This is good discussion and thanks for the info Erik!

I talked to my wife last night about this. She has been a key employee (from an engineering, deliver and sales perspective) for 20+ years with an industrical manufacturing company, building everything from pressure vessels to nuclear pumps), and has had lots of gear sets made for various applications. They do a fair amount of design/machining for extreme environments, and deal with a lot of different materiasl and alloys.

It seems to come down to the materials selected (ie. which alloys), specifications (type of gearing, tolerances), and finishing (hardening, etc.). What would be the issue of taking an ideal Porsche gearset and duplicating it? Not sure if they have explicit copyright on gearsets, give other people seem to make them. Its seems the large cost is the gears themselves. (Hope I do not get flamed for even suggesting this but I am a cheap bugger.. :-) ).

Erik, are the gearsets you are quoting Porsche sets, another vendor or yours?

Cheers,

Mike

 

Since I have strong ties with Hewland and now Ricardo with their racing gbx business, a few years back I sent Hewland a few G50 gear sets with the notion to make them in several ratio's. They were interested but the buy in quantities to make them affordable, i.e under a grand each, we'd need at least 25 of each set made.

That pretty much ended my quest.

Hollinger, Guard and of course Porsche already make them.

Key to gbx parts in general, as Mike touched upon above, is heat treat!! Its everything really.

 

In reference to what gear sets I tend to use here, that is kind of a combination. It somewhat depends on the application. I would tend to use Guard gearing quite a bit. In a racing application, meaning GT2 and GT3 Cup Cars, my preference is to continue to use Porsche Motorsport gearing, but that is not always cost effective. For the sequential gearboxes I like the Emco gears. They are really well designed and have shown to be very strong.


Heat treat is a big thing, yes but certainly not the only thing.

I hope that this answers your questions.

Erik Johnson
GBox Sales Manager
(303) 440-8899 work
(303) 895-4828 cell

 

Do you have knowledge of Albins gears link below:

http://www.albinsgear.com.au/product...rbar=5#porsche

They seem to be very big in the Off-road buggy sceen, and they use Porsche transaxles.

 

Here's where the money goes:

One of these costs about as much as a nice 993 coupe and goes on a machine that costs more than a GT3 RSR!!! When I toured our gearcutter's factory this summer he told me he had several Million dollars invested in machinery. The cost of the gears is paying the note on those machines.

The big boys like Ricardo and Hewland get huge economies of scale on some of this stuff, because they make in giant volumes. They probably pay off one of those machines in under a year. The small guys, like our gearcutter and diff. maker, who is a 12 person operation, basically carries a mortgage on the machine. I guarantee you that Porsche makes 3-4 times the profit per gear that we do because they make them by the thousands. We make a dozen or two of each ratio we sell about once every year or two. For some less popular ratios, 12 gears is a 2-3 year supply. Basically, what I am getting at is that in the Porsche aftermarket the volume isn't there to get them made much cheaper.

 

I took a 993 gearbox to Copans nearly a year ago. While the shop iteself was amazing, the fact that they had more than $100,000 worth of new Porsche gears in stock floored me.


Andreas

 

When I re-geared mine, we tossed 6th, made 5th the new 6th, made 3rd the new 4th and put in new 2nd, 3rd and 5th. To me it seems perfectly spaced and eliminates the gap between 1st and 2nd. Top speed is "limited" to 155'ish which is fine by me. The car actually accelerates in 6th gear now without being revvy on the freeway. Much more usable and I love the gear whine in 2, 3 and 5!

I will dig out the ratios and post if interested.

MC

 

please post the ratios when you have a chance.

 

Ok, so here goes... In 2005, I contacted Paul Guard and discussed the options in great detail. Price was a consideration but not the final decision factor. Ultimately, we agreed that the best option was to replace 2nd, 3rd and 5th, keeping stock 3rd for the new 4th and stock 5th for the new 6th. We also replaced the synchros with steel units at $172 each (3 total) and replaced the mainshaft with an early 993 model that allowed swapping of 2nd gear ($400). In addition, I purchased a bearing race, shift spindle and 5th/6th spacer at Mr. Guard's recommendation. Total cost of parts was $3,583.82 including tax.

The replacement ratios are as follows:

2.375 (16:38) 2nd gear
1.789 (19:34) 3rd gear
1.174 (23:27) 5th gear

The rest of the ratios are stock except 3rd is now 4th and 5th is now 6th. 1st remains unchanged.

Mr. Guard was a remarkable source of information, even if coming across as a bit cantankerous (sp?). I also purchased a beautiful billet torque biasing differential ($1050 plus tax) from him and had RMG Enterprises perform the modifications to the tranny plus some other work for $4,100.

I have extensive G-50 repair bulletin documentation produced and provided by Mr. Guard related to:

- Stock spindle #950 303 134 05 - weakness and unsuitability for racing or high performance use ( I purchased the case hardened 8620 model as part of my mods)
- G50 / 993 Open Differential Preventative Modification - shortens spacer to reduce by 2mm the pinion gear into the spider gears due to a factory "design error".

At the same time the tranny mods were installed, I had a Porsche RS flywheel and 993 Turbo Clutch installed. The collective value of these mods felt like a 50hp increase in power. The car has been an absolute joy to drive since.

I'm not in a place where I can scan docs now but, if anyone would like scanned copies of the above-referenced materials plus, a graphic representation of shift points, top speed per gear, etc. I will provide next week. In the short term:

Gear Top Speed (6900?)
1st 39.6
2nd 63.5
3rd 84.4
4th 107.2
5th 129.2
6th 162.7

Tire Diameter: 25"
Ring & Pinion: 9:31

I hope this is helpful. I'm happy to answer additional questions. If you are in the SF Bay Area, you can drive the car to see how you like it.

Matt

 

could you double check your ratios? particularly 5, I get a real mess when I map yours
here's what I think you are using
11:42
16:38
19:34
27:38
23:27
38:35

 

Bill,

The ratios ended up being:

11:42 Stock
16:38
19:34
27:38 stock 3rd in 4th
23:27
42:39 stock 5th in 6th

MC

 

Thanks for sharing. Maybe Bill could plug those numbers into his spread sheet chart.

I am local to you (North Bay) so I will be taking you up on the offer for a ride. Do any of you 993 guys get together and drive down skyline???

 

You see my problem w/ those ratios?

 

I think something is wrong with your formulas. On the previous page, you show 27:38 3rd gear (USA G50-20) as having a top speed of 103. That is my 4th gear now so the top speed should remain the same with that gear combo, yet you show it as a top speed of 116 in the chart above.

On the previous page you show 27:38 as a 1.407 ratio. On the graph above it's a 1.241. It should be the same, correct?

MC

 

Good catch, MJB didn't provide the tooth count so I had to enter his gearing by hand, I did yours as a derivative of his and had forgotten that little tidbit.
here's yours, 6th looks to be set up for cruise rpm relative to the lower gears