UN1 vs Audi 01E or 01X vs Boxster/Cayman gearbox

Hi all. First post on the forum now I've finally got registered!

Now I'm sure this has been chewed over many times and that most of the information is somewhere out there but it would seem slightly elusive to me.

I'm in the process of putting together a GT40 replica and will be using a rebuilt UN1 in the first instance.
However, the follow up project will also require a transaxle system attached to a tuned small block Ford.
My research has shown several personages advocating the avoidance of an Audi gearbox as the engine will need to be significantly higher when compared to the use of the UN1 - although the Audi boxes have been used by many others over the years.
What is the problem/difference in installation in comparison with the UN1?

The other option is to use a Boxster/Cayman gearbox.
Are these just a posh version of the Audi unit and dimensionally the same or do they offer a benefit over the Audi item?

If anyone can provide a few dimensions of each to help me understand it would be appreciated.
I'm after the horizontal distance from the bellhousing face to the output shaft centreline, the vertical distance from input shaft to output shaft centreline and vertical distance from output shaft centreline to the lowest parts of the gearbox casing/bellhousing.
Would be useful to have some offset distances for the output shafts from the input shaft centreline as well.

Hopefully when armed with that information I can finalise which route to follow.

Sadly the G50, RBT or Quaife route is slightly out of budget although they would be a nice way to go.

A big set of questions for a first post but I have been lurking for a while :)

Paul Hendrickx

the distance between input shaft and drive shaft flanges is exactly the same as an UN013 box : 75mm however the Audi box has a lower"sump tha UN013 where their is a provision in the castings for an aditionnal oil-pump , so yes the box could be sitting a fraction higher tan a UN013 .
the re-inforced 03 box has a bigger dif and the distance is 82 mm between shafts....... like the old 016/012 boxes ....


Howard Jones

My advice is spend more than you want on the gearbox and less than you want on the engine. The gearbox will determine many things that are nearly impossible or prohibitively expensive to change later like all the power train mounting positions, drive shaft measurements, shifting cables or rod design, and just about everything else's location in the engine room. Gear ratios are more important than just about anything else when it comes to driving enjoyment and there's the strength issue of the least expensive designs.

Then there is the overall design issue of flipping the gearbox to lower the engine a bit more.

In the end the Porsche G50 01-03 series gearboxes stand out.

1. They can be flipped easily and are routinely built this way.
2. Can be used with +500hp with widely available upgrades and 400hp in standard configuration .
3. They are numerous and will remain so for some time.
4. There are several highly qualified rebuilders.
5. The gear ratios (especially 1st and 2nd) can be changed to suit a V8 and the parts are readily available to do so.
6. They have been mated to just about every V8 (and just about everything else) so there are adapters are in stock available from several sources.
7. Shifter systems are also available without the need to custom design anything other than cable length.
8. Several LSD or TBD type differentials are available. I personally recommend a Quaife TBD.

My advice is to build the car with a G50 than has been built to suit your V8 type. Build you engine to accommodate the remaining budget with the idea to add power at a latter date if you want to. Remember 275-300HP is just fine in a road going GT40. Any decent 302 will make that much, including most used 4 barrel HO spec versions.

I would much rather start with $1000-1500 motor and a gearbox that cost 4-6 times that much than the reverse.


I agree with Howard, the main concern should be the transaxle rather than the engine. Your transaxle choice will determine many things that would be difficult to change later if you were forced to upgrade to a stronger unit. Your engine can evolve to provide more power. Your transaxle choice is pretty much cast in concrete.

Regards, Neil Tucson, AZ
I know exactly where you're coming from Howard and would agree entirely if this was a one off build and never to be repeated again.
I've looked at the G50 option along with the RBT option and have to say that they tick all the boxes for performance and installation - as long as you have sufficient budget to buy and also budget to repair in the event of any issues.

My mission is to understand what lesser options are viable and why some are less viable than others.
The UN1 is a well used option but availability is now much reduced.
This opens the door for the Audi and Porsche (not G50) options to be fairly considered.

To understand the application differences I have two choices - acquire one of each and test or chase for the knowledge from those who've been there.
Currently in chase mode.

