Opinion on Diff Gear
Thread Starter
NCM Grand Opening Veteran
Joined: Sep 2005
Posts: 20,979
Likes: 384
From: South of giving a damn
St. Jude Donor '11, '17
Opinion on Diff Gear
79 in the barn (keep finding the damn thing there, must be a barn find)
396 SBC built & ready & a TH400 will sit behind it (out of cash for a 4speed) Hopefully this will make close to 500hp, anyway rear gear is supposed to be a 3.55 but turns out bubba swapped in a 3.08. I have sourced a 3.55 & it needs rebuilt anyway. Should I stay with the 3.55? I'm leaning towards a 3.70 myself as this will be a weekend car with very few, if any long hauls.
What says the forum?
396 SBC built & ready & a TH400 will sit behind it (out of cash for a 4speed) Hopefully this will make close to 500hp, anyway rear gear is supposed to be a 3.55 but turns out bubba swapped in a 3.08. I have sourced a 3.55 & it needs rebuilt anyway. Should I stay with the 3.55? I'm leaning towards a 3.70 myself as this will be a weekend car with very few, if any long hauls.
What says the forum?
Burning Brakes
Joined: Feb 2009
Posts: 780
Likes: 1
From: Shelby NC
79 in the barn (keep finding the damn thing there, must be a barn find)
396 SBC built & ready & a TH400 will sit behind it (out of cash for a 4speed) Hopefully this will make close to 500hp, anyway rear gear is supposed to be a 3.55 but turns out bubba swapped in a 3.08. I have sourced a 3.55 & it needs rebuilt anyway. Should I stay with the 3.55? I'm leaning towards a 3.70 myself as this will be a weekend car with very few, if any long hauls.
What says the forum?
396 SBC built & ready & a TH400 will sit behind it (out of cash for a 4speed) Hopefully this will make close to 500hp, anyway rear gear is supposed to be a 3.55 but turns out bubba swapped in a 3.08. I have sourced a 3.55 & it needs rebuilt anyway. Should I stay with the 3.55? I'm leaning towards a 3.70 myself as this will be a weekend car with very few, if any long hauls.
What says the forum?
Burning Brakes
Joined: Jul 2005
Posts: 866
Likes: 1
From: Northeast Ohio
I agree. 3.55 still give nice performance but can get you by on the highway if you do take a road trip. The little gain with the 3.73 is not worth the RPM's you give up on the highway.
Melting Slicks
Joined: May 2005
Posts: 2,209
Likes: 12
From: Montgomery Alabama
Cruise-In VII Veteran
St. Jude Donor '06
For your situation, you won't need any more gear if you truely put 500 HP to the rear differential. What you will need is one of Gary's Super 10 bolts or a 12 bolt with the bigger axles, u-joints, and half shafts.
Do what I did, drive it until you break an axle, then build a better one.
I went from a 3.36 to a 3.73 in my 72 (warmed over ZZ454). I had already installed the TREMEC 5-speed.
I got a little more umph out of the hole, where all I had before was tire spin anyway. First is basically useless at the dragstrip.
The place I got the best bang for my buck was from 55 to 120, where I can hold my own against a C6 with the LS3 or a new Z06.
When I shift from 4th to 5th (0.64 OD), I wave bye, bye and watch them get smaller in my windshield 
If i had it to do over again, I would get the 0.82 OD TREMEC and stay with the 3.36 rear gear.
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
It really depends on your bore and stroke combo. Short stroke = short gear. Long stroke = tall gear. Also your cam duration plays a big role.
Don't plan on re-using the 3.55's if they are the stock GM gears. Because of the 9 32 tooth count most likey the ring gear is worn out. New 3.55's use a 41 tooth ring gear.
Mike
Don't plan on re-using the 3.55's if they are the stock GM gears. Because of the 9 32 tooth count most likey the ring gear is worn out. New 3.55's use a 41 tooth ring gear.
Mike
Safety Car
Joined: Sep 2005
Posts: 4,056
Likes: 99
From: Southeast, Tennessee
St. Jude Donor '09 thru '26
also. unless all you want to do is drive around city streets in a rather sedate manner, stay with the 3:55. if you want to build a cruiser, go with a 3:36 set up for the gas mileage. give a little on the slower end, but it will cruise like a dream. pick your poison based on your intentions. if you are going to track the car, you actually might want to consider the 3:70 otherwise, not a good choice in my opinion.
