Seattle Active Power GT40 - A Father/Son build

Peter,

Thank you so much for getting back to me so quickly!

- you were right, Chris is a great guy I have been emailing with him. Thinking about planning a visit soon to check things out.

I hope you don't mind but I have some follow up questions for you...

1. Chris explained how helpful the engine plate is to stiffen up the chassis... this pretty much convinced me that that is the right decision. I just wanted to double check with you that the resulting vibrations don't degrade the "Sunday cruise" ability of the car (so to speak).

2. I would be very grateful if you could dig up the pushrod suspension notes! Are the shocks the ones that come with the Roller Kit?

3. Okay great! LSD it is!! you wouldn't happen to know if any Porsche G96 transaxle comes with LSD would you? I did some reading and think I found that only the 2WD versions (C2) come with LSD... I know you run a different transaxle so no problem if you don't.

4. Which cage option did you choose from Chris? The "Roll Cage front hoop upgrade" or the "SCCA/NASA approved competition roll cage"? The extra pin arm you installed is so cool... Just to clarify that is the only modification you did to the cage right?

5. hmmm interesting fuel tank information... it is funny having two fuel tanks is quite the topic of debate on these cars as to how to best utilize them! I will do some more research. I will keep the "analysis paralysis" comment in my back pocket for later... I think your way of moving forward is a great philosophy...

6. Very interesting... So the general rule of thumb is that you need full R spec racing slicks to pull enough G's to really utilize the dry sump? I will look into the accusump system as well.

7. Chris said that modified roll corvette roll bars are included with the roller package... Why did you choose to use other ones? Just curious.

8. Perhaps the options available have changed since you ordered... but would you be willing to share what other options you got through Chris? I am tempted by the "parking brake kit" and "electric wiper kit" as building those system from scratch would be tough... Thoughts?

I can't thank you enough for your time thus far!

Nick
 
3. Okay great! LSD it is!! you wouldn't happen to know if any Porsche G96 transaxle comes with LSD would you? I did some reading and think I found that only the 2WD versions (C2) come with LSD... I know you run a different transaxle so no problem if you don't.

They do have 996 with LSD. They are hard to find. I plan on having CMSD install a wavetrac

stack
 
3. Okay great! LSD it is!! you wouldn't happen to know if any Porsche G96 transaxle comes with LSD would you? I did some reading and think I found that only the 2WD versions (C2) come with LSD... I know you run a different transaxle so no problem if you don't.

They do have 996 with LSD. They are hard to find. I plan on having CMSD install a wavetrac

stack
Thanks for the info! Good to note. I looked up CMSD and did not find what shop it stands for, can you help me out?

What are some other common LSD units used in these boxes?
 
1. Chris explained how helpful the engine plate is to stiffen up the chassis... this pretty much convinced me that that is the right decision. I just wanted to double check with you that the resulting vibrations don't degrade the "Sunday cruise" ability of the car (so to speak).
I ended up going away from the engine plate; I was struggling to find an accessory kits (water pump, alt,...) that would fit both the tight space, and also figure out how to account for the thickness of the motor plate. so I opted to get a regular engine mount, and then replaced the rubber bushings w/ Delrin.


2. I would be very grateful if you could dig up the pushrod suspension notes! Are the shocks the ones that come with the Roller Kit?
will do. No, I replaced them w/ QA1 double adjustable shocks...they are on the cheaper side of double adj, but get the job done and have been effective.


3. Okay great! LSD it is!! you wouldn't happen to know if any Porsche G96 transaxle comes with LSD would you? I did some reading and think I found that only the 2WD versions (C2) come with LSD... I know you run a different transaxle so no problem if you don't.
Yes, some came w/ them...but many did not. I agree w/ the CMS link, that's who I would've used if I went w/ a Porsche unit.


4. Which cage option did you choose from Chris? The "Roll Cage front hoop upgrade" or the "SCCA/NASA approved competition roll cage"? The extra pin arm you installed is so cool... Just to clarify that is the only modification you did to the cage right?
The SCCA Approved competition package. Chris was great to work with, and accommodated our different design ideas.


