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930 vs 915 transmission.

Gentlemen.

My turborized -82 SC seems to suffer from transmissiorites. The 915 5 speed can at times be hard to get in gear. In fifth, it makes a whining sound. When I did my trans oil change, quite a few small teeth stuck to the magneto plug. Lately I also have a funny sound which I only can hear when in second.
I have been thinking about a rebuild of the 915 but after reading a little about the subject I may go for a 4 speed 930 transmission. The G50 would be nice but I think that will be to many mods involved.

Porsche 930 Transmission 4 Speed LSD 93030090100 | eBay

The above is on ebay right now. It says its a modified 87 trans. Something to consider?

What would be the best way to?

G


Last edited by Hoyo; 09-16-2011 at 12:34 PM..
Old 09-16-2011, 09:55 AM
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Quote:
Originally Posted by Hoyo View Post
Gentlemen.

My turborized -82 SC seems to suffer from transmissiorites. The 915 5 speed can at times hard to get in gear. In fifth, it makes a whining sound. When I did my trans oil change, quite a few small teeth stuck to the magneto plug. Lately I also have a funny sound which I only can hear when in second.
I have been thinking about a rebuild of the 915 but after reading a little about the subject I may go for a 4 speed 930 transmission. The G50 would be nice but I think that will be to many mods involved.

Porsche 930 Transmission 4 Speed LSD 93030090100 | eBay

The above is on ebay right now. It says its a modified 87 trans. Something to consider?

What would be the best way to?

G
It should fit into your car or a pre 1978 930 chassis. Seems a fair price for a limited slip as a complete rebuild using new parts, and the modifications done to fit the short chassis cars, can be pretty pricey.
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Old 09-16-2011, 11:45 AM
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Yup---I have an 82SC--Rebuilt my 915- the same time I put in my 3.3 Turbo..

Not sure the G50 would fit much wider than the 915-..It would be good choice.

Brian would know the answer
Old 09-16-2011, 11:53 AM
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Crotchety Old Bastard
 
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There are many considerations:
- HP level,
- How the car is used
- Budget
- Your driving style
My decision to build a couple 915's was based on power level, vehicle use and economics. I can blow up a dozen 915's for the price of a G50 conversion. The 930 tranny is too tall geared for my use (curvy mountain roads good for 2nd and 3rd gear on the 915).
If you like high HP and taking it to the highway get a 4spd 930; medium HP and lower speed fun factor, build a 915.
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Old 09-16-2011, 07:05 PM
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A 930 trans with a 8:41 or similar R & P is like a turbo G50 without the 5th gear. I have them both in different 930 turbos and find I seldom use the 5th gear with the G50 so to me I would never spend the many $$$s for a G50 unless I planned to drive a lot over 90MPH or be on a race track with a car with at least 600HP. Top speed in the 8:41 4spd is around 150mph and 3rd gear with the 9:36 is around 135 Mph so yes the stock 930 is, in 3rd a little high RPM and the 4th a little low RPM for our highway speed use. I like 3K as a minium RPM especially in one that has been warmed up for more HP.
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Last edited by voitureltd; 09-17-2011 at 07:42 AM..
Old 09-17-2011, 07:32 AM
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Thanks.

Lets say that the G50 is out of the equation. If my aim was around 450 hp. Would a standard 915 do the trick if not used on track? is it possible to get parts that can withstand 450 at a usually nonagressive driving style? I say usually because it is impossible to not floor it on occation.
What would a rebuild cost,or for that matter, to buy a rebuilt 915?
I like the 5th but would prefer strenght.
G

Last edited by Hoyo; 09-20-2011 at 07:32 AM..
Old 09-17-2011, 08:29 AM
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I have 420hp at the wheels and I am going with a G50 conversion. I was told over 325hp is hard on the 915's.

I believe the weak point is in the case not being able to keep everything together with high HP engines.
Old 09-17-2011, 09:19 AM
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Quote:
Originally Posted by IMR-Merlin View Post
I have 420hp at the wheels and I am going with a G50 conversion. I was told over 325hp is hard on the 915's.

I believe the weak point is in the case not being able to keep everything together with high HP engines.
Factory writing from early turbo development indicated the 4speed was necessary as the 915 could not be modified for the Torque/Hp capabilities of the turbo motor. Keep in mind they built the 930 project to compete in group 4 and at that time the 3.0 liter turbo in group 4 development was getting to 500HP. The 930 4 speed is good for well over 700HP using a trans oil cooler for extended track time. I personally would go to different R&P for reasons outlined in my last post or gear changes in the 930 trans as it will cause no other expensive alterations. If you can stay away from more HP mods a 915 with some upgrades as RarlyL8 alluded to should work as I think he has modified his 915.
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Last edited by voitureltd; 09-17-2011 at 09:59 AM..
Old 09-17-2011, 09:47 AM
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I had both trannys in my car.. I have an 83sc. I have alot of power. When I was at 325-350hp I used the 915. I never did any hard lanches and it was fine. 1st gear was usless.
Know I have a a 930 4 speed tranny in there. I do have alittle shorter gears though.
1st goes to 60 2nd to 90 3rd to 130 and 4 i could not tell you did not go there.
you are going to have to go with a early year 4 speed turbo tranny. They were shorter. The original 930s where the same chasis as the sc the later 930s were longer and will not fit in your car. Unless you do modifications. You will need a 4 speed tranny from a 76-77 yr 930.
I love my 4 speed by the way,I had it rebuilt and works flawlesss.
Old 09-17-2011, 10:02 AM
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My car know is over 400rwhp....
Old 09-17-2011, 10:04 AM
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Quote:
Would a standard 915 do the trick if not used on track?
Not for long. A stock 915 can be used with 300WHP on the street only and with no drag racing starts or shifting on boost. The problem is not HP but torque. The turbo engines make a bunch of torque which will eat up a 915 quicker than the same power in 911 form. A modified 915 (side plate and bearing retainer) can take 350WHP under the same constraints. Above that you can litterally destroy one at will. One speed shift and second gear will shuck all the teeth, one drag start and the pinion gear will blow out the side of the case.
Another consideration is resale, any money spent on the tranny is deminishing returns.
If you are planing on 350+WHP then the 915 really is out of the question. Plan on spending about 3-4 times the price of a 915 for a 930 with low gears. Add $1000 for 930 case/shaft modification if you want the engine to stay in the stock location.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 09-17-2011, 10:10 AM
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Quote:
Originally Posted by RarlyL8 View Post
Not for long. A stock 915 can be used with 300WHP on the street only and with no drag racing starts or shifting on boost. The problem is not HP but torque. The turbo engines make a bunch of torque which will eat up a 915 quicker than the same power in 911 form. A modified 915 (side plate and bearing retainer) can take 350WHP under the same constraints. Above that you can litterally destroy one at will. One speed shift and second gear will shuck all the teeth, one drag start and the pinion gear will blow out the side of the case.
Another consideration is resale, any money spent on the tranny is deminishing returns.
If you are planing on 350+WHP then the 915 really is out of the question. Plan on spending about 3-4 times the price of a 915 for a 930 with low gears. Add $1000 for 930 case/shaft modification if you want the engine to stay in the stock location.
This is what I was talking about, the side case is weak and flexes under load destroying the ring and pinion. Am I correct in this?

