Jason
Jones
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.
This is the gospel on Porsche transaxles...
Mid Engine = When the engine is before the rear axle like a 914, Pantera,
Indy car, etc. This puts the transaxle in the rear of the car.
Rear Engine = When the engine is in the rear like a 911, Corvair, or
Deloreon. This puts the transaxle under the back seat.
Transverse = When the engine sits sideways and the transaxle is (for
the most part) under the motor. This might be found in a front wheel (Honda
Accord) or a rear wheel drive car (Fiero).
901 = Available from 65 to 69 in ONLY 911 and 912 rear engine cars. No
need to use this box for mid engine applications because the 914 transaxle
will do the job. (See 914) Good to 300 HP and 300 FPT if you do not use
first gear and if you do not abuse it much.
914 Tail Shift = Available from 1970 to 72 in 914 mid engine cars ONLY.
Some people will call this box the 901, but it is truly a box designed
for the mid engine 914 application. Even the gear ratios were changed
for the 914 from the similar 901 box design. This is not a favorite box
due to linkage issues with the tail shifting design. Good to 300 HP and
300 FPT if you do not use first gear and if you do not abuse it much.
911 = Available from 1970 to 71 in 911 cars only. This trans axle was
a modified 901 box with the ability to accept larger clutch components
that were later used in the 915 style transaxle (see 915). In addition,
larger sized CV joint output flanges were installed in increase strength
and reliability and to accept bigger CV axles. Good to 300 HP and 300
FPT if you do not use first gear and if you do not abuse it much.
915 = Available from 1972 through 86 (or 89...I forgot) in 911 cars ONLY.
With two different case materials and numerous gear combinations, the
915 was the work horse for most 70's and 80's 911's. This box may be modified
to work in a mid engine application by splitting the case, making some
modifications, and flipping the ring and pinion. This will give you the
five forward gears with the motor spinning the opposite direction as it
is in a rear engine 911. This is one of two transaxles that many 914 owners
will choose to use for bigger HP. Good to 450 HP and 400 FPT if you do
not abuse it much.
930 Early/Short Bell = Available from 1976 to 1977 in 930 cars only.
When the 930 turbo was introduced, the HP of the stock motor and the gear
ratios required, made the 915 a poor choice for the big 930 motor. The
930 four speed transaxle was born with a much larger ring and pinion,
larger main shaft, stronger gears, the ability to accept 240mm (giant)
clutch components, and a stronger case. Furthermore, it had a much taller
set of gears in a four speed pattern. Capable of withstanding lots of
hard driving at 700 HP or more, this is a very good choice mated to an
American V-8 for several reasons. This two year only box was also a favorite
choice for racers throughout the late 70's and 80's. Many 911 owners were
able to make only minor modifications to their chassis to accept the 930
transaxle when the 915 was not enough for their big motors. If you are
lucky, you might find one, but most are hammered due to their fondness
with racers. This box may be used two ways in a mid engine application...
The first way is to do extensive case modifications and flip the ring
and pinion...which Renegade can do very expertly, or the other is to run
this box inverted. An inverted 930 rear engine type transaxle will run
in a mid engine configuration perfectly with only minor modifications
to the case. The only drawbacks are the box will be running "belly
high" and you might loose your trunk in some cars, and the outputs
of the axles may not line up with the hubs, depending on your situation.
930 Late/Long Bell = Available from 1978 to 87 (up to 94 in some cars)
in 930 cars only. With the quickly increasing HP of the 930 turbo motors,
and the lack of good clutch materials for the street, Porsche was forced
to add an inch to the bellhousing of the 930 transaxle and change the
pan design of the 930 cars, just to get a bigger pressure plate in the
clutch assembly. Since there is more chance of finding a later 930 transaxle
in good shape, we actually shorten the bellhousing approximately one inch
(like the early 930) for most kit car applications. Since the streetable
clutch materials have been improved greatly over the years, the 930 short
clutch components can be used with much success. In addition, there is
much less spinning mass in the assembly which aids in HP.
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