Erik@GBox

Hey there everyone, so I know that we discussed this a bit in a earlier thread, but I couldn't sleep last night and decided to really take a look at the 993 in a bit more detail to see what I could come up with for a re-gearing option.

THE CHALLENGE:

To put together a cost effective option for the 993 owner to address gearing issues for both street and track. (This one is mostly for the street)

First let's review what most 993 owners currently have, gearing wise, so that we are all on the same page and understand how complicated this challenge actually is.

Let us all assume the following information to be correct:

RPM Redline = 7000
Tire Dia = 24.732 inches
Final Drive = 3.444 or 9:31 (tooth count on the ring and pinion)

1st gear 3.818 or 11:42 offers a top speed of 39.178 MPH
2nd gear 2.048 or 21:43 offers a top speed of 73.055 MPH
3rd gear 1.407 or 27:38 offers a top speed of 106.287 MPH
4th gear 1.118 or 34:38 offers a top speed of 133.843 MPH
5th gear 0.921 or 38:35 offers a top speed of 162.411 MPH
6th gear 0.775 or 30:31 offers a top speed of 193.018 MPH

Here is where it gets tricky, different drivers like their Porsche to handle and drive in different ways. Most commonly, however, I hear requests for a taller 1st and 2nd, slightly shorter (closer together) 3rd, 4th, 5th, and a good highway gear for 6th.

With these drivers in mind lets start at the top - 1st and 2nd gear.

Porsche 993 owners of cars built prior to 1996 catch a bit of a break here. The main shaft of the 993 has what we call a 'slide-on' 2nd gear, which forgive me if I sound a bit remedial here, allows the 2nd gear to be replaced without replacing or modifying the main shaft.

For owners of 1996 and on you have what is called a 'integral' main shaft which means that the 1st and 2nd gears are cut directly on the main shaft.

Either way 'slide-on' or 'integral' I think that we can agree that these two gears need to be changed out. Here is the next bit of trickiness. How much do we change them? For instance, if we make both 1st and 2nd too tall, we run the risk of difficulty getting the car to take off from a stop. This is felt even more so if you have installed a lightened flywheel. Yet, if we go too short, we haven't addressed the original issue, and run the risk of feeling like we spent a lot of money on a solution that didn't quite fit the build.

So remember where we are starting from here, with regard to the 1st and 2nd gear?

1st gear 3.818 = 11:42 = 39.178 MPH
2nd gear 2.048 = 21:43 = 73.055 MPH

In we borrow a little bit from Porsche Motor Sport and replace these ratios with 2.333 or 15:35 for 1st, and 1.773 or 22:39 for 2nd here is what we get.

1st gear 2.333 = 15:35 = 64.109 MPH
2nd gear 1.773 = 22:39 = 84.383 MPH

Does this seem a little too tall to everyone? well let's not forget the other half of our challenge. A shorter 3rd, 4th, 5th (closer together) was also requested. So let's see what happens when we change the final drive to 4.0 or 8:32.

When we change our ring and pinion from from 9:31 (3.444) to 8:32 (4.0) our gearing with the new 1st and 2nd looks like this.

RPM Redline = 7000
Tire Dia = 24.732 inches
Final Drive = 4.0 or 8:32 (tooth count of ring and pinion)

1st gear 2.333 = 15:35 = 55.205 MPH
2nd gear 1.773 = 22:39 = 72.663 MPH
3rd gear 1.407 = 27:38 = 91.525 MPH
4th gear 1.118 = 34:38 = 115.253 MPH
5th gear 0.921 = 38:35 = 139.854 MPH
6th gear 0.775 = 40:31 = 166.210 MPH

But what about our desire to maintain a good highway gear? Well let's see how much it actually changed.

80 MPH with 9:31 (3.444) Final Drive in 6th gear = 2950 RPM
80 MPH with 8:32 (4.000) Final Drive in 6th gear = 3300 RPM

Obviously this gear set could be changed out, as well, but for me at least I think I would leave it alone. I love the sound of my Porsche's engine, this would allow me to hear it a bit better without killing my gas mileage.

Okay, so the last part of this equation, was I able to make it cost effective?

Well you decide, here is what I came up with:

Replacement of the main shaft 1st and 2nd with Guard Transmission's excellent 2-piece main and slide on 2nd gear set.

$3945.00

Combine this with a Albin's ring and pinion 8:32 (4.0)

$2625.00

Labor on this assuming 10 hours @ $90.00

$900.00

For those of you that have a gearbox that is a bit tired we can give it a good freshening up at the same time. Cost on this will vary a bit from box to box, but let's average it out here at $2500.00

As a additional Rennlist bonus here though we will install a set (3rd - 6th) of our steel synchronizers, as not additional cost. (Beyond the normal cost of the brass ones.)

