Porsche G50 gearboxes
Discussion
I know somebody with a smoking old 964rs in Wycombe. After trying to keep up with the Ultima last weekend I think the car is good for parts. Give Domster a bell- he may know somebody thats breaking one. Have you thought of audi as they had a simlair transaxle?
>> Edited by bluesatin on Thursday 29th August 10:08
>> Edited by bluesatin on Thursday 29th August 10:09
>> Edited by bluesatin on Thursday 29th August 10:08
>> Edited by bluesatin on Thursday 29th August 10:09
Got one from Chilham Sportscars, ad in Exchange & Mart, they seem to have a regular supply of 964s for breaking. On rating, torque is the thing rather than HP. Porsche apparently rate all their boxes to a little bit higher torque than the engine its bolted to, but use a pretty conservative safety factor - so you can double rating before anything goes bang. Not sure if same applies to Audi though.
Hello everyone. Brad Z from Chicago signing on...Stateside GTR builder (haven't started yet :-( although the kit is in hand since December). Has anyone tried the Getrag 6 speed that Ultima is offering? I have a G50-03 set aside but don't know anything about the Getrag unit. Any thoughts would be appreciated! I enjoy reading your posts!
Hey Brad.
The Getrag unit is fine from what I know, it is a bit shorter than the G50 (111mm) so doesn't risk sticking out of the rear grill. There's a cable operated shifter available aswell as an alternative to the linkage.
They're available new from the factory at a good price.
If you're just starting out on the build, have a look at my site www.ultima-gtr.info to see mine in progress.
>> Edited by stig on Friday 30th August 11:09
The Getrag unit is fine from what I know, it is a bit shorter than the G50 (111mm) so doesn't risk sticking out of the rear grill. There's a cable operated shifter available aswell as an alternative to the linkage.
They're available new from the factory at a good price.
If you're just starting out on the build, have a look at my site www.ultima-gtr.info to see mine in progress.
>> Edited by stig on Friday 30th August 11:09
quote:
I know somebody with a smoking old 964rs in Wycombe. After trying to keep up with the Ultima last weekend I think the car is good for parts. Give Domster a bell- he may know somebody thats breaking one.
Cheeky sod.
Mind you, I did offer Stig the gearbox for £25k, with a free 964RS thrown in
quote:
Gemini Transmissions do a nice 6 speed sequential Porsche G50 dog box only £10K.
Why not a Porsche G50/21 6 speed ??
The torque curve on the sort of engine that you're going to fit to a road car is so wide, that by fitting a 6 speed box, all you're going to do is increase the number of gear shifts, for no real benefit. The ratio of 6th gear on a 6 speed box is generally pretty much the same as 5th in a 5 speed, so it's not like you're going to be getting an extra bit of top speed out of the car. With the long linkage you're going to have to work with, you want as few gear changes as possible
Actually, the ideal transmission would probably be something like a 3 speed. 1st for pulling away. 2nd for driving on the road, and 3rd for the quick bits on a circuit
James
James,
This was concluded in my research as well. I'm not sure about the Getrag, but on the Porsche 6-speeds typically there is not a whole lot of difference between 5th and 6th. John Castle helped me put together a real neat package of custom gears for the 5-speed G50. Its a better compromise for the street and track. I rebuilt the gearbox myself, which is not too difficult, but does require a few gear pullers, special Porsche tools, and the Porsche service manual. Since the Ultima does better at 0-60 starting in 2nd gear, w/ this gearbox, we raised 1st gear close to the original 2nd, and then closely spaced 2nd, 3rd, and 4th. 5th has been pushed way up for highway cruising. 1st:2.33, 2nd:1.68, 3rd:1.286, 4th:1.04, 5th:.756. With a 3.44 R&P and 25.6" rear tire diam., the resulting top speeds for each gear at 7500rpm are 1st:71mph,2nd:98mph,3rd:129.01,4th:160mph,5th:219mph. What I love about this arrangement is that its basically a 4-speed close ratio box with an overdrive 5th gear. This should result in less shifting on the short/twisty local tracks.
Cheers!
