Limited slip conversion?

SkipB · #1 (**permalink**) 10-31-2008, 06:30 PM

Guys,

Who has a limited slip differential on your Backdraft? If you converted from the "open" version most are shipped with, what did you go with for gearing? I think the open is about 3.10 or 3.15 ( I have seen both listed as stock). I have a Tremec 1550 and would like to have more acceleration in the lower gears, but it seems I am already shifting out of first very early. Any ideas would be appreciated. Also, if you have done the conversion, please let me know your supplier, but only if you are happy.

Thanks,

SkipB

thunder1 · #2 (**permalink**) 11-01-2008, 06:06 AM

I also would like lower gear , my car does 85 mph in second gear so i also would like to know any info on reblilding this rear end.
ED

mln385 · #3 (**permalink**) 11-01-2008, 06:38 AM

The Standard gear is either a 3:46and I think it was a 3:08.

I have the LSD with 3:46 opition installed by BDR,I also have the Roush 427SR/TW motor with the Tremec 600.

85 is about 2700rpm in 5th.
The rear gearing will depend on your transmission final ratio and your motor hp and tq to get a good combo.

I am happy with mine the way it is set up and for my needs.

Marc

rocket7171 · #4 (**permalink**) 11-01-2008, 07:15 AM

I switched mine out for a 3.64 ratio. Could even went up to a 3.73. I still don't use 5th unless I'm on freeway doing 75mph. The best thing is to buy another unit from a good company that does the rebuild. I happen to find a good deal and had it sent to Jay at Vintage and had them install it.

Here is a great web site. Use it to find your ratio. Alittle research on your speed and tach and you will have the perfect ratio.

www.diffsonline.com/techinfo/index.shtml

I hated that my car would only spin one tire unless I unloaded it. Now you better hold on. Yee ha

Good luck
tom

Dinobyte · #5 (**permalink**) 11-01-2008, 01:35 PM

Skip,

I would recommend the 3:46, since you have a 351, and I am assuming around 400hp. It won't be too low for driving on the freeway at 65, and will give your motor the torque equalizer advantage off the line. If you want to go gonzo, the 3:73 is the way to go.

With the LSD, you will notice chirp when going around tight corners, as both wheels will want to keep turning.

Cheers
Michael

MrMagoo · #6 (**permalink**) 11-01-2008, 02:39 PM

I swapped in a Quaife ATB unit, with 3.73 gears. This works quite well for me. Hooks up really well off the line, and the rear tends to stay planted when accelerating out of the turns.

Pulling and installing the differential housing is doable by yourself, you can ship the whole thing to a shop and they'll swap in the new differential with your desired ratio.

JayBar · #7 (**permalink**) 11-01-2008, 06:38 PM

I had the stock gears 3:10 with an open differential. My engine was a warmed up 351 that dyno'ed at 325 RWH. I ran a 12.2 sec at 116 mph.

A while later with a 408 engine dyno'ed at 426 RWH I had a 3:73 with two clutch packs installed. With the same tires I did a best of 12.2 sec at 122 mph.

So what does that mean? I don't know, the 408/3:73 is a great track combo but on the street who knows?

SkipB · #8 (**permalink**) 11-02-2008, 10:02 AM

Thanks for all the input. I am going to check out diffsonline and see what they have to offer. I do have a 351 with about 400hp, so perhaps the 3.46 is the way to go. I too would like to lay two stripes of rubber instead of one. Is this my carbon footprint? Ha!

SkipB

jp65cobra · #9 (**permalink**) 11-03-2008, 12:16 PM

Skip,

I saw a few posts on the Backdraft Boys site and some guys have used http://metrixmotorsport.com/. They are in CA so I was going to check them out. Apparently they know our cars and they are good to work with and will help with recommendations.

John

cobrak · #10 (**permalink**) 11-19-2008, 10:14 AM

I switched to the 3:64 LS. I have a Roush 427SR with TKO600. I love it. I got my diff from Jay at Vintage.

CobraK

round_midnight · #11 (**permalink**) 11-20-2008, 11:28 PM

Skip-
I just saw this thread, but thought I'd chime in, even though it may be too late. I have gone with substantially shorter gears in my diff than the other responders on this thread. I bought a 3.91 lsd from a BMW recycler in the Bay Area called Bavarian Auto Recycling. It is the stock diff from a 1993 325is coupe and cost $539 including tax and shipping. My motor is a Windsor stroker that puts out 400 rwhp at 5500 rpm. It is mated with a TKO600, and gives shift points that are around the same as for my BMW M3. The acceleration is awesome (my data acquistion says .6g) and the price was much less than the places that do custom diffs.

There are a couple of downsides. 1) I'm sure such short gears are one of the things that is killing my gas mileage. 2) During hard track driving, I get oil being pumped out of the vent hole, so I need to improve the cooling, either with an external cooler or a finned cover, which may negate some of my savings by using a recycled stock unit.

Hope that helps a little.

(the other Skip)

SkipB · #12 (**permalink**) 11-21-2008, 09:30 PM

Skip,

Thanks for the input. I haven't done anything yet. But, I like the idea of spending less! I am not too concerned about gas mileage. I just want to lay down two stripes on the pavement when I take off! Nothing more, nothing less.

Skip

Ps. Great name, BTW!

Randy Moudry · #13 (**permalink**) 11-22-2008, 08:23 AM

Switched mine out to a 3.73 Vari Lock from Metrix in CA. Mated to T5 with a Roush 402SR-TW.

Mac VABCH · #14 (**permalink**) 11-22-2008, 09:11 AM

Skip,

I did this myself and it was easy and cheap. First find out what gear you have. My car came with the 3.6ish gears. If you are ok with the gears you have its very simple. Find a used LSD on e_bay or Craigs list or from a salvage yard. I got mine from a salvage yard. Just swap out the lsd for the open. Your must make sure that you use the end caps that the axles bolt to and shims from the third member that the gears came from. This is what sets the gear pattern. There are shims between the end caps and the housing, make sure that you that the end caps and shim stay oriented left to right. The other issue is the speed ring. Just make sure the speed ring matches the gears that you use.... This cost me less the 300 to do the whole swap...PM me if you need anything....Mac

native1 · #15 (**permalink**) 12-07-2008, 07:14 PM

I have 3.64 gears with 80% lock up diff from Metrix Racing. Also went with polished gears and solid mounts. I think it is perfect for my Roush 427 srtw T56 package. 6400 rpms = 65 mph 2nd gear. If I were to do it again I would consider 3.73 gears. I love the way they pull with lower gearing. Regg told me he runs 3.91 gears in his race car but his motor is a 7000rpm+ screamer. Just my 2 cents.