The BIG tranny swap:915 or 930
transaxle in a 914 chassis? Decide for yourself.
By now, you have probably been well educated on the
limitations of the stock 914 transaxle. If not, here is a quick
recap…
1. Don’t use 1st gear period.
2. 300 HP and 300 FPT are the streetable limitations.
3. Shock loading will kill the tranny in no time.
4. No speed shifting or excessive abuse.
5. Have your 914 tranny converted to a four speed
with taller gears by Renegade if the following scares
you!
If 300 HP is not even close to what you had in mind for your
914, well…you might want to read what it takes to go really
big!!! Don’t get me wrong… We have many customers that choose
the upgrade after they have gone through a few stock 914
transaxles, but it take a pretty hefty contribution to the
conversion God’s to afford this conversion done correctly.
Let’s first consider your transaxle of choice. The 915 is
easily obtainable but it really only increases your HP and
torque capability a little. I would push the 915 to about 400HP
and 350FPT, before your odds of failure increase greatly. Plus,
the stock 915 gear ratios are really quite short and very close
together. For a V-8 conversion, your final drive (5th
gear) puts your cruising RPM’s at over 3000 at 70 MPH in most
cases…and your first gear is so low that it is virtually
unusable.
We do have a taller 3:10 ring and pinion available for the
915, which makes that tranny really excellent for a V-8
conversion, but the cost is rather high, and the availability of
that custom ring and pinion is minimal at best.
By the time you invest in the 915 with the taller ring and
pinion, a tranny rebuild, the clutch components, and all the
other bells and whistles, you might as well consider the 930
turbo 4 speed trans from a 911 turbo!
The 930 is quite the excellent choice for the 914 conversion
for many reasons, but there is a lot to learn before you race
out and grab the first 930 you find.
First of all, the good stuff. 700HP and 700FPT are not a
problem with the 930 trans. The stock gear ratios are just about
perfect for a V-8 conversion. Tons of custom gears and multiple
high performance upgrades are available. The giant 240mm clutch
components are excellent for high HP applications that still
require "streetability." The ring and pinion can be flipped to
run in any mid engine application. …And the list goes on.
The drawbacks are fewer, and most are easily rectified. With
the following brief history lesson, you will see the pros and
cons of this workhorse of a transaxle.
The first two years of the 930 turbo trans (‘76 and ‘77), the
length was one inch shorter than the years to follow. The early
930 chassis was very similar to the 911 NA design, because the
trannies were about the same in physical dimension.
Porsche used a typical pull type pressure plate, like the
915, with a greater surface area, and that was quite adequate at
first. However, with the rapid increase of HP in the turbo
motors, slippage became an issue by the very late 70’s. Because
high performance materials available for the clutch disc surface
were quite limited and rather temperamental, the only solution
to getting more grip with smooth engagement was to increase the
clamping force of the pressure plate. So Porsche added
approximately one inch to the 78 and later bellhousings so that
a thicker/stronger pressure plate design could be implemented.
This also made the chassis designers go back to their desks
and look for some more space under the back seat for the bigger
tranny. The compromise was to move the transaxle forward a bit,
and skew the rear motor mount back a little, to accommodate the
longer motor assembly. As Mike would put it… "It’s like putting
10 pounds of crap in a 5 pound bucket!" It was tight.
In the years to come after the introduction of the early ’76
and ’77 930 transaxles, the 911 NA racers started grabbing up
any early boxes they could find and installing them in their 911
chassis. The later ’78 and up 930’s, were to long to fit in the
911’s so the box of choice was this first generation turbo
trans. If you were lucky enough to find one of those two year
only trannies today, you might find it to be quite tired and
stressed.
Well, guess what? That short 76/77 early 930 box, is the only
one that fits perfectly in the 914 with minimal increased axle
angle. Since this tranny is not easily available, we have
developed a method of shortening the longer (late model)
bellhousings and the main shafts to accommodate the 914 mid
engine application. But, there is a trick to doing this that can
make this seemingly easy process a difficult mess.
