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Smart quod bastardus
 
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930 tranny upgrade

I am considering upgrading the 4 speed tranny on my 79 930, and wanted opinions and options from guys with experience on the forum.
I have a stock 4 speed, but would like to get some more performance out of the car without engine mods, and thought that a real great improvement that most guys don't think of would be a tranny mod.
What improvements can be made with regards to gearing changes or diff changes on the stock 4 speed?
What would be the costs associated with this versus the other route of getting a 5 speed unit.
Can the 915 box handle it or what other options are there to get a 5 speed without having to modify the rear torsion housings or changing over to hydraulic clutches (I want to avoid such extensive work)?
Old 01-02-2007, 12:36 PM
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check bruce andersons porche performance handbook, i think it has gear ratio charts for all the different transmissions
pete
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Old 01-02-2007, 04:29 PM
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The 915 can handle the power for a little while but it's not a long term solution.

You can change the ring and pinion for about $2000 plus $1000 to install it. This would make your 4 speed similar to the first 4 gears of a G50/50 with 4th gear being a little taller than the G50/50 4th.

You can change the gears for $600 per gear but you could do it yourself since there's no ring and pinion alignment to deal with.
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Old 01-02-2007, 04:33 PM
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i heard the 930 trannys are pretty easy to go thru . they are bulletproof transmissions ,they were designed to handle big horsepower from porsches race cars.if im correct i think the 934and 935s used this trans flipped over to decrease the halfshaft angles with a oil pump on them.
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Old 01-02-2007, 04:42 PM
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As the guys on Rennlist have suggested the shortened G50 is quite expensive to get in her without tub modifications.

I understand that you really don't wish to modify the engine radically, but why not consider bolt-ons that don't effect durability like exhaust? I'd think about changing the diff if your wanting faster accleration if you don't need the gear spread for mileage of the G50. Some have also warned in the past that the g50 isn't the ideal gear spread for a turbo in its NA USA setup. I've also heard many that claim a G50 is inferior in torque capability to the 930, though this shouldn't be an issue in an unmodified 930.

Sure you could then and therefore go with a G50/52 turbo tranny but now you've up'd the cost a few thousand more likely to source. G50's are also more costly to build so make sure you source a good one or you may have bitten the hand that feeds you.
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Old 01-02-2007, 05:24 PM
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I installed a shortened euro G50 in my SC. The gearing matches the 915 that I removed. I like the gearing. 1st is kinda short but I don't mind. It gets me going quickly, the tires light up and then I hit the rev limiter and I know it is time to shift.

A short G50 will fit your car with no mods to the tub or torsion tubes. I know of no way except a Ruf 5 speed to get a non hyd 5 speed in your car.

How much labor can you do? I did all the labor on my conversion and the parts cost me $4400.

I have only heard of one person blowing a G50 but I don't get out much.
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Old 01-02-2007, 06:03 PM
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Dean, $4400 doesn't sound too bad. Which G50 did you use and what was shortened? Did you have to move the engine back any? Is the body of the G50/50 bigger than a NA G50 which would cause more torsion bar interference?
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Old 01-03-2007, 03:23 AM
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A 915 will live behind a stock 930 engine.
That is the cheapest way to go; you can bust a half dozen of them and still be money ahead of a G50 swap.

Before spending thousands on re-gearing your 930 tranny or a G50 swap you might consider spending that money on engine mods. Once you get past 400HP you won't need shorter gearing.
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Last edited by RarlyL8; 01-03-2007 at 04:49 PM..
Old 01-03-2007, 04:47 PM
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Quote:
Originally posted by 125shifter
Dean, $4400 doesn't sound too bad. Which G50 did you use and what was shortened? Did you have to move the engine back any? Is the body of the G50/50 bigger than a NA G50 which would cause more torsion bar interference?
David,

I used a G50/00 I think. I bought it from Germany. The mainshaft and bellhousing gets machined. I had to move my motor back because I have an SC. You 78 and later 930 guys don't have to move your motor with a NA G50. I don't know if the G50/50 will fit cause I have never done that. I do know the G50/50 is bigger but I don't know if it is longer.
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Old 01-03-2007, 05:19 PM
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Quote:
Originally posted by h20cooled7
if im correct i think the 934and 935s used this trans flipped over to decrease the halfshaft angles with a oil pump on them.
Both 934's and 935's had up right turbo 4speed boxes.. the later 935's had flipped boxes and many of the earlier 935s had the flipped box modification done later for better axle geometry..935's used a ti axle with a rubber guibo coupling in the center of the axle and 934's used the standard axle like the road cars.. as a matter of fact 934's had to resemble the road cars down to the electric windows and cig lighter... that is why they had water intercoolers... like a 76/77 turbo no room for an air to air cooler under that stock deck lid.