I am planning on doing the billet case on my G50/01 that I have for my build car.


Sorry for thread jacking.
Old 09-17-2011, 11:39 AM
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Yes torque pushes the pinion towards the side plate. A way to eleviate this is to reinforce the side plate and use a LSD. The LDS will apply the torque to both sides of the case instead of just one. A buddy of mine built a cradle for his transaxle to use for street racing after exploding his 3rd 915. It still proved not up to the task when the actual case cracked while speed shifting into 3rd gear.
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Old 09-17-2011, 11:56 AM
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Quote:
Originally Posted by jbrown View Post
I had both trannys in my car.. I have an 83sc. I have alot of power. When I was at 325-350hp I used the 915. I never did any hard lanches and it was fine. 1st gear was usless.
Know I have a a 930 4 speed tranny in there. I do have alittle shorter gears though.
1st goes to 60 2nd to 90 3rd to 130 and 4 i could not tell you did not go there.
you are going to have to go with a early year 4 speed turbo tranny. They were shorter. The original 930s where the same chasis as the sc the later 930s were longer and will not fit in your car. Unless you do modifications. You will need a 4 speed tranny from a 76-77 yr 930.
I love my 4 speed by the way,I had it rebuilt and works flawlesss.
Yes the later 930 transaxle he is considering has the modifications needed ( shorten bellhousing and main shaft , a rare fine with LSD ), so will fit his SC chassis. Sounds like you have the stock 930 gearing with 60 Mph in first 90 in 2nd and 130 in third, that is MPH performance speck with a stocK 9:36 R&P.
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Last edited by voitureltd; 09-19-2011 at 06:12 AM..
Old 09-17-2011, 06:15 PM
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Torque kills 915 transmission, I use smaller tires to save 915 transmission.
I rather burn the tires than lost transmission.
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Old 09-17-2011, 07:20 PM
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That's actually a really good deal for a 930 trans that has new parts inside. I would be very leary about that trans actually having new parts inside. If you read the fine print, it says inspected and cleaned... that could mean they cleaned the outside of the case and felt that the main shaft had no play. It's a really cheap price when you consider that the synchs, brake bands and blocks alone will set you back 2G.
By the way... who says a 930 motor and "long version" trans won't fit in a plain old 911? I have a feeling that it will all fit
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Old 09-17-2011, 07:57 PM
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By the way... who says a 930 motor and "long version" trans won't fit in a plain old 911? I have a feeling that it will all fit [/QUOTE]

Probably can do, however you would need to move the trans mounts and torsion bar suspension tube forward to get the motor mounts to line up or move the motor mounts rearward for the trans mount to line up. The factory moved the motor mount location rearward to fit the longer1978 transaxle in the 930 chassis making it a little more tail happy and changed the recommended tire pressure from upper 30s to 43psi to compensate. Easiest way is to use a pre 78 930 trans or machine a later one to the earlier dimension.
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Last edited by voitureltd; 09-19-2011 at 06:18 AM..
Old 09-19-2011, 06:05 AM
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I have a 85 Carrera 3,2 Carrera converted to a 3,3 l twin turbo with a 915 gearbox.

Not long after i bought the car i stepped on the pedal(hard) and totally crushed first and second gear on the transmission.
The 915 gearbox was just rebuilt so that is one thing i will not repeat.

But it works okay as long as you take it easy using first and second gear. at least it works good enough for me.

Converting to a short G50 gearbox is to much work for me.

Last edited by MrShades; 09-19-2011 at 06:41 AM..
Old 09-19-2011, 06:39 AM
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Mrshades, how much power/boost were you running through that 915 if you could let us know? I'm trying to paint a mental picture of a safe level. Thanks.
Old 09-19-2011, 08:07 AM
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0,6 bar of boost so it is not much. About 350 hp at 4800 RPM according to the engine builder
But let me say it like this i was new to the Porsche and had not heard of the difference of a 915 or a G50 transmission so i really used/abused the car quite heavy
That was the only time i really tried out the car on the 2 first gears


Last edited by MrShades; 09-19-2011 at 08:49 AM..
Old 09-19-2011, 08:43 AM
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