Alot of mis-information is going on about the Audi trans's. I here some say they are totaly different than a 50\50 box and a 944Porche box. I know the outer cases are different but aren't the gears inside the exact same ones. In other words many of the components in these trans's are interchangeable. I think Bob lawrence may know more about this as he has has looked at the 944 and the Audi.
If anyone else has good info on the trans please post it here. I think it is an important part of the build and prospective buyers need to know.

Your Friend,
Hershal Byrd

Hi Hershyl

It's great to see this up and running. Anyway, try going to www.gt40club.clara.net which is the UK GT40 Enthusiasts Club old website. Leave a message for Ken Saunders the webmaster. I know he uses an Audi gearbox in his GT40 and has experimented with several. He has a heavy foot. Go to the section on his website titled "Technical Information for GT40 Builders" There you will find the various Audi gearboxes and their gear ratios.

Regards
Paul Campoli

Hi Hershal

Sorry I spelled your name wrong on the previous post. I just want to add a couple of more cents to the last part of your post. I have been working on a KVA GT40 replica for the past couple of years and would like to share my opinion with anyone building a GT40. The following only relates to cars being built in Canada or the U.S. My opinion would be different in other parts of the world. Assuming money was no object I would go with the ZF transaxle. Of course since the GT40 is expensive in the first place you may want to go for option 2 which is the 5 speed Porsche G50 transaxle or the 5 speed 944. These are very strong and resemble the original gear ratios. Third and final I would go with the Audi 5 speed gearbox. I know people who have used them in the UK and Australia and they hold up very well. I used a Renault 25 (same as the 30 with a higher 5th gear to replicate the original. They are also good gearboxes only you will have to import them as they are not available in North America. Most of the kit manufacturers can supply parts for them. I like them because bell housings are readily available to mate them to the Ford small block allowing for a big clutch and easy placement of the starter and clutch slave and clutch fork.

These are the options I am familiar with. I would be interested in hearing of other alternatives.

Regards
Paul Campoli

I'm using an Audi box as are a few others building the RF car. Mine isn't installed yet of course, still a long ways to go.

But, the 5N box like I have has a 4.11 ratio and an overdrive of something like 0.90.

The 3U box seems to be better, therefore I've got two buddies in Germany trying to get one for me. Hope that it is possible, the final is much better and the overdrive is something like a 0.64 or so.

I'll post what I can find out about availablity.

Ron

Hi Paul ,
Thanks for the info I surely will look that site up.
Although I am Quite a ways from putting in a trans I still want to find out all I can about these Boxes.
I plan on using my GT40 for touring and and very little track time. I am not one to abuse a trans or
put undue stress on the drive line. I have no intentions of putting gobs of horse power under the hood. a respectable 350HP is adaquite. Mr.Logan,the owner of RFGT40's says the Audi box is more than capable of taking 450HP. I think he is right because an Audi 5000 weighes alot more than a GT40 does and this does make a difference provided that you don't go overboard on the tire size.

Your Friend,
Hershal

SN Ring 1 2 3 4 5
APT 4.11 3.60 2.12 1.45 1.02 .85
3V 3.88 3.60 2.12 1.45 1.07 .80
MR 3.88 3.60 1.94 1.23 .90 .68
3K 3.88 3.60 2.12 1.36 .96 .77

There is the 3U box too, the one I'm referring to although it is not available in NA.

3U
3.89 Final
3.60 First
1.88 Second
1.19 Third
0.84 Fourth
0.64 Fifth

Ron

Well, my buddy in Germany has just found a 3U box for me and I'll be bringing it into the states for use in the GT40. This Audi box has good ratios giving a nice relaxed cruise at 70mph around 2000 RPM with a theoretical top speed of around 205 mph.

I'll probably use this transmission therefore I can probably sell my 5N if someone needs it. Or, might be cool to fix it up and use it for a short ratio box...

Wayne, what box does CAV use in their 40, I know it is an Audi box but what number?

Ron

I'm leaning towards the G50 or G50/50 myself.
I hear that the 944 transaxle will not work,
but the reasoning escapes me.
I'm also wondering if anyone knows if there
is a way to use the 98+ Corvette transaxle?
I have access to one for under $2000. Getting
a custom bellhousing is not a problem, my
concerns are getting the linkage and clutch
to work correctly. I like the idea of a 6 spd,
and I know it can handle whatever is thrown
at it.

