Custom Gearbox Recommendations

[Matt_West]

My car is a 1980 911 SC with a nice list of mods. In keeping with the upgrade when possible theme I am thinking about gear box options.

I will be having the gear box opened for synchro work. When opened I would like to make sensible improvements. I have decided on the Wevo internal shift gate. Here is where I need your experience or well considered thoughts.

I am interested in:
1. Parts recommendations
2. Parts costs
3. Parts Suppliers (Pelican Preferred when applicable)

The car does not have a limited slip. I have never had a car with a limited slip. I drive like a hooligan, like to go to the track, and enjoy auto cross. Would you recommend a limited slip if so please answer the three items above.

Secondly gear sets... What to do??? I found Steve Weiners sage advice below and would love an evaluation of it juxtaposed against my intended usage.

I like the idea of modifying the gear sets because people say things such as "feels like fifty horsepower". I use the car for daily commuting. Mostly country two lane roads. Don't spend much time on the highway. Tend to keep at least 3.2k rpm on the tach for a more immediate throttle response. Given the track I most commonly drive at, top speed of 135 to 140 should be adequate.

Also if you think I should do something like cooling let me know.

Thanks for your time and input!

Here is Steve's general recommendation:
As an example, here is an excellent and economical gear stack for a street-driven 911SC or Carrera 3.2 with an 8:31 and 25"-26" tire.

1st Gear- 11:35 (stock)

2nd Gear- 15:30

3rd Gear- 21:31

4th Gear- 24:27

5th Gear- 28:24 or 27:24

This is a very streetable gear stack that will make a big difference in acceleration!

[Elombard]

Or just slip in a 7:31 R&P and get most of it. Why not LSD? If your up for spending the bucks, the factory type are the best I think because they work on decel and accel. Unless your running big HP the accel is not that important to me. I dont break traction that much if ever on accel. I am sure Steves recomendations rock and close gears are fun but for most street driving maybe not that important. Cooler?? again no big HP and long track stints probably not that important but for ultimate reliability...its only money :-))

[Jack Olsen]

In your shoes, I'd put a 40% ZF LSD, plus the Wevo shifter and coupler higher on the list than gear sets. Aftermarket gears are not as quiet as the factory ones, which can make a difference in street driving. A cooler is important if you track the car, IMO.

How often do you track it? What kind of other mods have you already made to the car?

Speaking from experience, close-ratio gears don't feel quite like 50 hp -- but they don't feel bad, either.

[Matt_West]

I have my third track event scheduled as of now. So far I have hit every local event since my first one that I was eligible for Who knows I might be irrationally attached to the car...

As regards the other mods:
1. Poly bronze bushings throughout
2. Sanders torsion bars 22mm & 28mm
3. Elephant racing monoballs F&R + Triangulated strutbrace
4. Wevo: Shifter, PSC, Motor / Trany mounts, and Battery box
5. SSI's + Monty 76mm single outlet muffler (Sounds right)

Aside from maintenance / baselining a 20year old car eg replaced all pads, rotors, and soft brake lines... I have done silly things like: removed entire airconditioning & reversed wiper blades.

After tranny things on my list include:
A. Sway bars
B. 8&9 inch Fuchs
C. Brakes
D. High compression / Individual throttle body / twin plug ignition engine
E. Paint

[rdane]

Here are some more ideas for you Matt..

ENGINE:
100mm Mahle Pistol and cylinders
Electromotive crank fired dual plug system
ARP head studs
Solid film lube on piston skirts with ceramic tops
Boat tailed engine case
Half mooned cylinder skirts
3.2 Carrera crank (giving a 3.5 liter displacement)
Pauter billet light weight rods and rod bolts with 23mm wrist pins
EBS HD value springs and Ti keepers
B&B stainless front bumper oil cooler New preasure sender and oil tank sender
Turbo camshaft oil line restrictors
Clewett dual plug wire set
Turbo value covers
OEM Club sport mounts on the engine
Pre 1974 oil lines
High Torque IMI, light weight starter

