G50 question for beginners
Discussion
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
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
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'.
And thank you again,
V
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'.
And thank you again,
V
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
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
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
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
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
Thanks all. I plan to get together with the fellow who serviced my Porsche 930 (it only had 10K miles when I purchased it 3 years ago, and was essentially factory new but I sold it to provide the funds and garage space for the Ultima; a no-brainer for my tastes) so he can be sure of the exact transmission details and come up with a plan of attack. Much as I don't want to spend too much right now, it seems like I should look a three things: ring/pinion if possible; LSD install; shaft cover plate (or whatever it's called) to provide more strength to the housing. If there is no ring/pinion option, I may just consider stretching 6th to be a bit longer.
V
V
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