5. hmmm interesting fuel tank information... it is funny having two fuel tanks is quite the topic of debate on these cars as to how to best utilize them! I will do some more research. I will keep the "analysis paralysis" comment in my back pocket for later... I think your way of moving forward is a great philosophy...
The other thing to think about is how to detect a fuel pump failure. If you go w/ a dual fuel pump design (ex. in parallel drawing from their own tank), what happens if 1 pump fails...if it degrades your fuel delivery, you may not notice until you're higher up in the RPMs, and at that point you could be leaning the engine out. I like the simplicity of 1 primary fuel pump, if it ever fails, it's fairly obvious.

7. Chris said that modified roll corvette roll bars are included with the roller package... Why did you choose to use other ones? Just curious.
I wanted something adjustable. I like tweaking settings, and I also high a specific handling style that I prefer to drive...and I'm far more experienced with a Front Engine RWD set-up, so I was fairly sure I'd be changing a lot early on.

8. Perhaps the options available have changed since you ordered... but would you be willing to share what other options you got through Chris? I am tempted by the "parking brake kit" and "electric wiper kit" as building those system from scratch would be tough... Thoughts?
we got:
1) Brake kit - I would skip this next time...I ended up getting a Wilwood BBK for the fronts, as I was struggling to get enough force into the brakes/
2) Cooling kit: I'd do this again....everything mounts perfectly, and it's been more than enough on a 100F day sitting at a stop light. (and I've yet to install the oil cooler kit)
3) "Bundles of snakes" - Chris did a fabulous job, and is competitive on pricing.
4) Electric wiper kit: I haven't install it yet...but it's fairly simple
5) Lighting kit: It's a basic kit w/ old school tech...I ended up replacing most of it for more modern and better lighting.
6) Flip up gas caps: there's lots of options out there (Similar to the cobra)...these work
7) Upgraded Rims: We went with 18" so that it'd clear bigger brakes. These halibrand knock offs look really good...but spokes are somewhat inset, so it's hard to find brake calipers that will clear.
8) Aluminum rear spoiler: It's simple, works, and for the price is hard to beat.
9) FG Seats, bare: very simple shell, but the shape works well for the GT40. After sanding them down, cutting holes for the harness, painting, we had them upholstered localling...overall I like the look & they work well.

**Depending on your size, you'll want to sit in as many GT40s as possible ot get an idea of what works best for you. The seat, steering wheel, pedal box, and shifter are all super tight clearances...I'm 5'11" and 200lbs; I fit, but spent days figuring out the angle of the seat, how my feet would straddle the steering column,...and I still have some more tweaking to fine tune things. I elected not to do the Gurney bubble (didn't like the idea of my head protruding above the roll cage), and with my helmet on I still clear the roof.
 

Neil

Supporter
Peter,

A few observations regarding your suggestions:

Re #5: In a dual parallel fuel pump system, both pumps should be capable of delivering the required fuel flow rate. If one fails the engine still runs just fine on the other. A check valve would be necessary on the output of each pump to keep fuel from leaking back through the failed (or turned off) pump. An option is to use a "shuttle valve" to isolate the fuel pumps from each other. This is a special type of valve that has two inputs and one output port. The output is fed from whichever input port has the higher pressure. A shuttle valve may not be easy to find, though, being an aircraft/aerospace component.

Re 6): "Flip-up" gas caps are dangerous and should be avoided; they dump out fuel in a roll-over and drench everything in high octane gasoline. For looks, mount a dummy non-functional flip-up cap and put a proper fuel filler cap in a hidden location. A visit to a burn clinic is something to avoid.
 
Last edited:
Peter, thank you once again for the great info!!!

I have one last question for you.

I have been searching far and wide for the best information possible on the Porsche transaxles. My conclusion is that a 996 G96 box will work great for street use less than 490 ish hp. I have had two very reliable sources tell me different answers about track use. One guy said they are a little too weak and the other guy said he thinks it will be just fine.
My question for you is that in the end.. how did you decide on your transaxle? The cost difference is pretty large so I figure you had a pretty good reason. I know you race your car so I am very interested in you opinion. How did you justify the expense over the 996 box?

Thanks,
Nick
 
Peter,

A few observations regarding your suggestions:

Re #5: In a dual parallel fuel pump system, both pumps should be capable of delivering the required fuel flow rate. If one fails the engine still runs just fine on the other. A check valve would be necessary on the output of each pump to keep fuel from leaking back through the failed (or turned off) pump. An option is to use a "shuttle valve" to isolate the fuel pumps from each other. This is a special type of valve that has two inputs and one output port. The output is fed from whichever input port has the higher pressure. A shuttle valve may not be easy to find, though, being an aircraft/aerospace component.

