915 to G50 conversion on '85 911 - What's needed guide‏

[Rawknees'Turbo]

Originally Posted by cnielsen

591hp said I HAD to do something. The 915 would have been a ticking time bomb

A 915 is a ticking time bomb at anything over 300hp if the torque numbers are similar and you don't drive like a granny in 1st and 2nd gears - can't image it would work at all with almost 600!

[winders]

Originally Posted by cnielsen

591hp said I HAD to do something. The 915 would have been a ticking time bomb

A 930 transaxle would have been a better option. You would not have needed to move the engine back at all.

[Matt Monson]

Originally Posted by safe

I got the G50 here on pelican for 3500 and I don't think I have paid more than 1500-2000 for the rest of the parts.

It's not a short bellhousing, I cut the torsion tube instead because I have coilovers.
The engine looks to be in the original position, if I choose to in the future I could shorten it and move the engine forward.

Found an RS flywheel second hand, but unused. Got a free slave cylinder, free clutch plate (well not free, I've probably done something in the past to get them). Bought guide tube and bearing new.
The shifter I made from a 944 one, if ut turns out as good as I think I'll post something about it.
Clutching generic copper fuel line. Master cylinder, found used, made a linkage in the foot well, that I need to redesign in the future.

So depends on luck and skills....

How long ago?

[Tremelune]

G50 conversions have probably doubled in cost in the last 5-10 years. An unrebuilt transaxle alone seems to start at $5k. At $500, the shortened bellhousing isn't a significant part of the cost anyway, so engine location isn't much of a factor.

I've always feared the hydraulic plumbing...

[Matt Monson]

They've doubled in the last 2-3 years. Previously it was kit car guys. Now it is Singer.

[KTL]

Originally Posted by Tremelune

I've always feared the hydraulic plumbing...

The hydraulic plumbing is actually probably the easiest part. '87-'89 911 pedal cluster, hopefully with master cylinder included. It bolts right into the floor with zero modifications. If you need a master, get a reman from Centric or Wagner (********) and use the factory piping to the '87-'98 slave cylinder. Piping fits right in the car thru the tunnel.

Or get a little creative and use AN-4 teflon lined braided stainless hose with adapter fittings.

[Tremelune]

Well. Now I'm wondering what the real sunk cost would be. A good G50 will always be worth what I buy it for today, and if $500 gets me hydraulics, another $500 for the shortened bellhousing that avoids coilovers and cutting of the torsion tube...What's the next largest barrier?

$6k plus labor, plus maybe $1000 for stuff I can't think of yet?

If I keep my 915, I'm going to wind up buying all new gears and rebuilding it anyway (though some of that could be recouped by selling the existing gears).

[Matt Monson]

The gearbox gets totally disassmbked to shorten it. That would be the time for a proper rebuild on it with new Synchros and anything else showing wear. So add $2-3k.

[safe]

Originally Posted by Matt Monson

How long ago?

1 year ago. Not quite done yet.
It even had a Guard torsen diff.

[ALEX P]

Originally Posted by Tremelune

Well. Now I'm wondering what the real sunk cost would be. A good G50 will always be worth what I buy it for today, and if $500 gets me hydraulics, another $500 for the shortened bellhousing that avoids coilovers and cutting of the torsion tube...What's the next largest barrier?

$6k plus labor, plus maybe $1000 for stuff I can't think of yet?

If I keep my 915, I'm going to wind up buying all new gears and rebuilding it anyway (though some of that could be recouped by selling the existing gears).

Answer = somewhere around $12k!
You can save some costs by doing work yourself but it's not a cheap conversion.

Originally Posted by ALEX P

Ok, so I had a reply from Patrick Motorsports and the conversion parts from them came out to $3670 broken down as below:

$40 Engine case to g'box studs
$285 Mount adaptor
$90 ARB/Sway bar adaptor
$690 Hydraulic conversion kit inc reservoir, brackets, hoses, sleeves, clutch m/c, slave cyl, lines etc
$225 Shift rod adaptor
$650 Flywheel
$22.50 Flywheel bolts
$1400 Clutch set
$245 Starter ring gear
$22.50 Bolts

They also sell the guide tube for $130 - lots of info here:

Transmission > Porsche G50 SBH (Short Bell Housing) By Patrick Motorsports Porsche & Mid Engine Performance Specialists

I alsodiscussed it with an engine & gearbox specialist in the UK who thought the modification work to the the gearbox would probably be around £2000 / $3150. This is to deliver him a gearbox and for him to strip it, carry out the machiing work and rebuild it. Anything worn or broken whilst in there would obviously be extra.

