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Verde

Original Poster:

438 posts

68 months

[news] 
Saturday 1st September 2012 quote quote all
I was wondering if i could get some answers regarding Porsche G50 gearboxes.
Background: I purchased a well-constructed GTR a year ago. It runs wonderfully, with an LS7 with a G50 (don't have the info at hand re the sub-type of the gearbox, but if its required to get my question answered, I'll go and dig it out). I'm not sure if it's germane, but the LS7 install was done before the factory supported that motor. Thus a lot of quite excellent custom work to get it all put together.
It all works perfectly, although the shifting seems a bit more stiff than I would expect. But the ratios don't seem well matched for the car. I primarily use the car on the public roads, with only an occasional track day here and there. THe behavior is as follows:
1st gear is unnecessarily low for getting the car rolling. The prior builder/owner always got the car rolling in 2nd, using 1st only to roll the car at extremely low speed;
6th gear is seemingly too short. THe engine turns at more than 2400 rpm's at 70 mph. I recall that C6 Corvette's usually turn around 1700-1800 RPM at the same speed.
I was hoping to give the car a more relaxed top gear - with the possibility of a higher top speed - although that last point will likely go untested. And I'd like a true 6-speed gearbox. Where departing from a standstill begins in 1st.
So, I was wondering how complex it is to change this? Is a ring and pinion swap possible without pulling the whole drivetrain out of the car? Would it help in spreading the gear ratio range? Essentially shifting all gears to a longer ratio?
What is the typical gearing of other small-block/G50 Ultima's. That is, measured in MPH, what does the top gear yield - in MPH and RPM?
I'd rather not do a complete replacement of the gearbox (although I do not think it has an LSD) nor am I excited about the cost of changing out each of the gears, unless it was absolutely necessary.
I should also ask, if I was to consider a transmission swap, what would you suggest? From an uninformed perspective, a cable-operated box from a 997 seems appealing. I have a 997.1 and it works wonderfully. Are other manufacturers worth considering (bear in mind that I'm in CA)? Getrag? Others?
Thanks,
V

spatz

1,745 posts

66 months

[news] 
Saturday 1st September 2012 quote quote all
if you have a 6-speed G50 then it would be most likely from a 993 and not the more common G50 5-speed boxes.
I have installed a longer 5th gear to fix the problem it is a 1,5 hour job for an experienced tech and the good news is that with a five speed G50 it can be done with the gear box installed in the car. So maybe also possible with your 6-speed.
I was going for the 0,75 for the longest fith if I remember correctly however there is a 0,64 available. If the gear sets are the same for the 6-speed I cannot answer but maybe somebody else knows that.

andygtt

7,161 posts

144 months

[news] 
Saturday 1st September 2012 quote quote all
the gearbox swop may not seem appealing, however you also have to factor in that you can sell your box for close to what you may buy another for so the cost should mostly be labour.

swopping to the 997 cable shift box is possible, but its a lot of work... you need a new mechanism from the gearstick back to the box... new gearbox mounts etc.
Not difficult but expensive if you are paying some else to do the work.

worth mentioning I believe the stock 997 box is a getrag (like the 996) and you will need the GT2, GT3 or modified twin turbo or else it's a mass of work as clutch adapter starter etc etc etc are all different on the stock getrag to the G50.... also the 996 box wont have the gearing you want imo.

If you want to change first gear then you will need to remove the box and have it rebuilt as its on the input shaft itself I think.

In summary unless you simply change 6th gear its a lot of work to change the ratios... but I do agree gearing can make or break a car.

highflyer

1,623 posts

106 months

[news] 
Saturday 1st September 2012 quote quote all
Got to say Andy, although it was only a 4 speed the one in your Can-Am was a great box, out of interest did you change any of the ratios in it ?

F.C.

2,995 posts

88 months

[news] 
Saturday 1st September 2012 quote quote all
Ihave a G50 52. 5 speed geared for 210 mph.
A 6 speed box is a bit of a waste on the road as these cars have more than enough torque for am4 speed let alone 6.
Having said that I regularly gor for another gear when I'm cruising along @ 70 wink
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Steve_D

9,181 posts

138 months

[news] 
Saturday 1st September 2012 quote quote all
The 6 speed is likely the G50-20 which I have.
As said the 5th gear in the other boxes is the same gear set as 6th in your box so can be swapped in situ.
A crown wheel and pinion swap I believe is not possible, I don't think anyone makes them.

Steve



F.C.

2,995 posts

88 months

[news] 
Saturday 1st September 2012 quote quote all
Ring and gear pinion sets are available with different ratios if you have 7.5" Crown wheel

3.10/10:31

4.00/8:32

If you have 9" only the latter (I think) which won't help you at all.

CMS have them.

Worth a trawl on the net, if CMS do them ($3000 ish yikes ) then someone else may also.