TRANSMISSION:
OEM Club sport mounts on the transmission
Close ratio new gearing long 2, short 3, 4, stock 5th
ZF 80% limited slip
Sachs Power Clutch
Fidanza aluminum high Performance flywheel (59% lighter)
WEVO short shifter and coupler
WEVO internal gate

BRAKES:
Braided stainless steel brake lines
SCI 930 brake conversion from a ’86 with slotted, floating front calipers and OEM cross drilled rear rotor
New 930 master cylinder

SUSPENSION:
Elephant Racing triangulated cross bar
22 front with 30 rear, Sander's hollow T bars
22 front and 21 rear stock OEM ‘86 Carrera sway bars
Elephant front mono balls
Elephant polybronz control arm bearings
Elephant low friction control arm mounts
Elephant rear monoballs
Wevo spring arm plates with steel bearings
Bilstein sport shocks
new ball joints
Turbo Tie rods

[Bill Verburg]

Here is a graph showing the effect of the proposed gear stack

7000rpm rev limit
25.3" tire
8:31

using the taller 28:24 5^th

stock 915/63 on top, proposed on bottom


here is the stock 915/63 w/ 7:31 instead of the 8:31, all other relevant parameters are as in the previous set

[Matt_West]

Thanks for the replys! Some questions / requests:

Limitted Slip:
1. Is the ZF style a clutch type? (As opposed to a Torsion style)
2. What is more cost effective Guard or Factory?
3. Where do I source the part?
4. How much should I expect to pay?

Gears:
1. Who can supply the ring and pinion?
2. How much is it going to cost?
3. I believe there are variations on the R&P, is there a particular one I want
4. Does anyone make a quality aftermarket R&P
5. Bill would you please post the graphs a little differently? (Bring each gear down to the origin and set the shift point at 6.2k RPM)

[Matt_West]

Details of Steve's suggested stack:

[Geary]

I wouldn't recommend an aftermarket 7:31 R&P, when factory ones are readily available.

The latest Guard LSDs are so advanced, it would be silly to spend nearly the same amount for a factory ZF.

[Matt_West]

Gaurd appears to make two varieties, is on preferred over the other?

[Geary]

The GT LSD set at 50/80 is the most popular for track, while the TBD may be better for autocross. Guys wanting to do both usually opt for an LSD set at 40% (40/40).

[Elombard]

I think Andial sells a 7:31

[RLJ]

I started with a 83 SC box.

1st. /11:35 stock
2nd./17:34 (down three ratios)
3rd./21:29 (down two ratios)
4th./25:26 (down one ratio)
5th./38:30 stock

We used the stock 5th. gear for freeway cursin'. By the time she is wound out in 4th. gear I have run out to guts anyway.

I added a Porsche short shift kit, Sein Systens lock out, a ZF LSD

The box had a 8:31 R&P stock.

My motor red line is 8,000 RPM w/244ft./lbs. torque

I used an alloy flywheel and clutch package.
2300 lbs. car

The car pulls revs like an electric motor in a slot car. (Big slot car)

Guard makes very good gears, use them with confidence.


Randy Jones
1971 911 "Iris"

[rdane]

Carquip has the gear chart info (and any tranny parts or gears you'll need) so you can plug in any number you like and graph it out. They also have all the gear ratios (1 thur 5th) in another chart so you can look at your own builds and compare stock numbers. Carquip will also make a few suggestions as to what ratios will work for your use. I've had 4 boxes built over the last 2 years. You really don't want to do it more than once. To do that you need to match your box to the engine HP and torque curve and driving style. In other words what is best for a 3. liter SC engine may not be a good choice for a 3.2 liter 300 hp engine with ITB or a 993 3.6. Add in your track (and home track requirments) and street driving then you'll have other variables that you'll want to address when deciding what gearing you want.

http://www.carquip.com/parts/911/trans/gears/index.asp

Factory ZF works great up here in the rain. More than one driver has noticed the L/S equiped cars are staying on the track and on the road in the local wet drives. Most who run them on the track run a ZF at 80%.

7:31 r/p makes a lot more noise from the samples I been able to drive, as are after market gears. Guard seems to be the overwhelming favorite for quaility. 7:31 is not a good investment if you plan on adding more HP later. Although there are some who have done/ar doing it. But plan on rebuilding it sooner instead of later 'cuz it is just a matter of time if you up the HP from the 3.0 SC.