So as a quick tott up for the assumed total:

$3670 Patrick Motorsports conversion parts
$3150 Gearbox modification
$4000 (approx) for G50 Gearbox
$1000 (approx) Pedals, shift rod & sundries

It looks to be approximately $12,000 / £7700 for the conversion + a boat load of work + the unknown theoretical expense of a used G50.

all of a sudden I'm developing a new love for my 915! I simply couldn't justify that sort of expense. On the plus side it does give a new justification for dropping some coin into a killer 915 build

Hopefully this is of some use to anyone else considering the same conversion.

[Tremelune]

Originally Posted by safe

It's not a short bellhousing, I cut the torsion tube instead because I have coilovers.

I want to believe as you do, but cutting that tube might compromise structural integrity, even with coilovers:

Transmission > Porsche G50 SBH (Short Bell Housing) By Patrick Motorsports Porsche & Mid Engine Performance Specialists

"We then fitted early 911 & 930's with coil over shocks, cutting out the center of the torsion center, fabricating a center reinforcement for clearance, etc.. We thought this was less work, wrong. The cutting of the torsion tube is not a great idea, it's almost like the Achilles heal of a 911 & 930. We found this was only optional on track cars that we could tie the weld in cage to the torsion tube area for keeping proper structural integrity."

It seems that shortening and moving the motor back is the current optimal solution. This is a bit of a bummer, as I'd be happy to sacrifice my rear seats and bulkhead to try and fit a 6spd G50, and nobody wants the motor hanging further back. I definitely do not want to go the Brummie route with tons of cutting fabrication.

We're currently at $10-15k for parts and ~$5k for labor.

[safe]

Originally Posted by Tremelune

I want to believe as you do, but cutting that tube might compromise structural integrity, even with coilovers:

Transmission > Porsche G50 SBH (Short Bell Housing) By Patrick Motorsports Porsche & Mid Engine Performance Specialists

"We then fitted early 911 & 930's with coil over shocks, cutting out the center of the torsion center, fabricating a center reinforcement for clearance, etc.. We thought this was less work, wrong. The cutting of the torsion tube is not a great idea, it's almost like the Achilles heal of a 911 & 930. We found this was only optional on track cars that we could tie the weld in cage to the torsion tube area for keeping proper structural integrity."

It seems that shortening and moving the motor back is the current optimal solution. This is a bit of a bummer, as I'd be happy to sacrifice my rear seats and bulkhead to try and fit a 6spd G50, and nobody wants the motor hanging further back. I definitely do not want to go the Brummie route with tons of cutting fabrication.

We're currently at $10-15k for parts and ~$5k for labor.

I only cut away half of the tube, didn't dare to remove more. Then I welded up the tube again and welded in tubular support against the tunnel.

[69porsche]

Seems like this thread withered away-but very good info

[aston@ultrasw.c]

I'm selling some G50 conversion parts that I no longer needed after an engine upgrade.

Excellent condition = lots of life left

FS 3.6 Conversion Flywheel and clutch for G50

[safe]

Originally Posted by aston@ultrasw.c

I'm selling some G50 conversion parts that I no longer needed after an engine upgrade.

Excellent condition = lots of life left

FS 3.6 Conversion Flywheel and clutch for G50

930 pressure plate?
Is that the right part to get the ring gear in the right place for a pre 3.6 starter?

[aston@ultrasw.c]

Originally Posted by safe

930 pressure plate?
Is that the right part to get the ring gear in the right place for a pre 3.6 starter?

I'm sorry I don't know.

I used the 3.6 high torque starter.

[Kraftday]

This is a great thread, thanks ALEX P for sharing.
A great resource. And thanks to all that shared their experiences with this too.

>> Shifing gears into 2024.
G50.00/01 tansaxle core values are ~10-20K U$. They come and go.. next year who knows..aging like fine wine. Expect to rebuild.
Pedal assemblies, now even more scarce seem to be ~$1600+ *guy on ebay now @ $3500....yikes. Shifter assem also scarce complete with rod ~$1600+
Axles for 911 chassis ~900+ wheel hub updates depending on year.