my street turbo was geared for 145 MPH.. to me that was plenty . Car was much more responsive. Could probably keep your stock first and change the top three gears. 915 box could be risky even with a stock turbo motor.. it's the Tq when that sucker gets on boost.
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Old 01-23-2007, 11:26 PM
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Quote:
Originally posted by 125shifter
Dean, $4400 doesn't sound too bad. Which G50 did you use and what was shortened? Did you have to move the engine back any? Is the body of the G50/50 bigger than a NA G50 which would cause more torsion bar interference?
Keep in mind you also need a pedal cluster out of an 87-89 Carerra as the G50 uses an hydraulic clutch setup and of course a G50 shifter and linkage. I am having a G50/08 installed in my car with 915 gearing for the track, should limit me to around 160MPH and be fairly close ratio.
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Old 01-24-2007, 04:49 AM
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Set your gears in the 930 to match that of your torque curve. If you have a broad flat torque curve, keep your spacing wider that if you have a peaky torque band. Close ratio gears will keep you in the sweet spot of the torque curve.
Friedmeister, your idea is great idea. Like VZ935 said, 145MPH top end is plenty. Just change your 2nd, 3rd, 4th gears and you'll be amazed at the overall change of attitude in the beast.
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Old 01-24-2007, 08:39 AM
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Hi Gary,
Where did G50/08 boxes originate from ? I mean what car/country spec. ?
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Old 01-24-2007, 01:38 PM
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I'm told it came from an 88 Carerra, but I'm not sure if Dan was messing with me or not about the designation...
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Old 01-24-2007, 03:22 PM
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The more time spent shifting is time actually lost to negative G's that is not accelerating, the stock gearset is fine for both the 930 four speed and the G50/50 unless you are running short race tracks. My shortened G50/05 kit from Patrick along with steel synchros and a Guard diff ran almost 14k add to that 30hrs for the install, 17k for an extra cog is not worth the price of admission but I was caught up in the ether. I will let you know more when the weather breaks and it is tuned. Oh I also sprung for the Wevo G50 shifter... can't wait
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Old 01-24-2007, 03:25 PM
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Quote:
Originally posted by VZ935
Both 934's and 935's had up right turbo 4speed boxes.. the later 935's had flipped boxes and many of the earlier 935s had the flipped box modification done later for better axle geometry..935's used a ti axle with a rubber guibo coupling in the center of the axle and 934's used the standard axle like the road cars.. as a matter of fact 934's had to resemble the road cars down to the electric windows and cig lighter... that is why they had water intercoolers... like a 76/77 turbo no room for an air to air cooler under that stock deck lid.

my street turbo was geared for 145 MPH.. to me that was plenty . Car was much more responsive. Could probably keep your stock first and change the top three gears. 915 box could be risky even with a stock turbo motor.. it's the Tq when that sucker gets on boost.
This is EXACTLY what was done to my tranny. I have a final drive ratio of 5:1, I believe, and the top speed in 4th gear is around 145 m.p.h. With 400 HP, the acceleration is simply amazing. At 60 mph in 3rd gear, you go straight to red line and hit 110 mph in maybe 3 seconds, at the most. At 70 mph, in fourth gear you can hit 120 mph in perhaps 4 seconds. I cut my boost back because I was spinning my tires in fourth gear.

Totally awesome. I wouldn't change my gearing for anything else, but then again, I am not using the car at the track. If I did, I would find a track with a 145 mph top speed!
Old 01-24-2007, 04:11 PM
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DDDD, stock gearing in a 930 results in approximately 2000 rpm for 70 mph. Your box having a top speed of 145 mph puts you somewhere around 3400 rpm for 70 mph. How do you find driving the car at freeway speeds. Seems like the motor would be buzzing.

Jim
Old 01-24-2007, 04:32 PM
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Quote:
Originally posted by Jim2
DDDD, stock gearing in a 930 results in approximately 2000 rpm for 70 mph. Your box having a top speed of 145 mph puts you somewhere around 3400 rpm for 70 mph. How do you find driving the car at freeway speeds. Seems like the motor would be buzzing.

Jim
I drive 90 on the highway, doesn't bother me a bit. Notice that I am exactly in the turbo band in both 3rd and 4th gears at around town and highway speeds. Eliminates lag.

I also get reasonable gas mileage, probably not as good as others, but I can't complain. Seems like 20 mpg on the highway.

And I usually can goose 2nd gear from a slow roll in a turn, instead of needing to downshift to first.

I wouldn't change my gearing any other way. Yeah, some people want to do 180 mph, and some people track their cars. I don't. But I just love acceleration.

Drive your car at 3400 rpms and see if it bothers you. I don't even notice.
Old 01-24-2007, 06:10 PM
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The WEVO G50 shifter is a great piece.
Old 01-24-2007, 08:29 PM
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Quote:
Originally posted by Jim2
DDDD, stock gearing in a 930 results in approximately 2000 rpm for 70 mph. Your box having a top speed of 145 mph puts you somewhere around 3400 rpm for 70 mph. How do you find driving the car at freeway speeds. Seems like the motor would be buzzing.

Jim
I re-geared mine to ~154mph so I'm turning ~3000 at 120km/h up from I believe 2500? It is very livable as I drive mine to tracks all the time (by the time you change exhaust, rip out insulations, etc. another 500rpm wont matter any way )

Mine is geared with the few tracks I goto in mind. For street use, I agree with VZ935, even shorter gearing might work though as it is, its fast enough (for me) on the street.
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Old 01-25-2007, 04:25 AM
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