World's Lightest 930 Transmission

[Britain Smith]

Over the past couple of years I have been building a Porsche 914 dedicated Autocross car. When I purchased the car, it had 2.7L 6-cylinder engine and was a lot of fun to drive. After a bit, the need for more HP started creeping in so the car got a JDM STi Subaru Spec-C engine good for about 400whp. With that extra power, it was obvious that the car needed more grip so I grafted on 2005 Lotus Elise front and rear suspension and lots of rubber. Now with power and grip, it was time to start adding aero so a 8sqft rear wing from Dauntless Racing was mounted along with an overly large front splitter. At this point everything was good...until we blew up the 901 transmission 4 times in 2 weekends. Time for a better transmission option so in comes the 930 trans...but it must be light.

Here is a great thread documenting everything I have done to the car over the years.

And a good picture of the car:


Front Suspension:




Rear Suspension:

[Britain Smith]

Here are a couple of pictures of the old transmission. It was a 2-speed 901 with a F mainshaft and KA 3rd. There were spacers in place of 3rd/4th and all the misc. stuff that wasn't being used was removed (i.e. shift forks, rods, etc.).

This is when we blew up 2nd gear launching the car.


Here is the stripped 3rd gear that went going full throttle at about 65mph. The impact was so hard that it stripped the mainshaft nut off the shaft and cracked the intermediate plate.


So here is the old 901 transmission in all it's glory. All pulled apart for the last time. The final weight with a Guard TBD and fluid came in a 78lbs.

[Britain Smith]

Part of this conversion was dealing with the differences in bell housings depths between the 901 and the 930 transmission.


The deeper bell housing flange on the 930 trans puts the starter ring gear in a different location in relation to the flywheel. In addition, the 930 starter ring gear is 2mm larger diameter.


To adapt my 901/915 style flywheel to work in the 930, we had an adapter plate CNC machined. This will allow me to use my current flywheel/clutch set-up and a 930 starter ring gear.


Front side view of the starter ring gear adapter.


My current flywheel with 915 starter ring gear removed.


Adapter in place.


930 starter ring gear bolted on. This put the starter ring gear in the correct location in the bell housing.

[Britain Smith]

930 Limited Slip from Matt Monson at Guard Transmission.


When you run a 911 gear box in a mid-engine configuration, you have the either run the box upside down or flip the ring gear to get it to spin the other direction. For a 930 transmission, this requires significant machining to both the ring gear and the case. This is the stock ring gear before machining.


Here is a stock Diff sitting in the case. You can see part of the area that the case has been machined.


Ring gear chucked up on the lathe.


Cutting hardened steel...molten lava coming off.


After about 45mins of cutting...back of the ring gear cut to fit the case. There was additional cutting required after this, but didn't get a picture of it.

[Britain Smith]

Another thing we wanted to do was use the same hydraulic throw-out bearing parts that were used on the previous transmission. To do this we had to machine about 8mm off the guide tube mounting location in the bell housing.


Cut thru the case in one part...nothing a bit of welding can't fix.


After a significant amount of welding and some more machining. The burn marks are from the epoxy melting.


Additional material added to the inside for strength.


Throw-out bearing guide tube mounted in place after significant modification.


Hydraulic throw-out bearing mechanism in place.

[Britain Smith]

Because I am using the dual-plate clutch set-up, I had to source a early short bell housing mainshaft which has more spline engagement. Interestingly enough, the early mainshaft has a sealing surface machined on the shaft around the bell housing area that allowed for the use of a 915 style input shaft seal and guide tube. This allowed me to ditch the tube that encloses the mainshaft.


930 Shaft installed with the 915 release bearing carrier in place. Clearances are tight!


Hydraulic throw-out bearing in place for the last time. New fittings and lines with 45deg bends to run out the back of the bell housing.

[Britain Smith]

Here comes the weight reduction parts.

Because this a 2-speed for Autocross applications, we removed all the stock shift rails, yokes, etc. and made a longer shift rod that came out the back of the transmission directly. This also reverse the shifter throw to make it match what I had on the 901.


New shift rod location with a bung welded to the nose cone to hold the seal.


The longer shaft is the new one machined to match the stock rod.


Now that we have all the parts in place, it was time for assembly. I left out the majority of the parts associated with 3/4 gear. I also cut out the center splined area for the reverse gear to further cut weight.


Dog gear parts. This transmission has no syncro's which will improve the shifting speed significantly over stock.

[Britain Smith]

Here is the transmission almost together and sealed up. Total weight with fluid was 116lbs...so I only gained 38lbs over the 901 set-up.


Transmission in place, everything hooked up, ready to fire!


Success! Here it is behind the Suby engine.

[TRE Cup]

You have done some terrific fabrication and thinking outside the box on this one ! Bravo

What do you call it now: The Portaru ? Portus? Portoosoobe?

must be a heck of ride

[Britain Smith]

Originally Posted by TRE Cup

You have done some terrific fabrication and thinking outside the box on this one ! Bravo

What do you call it now: The Portaru ? Portus? Portoosoobe?

must be a heck of ride

Yea...1850lbs, 400whp, and 12" slicks makes one heck of a fun ride It is very stable and handles like a Lotus.

BTW, would you happen to have any used 1st or 2nd 930 gears sitting around? I am looking for the following:

1st:
17 : 34 2.000
15 : 38 2.533

2nd:
20 : 34 1.700
19 : 33 1.737
19 : 34 1.789

[TRE Cup]

I don't have any extra turbo gears
about 7 years ago, we did a house cleaning and i sold all my extra stuff to California Porsche Transmissions in Lake Havasu (bobby hart)

[Britain Smith]

Originally Posted by TRE Cup

I don't have any extra turbo gears
about 7 years ago, we did a house cleaning and i sold all my extra stuff to California Porsche Transmissions in Lake Havasu (bobby hart)

Cool, I will give him a call.

-Britain

[porsche930dude]

wow lots of work in that for an autocross car. we have such lame courses in my region i stopped going years ago. looks awesome though. looks like youve got that seat jacked way up for visibility. good idea

[Britain Smith]

Originally Posted by porsche930dude

wow lots of work in that for an autocross car. we have such lame courses in my region i stopped going years ago. looks awesome though. looks like youve got that seat jacked way up for visibility. good idea

Have you tried findings events in NY on Where2Race


As for the seat, it is only 1" off the floorboards...but we are on the taller side.

-Britain

[sc_rufctr]

Excellent write up and that's one SICK car. Well done!

[TRE Cup]

Can you post some videos once you get back to the AutoX course?
want to join the ride vicariously ;-)

[Flieger]

Crikey!

[Tippy]

That is full of win. I never thought someone would go to great lengths to rip up an autocross. BTW, have you ever ran a road course? Might need those missing gears. . Awesome.

[Britain Smith]

Originally Posted by Tippy

That is full of win. I never thought someone would go to great lengths to rip up an autocross. BTW, have you ever ran a road course? Might need those missing gears. . Awesome.

Ha. I haven't done a road coarse in this car...but I have done small kart tracks. I am planning on doing some hillclimbs later this year or next.

Here is my YouTube channel with a bunch of videos.

Britain Smith - YouTube

[Mr9146]

This is super cool.