Re 6): "Flip-up" gas caps are dangerous and should be avoided; they dump out fuel in a roll-over and drench everything in high octane gasoline. For looks, mount a dummy non-functional flip-up cap and put a proper fuel filler cat in a hidden location. A visit to a burn clinic is something to avoid.
Neil,

thanks for the pointers... I will definitely keep these things in mind. I really appreciate you sharing some knowledge.

Nick
 
Re #5: In a dual parallel fuel pump system, both pumps should be capable of delivering the required fuel flow rate. If one fails the engine still runs just fine on the other. A check valve would be necessary on the output of each pump to keep fuel from leaking back through the failed (or turned off) pump. An option is to use a "shuttle valve" to isolate the fuel pumps from each other. This is a special type of valve that has two inputs and one output port. The output is fed from whichever input port has the higher pressure. A shuttle valve may not be easy to find, though, being an aircraft/aerospace component.
Good points, thanks! I've worked w/ shuttle valves before, but on pneumatic valves (Aerospace)...and also considered check valves and other components; in the end, I figured simple was easier for me to get right.

a new issue popped up this weekend as I went for a drive in Seattle...I was at a stoplight on a fairly steep hill pointing downwards. I was on the way to get gas as I was low...w/ the GT40 long Fuel tanks, I watched as my 1/4 tank went to 0; My fuel pick-up and fuel-level-sender are all in the back, closet to the engine. I have ATL Fuel bladders w/ an incorporated sump that has a trap door. It was a long red light, and luckily the engine never died. How do others handle this? It got me thinking that when I add the 2nd tank, maybe I'll plumb in the fuel pump to the front....so that 1 side will always have fuel.

On the positive side, this was probably the worst case scenario...low on fuel, on a steep hill, and stuck for a few minutes waiting for the light,...and it never ran out of gas. I also figured that if it did die, I could just coast down the hill and restart once the road leveled out.


Peter,
Re 6): "Flip-up" gas caps are dangerous and should be avoided; they dump out fuel in a roll-over and drench everything in high octane gasoline. For looks, mount a dummy non-functional flip-up cap and put a proper fuel filler cap in a hidden location. A visit to a burn clinic is something to avoid.
Good point. Not sure if my flip-up caps are different than others...but it has a seal that is spring loaded. not sure how much it would leak when inverted...that's something I'll need ot track down. Thanks!!
 
I have been searching far and wide for the best information possible on the Porsche transaxles. My conclusion is that a 996 G96 box will work great for street use less than 490 ish hp. I have had two very reliable sources tell me different answers about track use. One guy said they are a little too weak and the other guy said he thinks it will be just fine.
My question for you is that in the end.. how did you decide on your transaxle? The cost difference is pretty large so I figure you had a pretty good reason. I know you race your car so I am very interested in you opinion. How did you justify the expense over the 996 box?
One of our main objectives when starting this build was to have a very reliable car that could be "streetable", but focused for autoX, Track, Drag Racing, and potentially top speed runs (ie. salt flats). So we wanted the transaxle to be able to handle abuse...which pointed us to either a Porsche unit from a 996/7 Turbo or GT2/3 (which we would have sent to CMS to be rebuilt, flipped, and plumbed for oil); at that point, the cost was on par w/ the Mendeola. I'm still on the fence between the Mendeola vs. Porsche...Porsche is more readily available & OEM feel, but the Mendeola we got to choose every gear and it's designed for hard abuse.

If I was tighter on $$, I probably would've gone w/ a descent 996 trans, and did the oil plumbing myself. The stock 996's made ~300HP, so I wouldn't expect them to perfectly hold up to 500+HP...but they still last a long time, and they aren't very expensive to repair or pick up a used unit; then it's just your own labor. (I started this project w/ my Dad & we split all of our costs...which helped fit things like the Mendeola into our budget)
 

Chris Kouba

Supporter
a new issue popped up this weekend as I went for a drive in Seattle...I was at a stoplight on a fairly steep hill pointing downwards. I was on the way to get gas as I was low...w/ the GT40 long Fuel tanks, I watched as my 1/4 tank went to 0; My fuel pick-up and fuel-level-sender are all in the back, closet to the engine. I have ATL Fuel bladders w/ an incorporated sump that has a trap door. It was a long red light, and luckily the engine never died. How do others handle this?
Swirl pots.