Ian

Sounds like a great idea. Someone should take a look at it. I know of several people in the UK who race GT40 replicas and use a chev engine. I hate to even suggest it as I think the Ford small block is more appropriate, but for someone who is strictly after performance, this sounds like a great option. Of course if you go with the chev engine, the linkage problems would probably be eliminated.

Another option which I've considered, but that's as far as I got is using an Audi automatic transaxle probably from a 3 litre engine. I liked it as it would have made my wife happy as she could then drive it and it would solve and shifter linkage problem. A ratchet shifter could be used and placed anywhere in the car without a problem.

Regards
Paul Campoli

i have a G50 for my 351W. what is the difference between this and a G50/50? i know that one has a LSD and the other is an open diff but if i install a limite slip in the G50 wouldn't i have just about the same thing?

my other option would be to sell this one and buy a G50/50 but the one i have has only 25k miles on it and cost me $1900 bucks versus a a G50/50 that is about twice as much!

any opinions, coments?

luis lopez
www.hotshotusa.net

Hi Luis

I don't know the differnce between the two, but I know of people who have used the G50. It would be one of my primary choices for a North American built GT40 replica although I'd probably use a Renault 25 or 30 only because I'm more familiar with them and the readily available parts to adapt them for GT40 use. I think Mike Starling is using G50 setup, if not check with John Donelly at Sabre Automotive. I know he builds his cars around the G50 - Ford small block setup. If not I could put you in touch with others who have used this. I believe the mating plate is readily available through suppliers as well.

I noticed your build pictures. What make replica are you building?

Regards
Paul Campoli
Toronto, Ontario

If anyone is interested I came accross a G50/50 with limited slip and Kennedy Engineered adaptor with flywheel for sale in Vancouver, Canada. I don't know if the adaptor if for a Chev or Ford. I think it was on Kitcar.com and the e-mail address is "colinford@nava.ca" I don't know what he's asking, just thought it may be of interest. Remember the exchange is about $1.00 U.S. to $1.50 Cdn.

Paul Campoli
Toronto, Canada

I found the info regarding why a 944 transaxle
won't work. According to Robert Logan of Roaring
Forties, the 944 transaxle was a derivative of the
Audi 5000 transaxle . Although very similar, the
944 will not allow for the correct clutch placement.
I guess the case is significantly different enough
(might have to do with the Audi having a transverse
engine and the 944 being longitudinally mounted).

FYI, from what I've found, the C5 transaxle has
Borg-Warner internals, but the case is made by ZF.

Ian

The 944 and Audi box have identical internals - that is, the same limited slip, ring, pinon, etc work in the transmissions.

However, in the 944 the transmission has no provision for a clutch as it is mounted at the rear of the car and power transferred to it using a torque tube.

The Audi version is a standard layout and has an input shaft, clutch provisions in including slave cylinder, etc.

I'd imagine maximum torque levels to be identical, that is to say, no one really knows.

paul

my car is a sabre(with extent modifications) and donnelly told me to use either a 50 or a 50/50 but i want to know if there is a difference if i put a limited slip on a 50. it would make them identical trannies or is the 50/50 for more top end speed(that's what i heard)? in the mean time i think that i will go with what i have. in the future i will call patric motorsports and buy the G50/50 flipped and ready to go for my car(if i really need it). i'm afraid that the 50 will not handle the power like the 50/50. the car will have a 351W stroked to 408CI so that's why i'm worried.

luis

Luis,

The ratios are different, and the G50/50 has a limited slip. Not sure what else is different inside the box. By the time you change G50 ratios and add the limited slip ... you have a lot more money in the box than a G50/50. This may not be true if we can find the source of gear sets from Australia ... I understand there are folks there supplying such parts. Standard G50 is supposed to be slightly stronger (whatever that means) than a ZF.

The ratios of a G50/50 are:

Rear end: 3.44
1st: 3.154
2nd: 1.789
3rd: 1.269
4th: 0.966
5th: 0.756

With a 26.2" tall tire, this yields 195 mph at 6500 rpm, and 70 mph at 2350 rpm. 6000 rpm shift points would be: 43, 76. 107, 140 mph.

