mug23

I have a decision to make. Here's the situation I have now. I'm building a cup car and I have 2 trans with me. One trans is out of a 924S I believe and I bought it from someone in Cali and it's like in excellent shape. It looks brand new. It drives very nice too and it's has a short 5th but the only problem is, it is a open diff.

Now, I have another trans and this one is from a 1985.5 944 with regular long 5th but it has a LSD in it. The trans came with the car I just bought and not 100% sure of it condition. From the outside, it looks rough as it seems like it's wet outside and perhaps leaking???

So to do the swap of diff from the lsd one to the open diff trans will cost 8 hours from a local Porsche shop I just talked to and they want $800 for the job. That's a bit too expensive I want to do now and I'm not even 100% sure the actual condition of the LSD.

Can anyone here recommend me on what to do? Just install the short 5th trans and call it good or continue to use the long 5th LSD trans? Does the 5th ratio make that much of a difference in lap time on most tracks? I would really like to use the short 5th gear trans as it's in excellent condition but it has a open diff.

Thank you for looking...

pontifex4

I wouldn't install a leaking transmission in a car under any circumstances, and you raise a good point about the condition of the LSD (even fresh stock units don't provide all that much lockup).

I would run the open diff if it doesn't have too much lash, and keep your eyes open for another unit. See if you even end up using 5th at all before you put too fine a point on the short fifth gear.

Charles A. Toupin

Depends on the track and tire size. WGI and Mosport requires the short 5th gear if you're in 15 inches. I could live without the LSD there, although both are preferable.

If you run smaller tracks, favor the LSD.

c.

f1rocks

What tracks are you targeting to run?
Are you racing right away or DE'ing for a while? If you're DE'ing for a while use the open diff and get the LSD rebuilt proper. I can suggest a very good shop and with shipping will be around $2200 but when it's done you have a solid LSD that hooks up like it should.

Many LSD tranny's need rebuilt. So just swapping might not gain you much. If the LSD tranny is good, swap out the short 5th and you have both. You can do that yourself. There is a very good write up. I did it in a couple hours.

mug23

Thanks all for the reply. I'm up in the Northeast region and run mostly in NHMS. This year is mostly DE since I haven't been on the track for 3 years now. I guess I'm just going to put in the good open diff trans in it to and run that. Later on down the road, I may perhaps either rebuild this lsd trans or just pick one up that's ready to go.

Van

I think there is a skill/competition level where the LSD makes a noticeable difference, but you might not be there yet.

I agree with the "put in the 924S tranny" and start building up to rebuild the LSD box properly. At that time you can either move the 5th gear over, or have the rebuilder put in the short 5th.

Matt Romanowski

Call or email Mark at Exotech (603-382-3599 or prschmn@comcast.net). He actually has a couple of those transmissions being done right now and will give you a pretty good price. Plus, he's at almost all the PCA and SCCA days at NHMS. Tell him I sent you.

J richard

Do yourself a favor and put the lsd in the short box. You will find yourself learning to drive the car differently to compensate for the lack of a lsd, both under braking as well as tight corners and sweepers. The NA doesn't have the power to afford soft peddling it around a corner because your picking up a wheel, you need it all to the ground...

M758

I ran with a short 5th open diff box for many many years. I always ran competitively. In fact I won more races with an open diff than the LSD box. I found that in race enviroment I could overcome the open diff, but never could overcome the gearing impact when 5th gear is required. However not all tracks use 5th gear.

Really the best thing is to install the short 5th in the LSD box. Here is a proceedure.

http://944spec.org/944SPEC/technical...-5th-gear-swap

jaje

I ran open diff for quite a while and never really noticed much improvement in acceleration in the dry (I did notice in the wet it did help some). I found the biggest improvement of the LSD in the dry was in trail braking into corners and allowing me to apply more trail brake without rears locking up as quickly as when I had an open diff.

txhokie4life

Our chump car has open diff (924S) -- and in the tighter corners -- you really feel it.

Carousel at TWS, Turn 7 & 10 at Harris Hill Road

Basically you spin it until it grabs. Rest of the time you don't really notice it that much.

Mike

GTgears

On a low powered car this is where having an LSD really shows itself. With a 944 Spec racer the car generally has more traction than power on throttle and in most instances having an LSD isn't going to offer great benefits. The really noticeable gains are going to be under braking.

Sterling Doc

An LSD does not add much in absolute lap times on a 944, but it makes the car easier to drive, and more consistent. Like Joe, I've run very competitively in a open diff car - won one Nationals, and was on the podium with open diff rental car in an 18 car field at Autoclub. The car setup changes, but it's not to hard to adapt between an open diff, and LSD equipped car from a driving perspective.

As for you situation, I'd drain the LSD box. A lot of gearboxes look pretty ratty on the outside from years of hanging under the car. Just clean it up, and make sure there are no obvious leaks when you refill it. If the oil comes out good, and there is not to much gear lash, I'd use that if NJMP doesn't require much use of 5th. If it's got a long straight away, where speeds get up into the 1teens, then the short 5th is the better option of the two.

renvagn

OS Gikin units are suppose to be a piece of engineering art and peformance and not that expensive.

944Cup

Both the short 5th and LSD will help your times overall. Short work to put the short 5th in the LSD tranny.