Tranny cooler up here in the NW? Hayden at WEVO didn't recommend them at all except for al track car in a post here. DE and track days don't add up to a track car for most of us.

3.6 Conversions, are any changes to the transmission recommended?

The new Guard LS is a close copy of the current Porsche LS and does give you a better product by being able to split the accel/decel which a ZF does not. Talk to Monty at R.E. he has added lots of them to older cars.

Pays to remember your engine currently is done at 6Krpm no matter what your seat of the pants tells you or where the rev limiter kicks in. 4 to 6K is the sweet spot on a 3 liter CIS engine.

Short gears won't get you 50hp but more importantly they will allow you to tap into the power you do have by more easily keeping you between 4 and 6K. And there it does make a big difference.

I went to a longer 2nd, short 3 and 4 and a stock '79 5th. Still have a cruising 5th but not a huge jump. Trust me you do not want a box that is gear limited at 135 for PRaceways or the highway. BTDT

The single biggest improvement on my 3 liter and then on my 3.4 and now on my 3.6 has been a carefully selected and specifically built gear box with a limited slip.

Craig (his 3.6) Jack (BBII) and my short box ratios have all been published here on Pelican and are worth looking at as well. These three all have 80% ZF or ZF type. But there are a bunch of custom gear boxes here I haven't keep track of. Randy's Iris is an awesome machine and I see he has posted his ratios as well. It is good info.

Here are a few links with more selections.
915 Gear chart! Anyone?

915 cooling help

Close Ratio Gearing

3.6 transplant gear box selection?

[Matt_West]

Thank for all the information and links. I had searched but you turned up different results than me.

[Bill Verburg]

I would also recommend the GT asymmetrical lsds.

The factory started using a version on their motor-sports cars in the '90s 964RS had 20/80 993RS had 40/65 even the stock 993s had a wimpy 22/40 or 25/40 version

[KNIGHTRACE]

I think on a 3.0 the 7 :31 is his best bang for the $$$'s but I would use the early 5th not the 5th from an 8:31. He will hate the later 5th on a street car. William

[Matt_West]

Thanks for all of the advice. It has been a longtime since I first started this thread and it is time for an update.

In the intervening months a set of welded Fuchs found their way onto the car along with a sump cover with a drain plug. I also replaced the starter, back dated the heat, installed a rebuilt alternator with a used fan housing, replaced an exploded CV, and installed a 23mm master cylinder. All in all it has been good running and pleasant wrenching.

Finally the car is in the shop for a proper transmission rebuild! Following the advice of the board and other knowledgeable experts the recipe reads as follows:

1. Sachs Power Clutch
2. WEVO internal gate shift kit
3. Guard bearing retainer plate
4. Guard 40/60 LSD
5. Gears as follows

1st Gear- 11:35 (stock)
2nd Gear- 17:34
3rd Gear- 21:31
4th Gear- 24:27
5th Gear- 28:24

Of course Syncros, Sliders, and other worn parts are being replaced as necessary. The shop owner has been very kind to let me swing by to observe progress. He has explained what is worn and how the transmission works and was even nice enough to snap some photos.



Needless to say I am very eagerly awaiting the completion of work and will update this thread with a subjective evaluation soon.

[Matt_West]

Initial impressions (30 mile drive moderate to heavy trafic.):
1. Much louder than stock. (WEVO engine / trany mounts will be replaced.)
2. Low bang for buck quotient
3. Have to learn to shift quicker
4. Need to learn new down shift points
5. Shift feels firm and slightly notchy (Needs to be snugged into gear but it seems like it will mature to a buttery slick rifle bolt like device.)
6. Car pulls quicker
7. Engine seems more responsive
8. Not apparent what the LSD is doing yet (Perhaps this will become more apparent when there is some open road or the next track day.)

Overall I am pleased.

[Matt_West]

Day two:
Light to zero traffic, hit all my favorite roads / turns with no intereference. Absolutely awsome, gear stack is worth every penny. Shifting is becoming slicker with only fifth to fourth needing a lot more excercise.