we`ll be going to Gulfport Ms in October 6-8 hr drive...we went toi estes Park colorado 2 yrs ago...once you do that you`ll regret not having 2.56 or close to it... just my 0.02

When I bought my 68 400 it had a 4:11 gear set in it. The previous owner had it set up (very poorly in my opinion) as a drag car. The 4:11 was useless on the highway. Awesome acceleration but a top speed of maybe 55 mph and constant overheat problems. I changed to 3:73 which was better but still pretty crappy on the highway. Last fall I changed again to 3:55 which was another step up. I still have the great acceleration but now I have an ok cruiser on the highway. I can cruise at 70-75 for as far as I want to go (no more than an hour or two to semi-local meets and shows). In hind sight I probably should have gone with something taller like the 3:08. You definitely dont need low gearing in the rearend with a pontiac motor. They produce tons of torque and lots of low-end power so anything more than 3:55 is likely to give you something you dont really want. Oh I run a 400 4-speed with a 12-bolt posi.

Thanks for all the advice. Looking into 355 now. As far as 200 mile cruises DEFFINATELY NOT in the car. It's got no A/C is hot as ever in the heat. To the track it gets trailered as the closest track is 80 miles away and if I break something I still can get home without paying a ton for a tow truck.

How did your shifter linkage work out? Do you have the factory floor shifter and console?

doubt it. All I know is the car was originally a 326 and the butcher before me threw in the 400

I would go no higher than 3:55 on gear ratio, 3:23 or 3:36 ratios will give a little less performance but will tolerate highway speeds better.

Steve