Transaxle Purchase

Early on in the planning stage I needed to make a decision between a Porsche G50 or a Mendeola SDR transaxle. Those were the choices. A great deal of discussion has taken place on the Factory Five Forums regarding these options. The G50 can be had in either 5 or 6 speed configurations. There are multiple gear ratio packages and kits to make sure transaxle runs inverted.

The Mendeola was plagued in the early days with delivery problems, but those seem to be old news. There are rumors of a 6 speed version. However, the production runs have been and will be limited runs. The SDR transaxle is a market opportunity as the G50 transaxles were scooped up for various build projects.

The transaxle doesn't exist in a vacuum  There are additional parts that need to be purchased:

• Flywheel
• Clutch release components
• Stage II Clutch
• Cable shift Assy
• Pump and cooler kit
• Bolt Kit
• Gear Reduction Starter 

The additional parts cost around $5000. I built the budget based on major systems for the car. The transaxle plus these parts represent the second largest cost for the build.

Transaxle cost works out as follows:

• A properly rebuilt G50 set up for inverted use costs around $9000.
• A new Mendeola SDR costs around $11,500.

I opted to go with a new Mendeola transaxle. My feeling was that there was less to go wrong with a new transaxle than a rebuilt one. I specified a Mendeola transaxle when I ordered the chassis from Factory Five.

Then I changed my mind.

Seven forward speeds. Two more than the SDR. One or two more than the G50. Factory new (and as of this writing) on a slow boat from Germany.

One of the benefits of not having all the money up front is that I can leverage changes in technology over the three years this is going to take to complete.

Early in 2013, Eric at Gbox posted a thread on the Factory Five forums asking if anyone was interested in a 7 speed 991 transaxle. The same transaxle that is in the new generation Porache 911.

My neck still smarts from the whiplash. Say what!?! Brand new, shipped from Germany, 7 speed Porsche transaxle!!!!

Good bye G50.

Good bye SDR.

Hello 991!

I am bouncing off the walls.

Gbox puts all the parts together and test beds it on an LS block before it leaves their shop for the Northern Man Cave. It is a brand new transaxle that is currently shipping in the 991 generation of the flagship Porsche 911s.

The bad news is this busts the budget. The 991 costs $13,500. Ouch!

Or does it?

One of the items high on the design list were paddle shifters. I contacted Master Shift (my vendor for the aftermarket paddle shift solution) and asked if they had done anything with a 991 transaxle. The answer was no. They had done a 7 speed pattern for a different transmission. I chewed on this for a  couple of weeks. I decided that I did not want to be the Mark I version for an aftermarket paddle shift solution. With great reluctance, I dropped the paddle shifter from the design plan and gained $3000 back to the budget.

The SDR option has the following costs:

• SDR - $11,500
• Additional Parts - $5000
• Paddle shifter = $3000
• Total cost is $19,500 plus shipping

The 991 option has the following costs:

• 991 - $13,500
• Additional Parts - $5000
• Total cost is $18,500 plus shipping

By dropping back to tradition bump shift and going with the 991. I am $1000 below the cost of a new SDR with paddle shift. This isn't funny money like what happens in Washington. This is my pocket book.

Originally, I had hoped to do the engine and transaxle in 2013. That is no longer going to happen. My concentration this year is the rest of the car and the transaxle.

As my wife's cousin said, "Someone is going to have some fun!"

I certainly am!

Budget Review - End of Planning Phase

Yesterday, I placed the order for the GTM. It should show up some time in mid June. This essentially ends the planning phase of the build. The kit purchase is the single largest line item of the entire build. So I think it is a good time to review the budget. My initial estimate was $68,200. When I refined this number, I came up with  $72,200. I set the budget at $70,000. My projected cost is currently 20% higher than that. So where did I go wrong, and importantly, why did I go wrong.

I think it is still possible to build the GTM for something between $55,000 and $60,000. This means you are making no upgrades, and use everything from a donor, including the engine and a recondition Porsche G50 transmission. There is nothing wrong this approach, but I wanted something better. If I'm going to pour three years into this project, then I want a car at the end of this project that is unique and tailored to my specifications.

The following chart shows expenditures to date, based on my original estimate ($70,000), adjustments to specific line items, actual costs and variance to the adjusted line estimates. I have actually done very well to date. I am well within my estimates. I think these categories are easier to price.