Unbeknownst to most Porsche enthusiasts, the 930 came in
three versions…not just two. If you look at the bellhousing on a
78 to a very late 80’s 930 transaxle, you will not see an extra
rib cast into the bellhousing approximately one inch back from
the stock lip. This makes the 80’s version a poor choice for the
modification without welding a lip around the mouth of the
bellhousing and pockets for the bolts. If you have ever tig
welded to a casting, you know that is a very difficult process.
The late model 930 bellhousings are a different story. At
about an inch back from the stock bell, there is a rib that
circles the mouth of the bell. This provides the lip that is
needed to securely locate the tranny to the adapter plate. Here
is the catch… The newer the 930 tranny, the more the price of
the core.
But wait… There is more! A lot more.
The flipping of the 930 ring and pinion is quite the miracle
if done correctly. Not only do you heavily modify the internals
of the case, but you also have to add extra support adjacent to
the main shaft which is evident just below the guide tube. There
are very few Porsche tranny technicians that even get close to
doing this process correctly and can maintain the high HP and
torque capabilities. Let’s not forget the electric speedo
modification to relocate the electronic pick up after the ring
and pinion is flipped.
Enough about the tranny… How about everything else! It’s
easiest to just give you a list at this point…and I am quite
sure I will leave a few things out!
You have the Renegade clutch components with a high
performance pressure plate, custom flywheel, Kevlar clutch disc,
custom pilot bearing, throw out bearing, and hardened ring gear.
Then you need a Renegade custom cable shift kit that usually
runs around 90 inches in a 914. It’s a particularly nice unit,
but if you would like to finish off your interior around the
gate shifter, a custom center console is recommended.
Then you have the Renegade custom pivot wheel and cable
extension assembly, which allows the stock 914 clutch cable to
be used with the 930 tranny. This usually attaches to the 930
clutch arm-broached finger-omega spring-bracket assembly, that
never seems to come with the tranny when you find one. All of
this stuff is strictly Porsche, and is very hard to get.
How about axles? You will need Renegade custom length axles
with 930 inward CV’s and 911 (very rare) 4 bolt and two roll pin
outward CV’s. Your stub axles are also 911, but they need to be
the larger diameter face with the 4 bolt and two roll pin
provisions, but still have the 914 axle spine. Don’t forget to
have the rear hubs drilled to accommodate the five studs for
your five lug conversion. We do it all.
Since the 930 has no ears on the rear housing like the 914, a
custom Renegade rear trans mount bracket is the next on this
list. The stock 914 rear tranny mounts are really unsafe at this
point, so a pair of modified 911 sport style motor mounts
actually work really well.
Your stock speedometer is cable driven, but your tranny has
two wires sticking out the side of the case. It’s time to get a
new 911 style electronic speedometer.
Some good news! Your current adapter plate will work as long
as you have the thicker style…AND, if you have used a gear
reduction style starter on your conversion before your tranny
upgrade, it will still fit and operate correctly in the 930
starter pocket.
The damage??? Are you sitting down? You will spend over 10k
on the tranny and related transaxle conversion parts, and that
does not include ANY of the V-8 engine conversion parts! That is
for just the tranny and all the related systems that make it
work in the 914.
Back to the 915, you might save about $1000 at best over the
930. It’s not worth it. Go for the 930 if you plan to do it at
all.
Don’t get me wrong. If you consider your 400+ HP 914 car,
with the complete 930 tranny conversion, can out perform cars at
5 times your investment, this is quite a bargain. We have sold a
ton of upgrade kits and 930 turbo trannies through the years
with not one of our customers wishes they still had the 914/901
tranny.
On the other hand, if you can keep your motor down under 300
HP and 300 FPT, and your driving might be considered a little on
the conservative side, the 914 transaxle might just be the box
of choice.
If you have any questions or comments, please feel free to
contact me in the office Monday though Friday. Thank you!!!
That's it! Thanks for reading it!!!
