Rumbles SLC Build

[Fran Hall RCR]

Its a reality...give Delynn a call or email...

He has made many changes ..some of which were requested to make the boxes have a more sophisticated shift and feel....triple cone syncros etc etc ...

 

[Bill]

Transaxle and Rear tire selection

Yup, I spoke with California Motrosports yesterday. That's where I got the estimate for the ring & pinion swap.

I'm widening my thinking to include other alternatives:

• There is a Porsche salvager here in NC that will give me a hand in finding a tranaxle that fits my needs.
• I'll look into other transaxle options such as Griffin, Mendeola, etc.
• One option is to mount taller rear tires. This may be a nutty idea but here are some possibilities

Your thoughts?

 

[Fran Hall RCR]

Also give Erik at Gbox a jingle and tell him its for an SLC and that I personally said to call.....also that you have spoken with CMS....

 

[Larry L.]

Re: Transaxle and Rear tire selection

• One option is to mount taller rear tires. This may be a nutty idea...

Why? Makes perfect sense to me. Tire diam has been used to solve ratio issues since...forever.

 

[Bill]

Transaxle selection

I looked at all the Porsche transaxle variations that I could find. So far I've found 83 different models. No wonder its hard to get your head wrapped around what transaxle to buy.

I compiled this spreadsheet from the Gbox website that shows all 83 gear boxes with their gear ratios, clutch type, shifter type, the Porsche that used it, etc. This helped me and maybe you can get some value from it as well.

View attachment Porsche Transaxle Specifications2.xls

 

[Doc Kaler]

Bill,

You must have a serious case of "cabin fever"!

Very well done!

 

[Schills]

When I talked to the Porsche transaxle vendors 2 weeks ago, a base level option from them with limited slip and everything else you'd need (clutch, starter, etc.) was between $10-$11k.

 

[Alex]

When I talked to the Porsche transaxle vendors 2 weeks ago, a base level option from them with limited slip and everything else you'd need (clutch, starter, etc.) was between $10-$11k.

My 930 gearbox w/ starter, flywheel, clutch, etc.. etc.. (complete) is costing me 11.5k

My Ricardo, complete (starter, flywheel, clutch, etc.. etc...) cost me about 11.5k complete.

I wish now I'd used a 930 in my slc - lighter and if anything happens to it, there are multiple people who can rebuild it. Ricardo, only 1 shop can to my knowledge.

 

[Justin]

I've talked to a couple of shops about using the 930. They all said to steer clear of it. Why is that? I know it's a light and solid box that can be serviced in many places (including here in Vegas). I also know that it's "only" a four speed, but who cares when you have a big V8 in front of it. So what gives???


Sorry for the off topic question.

 

[Dean Lampe]

Before I looked at 83 different boxes, I would call Fran and just ask "What gear box should I use?" That made things a lot easier for me. You need to remember that it needs to mount to the LS engine and mount in the car. It was helpful that Fran had already sorted out all the parts to make this work.

 

[Colin]

I've talked to a couple of shops about using the 930. They all said to steer clear of it. Why is that? I know it's a light and solid box that can be serviced in many places (including here in Vegas). I also know that it's "only" a four speed, but who cares when you have a big V8 in front of it. So what gives???

Doesn't sounds right to me either. The 930 box is extremely strong and race proven over many, many years.

 

[Michael]

Also give Erik at Gbox a jingle and tell him its for an SLC and that I personally said to call.....also that you have spoken with CMS....

Unless something has changed for him recently, Erik now works at CMS with Roger. He's been there for about a year or so now.

The two of them are probably about the largest knowledge bank that you're likely to find for Porsche gear boxes. :thumbsup:

Good luck.

Mike

 

[Fran Hall RCR]

Erik has been back at Gbox for quite some time.....come on Mike keep up...

 

[Bill]

Finding the Right Transaxle

I just clicked the PayPal button and bought my tranny. I probably made the selection process harder than it had to be, but I'm a total novice when it comes to transaxles. I felt I needed to educate myself on all the possible choices out there and then narrow it down to the one that best fits my motor and wallet.

This chart and a chat with Fran helped me narrow my choices down to a used Porsche box, since I plan to build a street car with a 430HP LS3 motor.

Within the world of Porsche, there are a staggering number of tranny variations. However, the adapter that RCR supplies will only fit the G50 style bell housing. In other words, the 4 bolt mount with the starter mounted on the transaxle (vs on the motor). This significantly narrows the possibilities down to the 20ish G50s, G64s, and a few of the high end G96/G97 transaxles (i.e. GT2/GT3, Twin Turbo, etc).

Many of the G50s and G64s transaxles a have very low stump puller 1st gear ratios and top gear ratios that will spin your motor 2700RPM at 70MPH. I can live with a low 1st gear, but a screaming motor on a long highway cruise gets old fast. See the Spreadsheet I attached in an earlier post below to choose the ratio that fits your needs.

So what did I buy? It was a G50/21. It’s a 6 speed with a top gear that should cruise at 2278RPM at 65MPH.


A couple of final notes

• You can use an all-wheel drive (AWD) unit. Fran tells me that it can be converted cheaply and easily.
• A long tail can be chopped to fit. Fran can do that for you quite reasonably.

Hope this helps others in their tranny quest…

 

[Jack]

Have we forgotten the "lowly" 930 gearbox? 4 speed, but great V-8 ratio's.
It should take 500-600HP without major issues.

 

[Bill]

Does the 930 have the same G50 style 4 bolt bellhousing?

Hmmm, just looked at some images of the 930 and it looks like it will work as a 4 speed option.

I'm still learning to speak Porsche...

 

[Scott]

The G50/20 or 21 is probably what I am going to end up getting and have the first and 6th gears swapped out for a 2.81 and .656 respectively. Of course I have no idea what that would cost and probably will not be able to afford it right off the bat. I have an email into GBox so well see what they say. Is the one in the picture the one you bought? Where did you acquire it from?

 

[Bill]

Scott,

That sounds like an ideal combination.

I'd be interested to hear what will cost.

 

[Vidal]

So what did I buy? It was a G50/21. It’s a 6 speed with a top gear that should cruise at 2278RPM at 65MPH.

Bill,
If it were me and I were planning to install the box as-is I could rationalize 65mph @2278rpm, but if I were going to have the box checked prior to installation I would have a taller 6th gear installed.

The G50/20 or 21 is probably what I am going to end up getting and have the first and 6th gears swapped out for a 2.81 and .656 respectively. Of course I have no idea what that would cost and probably will not be able to afford it right off the bat. I have an email into GBox so well see what they say. Is the one in the picture the one you bought? Where did you acquire it from?

Stan installed a taller 6th in my G50 20. The gear was just over $900 (not sure of the labor cost).

 

[Bill]

Vidal,

I agree that a taller gear would be ideal, but for now I'm going to see if I can live with it as is. Its fairly easy to yank the transaxle later if needed.

I would rather spend that $1000+ on something else, like the motor, exhaust, interior, etc :juggle: