[66 joe]

In my 66 goat w/455, Ive got a t400 attached to a chevy .308 open rear.
(converter is approx 2400 stall)
This car is mostly street, probably never strip. I do like the freeway cruise 60mph @ 2500, but just starting to wonder, if I'd get more with better gearing and is it worth it.
Was thinking of 343-351 something like that.
And what recommended route should I take as far as changing this rear?
Thought I'd start checking around before spending $$$.
Thanks, Joe

[TTS]

Your signature says Ken B built your engine. I'd call him, he knows the engine and can put you down the right path.

3.08

[steve25]

I would not change the 3.08 gearing at all then, just get a new Auburn posi unit for better hook up of your 455 power when you hit it.
One thing to watch out for though with those long body models and a posi rear is fish tailing on a wet curved roadway under high torque!

[RAIV55]

Been considering changing out my .308 to a .338 WM. Hear it's a good elk round....

[66 joe]

I do remember asking Ace, "is my open .308 gonna handle the torque of the new 455?"
and he told me, "should be ok, cause it wont grab" He was right, very easy to break tires (or in my case tire) loose. Probably will start looking into POSI and one friend told me to look in chevy 12 to replace my 10. and should bolt right in
Joe

[95ramairformula]

When you go with a posi 3.08 and a 455 the massive torque will easily break both tires loose. I doubt the rearend will break since the tires will always break loose first. Now go with Drag radials and you might start breaking drivetrain parts.

I remember over 25 years ago a 455 1970 GTO auto with 308 gears. It was monster on the street. I remember him feathering the gas off the line and then nailing the gas at 40 mph and breaking the tires loose. Gotta love the torque.

[66 joe]

Ill more that likely stay w/.308 and look into just adding POSI.
Should I just upgrade the chebby 10 bolt I have now. (is it 10 bolt or 10 inch? all I know its the smaller rear end)

I do like the .308 on the freeway too!!!

[440GP69]

na .338wm is too much for anything in the lower 48, 30-06 or .308 is great!, your 10 bolt is 8.5 inch ring gear if its chevy or 8.2 if its a BOP rear

[TTS]

Originally Posted by 440GP69

na .338wm is too much for anything in the lower 48, 30-06 or .308 is great!, your 10 bolt is 8.5 inch ring gear if its chevy or 8.2 if its a BOP rear

I resisted at first. I was thinking .260, it's the same action length, can reach 1000 yards with more energy, with less wind drift and still take Elk inside 300yds.

Probably a 8.2 10 bolt

[scott cedergren]

In your 10 bolt it will matter what year the rearend is on the size of the ring gear. You would be better off finding a 12 bolt and setting it up as you need it. If you want to run a different gear do it then. I hate to see people pour a bunch of $ in a ten bolt with a 455 and break it. Do it once and never look back.

[78 GHOST]

I run 3.08 gears in my '70 GTO with a 12-bolt. I think a 10-bolt is OK, unless you start running slicks or a stick which hammer the piss out of the driveline.

I think the idea is to get a posi in that thing, I installed a Detroit True-Trac which was easy to install assuming you have the right tools. The "right" tools can add up to some serious coin, and you might be much better off having a professional set things up for you.

I also don't think there is any percentage in doing the posi install without replacing all the bearings and seals.

[Stuckinda60s]

One advantage to longer gears is that they're actually stronger. A 3.08 will be a lot stronger than say a 4.11.

I really like the .264 WM, myself.

[66 joe]

Since time is not a factor, I think Ill start looking for a 12 bolt.
Now, am I looking for a 12 bolt chevy/gm, or is it a 12 bolt BOP.

For my .308 magnum!!! lol,, make 1 mistake and NRA takes off

lol,,,,,,,,,Joe

[78 GHOST]

Joe, any "A Body" GM 12-Bolt will work. Just double check the dimensions flange to flange to ensure you don't buy something too wide for your GTO.

If you're going for ultimate affordable strength, Moser makes a complete 12-bolt which comes all set to your specs for high teens to just at $2000 depending upon your optional choices.

You can also get a Ford 9" configured to bolt into the GM A-Body platform. The Ford 9" is slightly more HP hungry, but very strong. My favorite of this diff. is the ease of changing rear ratios. You could have one diff. with steep dragstrip gears and another with tall highway gears, and swap back and forth with little effort.

I guess these ideas are just another way of asking: How much do you want to sink into this?

Personally, unless my 455 was very wicked, I'd strengthen up the 10-Bolt, have a True-Trac professionally installed and go from there. You can install some goodies to beef up the 10-Bolt and it would be suitable for a mild 455. I think you could probably do this for under $650 if you find a shop with a reasonable rate.

[Skip Fix]

Been considering changing out my .308 to a .338 WM. Hear it's a good elk round....

I was thinking more .50 cal

[440GP69]

should have seen the look on my local gun range guys face when i carried in my friends Barret 50 cal sniper rifle, LOL all he did was point back out the same way i came in lol!!! i said what its just a 50???

[Skip Fix]

Shot a buddies sniper .50 cal bolt action-quite the recoil.

[440GP69]

yeah it will grab your attention real quick if you don't shoot one regularly!!

[66 joe]

Im pretty sure my 10 bolt is a chevy model, being perfectly round without those little tabs on the BOP. My car will probably never wear drags or see a track, so I do like the idea of beefing up what I have. especially if its under say $750
I shouldve proof read what I wrote, being the owner of a .22, .243, 30.06, .40

[scott cedergren]

Remember not all "12" bolt rearends are the same. Some have a 12 bolt cover and a 10 bolt carier, be careful. Always open a rearend and count the ring bolts.