So how did I do here? This option, I think, has a lot going for it, as at the end of the day you are basically going to have a new gearbox right? I mean new main, and ring and pinion, at least, as well as new 1st and 2nd gears.

One last note here everyone. I know that I have not been on Rennlist for a bit, until recently again, and that I am now with a new company - GBox. I have in the past been accused of coming off a bit strong here, and a bit too much like a sales person. I would just like to say that I love my job, and what is sometime confused for a sales push is actually just a passion for what I do.

I enjoy the opportunity to help as many people as I possibly can not only hear but on several forums across the net. I have worked very hard to earn the respect of the people I work with and look forward to that same opportunity here.

I realize that no one likes to be bombarded with sales thread after thread, and believe me I do try to put in my .02 cents into other threads here as well. Please allow me a bit of slack for just a bit, so that I can show my new owners that being a part of the Rennlist is a good thing, not only for the members but also for GBox. This is a truly great forum, with a quality of people overall that is unmatched. I feel fortunate to be a part of it again.

So okay let me have it - let the flames begin. LOL

Warmest Regards,


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

chris walrod

One thing I dove into a little a few years ago is taking an integral layshaft, grind off the second gear, respline the shaft to fit slide on 2nds. Local heat treat would be required then monitor shaft runout.

I do think its possible as its something we do on similar racecar bits.

Cactus

I need to do more research to see what the best gearing seems to be and to really understand what all the numbers mean. Thanks for all the info and I never mind seeing these type of threads as long as they are legit.

timothymoffat

+1, thanks Erik. The spacing seems about right. My only criticism would be the now-very-tall (too tall?) 1st gear.

Arena993

I'm Lost. My car is very shiny though.

Mike

VNTGSPD

I agree. The tall first would be a bit of a nightmare for anyone who spends any time in traffic at all. Admittedly, the number of consumers willing to spend money to regear a trans who drive their cars often enough to spend time in traffic yet do not track the car has got to be very small. I do know of one.

So, for those of us lucky enough to have an early gearbox, does the 2nd gear ratio cost the same as the other ratios quoted at $900 each?

I'm thinking that a shorter 2nd and a progressively smaller reduction in 3rd and 4th would work for me as long as I could keep the rpm drops between the upper gears low enough.

Great info either way! Thanks for your efforts to look at this puzzle several different ways.

Bill Verburg

If you were going to change cwp & only 1 & 2, here's what I would do


the tradeoff w/ just doing a 3, 4, 5, move 5 to 6 regear is that this fixes the bottom at the expense of top. The 3, 4, 5, move 5 to 6 regear is already a bit of a compromise at the top end.

if it's ~$4k for the mainshaft and 1 & 2 and each additional gear set is somewhat less than $1k, in other words instead of a cwp you can do roughly 3 gears and just need to buy 1 more set. you could do all 6 for <$8k

I am not in the business so I'm just going by your #s and the #s i've been quoted in the past

also when comparing prices to a factory /3x remember that these also come w/ a motorsports lsd.

Bill Verburg

Just a comment on the 55mph 1st.

I had a stock 3.6 in my 993 when I first had the /30 installed. 1 is ~43mph and there was noticeably more clutch slippage necessary to get going, the extra torque of the 3.8 overcomes that issue

csertich

Erik,

Thanks for continuing to post gearbox options. This information is helpful and very tempting. I also appreciate the input from Mr. Verberg and Mr. Walrod.

Thanks very much to all,
chuck

trophy

Erik and/or Bill what would be the RPM drop with the ratios Erik is proposing?

Erik, you should look at using 6700 +- rpm as the max as this is the stock redline for our cars.

Great food for thought, a regear is in my cars future. I am still not sure if I am going the replace or rebuild direction as yet.....

I notice you always quote steel syncros for 3,4,5 6. What are you using for 1 & 2?

Regards

Tango635

Hi Erik,

What do the numbers (term speed w/ 6800rpm, rpm drop, price) look like if you leave 1&2 alone, change 3,4,5 as you propose, drop in a motorsport 4.0 LSD?

Thanks,

okindao

great question and i look forward to seeing the answer

Bill Verburg

Here's what many consider to be the perfect street trans for a 993. This is a g50/21 used on '95 & 95 RoW, you could emulate this by changing 3, 4, 5, 6. Personally i'd prefer a tad shorter 6, but for those that like a litle more relaxed cruise this is fine

Bill Verburg

For comparison here's regear where you buy 3 gears, you save a gear purchase by moving 5 to 6 and leave 1 & 2 alone

****ignore the tooth counts here, the ratios are correct

trophy

The 3 gear replacement looks good, especially for a street car... The spacing and resulting rpm drops look great..... Any street car (except the stop light racers) would benefit from that setup..