Anecdotal information suggests that the use of an Audi box creates driveshaft angle issues.
There is also the suggestion that the Audi box sits too low necessitating the engine to be raised.
This could well be true but without dimensional information it's impossible to understand how big the problem is or whether there is an engineerable solution that hasn't been engineered!
Paul Hendrickx indicated that the Audi box sits low as it has the capacity for an additional oil pump (thanks Paul) - has a solution been considered to modify this area to pinch some ground clearance back?

Not much information on using Boxster gearboxes but I have been told they can be flipped - not that I can find anyone offering this service.
When armed with more knowledge I can fully assess which way I go in the future.

Car no.1 is a road car but no.2 will see a bit more abuse.
I don't envisage having to rebuild the gearbox in no.1 but no.2 is a whole different likelihood.

Randy V

Lifetime Supporter
X5 on the G50. And if you go to my build site and poke around, you will find the mods required to make it fit inside the bodywork well documented...

Cliff Beer

It's true that the Audi transaxle (016) extends a little lower relative to the output shaft centerline (relative to a UN1), resulting in the engine having to be tilted forward more to keep the whole thing under the overall height limits. However, we're not talking inches....we're talking fractions of an inch.....so it's not dramatic.

Not all GT40 replicas are equal in terms of engine/transaxle mounting and spacing. Best thing to do is get some first-hand knowledge with the options that fit your particular application and spacing....and within the budget. I know when I was at that stage of experimentation I had two audi 016's, one UN1, and a porsche 915, all for the purpose of figuring out first hand if one or another fit better within my particular spacing and mounting configuration. Tough to gain that understanding in a virtual format.

On the topic of where to spend your money, agree with Howard and others here - the importance of the transaxle shouldn't be under considered in the overall picture. What I would say is that what you plan to use the car for colors the range of options. If you're mild mannered Sunday driver then you can use just about any transaxle. However, if you're going to put your foot into it repeatedly on the road or on the track then you're going to need a much beefed up UN1/Audi....or better yet the G50 or RBT.
I'm only considering the 01E or 01X gearbox in 5-speed or 6-speed format.
Isn't the 016 an earlier version of the 01E?
If it is then it won't be a consideration.

I'm in the fortunate position that a virtual methodology is a straightforward one.
I have all the dimensions for a UN1 and very low engine install as I keep tripping over all the bits.
With clear dimensions for other possible transaxles I can then evaluate :-
a) whether engine vertical position is an issue
b) whether drive shaft angle is an issue
c) whether fore-aft position of the output shafts is an issue
If any are then the search for a solution begins.

Fairly certain that the engine height installation is going to be the main problem but I might as well put a full package of details together and understand why I'm doing whatever I do.

It would be so much easier if you could invert the 01E or Boxster gearboxes and still have 5 or 6 forward gears :)
The 016 is dimensionally the same size.
Would it be safe to assume that it's dimensionally the same as the 5-speed variant?
Images I've seen would suggest that the 6-speed has the extended sump but the 5-speed doesn't.

Hopefully, when I've amassed the relevant details I can give a clear opinion of which and why - benefits for all.

Cliff Beer

I think Scott at Advance Automotion (www.advancedautomotion.com) would be best qualified to answer that question. He checks out the forum periodically, and knows all about the intricacies of each audi transaxle variation so can probably confirm most precisely.

Indeed, with the typical height limitations in most GT40s a half inch or so may make a difference.
The O1E and 016 are almost identical in dimensions except the 01E is slightly longer and has the differential offset so one axle is longer than the other. They are the same distance from the output to the bottom of the case. With a standard oil pan on the engine the transmission is not any lower than the bottom of the engine oil pan when installed. I have installed several of these in tube frames (not GT40) and there is no problem putting the oil pan flush with the bottom of the frame and having the axle angles be OK. That is with the engine sitting level front to back.
I'm only considering the 01E or 01X gearbox in 5-speed or 6-speed format.
Isn't the 016 an earlier version of the 01E?
The 5 speed 01E is much more difficult to locate, and 01X's are all 6 speeds. No the 016 is not an earlier version of the 01E.

It would be so much easier if you could invert the 01E or Boxster gearboxes and still have 5 or 6 forward gears :)
It' not been done to my knowledge, but that doesn't mean it can't be done.
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Lifetime Supporter
I went off the beaten path and put in a Mendeola. I am always up for a challenge so lets see how this thing last over time. They put them in dirt racers with big hp and torque and they get beat on so should be good in the 40. They run slightly long and rear lower needs to be trimmed or removed. We removed and installed a nurf bar.