DFASTEST951

I am mostly on the street but want to be able to do well should the car ever hit the track. I'd like the best of both worlds as I drive the car hard on the street. I've found the tranny, but I've been talking with Chris Cervelli. He has sent me the actual data on the rpms and what speed I'd be at with both. The guy really knows his ****. 6th is a tad shorter than the 951 5th. Looking to get slightly taller without losing to much space in the powerband. The Audi gears sound good and I'm sure a hell of a lot cheaper than going to Powerhaus II. Anyone know where to get the gears? Also, how about some information on the lsd that Jet uses.

AL951

Hey joe Why don't you jest get a taller final drive and be done with.

I think the factory spacing is petty good, so why mess with a good set up. Save the money and get your self a high quality LSD, a final Drive set. this will give you alittle better fuel economy too.

Regards,
AL

DFASTEST951

AL951, man....that's what I'm trying to do. That's exactly what I want to do. I just want to make sure I don't get a final drive where I leave a hole in my power band or get one that made such a minimal difference that it wasn't worth the extra time and money to do it instead of just throwing it in and calling it a day.
I'm almost there though. This thread and all of you really helped me out a lot. Thanks. Now who knows who I need to talk to about looking into the audi stuff and most importantly, a gearhead who knows what gear I exactly want for my car's power. Thanks again guys.

Robby

Changing the FD & keeping stock gears the same will not leave a hole anywhere- it will merely lengthen all gears proportionally. For instance, if you changed the FD so that the overall ratio in 1st is 10%, then each gear will be 10% different, not just 1st. So, 1st becomes 44 instead of 40 & by the time you get to 6th, it's more more like 179 instead of 163... Again, all my #'s were done at 6500 b/c that's what I assumed the 968 to redline at- depends on individual redline- your engine is so tricked out that it's redline may have changed(?). This will make's gears seem even taller. The 3.22 idea was pretty cool- Powerhaus II was doing it, so they'd be the ones to know if it's still a go. Did you like where the 3.22 put the redlines? The Audi gears may open up a new world of possibilities, either w/stock FD or 3.22. The math, to figure out gears or FD changes, is pretty easy- just need to know where you want your redline speeds to be in each gear & what # your redline actually is...


Nick- I'm sending you a PM....

AL951

Exactly my point Joe. If you change the FD like Robby said, it wouldn't make changes or holes bettween gear shifts, it is just taller all the way from first to six. It is good because it will give you a better of the line load and boost.

Regards,
AL

Robby

Yes, most NA's want shorter gears to come off the line, but turbos like taller gears to build boost- like getting more boost in 3rd than in 1st & 2nd- gearing can be a fine line, but w/the your TQ, you can definately go taller- like big-HP Vettes & Vipers. 968 gearing was sort of strange, but good for track- the top 2 are short & could almost stand to be changed no matter what you do w/the FD, so if Audi gears work, like Nick suggested, they're the answer, especially combined w/taller FD. The custom FD would be much cheaper than custom gears too- you'd pay $1800/gear! And the only way to change 1st is w/a taller FD. Someone here (5 or 6 pages ago) said you could change 1st, but it was WAY too expensive- when I talked to PHII, they said it couldn't be done- maybe it's just a case of huge bucks & isn't worth it...

Duke

With a bit more free time this could be calculated, but I suspect that in a highly modified 951 (400+ rwhp) you are better off accelerating att full throttle/full boost than changing gears more often.

Sure the acceleration at full throttle is better with lower gearing but remember that during every gearchange the car actually slows down. Not by much but my point is that the acceleration ceases during shifts.

JET951

the LSD we use is made in melbourne australia. i currently use a 80/60% on my LSD, these are very high quality products, some of the best ive seen. these are much more robust then a lot of the other aftermarket LSD available. they are the only clutch plate available for our 951s with 4 cluch plates. they do not "wear out" as fast as the twin plates. that was for the 5 speed. they also make a a 4 plate for the 968 6 speed, which as said before is the same as a G50 LSD. the manifacturer of these LSD makes extremely high quality gearsets for Ferarri, Porsche and Audi, also custom gearing. but if you want custom that takes time. these guys are in demand. their main market is export to America and UK. we are currntly about to put an order in for 2 951 80% LSD and a 1 Torsen LSD for a 944. as pricing goes the 80% is about $2500 AU
the torsens are on special for about $1500 AU
and the G50 is around $3000 Au
all the manifacture is done in house. the housing is a one piece work of aluminium art, with their own clutch plates, spring plates, intermediate plates and planitries. these might seem expensive but ive believe they are well worth it.
sean buchanan

Oddjob

Who is the manufacturer in AUS? Website/link?