I've personally helped many of you with parts and conversations over the years and during my combined ~7 years at Patrick MS (pre 2015). Costing then it was typically ~$12-16k all in depending on core & options. Many of those directly for 911 RSR or high power 930 EFI projects. The motivation to convert was usually that they are at an impasse to overhaul or simply need more durablity than 915 for racing. Several 930 customers having completed the conversion, rave about how it's the must do. Years later some wanting to convert back to stock, simply because they received offers from European buyers to purchase with the stipulation that the car has to be 100% original. These were the times when 930 owners in @ say 40k selling for 80k range.

Now and since many more are in werks or done. Special call out and thanks to Roger B. and crew at CMS. Most of the cores are worn tired, or from crashed cars with broken nose cones and mounts. Most the types or serial number stamps on the bottom are ground off and shady. Common too people sell as G50.00/01 but then turn out to be G50.03 (964) but with G50 nose cone, so check the number stamps! Many cores require 4k plus in parts. Many have worn out R&Ps witch are now ~$2600. Now too if your wanting say 3 gears updated, that adds a min of ~3k (for aftermarket gears which is not recommended for street).

Now a 915 core typically ~3-4k and with that your wanting latest version possible, alum case. Most cores are basket cases, incomplete and typically require proper releaser shafts and forks. It is easy to spend $20k for a proper sored 915 with diff and updates. Any of these transaxles benifit from coolers even if simple feed and return and especially if pushing big torque thru a 915. Sorry that's the reality.

Other notes:
The torsion tubes are still available to buy.
It is necessary to either modify or replace the OE tube or machine to G50 SBH for clearance of the nose cone. The variations in clearnace are to do with the year and versions of the chassis. Later 911s and the 930 turbo had engine mounting further back. The 930 trans mount bosses typically get updated or yes you can use a modified 915 mount. They need a slotted plate..or yes can do new billet. My friend Daryl Williams designed these during his time at PMS.
Earliest G50 SBH conversions were based on original Ruf R50.50 and those are G50.50 shortened with an extra gear on nose cone to make it a 6 speed. Bob Holcombe of MODE ~Y2K would do SBH conversions..earliest authority I know off. I was a machine operator during that time. We also made shifters for the purpose of Motorsports.
Porsche did many features to suppress nose and judder; including, rubber torsion disc, padded shift rods with rubber couplers, bands in the shifter, etc.. they tend to rattle when at idle. You can use a Lucas gear oil additive to dampen the rattle too. No metal to metal contact! Get your hammer and dimple that torsion housing. Ultimately the next generation 964-993- featured new nose cone mounts and dual mass flywheel / clutch.
The starter is the same 901, 915, 930, G50. The starter ring gear needed is from 75-77 911 Turbo Carrera as this features some additional clearance holes for clutch cover limit pins. The 964- starters, clutch, ring gear placements are different and not compatible. Pedals, releaser, length, etc make 964-G50.03, 993-G50.20 not easy to install in 911-930. This is why Rob at Singer convinced to use the 964 shell. Sure the Vram and 6 speed in the short 72 911 was made to fit but not without many updates to the package tray, torsion housing etc..$$

Flywheel / Clutch basically uses early 77 911 Turbo Carrera 240mm. It's low profile. Porsche has recently discontinued Sachs from supplying. So if want one, Porsche 77 or Sachs RE 594 (old Ruf 5 speed) or 935 (high power w RB), or KEP. Yes the release bearing G50 is compatible w 911TC / 930 cluch covers. Flywheel for G50 SBH a standard 930 240mm. G50 flywheel only for G50 standard length.

Another item needed for 930 or 3.6L to G50 SBH are shorter engine case studs.

(Available 3x NOS w LSD ~$18k)

Hopes this helps guys, subscribed and updates as we go.

911 331 006 01 : Rear Torsion Bar Tube (1987-1989) 911 Carrera G50.00/01, (1989) 930 Turbo G50.50 - List: $1885.57
** Still Available new / used ~$1250.00
These can be graphed in place of a for installation of the standard G50 trans.