-Mack
This was concluded in my research as well. I'm not sure about the Getrag, but on the Porsche 6-speeds typically there is not a whole lot of difference between 5th and 6th. John Castle helped me put together a real neat package of custom gears for the 5-speed G50. Its a better compromise for the street and track. I rebuilt the gearbox myself, which is not too difficult, but does require a few gear pullers, special Porsche tools, and the Porsche service manual. Since the Ultima does better at 0-60 starting in 2nd gear, w/ this gearbox, we raised 1st gear close to the original 2nd, and then closely spaced 2nd, 3rd, and 4th. 5th has been pushed way up for highway cruising. 1st:2.33, 2nd:1.68, 3rd:1.286, 4th:1.04, 5th:.756. With a 3.44 R&P and 25.6" rear tire diam., the resulting top speeds for each gear at 7500rpm are 1st:71mph,2nd:98mph,3rd:129.01,4th:160mph,5th:219mph. What I love about this arrangement is that its basically a 4-speed close ratio box with an overdrive 5th gear. This should result in less shifting on the short/twisty local tracks.
Cheers!
-Mack
Mack and James
If I read what you're saying....basically there's no advantage to the 6 speed Getrag and I should just add LSD and regear my G50. Mack....where does one find the tools to work on the G50 and how expensive are they? My builder has the G50 manual and planned on doing the work before I got started on the Getrag route which Ted recomended. Thanks for the great info....I enjoy all your posts! Have a great weekend all!
Brad Z
If I read what you're saying....basically there's no advantage to the 6 speed Getrag and I should just add LSD and regear my G50. Mack....where does one find the tools to work on the G50 and how expensive are they? My builder has the G50 manual and planned on doing the work before I got started on the Getrag route which Ted recomended. Thanks for the great info....I enjoy all your posts! Have a great weekend all!
Brad Z
Hi Brad,
I really don't know anything about the Getrag unit. I've just seen the ratios for the Porsche 6-speed. Like James said, there's no benefit to the 6-speed but added shifts and 1st gear in these boxes are useless anyway with our Chevy powerbands. Another point to make is that the U.S. and European ratios can vary slightly. Which G50 do you have? Is it the long or the short version? The long has a big rubber donought on the end of it. I didn't think the gearbox was that difficult to work on, and you can find the manuals on microfiche floating around on Ebay. This is where I got mine for about $30. It will be for the model year of Porsche the gearbox came with. If you want to run a LSD, then it might be best to let a rebuilder install it and setup the R&P correctly. Actually, if the LSD diff is similar in dimension to your open diff then you may not need to reset the R&P. I've not done this conversion, but this info comes from other rebuilders who have. Personally, I prefer not to run a LSD diff in my car. The tools to setup the R&P run over $1500 alone. To change out all 5 gears, however, requires a few gear pullers of various sizes and two special Porsche tools that can be ordered from Baum Tools online. Baum sells all the Porsche transaxle tools. I'll look up the part numbers for you. I don't think I spent over $500 for all the tools including gear pullers, and the cost to add new gears will run at least $800-$1200. This all started b/c the original rebuilder used a 1st gear that was not to Porsche specs. The synchro hub dimmensions on 1st gear were way off! Imagine, spending $2000 for a rebuilt box, letting it sit a year, and then not being able to shift into 1st gear when everything's together. Argh!!! So I got so pissed off, that I decided to rebuild the box myself and throw $5k worth of PHII gears into it, new synchros, and a billet shift fork. I also was able to obtain a brand new input shaft that had never been used. The only other mod I want to do next is run a gear and diff lubrication pump and possibly a cooler so that I can skin the underside of the engine bay. Let me know if I can help in anyway. Cheers!
-Mack
I really don't know anything about the Getrag unit. I've just seen the ratios for the Porsche 6-speed. Like James said, there's no benefit to the 6-speed but added shifts and 1st gear in these boxes are useless anyway with our Chevy powerbands. Another point to make is that the U.S. and European ratios can vary slightly. Which G50 do you have? Is it the long or the short version? The long has a big rubber donought on the end of it. I didn't think the gearbox was that difficult to work on, and you can find the manuals on microfiche floating around on Ebay. This is where I got mine for about $30. It will be for the model year of Porsche the gearbox came with. If you want to run a LSD, then it might be best to let a rebuilder install it and setup the R&P correctly. Actually, if the LSD diff is similar in dimension to your open diff then you may not need to reset the R&P. I've not done this conversion, but this info comes from other rebuilders who have. Personally, I prefer not to run a LSD diff in my car. The tools to setup the R&P run over $1500 alone. To change out all 5 gears, however, requires a few gear pullers of various sizes and two special Porsche tools that can be ordered from Baum Tools online. Baum sells all the Porsche transaxle tools. I'll look up the part numbers for you. I don't think I spent over $500 for all the tools including gear pullers, and the cost to add new gears will run at least $800-$1200. This all started b/c the original rebuilder used a 1st gear that was not to Porsche specs. The synchro hub dimmensions on 1st gear were way off! Imagine, spending $2000 for a rebuilt box, letting it sit a year, and then not being able to shift into 1st gear when everything's together. Argh!!! So I got so pissed off, that I decided to rebuild the box myself and throw $5k worth of PHII gears into it, new synchros, and a billet shift fork. I also was able to obtain a brand new input shaft that had never been used. The only other mod I want to do next is run a gear and diff lubrication pump and possibly a cooler so that I can skin the underside of the engine bay. Let me know if I can help in anyway. Cheers!