My sill tanks feed into a 3rd tank of ~4 gal capacity. My EFI high pressure pump uses this for a source, and I have two low pressure (carb) pumps feeding it from the sill tanks. It is actually the aft portion of the driver side sponson and I put the anodized cover plate over it to seal it up:



This pic was during my build when I was pressure testing it. The set of three blue 90° elbows are the two sends and one return (single return goes to manual diverter valve so I control the tank to which the gas returns). The stainless plate has a pickup tube extending from it almost to the bottom of the swirl pot and this is the source for the high press EFI pump and the single 90° elbow at the right is my EFI return.

You don't need to have one this large, it was just convenient as that was the size the cavity happened to be. With upwards of 4 gallons (a mostly full 5 gal can didn't fill it), I can still get almost 100 miles on the swirl pot alone if I stay off of the happy pedal.

If you're ever down PDX way, drop a note.

Chris
 
One of our main objectives when starting this build was to have a very reliable car that could be "streetable", but focused for autoX, Track, Drag Racing, and potentially top speed runs (ie. salt flats). So we wanted the transaxle to be able to handle abuse...which pointed us to either a Porsche unit from a 996/7 Turbo or GT2/3 (which we would have sent to CMS to be rebuilt, flipped, and plumbed for oil); at that point, the cost was on par w/ the Mendeola. I'm still on the fence between the Mendeola vs. Porsche...Porsche is more readily available & OEM feel, but the Mendeola we got to choose every gear and it's designed for hard abuse.

I talked to Roger at CMS today and he and I came to just about the same conclusion you did... very helpful to hear the same thing from you as well. The 996 base box seems like a great deal but after one rebuild you are set back a few grand (not including labor). I am beginning to look for used turbo boxes and GT2/3 boxes but even then I would be rolling the dice that they wouldn't need a rebuild right away... After a rebuild you are right I could just buy a brand new custom built Mendeola.... the transaxle topic sure is a tough one.... a few questions on the first part for you...

- How did you choose between the S5R and the SDR5?
- Was it hard to hook up the shifter? How is the feel? Do you terribly miss the H pattern? A sequential could be bada**
- what gearing did you choose?

If I was tighter on $$, I probably would've gone w/ a descent 996 trans, and did the oil plumbing myself. The stock 996's made ~300HP, so I wouldn't expect them to perfectly hold up to 500+HP...but they still last a long time, and they aren't very expensive to repair or pick up a used unit; then it's just your own labor. (I started this project w/ my Dad & we split all of our costs...which helped fit things like the Mendeola into our budget)
I would actually be happy to do my own labor... just a question on how much I want to worry about blowing it up I suppose.

- when you said a "decent 996 trans" did you mean a nonturbo or turbo?

AS ALWAYS A HUGE THANK YOU FOR YOU TIME AND HELP!!
 
I would actually be happy to do my own labor... just a question on how much I want to worry about blowing it up I suppose.

- when you said a "decent 996 trans" did you mean a nonturbo or turbo?

AS ALWAYS A HUGE THANK YOU FOR YOU TIME AND HELP!!
I was talking about a non-turbo. I think the base and S models are the same. FWIW Renegade Hybrids does a lot of LS3 swaps into the 996, so there's plenty of people who have used an OEM 996 transaxle w/ LS3 torque...I did that swap on a 996 C4S a few years back, and it was working great; I ended up having a steering tie rod failure and totaled the car before it was 100% done. At the time I was on a tighter budget and didn't want to spend the extra $$ to upgrade to a turbo trans...so I just used the existing tranny.
 
Swirl pots.

My sill tanks feed into a 3rd tank of ~4 gal capacity. My EFI high pressure pump uses this for a source, and I have two low pressure (carb) pumps feeding it from the sill tanks. It is actually the aft portion of the driver side sponson and I put the anodized cover plate over it to seal it up:

This pic was during my build when I was pressure testing it. The set of three blue 90° elbows are the two sends and one return (single return goes to manual diverter valve so I control the tank to which the gas returns). The stainless plate has a pickup tube extending from it almost to the bottom of the swirl pot and this is the source for the high press EFI pump and the single 90° elbow at the right is my EFI return.

You don't need to have one this large, it was just convenient as that was the size the cavity happened to be. With upwards of 4 gallons (a mostly full 5 gal can didn't fill it), I can still get almost 100 miles on the swirl pot alone if I stay off of the happy pedal.