Really only Guard offers an aftermarket LSD (Clutch Type) in the US, and I have heard the rumor is that the Guard units may be the same as this AUS made unit. Not sure if I picked that up from you, or where I heard that in the past (it was on rennlist).

The housings are alum?

Oddjob

I don’t think you can make the claim that no factory 944 LSD is still close to the original 40% lock. Wear has nothing to do with age, and all to do with mileage and usage. A 100k street driven LSD will still have significant lock left, but a 25k track only, may be completely worn out.

There have been premature wear problems on the LSDs used in certain 964s and 993s, even on relatively low mileage street cars. But I have not heard or seen similar problems with the 944 series LSDs. I believe 996s have seen a few failures/cracking of the factory stock/street differential cases (cast part). That is why there is a recommendation of using the Motorsports diffs (from the 996 Cups and/or GT3R series cars), which is supposedly a machined billet or forged part. But there is no Motorsports differential available for the 944 series.

I disassembled and checked an LSD out of a 135k ‘87 951. Friction discs were still ok, and the slip torque was still within factory specs. If you read the factory manual it shows how to check it – put one end in a vise, and turn the other end with a torque wrench. Need to make a little fixture to do it, but very simple. A quick guess is that you could also check the slip-torque with the trans installed. Put the trans in neutral, lift up the back end, block/lock one wheel (figure out a way to safely do this), and put a torque wrench on the opposite side wheel hub nut, and see how much torque it takes to start turning the wheel. But note, this is checking the unloaded lock. To check the loaded lock, you would need to turn the trans input shaft.

In the end, I think that the percent lock rating on LSDs is a bit arbitrary. Fully open (0%) or fully locked (100%) is obvious, but what is 40% lock? It allows some locking and some slippage. An 80% lock, allows less slippage. Really, the torque that is required to make the output shafts spin independently of each other is what needs to be measured/compared. But that can vary based on many factors, including what trans fluid is used. So its ballpark number, or a range (like what is given in the factory service manual).

So I don’t think you would notice any difference between a 40% and a 50% lock, certainly not enough to justify the expense of buying custom replacement guts for your existing ZF LSD.

For a dedicated track car, you may want to play with other %’s for both loaded and unloaded lock. But I don’t think you need a higher lock than a “40%” for the street. And its interesting that the 964 Euro RS’s and I believe the 964 Turbos use a 20/100% LSD – although the rear engine weight bias loads the rear wheels differently than a front engine car, its surprising that Porsche determined that a low loaded locking diff (20%) was sufficient for the relatively high hp/torque 3.3 and 3.6 Turbo motors.

JET951

yes the housings are alloy. the manifacturer company in called....... im not sure who makes the LSD for Guards

Oddjob

It would not be Modena then, the Guard units are chromoly steel.

Robby

Jim- good points- my wording may have been a bit harsh- the typed word loses a bit... But in all honesty, I was considering that most of these cars do have some mileage on them & I would think that most of the harder driven street cars w/average mileage (average to the 944 world) have lost at least some. But the main point I wanted to make was not to assume your car has a full 40%- it might, but for ex, let's say one's LSD was almost completely worn out- for #'s sake, let's say it was down to 5%. But let's say they didn't know it was worn & assumed it was doing fine at 40%. Then, they go to rebuild the tranny for other reasons & decided to upgrade the ZF b/c "40%" felt weak, & went to 80%...? One might end up a very unhappy camper. Kind of what you're saying- don't get stuck on the #'s too much. Personally, I wish I understood how the #'s worked, a little better- all I know is 0% is fully open & the closer one gets to 100%, the more locked it is...

As for going to a 50% from a 40%- I'd only recommend considering such a minimal change IF the trans was already being pulled to rebuild to begin with.

I had no idea the 964's were 20%- based on the fact that our cars started at 40% & 968 turbos were 60% (based on what I've read), I'd think they'd be higher than 20% despite their completely dif layout- I wonder how those cars did, coming out of corners, etc, compared to 951's, etc...?

DFASTEST951

I'm on overload taking all this in. What is the currency exchange for Australia. Jet, do you have an idea on how long it might take to get here?

JET951

it depends if theyt have them in stock. i think we are 75cents to your dollar. if that makes sense.