My understanding is that a ZF's gears are slightly longer, but the ring and pinion is a bit shorter resulting in the package being somewhat shorter (that is, takes more rpm to get to speed).

You mentioned using a Wilwood pedal set. Where is data available on that?

thanks,

mike starling




mike starling
FFR 1667
Sabre GT40 6210

mike

the gear ratios that you posted are for a G50 or a G50/50? if those aren't the G50's ratios, do you know them? my tires are 335/35 R17 or about 26.3 inches tall.

well, about the pedals, they are wilwood part # 340-3950. the master cylinders go towards the firewall and they have remote fillers. this pedal assembly has a balance bar to eliminate the proportioning valve. i will try it and see if it works. i think i shouldn't have a problem with it. it's a very nice unit so i definitely want to use this.

luis

Luis,

I don't have the data on the standard G50. I was told the standard gearing was "awkward." The data I provided was for the G50/50. I'll try to find the G50 data for the sake of completeness.

The tire size used in my calcs was from the GT40 Claranet site and corresponded to the 335/35 R17 tires you are going to run. The actual height of a tire will vary slightly depending on the manufacturer of course.

Where can I see data on the Wilwood part you've mentioned? anything on the web? A specific catalog?

Thanks a bunch for the reply!



mike starling
FFR 1667
Sabre GT40 6210

Hi Mike

Check the Wilwood website at www.wilwood.com I was looking at these as well and are very popular in the GT40 application. I also like the Tilton floor mount pedals. If I recall the Sabre replica uses hanging pedals which is what I used in my KVA. This worked out okay for me as I'm about 5'10" tall and the steering column did not interfere with the pedals. Taller people should consider the floor mount option as it allows you to clear the steering column easier, and in addition the floor mounts resemble the originals.

Regards

Paul Campoli
Toronto, Canada

I have looked at many differnent gear boxes and recently completed one for my RF GT40. On the G50 boxes you might want to contact Patrick Racing in AZ. I remember that the one from the 930 was best for a GT40 because of the gearing.

I also crawled under a new Corvette that was on the showroom floor and found that the axles exitied the box at the very back and that it was a very long transmission. to put the wheels in the correct spot it looked like the engine would end up in the passenger area, so I gave up on this idea.

The 944 has almost the identical case except there really isn't a way to mount the clutch slave cylinder and the input shaft (which is also the main shaft) is not made to accept a clutch but rather a torque tube. I purchased an Audi box and a 944 box so that I could swap some parts and create my own combination. Someone earlier mentioned that he would prefer the 944 over the Audi but there is no difference except with the 944 Turbo which has a nice 3.48 final drive. I got my hands on that 3.48 final drive and found it would not fit into the Audi box or the standard 944 box because the head of the pinion gear is too large and requires a larger opening in the case along with a larger bearing.

The Audi box I found was the 5N with a .73 fifth gear but a 4.11 final drive. The AAZ is also available here and has the 3.89 final drive but a .86 fifth. It would be easier to put a taller 5th gear in a AAZ than what I ended up doing. Since I was able to get both transmissions for under $200. I took the 3.89 out of the 944 trans and put it in the 5N along with a quaife type posi. There was a slight difference in the gears so I ended up using the 944 gears as well. The whole thing did not cost me very much at all so I consider this to be a Bic transmission. I have heard they can take a lot of power and I will find out if that is true. In front of my Audi box will be an injected 347 stroker with close to 500HP. I have been told by the Porsche/Audi mechanics that they were way over enginered and should be able to take lots of HP and torque. This claim wouldn't suprise me since I rebuilt mine. While both transmissions came from old wrecks at Pick-N-Pull I was very suprised when the mechanic told me that neither transmission needed a single part. He only billed me for labor, seals and gaskets. Even the syncros were perfect. He said that this was typical.

I would love to find a part number for the fifth gear in the 3U box. The local dealers can't find it. They said with a part number they could get anything.

Luis,

John Donnelly provides the following G50 ratios:

1st 3.50
2nd 2.059
3rd 1.409
4th 1.125
5th 0.888

Final drive 3.444

I calculate that the 6500 rpm 5th gear max velocity is 165 mph, the rpm at 70 mph is 2750, and the 6000 rpm shift points would be: 39, 66, 97, and 121.