-Mack
Anyone experienced any overheating problems with the G50. After a good thrashing my car is tricky to get into 1st & 2nd. The box gets hot (too hot to touch). This could be conduction from the engine but I am not sure. After the car cools off a bit 1st & 2nd are easy to obtain.
Has anyone else experienced similar problems?
I am thinking of fitting a temp gauge to the box – does anyone know what is a normal operating temperature?
I am using API GL5 synthetic gear oil – I presume this is OK?
www.rensport.com recommend oil cooling on the G50 for over 350bhp. They have a picture on the site of an oil injected box but the link does not work – too bad
I am considering fitting an oil cooler using the mocal pump available from Think Automotive and some form of oil injection back into the box.
Where is it best to inject the oil? I presume the ring & pinion is one area.
Are there any special injectors or do I just a pipe fitting
Has anyone else experienced similar problems?
I am thinking of fitting a temp gauge to the box – does anyone know what is a normal operating temperature?
I am using API GL5 synthetic gear oil – I presume this is OK?
www.rensport.com recommend oil cooling on the G50 for over 350bhp. They have a picture on the site of an oil injected box but the link does not work – too bad
I am considering fitting an oil cooler using the mocal pump available from Think Automotive and some form of oil injection back into the box.
Where is it best to inject the oil? I presume the ring & pinion is one area.
Are there any special injectors or do I just a pipe fitting
Hi Adequate Speed,
You can see a better photo of the pump setup at www.brammo.com. Craig is running the mocal pump, and the fittings into the gearbox are just pipe and AN fittings. Nothing real fancy. The idea is to inject oil at the R&P and at least the 1st four of the 5 gears. If you are thrashing on this box, I can see it getting hot pretty quickly. I had no idea that it would affect gearshifts on 1 and 2, but having been in this gearbox many times I can understand why. Most of the heat will be generated at the R&P. 1st and 2nd gear are closest to the R&P. This is probably why your having difficulties. I think the fact that the G50 has steel gears with brass synchros must have something to do with the shifting difficulties. When I had problems shifting into 1st gear, it was because the synchro hub was too large and not allowing the brass synchro to sit completely with the recommended gap. It might not be your problem, but I just can't help but imagine that an expansion of metal is occuring. Maybe you have the opposite problem and the brass synchros are expanding too much and this keeps them from rotating freely giving you difficulties. You don't want to warp the synchros though, so I'd try to go a little easier on the gearbox until you can strip it down. However, you can always replace the synchros while your in there. You'll have to teardown the gearbox to install the pipe fittings. Let me know if you need any help or advice. Another thing you might try is running steel synchros on 1 and 2. Maybe they'll expand at the same rate as the steel gears?
Cheers! I'd like to hear how this story plays out. Keep me posted on it.
-Mack
You can see a better photo of the pump setup at www.brammo.com. Craig is running the mocal pump, and the fittings into the gearbox are just pipe and AN fittings. Nothing real fancy. The idea is to inject oil at the R&P and at least the 1st four of the 5 gears. If you are thrashing on this box, I can see it getting hot pretty quickly. I had no idea that it would affect gearshifts on 1 and 2, but having been in this gearbox many times I can understand why. Most of the heat will be generated at the R&P. 1st and 2nd gear are closest to the R&P. This is probably why your having difficulties. I think the fact that the G50 has steel gears with brass synchros must have something to do with the shifting difficulties. When I had problems shifting into 1st gear, it was because the synchro hub was too large and not allowing the brass synchro to sit completely with the recommended gap. It might not be your problem, but I just can't help but imagine that an expansion of metal is occuring. Maybe you have the opposite problem and the brass synchros are expanding too much and this keeps them from rotating freely giving you difficulties. You don't want to warp the synchros though, so I'd try to go a little easier on the gearbox until you can strip it down. However, you can always replace the synchros while your in there. You'll have to teardown the gearbox to install the pipe fittings. Let me know if you need any help or advice. Another thing you might try is running steel synchros on 1 and 2. Maybe they'll expand at the same rate as the steel gears?
Cheers! I'd like to hear how this story plays out. Keep me posted on it.
-Mack
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