[MRGTO2U]

Hello everyone, As a novice I am learning so thank you all for your patience. I have a 68 GTO with a 428 4 bolt main. When I bought over eBay last Jannuary, the owner stated everything was new or rebuilt. Bologna!! The Turbo 400 was sluggish and chattered in reverse. I just paid $800 had it rebuilt and put a B&M Mild Street Shift Kit. What a change!!!! Now for the rear, it has a 8.2 10 bolt 2.78 open. I want faster acceleration (Launch) from 0-70. My mechanic say's thae best and cheapest way to go is a Auburn Posi with 3.55 Richmand Gears plus the kit. About $700 W/O labor.
I dont want a highway car. I have a 2000 Lincoln that cruises at 100 MPH and it feels like 60.

What are your thoughts???
Thank you.

[86t/a455]

I wouldn't go lower than 3.55, the 428 makes lots of torque so anything lower than that would not take full advantage of this

[Half-Inch Stud]

Get a cheap 12-Bolt or:
Buy a $2000 Dana60 from Strange Engr.

a 428 68GTO ought to be worth it.

[MRGTO2U]

Hi Allen , Could you be a little more specific? Do you mean 3.55 or above would be better/ Like a 3.73?

[mr68]

I personally think you will out grow that 8.2" faster than you think. Look for a 12 bolt and be done with it. I would stick with the 3.55 gear set any more and you will not use all the torque the 428 will make.

Before I would use the Auburn unit check out the Eaton carrier. I used the Eaton unit and love it.

[runningbwdog]

Hi,
You also need to consider rear tire tread width.
If you run 195 to 205 width tires on the rear, all you will do is smoke the tires with 3.55 or higher diff ratio. You will probably need 245 to 265 width to handle the bottom end torque. My 455 with 4-speed and 3.55 will spin the tires in first gear at any speed below 40 mph with wide open throttle. I'm saving for a set of 15x8" Cragar SS mags and BFG 245-60-15 tires.
Mike

[JoePapa]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Half-Inch Stud:
Get a cheap 12-Bolt or:
Buy a $2000 Dana60 from Strange Engr.

a 428 68GTO ought to be worth it. </div></BLOCKQUOTE>


I've got a Dana in my car too - dang nice!

[MRGTO2U]

Ok runningbwdog but as it is now, I do nothing but smoke the rear right tire with the 2.78 open. When the tire gets grip is what I'm not to happy with. All that power and she is really not that fast launching. I agree, I have 235-60-15 and I need a wider tire. But my question remains will I have better acceleration. I know about the 12 bolt but my budget decides not me...

[Half-Inch Stud]

JoePapa,

Ya know...I looked at a Black 1976 T/A a few roads away with a Dana60, 4speed and a Jim Butler 400 engine. $6000 asking, good paint and turn-key condition. I didn't have the interest in another "F-body" after selling the 69Firebird.

Technically & practically, I shoulda bought it to drive, then resell when the 68GTO got on to the road.

[CH3NO2 Pontiac]

Roger Hanska (Ol'Pinion Head). He'll steer you right.

Send him a private message.

I doubt he'll be able to tell you how to mount your upper control arms to the Dana center section, though.

[runningbwdog]

Hi,
With a posi both tires will be driven. That means twice the effective tire patch area. With an open diff, you are not using the undriven tire for anything but keeping the car level. You should see a big improvement with your acceleration once the posi is installed. The next problem you may experience is rear wheel hop when you WOT. That depends on a lot of factors such as weight distribution, tire grip, shocks, anti-sway bars and traction bars. Others on the Forum can help you solve those type of problems.
Mike

[86t/a455]

JG, I would not go lower than 3.55. (3.73, 4.10 exc) The gearing is essential to keeping the engine in it's torque curve. If you were to put in 4.10's i think you would find traction to be non-existent and at the end of a 1/4 the 428 would probably be gasping for air and out of its prime operating range. I know everyone has different setups that work but this is just my opinion

[MRGTO2U]

I agree Allen, as it is now when it reaches about 52-5300 RPM (according to the original Tach in the cluster) she's done! I need my max acceleration power before that point.
Thanks.

[86t/a455]

Another point, the 400 turbo has a high 1st gear which doesn't help takeoff and makes for a wide jump in gear spacing. with my car i found even with 3.73 (that i hate) and the 400, i have to slightly over rev 1st to compensate for second. 350 turbo's are better for the gears but durability becomes an issue

[Shadowjack]

Ratios on a TH350 are 2.51, 1.52, and 1:1. TH400 is 2.48, 1.48, and 1:1. I wouldn't call that much of a difference. It's the 700-R4 that has the big spread from low to second.