Looks like this is a fairly significant drop in leg length from the G50-50!



mike starling
FFR 1667
Sabre GT40 6210

mike

thanks a lot for this great information. yesterday a guy that works on porsche trannies came in to leave stuff to get ceramic coated and i asked him about the whole deal. he told me that the max speed would be 165 m/h, exactly what you just said. so i asked him about doing a limited slip and the flipping over and all the things needed for the aplication and he said $2200 bucks. is there a posibility on changing the ring and pinion on the G50? can i get a 2.8 or a 3.0 or something like that for a final drive? i'm sure that i could change that and have a nice 80 m/h at 2500 rpm.

any thoughts?

thanks

luis

I am planning on a ERA MK II kit, and thinking of useing a shelby 427 with around 750-800hp. The issue I am having is, What transaxle can I get to take the pounding Im gonna give it. The folks at RBT say treir reworked ZF and their RBT-6 should be able to take the hp. Wondering about the torque is the real issue. I would like the 5 or 6 speed boxes from RBT, any ideas on this one?

Whoa! That should be a really nice setup, but those transmissions are expensive. A Shebly 427 ain't cheap either, those two together might cost more than my entire car!

That transmission should do the trick, and with ERA's waiting list you've got plently of time to think it over.

Ron

Bottomline, if you can afford an RBT ZF tranny, and
you're concern is torque, than that's the best choice.
Everyone I've spoken to says the same thing: all of
the various transaxles can handle the HP, but the
torque is the problem. For mildly tuned 302s with
350 lbs/ft max, I figure any transaxle will suffice.
When you breach the 400 lbs/ft mark, I'd only look
at the G50/50 out of a 930 or a ZF. The G50/50
is rated for something like 700HP, and the 930 Turbo
had a lot of torque for a turbo flat 6, but ZFs
are rated for 500 lbs/ft of torque.

I was looking into RBT's 6 spd, but at $18K+ (my
guesstimate), it may not happen.

The MkIIs did not use a ZF originally, Shelby modified
some Ford toploaders. I'm not sure if they ever got
ZFs since the original tests with a ZF proved fatal
to the transaxle. The 427 Side Oiler pumped out
too much HP and torque.

Ian

The MkI's and MkIB's were the only cars to use the ZF.
Ford had Car Craft build 4 speed boxes for the MkII's. I beleive they experimented with an automatic also, but didn't have much success with it. Since the 427 had so much torque, the 4 speed was able to provide gearing for 200 + mph while only running the engine to the low to mid 6000 rpm range.
When I was at ERA, they had a raw casting (replica) of a Car Craft box that they were planning on developing. Don't know if they've done any work on it since then.
You might check with Hollman Moody to see what they're using on the MkII's that they build. Whatever it is, I doubt that it's inexpensive. I found an NOS -2 ZF for my car, an ERA MkI. While all ZF parts and new boxes are available, nothing is inexpensive for them either. Figure $7000 - $8000 for an NOS -2.

Dave

Dave

There are a bunch of different Audi transmissions, I have taken Ron Earp's spread sheet and added to it showing 14 trans and all ratios, 70 mph 5th cruise RPM, RPM drop at shift, RPM % drop at shift and max speed in each gear. You can also switch any gear to see what the gross and net change. I can email it if you are interested.

While there are many Audi Transmissions only two of them are suitable for a GT40. The 016 type and the newer 01E. The others were four the four cylinder cars and/or have the shift lever in the wrong position. I am interested in looking more into the 01E at some point. This trans is very stout with good gearing including a 6 speed. It has been used behind Audi's V8 and W12. The problem we face with the 01E is it only came in Quatro in the U.S. which means we have to find a non Quatro 01E in Europe. It also has an electronic speedo sender which we may be able to work around if we can still use the Smith 200mph speedometer. Other than that it looks like it would almost bolt right in where the 016 was.

After asking around in WA and CA this is the info I have

porsche 915 350ft lbs, good enough for any mild 302 and a lot less expensive and lighter than the G50
you have to take the box apart and flip the ring gear

porsche G50 500ft lbs
this is what I ended up with since I plan on about 400hp and similar torque
you can't flip the ring gear on this box so you flip the whole box

anything more than 500 hp is wasted on this car, it won just as many races with the small block


I like the G50 ratio just the way it is. In the states your rarely going to go 165 unless your on the superspeedway. And a lower ratio means better acceleration to 165.