Item	Estimate	Adjusted estimate	Actual	Variance
brakes	2000	2000	1945	55
donor	11000	11000	4649.02	6350.98
wheels	3200	3200	1380.99	1819.01
Kit	25000	22967	22692	275
Totals	41200	39167	30667.01	8499.99
Pct of original Estimate	58.86	55.95	43.81
Pct of Revised Estimate	50.24	47.76	37.4

I saved money by going with a donor parts kit, and I haven't purchased the Nitto Invo tires.

Technology and add ons have increased the cost. Yes, mission creep has struck!

These are the categories where I blew the budget estimate:

Item	Estimate	Adjusted estimate
ISIS	0	3108
harness	1500	0
Paint	3000	9000
options & add ons	4000	7714

When I started this project, I didn't even know that ISIS power existed. Sometime last fall I came to realize ISIS was the only sensible power system for the GTM. It provides a programmable and scalable power management system.

The engine harness fits nicely with the engine budget. I think I'm within 10% of both the original transmission and engine estimates. The current engine  slated to drop into the GTM is a LS376/525 with electronic fuel injection. I think it will be relatively simple to get this to just under 600 HP with the optional cold air intake (part of the kit order) and the Kooks custom exhaust (part of the options).

I had no idea how much the paint job would cost and I plugged a number in. I was way off. 

The real mission creep is in the options and add ons section. 

• There are a bunch of body work pieces that I will order from Vraptor Speed Works.
• The paddle shift system to replace the conventional shifter in the center console. This is to make room for additional electronics and ISIS hardware.
• The Ram Lift system to protect the GTM body from unsightly scrapes and damage.
• One thing not reflected at the moment is the APR Racing Wing and mounting hardware. This is an enhancement that is not required to complete the car and can be added at a later date. So I have not reflected this in any of the budget figures.

My conclusions for the over budget issue. The GTM is a work in progress and the build is stretched over 3 years. Technology and ways to do things better will present themselves through out the build. If this were a 3 month project and I had all the money up front, then line items would be cast in stone. Due to the length of the build and the nature of the car, it is foolish to ignore technological innovations that will enhance the finished product. Obviously, I should have included a bigger number for the options and add ons.

The Great Parts Round Up Begins

At my birthday party last night, the guys from my small group asked me what I was up to. I mentioned that I was planning to do a GTM build. It was very reassuring to hear Don give his stamp of approval to Factory Five and the quality of their products. Don is a gear head from way back. Most of the guys were wondering if they could come over and turn some bolts. Certainly! One of the things this kind of project needs is friends.

Don asked if there was much welding. I don't think there is, but he has a spot welder I can use if it comes to that. Again, it is good to know there are friends there to help when (not if) I get into trouble.

I purchased the first real parts for the build: Porsche 930 CV Joints. Porsche OEMs are still making these parts even though they appeared in the 1979 Porsche 911 Turbo (model 930). The Mendeola SDR transmission requires these parts to hook the back wheels into the gear box. These aren't the biggest piece of the car, but it has to start somewhere. Besides the love of my life told me I had to make sure the wheels stayed on the chassis.

Old vs. New: Transmission

There are many issues that you need to confront. One of the biggest is old parts versus new parts. Aside from the Factory Five kit most of the rest of the car can be built from used parts, including engine, transmission, brakes and suspension.

Transmission:
The first generation GTMs used a Porsche G50 transmission. The G50 was introduce in 1987 and retired in 1999 or there abouts. I know of 5 variations on this transmission, plus a long and short version of the case. To make the G50 work with an LSX engine, you will need an adaptor plate. In addition, make sure you get the following parts with the G50:

• speedo sender
• pressure plate
• friction plate 
• release forks
• driveshaft adaptors
• slave cylinder
• rear mount beam ("short only")

You probably want to make sure the unit has been rebuilt/refurbished and has documentation. By the time you have all the pieces, the rebuilt transmission, and pay for core exchange (which you don't have to exchange), the bill is anywhere from $6500 to $9000. This is for a very good transmission. But it was built in the last century and you are going to hook this up to your brand new, dyno tuned LS3 engine.

The other option is to go with a new transmission built for Factory Five by Mendeola. This has limited slip differential standard, a torque rating of 475 ft lbs (warranty 400 ft lbs) and a horsepower rating of 525 HP (warranty 450 HP). It costs (with shipping) $8900. It bolts directly to a LSX engine.

Nothing against Porsche. They are fantastic machines (I love my little Boxster). I have had some wild times on empty country roads in North Western Minnesota. However, I can't see bolting a 15 to 20 year old transmission to the back of a new engine. When you get right down to it, the dollars aren't that far apart.

If you go with the Mendeola, remember to order early. There is a minimum three month wait on these units.