Verde

Original Poster:

438 posts

68 months

[news] 
Saturday 1st September 2012 quote quote all
Thanks very much. More suggestions are welcome. This is a great place to learn.
What I've understood so far is that:
1. I've got a box from a 993 (which is what I discussed with the builder/first_owner) but I didn't know what model correlates to that, so I left it as an open question in my last post.
2. So far, if it can be done in place, the quickest and lowest cost improvement is to replace 6th-gear. At least I can get a more comfortable cruise and/or a higher top speed.
3. It looks like replacing the gear box with a cable-operated box is not cost effective. That is, unless I am really unhappy with the shifting experience, I should avoid this route. And I am not that troubled by it. It is certainly slower and requires more exacting shifting, but the muscle memory has been acquired for some time now.
4. There may be a method of replacing the final drive gear (ring/pinion) ratio which, to me, seems like a better fix than just 6th. Would both be prudent? Does the box have to come out to do a ring/pinion in this config? (intuitively, I would assume that you wouldn't have to pull the gearbox for a ring/pinion if it was installed in a Porsche). More info hear would be appreciated.
5. I did not quite understand the Getrag reference. It sounded like the post was saying that Getrag builds the transmission. Is that so? I am still curious (i.e. unlikely to follow such a path) about what other transmissions fit in to the GTR/L7 config.
6. I failed to ask about the power levels that the 993 gear-box can tolerate. On the one hand, I have heard the factory note that they've never (rarely?) seen a Porsche gearbox failure with any of the Chevy small blocks. OTOH, that is a lot of power for a 993-designed gearbox. For e.g., by LS7 was rated at 575 HP and about the same in foot/lbs. That's about twice the output of a typical 993 (non-turbo) motor. Seems like quite a challenge.
7. Any other comments about adding a LSD to the 993 box? Does that require removal (I didn't think so after reading a bunch of posts in 6Speed forums)? Is it worth the effort?
Please keep those cards and letters coming, and apologies for the rookie questions but having not built the car, there is much in the way of knowledge of the internals that is my 'quest'. smile
And thank you again,
V

Storer

2,689 posts

95 months

[news] 
Saturday 1st September 2012 quote quote all
My G50-52 5 speed is a great box. Well spaced ratios with a low revving top for relaxed cruising. Drop a cog and you leave others in your wake. 1st is a little quick for maneuvering but my tick-over is a bit high.
The rod linkage change is a little noisy and not the slickest but simple. The cable shift I tried in another car was even more reluctant to operate smoothly so probably needs even more fettling to get it to work well.

To the OP. You do need to find out exactly what box you have and put it into Dom's calculator http://www.spatz-tech.com/ultima/Doms_Gear.xls

From there you can make an educated choice.


Paul

Verde

Original Poster:

438 posts

68 months

[news] 
Saturday 1st September 2012 quote quote all
Thanks. I have a few large boxes of documentation and will pour through them shortly. With regard to your post, can you give me some idea of the speed/rpm's you are seeing in your application? For example, 6th gear at 70 MPH?
WRT ring/pinion, I've come across this:
http://www.californiamotorsports.net/G50%206%20spe...
And a ring/pinion set designed for V8/longer ratio applications.
Anyone know of this change. I know that the CA Motorsports folks have a good rep.
V

Storer said:
My G50-52 5 speed is a great box. Well spaced ratios with a low revving top for relaxed cruising. Drop a cog and you leave others in your wake. 1st is a little quick for maneuvering but my tick-over is a bit high.
The rod linkage change is a little noisy and not the slickest but simple. The cable shift I tried in another car was even more reluctant to operate smoothly so probably needs even more fettling to get it to work well.

To the OP. You do need to find out exactly what box you have and put it into Dom's calculator http://www.spatz-tech.com/ultima/Doms_Gear.xls

From there you can make an educated choice.


Paul

Storer

2,689 posts

95 months

[news] 
Saturday 1st September 2012 quote quote all
I only have 5 gears and speeds are as follows

70mph is 2400rpm
100 is 3400rpm
200 is 6800rpm
All are give or take and no, I have not done 200mph so it is a calculation.

I have an LSD which my old G50.01 didn't have and it improves traction no end.

I would check the box itself for the number. Can't remember if it's on the top or the bottom.


Paul

dal2litrefrogeye

317 posts

57 months

[news] 
Saturday 1st September 2012 quote quote all
Hi , I have a G50 03 2 box c/w LSD which adds to the fun of driving ( steps out at will ) , and when the the back end does step out its a lot more comunitive and a better feel from the rear end , and i also have the longer top gear fitted well pleased with it ( just over 3000 rpm @ 100mph/ 1500 rpm @ 48 mph , just off tickoveryes and 189 mph so far hehe) looking to try and crack the double ton

Steve_D

9,181 posts

138 months

[news] 
Sunday 2nd September 2012 quote quote all
When considering your options don't put too much weight on the 'gearbox removal' as it is not a difficult job. There are owners on here who have it down to a fine art for all the wrong reasons.

Steve

Verde

Original Poster:

438 posts

68 months

[news] 
Sunday 2nd September 2012 quote quote all
Thanks for the tip. That's great to keep in mind. Can I extract the 'box w/o extracting the motor? Or do you pull them out together before cracking them apart? I assume that if could easily remove 'just' the gearbox, I could tuck it under my arm, and bring in down to the local shop that specializes in servicing older Porsche's near my home.
V

Steve_D said:
When considering your options don't put too much weight on the 'gearbox removal' as it is not a difficult job. There are owners on here who have it down to a fine art for all the wrong reasons.

Steve

Steve_D

9,181 posts

138 months

[news] 
Sunday 2nd September 2012 quote quote all
The build sequence would be drop the engine in from above then fit the 'box from behind posting it through the chassis. To remove the 'box from a finished car you need to take off the rear clip and work from there.

Steve

F.C.

2,995 posts

88 months

[news] 
Sunday 2nd September 2012 quote quote all
The ring is attached to the diff and is accessible through the side plate. Not sure about removing the pinion without removing box. LSD is worthwhile but get the pre-load wound back a little to suit the car. Std LSD is fine and for me gives just the right amount of feedback, you could go the ATB route but to me they are missing the "lift off" feedback (which is kind of the idea I'm told ??)
These boxes handle torque very well but I would change the side plate for a CMS Billet item which is stronger and stiffer than the standard cast item and greatly reduces the likelihood of ring gear jump and consequent damage.
Cable shifts are available, I have one and it is nice and slick. Adjustment is everything though.

cito quod fortis

166 posts

69 months

[news] 
Sunday 2nd September 2012 quote quote all
I don’t know about any of the technical stuff, other than removing the gear box from an Ultima is quite easy – it’s one of the few things I can actually do myself! I was however looking at different ratios and LSD for my G50 a couple of years ago. I found these guys http://www.albinsgear.com.au/products.php who I’m told supply CMS, amongst others. They were very helpful about the options and would make whatever ratios you wanted, albeit there was about a 6 week wait for the manufacture, then time to ship from Australia and they were cheaper than anyone else I could find. If I remember correctly, Albins also did a CWP set for around AU$1,500, but that might have been GB pounds.

In the end, the Steve & Jason at Autobionics fitted a G64/51 (993 turbo converted to 2wd) box for me, which had LSD and a long 6th gear. 1st is still only for manoeuvring the car, but overall this was a quicker solution to what I wanted and, even with the new mountings, it worked out cheaper than new ratios and LSD, once the old box was sold.

Good luck. Andy

andygtt

7,161 posts

144 months

[news] 
Monday 3rd September 2012 quote quote all
Verde said:
5. I did not quite understand the Getrag reference. It sounded like the post was saying that Getrag builds the transmission. Is that so? I am still curious (i.e. unlikely to follow such a path) about what other transmissions fit in to the GTR/L7 config.
6. I failed to ask about the power levels that the 993 gear-box can tolerate. On the one hand, I have heard the factory note that they've never (rarely?) seen a Porsche gearbox failure with any of the Chevy small blocks. OTOH, that is a lot of power for a 993-designed gearbox. For e.g., by LS7 was rated at 575 HP and about the same in foot/lbs. That's about twice the output of a typical 993 (non-turbo) motor. Seems like quite a challenge.
the stock porsche 996 box is a getrag... its what porsche moved to for the 911 after the G50.
The 996 twin turbo GT2 and GT3 all used a cable shift box (so it feels like the 996 Getrag) but with the stronger G50 internals.

There have of cause been failures of G50's and other porsche box's over the years, but they are very strong (G50 is stronger than the getrag btw) and failures are hardly common... I dream of having as strong a box as your G50 in my Noble and i run silly power!

as Steve says, taking the box out isnt a tough job so dont let that sway you overly.... I had a special CWP made by CMS for my 996 GT2 box (same internals as large diff 6 speed G50 which gives me over 250mph in 6th at 7000rpm ... its the best option IMHO as it changes all the ratios upwards... but its very expensive.

F.C.

2,995 posts

88 months

[news] 
Monday 3rd September 2012 quote quote all
andygtt said:
I had a special CWP made by CMS for my 996 GT2 box (same internals as large diff 6 speed G50 which gives me over 250mph in 6th at 7000rpm ... its the best option IMHO as it changes all the ratios upwards... but its very expensive.
Could you divulge cost here?

UltimaCH

2,279 posts

69 months

[news] 
Monday 3rd September 2012 quote quote all
You probably need to win a chunk of the Euro lottery to afford the upgrade biggrin
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