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Upgrading to a 930 transaxle from a 915

I'm in the middle of adding a turbo to my 3.2 with a stock euro 915, I lowered the CR down to 9:1 so I will be able to rise the boost level in the future which is not good news for the 915, I thought about converting to a G50 but it involves so many mods thus more $$$, so my choice went to the 930. I need to learn from anyone who did the conversion, what was involved? what parts that I will need to get in order to fit and run the 930? Will I need to cut into the torsion bars housing to fit a long bellhousing 930 into my '77 body?

I would like to hear from anyone who have been there before.

Thanks!

Old 06-16-2019, 01:33 AM
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In a long bell housing 930 the rear motor mounts sit further to the rear
Better idea is a short bell 930 from 75/77
Modify trans mount, turbo sheet metal to seal engine compartment, modify the rear motor mount to reach the 77 motor mounts
Half shafts to match turbo flanges on trans.
Just a few ,needs
Bruce
Old 06-16-2019, 03:48 AM
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What about talking to some of our resident gbox experts on modding your 915 to be more robust. Matt Munson might have some thoughts on this. How much tq/hp is expected?
Old 06-16-2019, 04:15 AM
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I think the only answer is the short bell housing 930 trans, that was my long term plan, though prices aren't going to get better on them... :|
Old 06-16-2019, 05:37 AM
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Quote:
Originally Posted by Flat6pac View Post
In a long bell housing 930 the rear motor mounts sit further to the rear
Better idea is a short bell 930 from 75/77
Modify trans mount, turbo sheet metal to seal engine compartment, modify the rear motor mount to reach the 77 motor mounts
Half shafts to match turbo flanges on trans.
Just a few ,needs
Bruce
So a long bell 930 sits just like a G50? further to the front of the car in between the rear torsion bars housing?

I think my best bet is to either shorten the bellhousing, or try to find a 75-77 930 trans., which I don't think its easy!

As for the half shaft, I already have a good set.
Old 06-16-2019, 05:42 AM
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Quote:
Originally Posted by OldSpool87 View Post
What about talking to some of our resident gbox experts on modding your 915 to be more robust. Matt Munson might have some thoughts on this. How much tq/hp is expected?
Thats not possible simply because I'm not in the US and no one local to me would even come close to anything related to a Porsche!

My goal for now is 350whp with .5 bar, but I'm sure I will eventually go higher with more boost, some north of 450whp.
Old 06-16-2019, 05:45 AM
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Quote:
Originally Posted by kamaro View Post
Thats not possible simply because I'm not in the US and no one local to me would even come close to anything related to a Porsche!

My goal for now is 350whp with .5 bar, but I'm sure I will eventually go higher with more boost, some north of 450whp.
Makes sense. Have you driven a car with a 930 box? BTW- im not questioning your approach here. The 930 gear box feels a lot different than 915/g50. They can be a little cantankerous and have very long throws and long gearing.

Also- Matt’s last name is Monson not Munson as spell check graciously corrected for me.
Old 06-16-2019, 06:13 AM
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I am restoring a 930 conversion of a 78 SC where the building PO left the 915. my build thread is active on the 930 forum.

as you have I went through reading a lot of options, most would be huge work and huge $$. but leaving the 915 or trying to build a 915 that could take the ~400hp/tq was not a good option. sold the 915 to a friend who tore it down and rebuilt, said it was badly worn, burned gears, etc. surprised the PO did not blow it up.

I have been working on this for over 5 yrs and just found a short bell housing 930 gearbox at a reasonable price. been looking for 3 yrs, keep seeing them in the $10-12k range. and from research if you buy a long BH and have it rebuilt and shortened could hit that same cost level. as I approach the 'build' phase of the project was resigning myself to that price, but got lucky.

now that I have the gearbox starting to figure out how to connect all the pieces. I am working with Steve Weiner at Rennsport System on this, he is in the middle of rebuilding the bottom end along with the heads, rods, rocker arms, etc engine parts.

good luck.

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Old 06-16-2019, 07:18 AM
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Has anyone tried the Subaru STI box idea?
Old 06-16-2019, 09:30 AM
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You’re not going to sit forward. The G50 sits forward because the torsion tube is split, 87 and later.
Bruce
Old 06-16-2019, 10:19 AM
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Quote:
Has anyone tried the Subaru STI box idea?
I had an interest in the mirror-image Subie R&P too ... but these have a marginal mesh pattern, and power is applied to the weaker coast flank. Not going to hold up to 930 Turbo, IMHO ..

pattern https://www.thesamba.com/vw/gallery/pix/1538515.jpg
pitting https://www.thesamba.com/vw/gallery/pix/1665767.jpg
failure https://www.thesamba.com/vw/gallery/pix/1848909.jpg
Old 06-16-2019, 10:42 AM
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Many STi's are making double 930 power these days and launching it through stock 6spd's to all four wheels... just sayin'

That said the cost and amount of work to fit one would pay for a SBH 930 trans.
Old 06-16-2019, 12:28 PM
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With these astronomical figures that 930/G50 transaxles are selling for, I'm surprised that no one came in with a commercially sold kit to convert a Subu transaxle to fit a 911.
Old 06-16-2019, 12:37 PM
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Quote:
Many STi's are making double 930 power these days and launching it through stock 6spd's to all four wheels... just sayin'

That said the cost and amount of work to fit one would pay for a SBH 930 trans.
So .. is your plan to reverse the rotation of your engine? .. or will you be using the adapter Subie R&P that I referenced?
Old 06-16-2019, 01:03 PM
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If you stay below ~350whp a mildly modified 915 will work fine.
If going 450whp you'll need the 930 4spd.
Short bell housing 930 fits in 915 spot, long BH model can be modified.
You can have a 915 or 930 trans modified in the US and shipped to you, cheaper than G50.
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Old 06-16-2019, 01:36 PM
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The new Martin Bott differential case may be an option.

Our new reinforced 915 differential cases are nearly ready for sale. We are currently doing the final milling procedures on a 5-axis machine to the casted gearbox cases. The cases are made from casted alumnium and are heat treated. Very solid material, which has been used on many other very stabile products yet. They were engineered much stronger than the original cases ever were. Differential bearings of 930 gearbox can be mounted. Differences on shape only on 2nd sight.
First finnished parts in the next two-three weeks.
First internal project is building a 915 gearbox with this case for a G-model with 964 engine.

More info at short notice on:
www.bott-fahrzeugtechnik.de
Innovative Spezialteile für klassische Fahrzeuge der Marken Porsche, Volkswagen und artverwandte Autos - CNC Dienstleistungen | Bott Fahrzeugtechnik - innovative Spezialteile für klassische Fahrzeuge

pictures to follow

Martin

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Old 06-16-2019, 06:05 PM
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What are the weak spots in the 915 - is it the case or the internals or both?
Old 06-16-2019, 06:09 PM
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I question weather a 3.2 with added turbo making north of 450 whp will outlast the trans. Anyone care to comment. Rob
Old 06-16-2019, 06:14 PM
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Quote:
Originally Posted by Coastr View Post
What are the weak spots in the 915 - is it the case or the internals or both?
Curious to know also- have heard conflicting details
Old 06-16-2019, 09:08 PM
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I think I got all the info I need to make a good decision.

How the 930 4 speed shifts like? is it notchy and precise like the G50 or is it vague and sloppy like a 915? is it something in between? I know I can't shift fast from 2nd to 3rd in my 915 (need to give some time for the synchros to rev match), can the 930 shift faster than a 915?

Old 06-19-2019, 03:43 AM
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