Rear Diff

rocket7171 · #1 (**permalink**) 03-11-2007, 02:45 PM

FYI,
Just to let everyone know I had vintage motorsports install a 3.64 LSD in my car during winter. Today was the 1st day to check it out. RPM went up as expected 750. This is a great improvement from the open rear with 3.15 gears. I got on it once to check my fuel problem and going into 2nd the rear kicked out for 5 feet.

This ratio will let me use 5th on the highway but also I can still cruise in 4th gear doing 50-60 without pushing the motor and 1st is not a waste of a gear.

tom

Doug I · #2 (**permalink**) 03-11-2007, 10:54 PM

Yup - everything I've read and heard indicates to me that a ratio in the mid 3.5's hits the sweep spot with a TKO and the tires that are typically used. That extra 750 can make a big difference as it keeps the engine spinning above the idle step in the torque curve.

450 horses .... you can chirp 2nd to 3rd ?

Speedysnake · #3 (**permalink**) 03-12-2007, 05:21 AM

Rocket,

I've been thinking about making a similar differential ratio change. What do you mean by a 750 rpm increase? At what speed & gear?

Thanks, Paul

rocket7171 · #4 (**permalink**) 03-12-2007, 07:19 AM

The 750 rpm change is the increase the rear made with the gear change. I checked my speed to the rpm and noted all speeds and rpms with all gears. Then increased my rpm 750 on paper for every gear to see if the increse would be good. I have the other sizes on paper at home if you want them. I knew the 750 increase wouldn't hurt me. There are some that are not happy with the lower rears. I found a great web site on BMW diffs with alot of info. Many questions with great info from the group. Their research was my gain. I can't find the site but I printed out everything before my dell crashed. No bookmarks left.
tom

rocket7171 · #5 (**permalink**) 03-12-2007, 02:39 PM

Here's the numbers that I came up with from a standard 3.15 diff to 3.46=600 plus rpm,
3.64=750 plus rpm, 3.73=840 plus rpm, and 391=1050 plus rpm. These are only for going from 3.15 diff changes. I hope this helps. Jay and Brian can help you locate and install a upgraded diff if needed.

Doug I

Not sure if I can chirp from 2nd to 3rd yet but I think that only depends on the driver. I have to wait for the break-in to further play.

tom

Cashburn · #6 (**permalink**) 03-12-2007, 02:43 PM

Keep in mind this is with a Tremec TKO-500 and not a T-5 or TKO-600.

thunder1 · #7 (**permalink**) 03-12-2007, 03:39 PM

how much for 3:46 lsd I live in fla any ideas
ED

SkipB · #8 (**permalink**) 03-13-2007, 12:04 AM

I am curious as to what the (approximate) cost was on your new 3.64 LSD?

I have been quoted $2450.00 for a rebuilt E36 LSD diff with all new parts and a 40% lockup. This is the diff only and no labor at all. It seems a little bit high to me, especially if I have to add freight from the midwest to California.

Any ideas to save me some money?

SkipB

rocket7171 · #9 (**permalink**) 03-13-2007, 07:56 AM

Keep a eye out on ebay or contact your nearby backdraft dealer for a diff price. Watch what you buy on ebay. You may have to rebuild 1st.
tom

Speedysnake · #10 (**permalink**) 03-13-2007, 08:09 AM

Rocket,

Did you try Metrix Motorsport in CA? I got a quote from them, but never found out how much of a rebuild they do. Do you have any specs. on rebuilding? It might be a fun project for next winter.

rocket7171 · #11 (**permalink**) 03-13-2007, 08:19 AM

Yes metrix is the place. I was able to get mine on a ebay deal. They wanted around 800.00. No specs only complete diff with 40 % lock.
P.S. Winter is over........Look outside.....
tom

cobrak · #12 (**permalink**) 03-13-2007, 10:47 AM

I had Vintage change my rear diff at the end of last year to a 3:64 LS. I have put 500 miles on it. I love it. It was the correct choice and a job well done. They even took care of my leaky CV joints.

cobraK

Speedysnake · #13 (**permalink**) 03-13-2007, 10:54 AM

cobraK,

what engine / tranny do you have? Tire size?

newBDR · #14 (**permalink**) 03-13-2007, 10:56 AM

what advice would you all have for a T-5 with the 17" wheels? To me, 1st - 4th are too short and 5th is useless below 75mph (.68 I think). I'm not sure what my rear ratio is but it's LS. I have BDR031. Just swapping out 5th for a .82 might make me happy.

cobrak · #15 (**permalink**) 03-13-2007, 11:48 AM

Quote:

Originally Posted by Speedysnake

cobraK,

what engine / tranny do you have? Tire size?

I have a 392W and a TKO 500.

cobraK

uncltodd · #16 (**permalink**) 03-20-2007, 07:50 PM

Long story short, #139 did a 11.8 Q-mile granny shifting with 3.23??? rear end last year. Whatever BDR delivered it with, I have forgotten the ratio.

She LOVES 3rd gear after dropping on a bigger carburettor and backing off the timing 1 degree for pump gas.

I swear to God, she will lug from a dead stop in 3rd to the ... legal speed limit... in a heartbeat. Ask my local cops.

Yeah, 3rd feels like 1st on a new TKO 500 shifter when you are pulling out into 70 MPH traffic.

UT

SD5805 · #17 (**permalink**) 03-26-2007, 01:33 AM

Hi guys, I took ownership of my BDR 426 from Jay at Vintage as well in 10/06 It was great speaking with Jay and Bryan about how I wanted the car to be set up. I wanted a driver. I'm also a commuter of about 50 miles one way and sometimes work on weekends, so I wanted a cruiser. They reccomended the 3.46 rear for me originally for a 302, but later went with the 351w crate moter. And WOW, what a lot of fun. And I can even use my cell phone on the highway in the 5th gear crusing along.

GAry BDR426

SD5805 · #18 (**permalink**) 03-26-2007, 01:35 AM

Ohh I forgot to mention, I have just under 2500 miles thus far since 10/06. I even went to Cape Code MA for a few days with her.