[389]

I would put a 2.75 first gear set in the Th-400. With the 2.56 and a long stroke engine it will preform nicely.. Run a nice 068 or a Nunzi 2042 if you can even find them..

[geeteeohguy]

Originally Posted by 389

I would put a 2.75 first gear set in the Th-400. With the 2.56 and a long stroke engine it will preform nicely.. Run a nice 068 or a Nunzi 2042 if you can even find them..

I'm running just the stock 2.48 first gear set in the TH400 in my '67 with the stock 400 engine and the 2.56 and it's fine for a cruiser. I agree that 2.75 would wake it up a bunch from the dig. But 2.56 rears came with straight 6 and 326 powered A bodies, so a 389-400 really has zero issue pulling that gear. My 400 is a 9.3 CR with an 068 cam and runs great.

[PONTIAC LARRY]

Originally Posted by JLBIII

Currently have 2.56 gears and Saf-T-Trak rear un my 68 FB with 400HO and TH 400. I'm looking at replacing gears and carrier to either 3.36 or 3.55 and the correct posi unit. Plan to eventually put in an OD. Which would be the better street gears for the 400HO engine? Thanks

Assuming tire wheel combo is close to stock sizes. I am partial to less is more especially since TH400 stays a while longer. The next series gear OEM is 2.93/3.08/3.23 and a good set of any of those is a solid improvement but still good drivability with 3 speed AND with a a ring spacer one could retain the 2.56 Safe T Track unit if its in good shape currently. The new Eaton posi is in the 3.36/3.55 and up series and either of those ratios is probably perfect WITH the OD but also a new Auburn can be bought that fits the 2.93-3.23 gears.. Used open gear set is pretty easy to find cheap in decent shape. For me the final answer is 3.23

[Skip Fix]

On my old 64 Impala tipping every ring gear bolt out because there was a spacer(did not know about those until then) I'd sure pass on doing that. Buddy in college had a 64 GTO put a wagon 2.56 in to get batter gas mileage going from College Station to Dallas. I swear idling in first gear was 20 mph!

My 78 TA had 2.56s for a long time and for just a street car they were OK. mid to high 14 second 1/4 miles, barely in 3rd.

[389]

You have an excellent drivetrain. The 068 is an excellent cam for a Pontiac street mill. We used to get the Nunzi version of this cam called the 2041..

There is an amazing amount of power just sitting there under your hood, get a custom torque converter. You have an excellent drivetrain. 9.3 compression is perfect. Use only 87 octane I like B.P. A higher octane will make the engine run slower. I used to tune them and get them run real strong. First thing is keep the points distributor, disconnect the vacuum advance and screw down the points plate. Next set the initial to 20 and the mechanical for 16 to 18. Have it all in by 2000 rpm, this will work so well with the 2.56.. Next pick up a CD box. I like the Vertex Z-6. This will give the ignition some real power. Unless you want to run a Magneto. I ran one on a 389 with dual quads back in the seventies. I got it for nothing, it was a Ronco..

Hurst made the best automatic shifter for the Turbo 400 called the Autostick I. I use them in all my Turbo 400 cars.. They bolt to the transmission and have direct linkage. They look just like a four speed too.. This is the Autostick I in my 69 el Camino SS396 TH-400. It shifts as well as it looks.. I also had one in my 64 Bonneville..

These places are were you should be at with your car. The driveline is perfect!! It just needs some tuning.