If you're ever down PDX way, drop a note.

Chris
Chris - Thanks!! When we set-up the fuel system, I only thought out being on track (long sweeping corners or extended braking sections) and wanting to ensure the engine wouldn't fuel starve...the ATL has a "surge tank" with trap door that contains ~1 gallon; sufficent for anything on the track. I may add an external swirl pot to add a bit more capacity. (This is 1 of the things I love about building a car...there's so many unique challaneges, even as simple as just getting fuel to the engine!)

next spring I'll start venturing farther away from Seattle and will likely head down to Portland; would love to meet up and see yours in person. thanks!
 
I've been spending lots and lots of hours on the GT40...the primary goal for this winter is Paint! I've done lots of small paint jobs...but nothing like this before. I've turned my modest 2 car garage upside-down in making it a reasonable paint booth.

Due to limited space, I've elected to paint it in 3 phases:
Phase 1: Rear Clam & side skirts

Lots of little clean up areas...general progression was:
1) Filler: primarily around the mold seams.
2) Polyester: This is a super high build spray, similar to laying a very thin layer of filler across the whole body. I probably sprayed 5lbs, and then sanded off 4.5lbs...trying to get everything straight
3) Primer: I elected to do a high build primer, as I knew I'd miss some areas w/ the poly,...glad I did this. It was a good chance to catch any last issues
4) Epoxy Sealer: A good final coat to provide a consistent base for color to be laid down.
5) Base Coat: I'm using "Oslo Blue", a 1960's era Porsche color...I wanted a darker blue of similar vintage. Plan is contrast it with white features (Door #'s, GT40 side stripes,...)
6) Clear
image0.jpeg


Rear done (in the pic, the side sills weren't cleared yet): Lots of little mistakes...I'm learning a ton, and while it's far more work than I had assumed, I'm enjoying this!
image2.jpeg



Phase 2: front & Radiator extractor:
-I bought a FORD decal, laid a layer of white down, then applied the decal, paint the blue....then pulled the decal. I laid on the clear really heavy in this area...plan is to cut/buff to get it perfectly flat.
-I also painted the radiator extractor areas white, similar to how the new race GT40 looks.
image1.jpeg



Phase 3: Doors & spiders...I'm just starting this now. I cut apart my door interiors to clear the roll cage door bars...so I've got a good amount of FG'ing to do first.
 
Daily progress...starting to look like a real GT40 now!

Starting to add the graphics...lots of work to align all the panels!
5FD6AD68-F866-400B-8C0E-F5985F2D0901.jpeg



made a simple license plate holder...better than the metal zip ties that I was using before. Wanted it to stand off the rear vent so that it wasn’t preventing airflow.
4CF44A6A-1C15-419C-9092-4E76E316631C.jpeg


Front coming together...still need to paint the headlight boxes.
FAC53C47-17B5-4D1F-BB18-07F946AE0EA5.jpeg


License plate frame done! It Always seems to surprise me at how long even simple parts take to custom make.
8CCC5F22-7678-48A5-94D1-EEEAA944B079.jpeg
 
Few more updates...paint is all done, now putting everything back together.



sunny day in Seattle, had to pull her out
5AD4C012-2E5C-482E-9C9A-21AEA91E02EA.jpeg
3ACF3D9A-C039-4E00-A018-870E9C7572E7.jpeg
BC7C3A12-8A5F-4071-AA1F-F0A3FE23221A.jpeg


headlight. Painted the bezel matte black...like the look far better than before. Key is that it tones it down a lot.
11FF5331-02B1-44DD-9558-680DEAEA835E.jpeg

Door is complete. Handles work, window installed, slider and mini pop out vent.
D0C592E0-97E4-4CDB-AAD5-4661AFF815DE.jpeg

Sanding the edges...cutting can leave such a sharp edge!
54A3F66F-F5B6-4BFC-B3F0-63BAF11A1B38.jpeg


I ended up making my own door eyebrows from Aluminum and a bead offset roller. I then attached them w/ countersunk rivets and a little epoxy. Then paint. I really like how they turned out. (I had noticed that at highway speeds, the leading edge of the door tops was letting in more airflow...I needed to adjust the doors a bit to help prevent that, but I figure these ensure any pressure gradients won't cause them to open up. I plan to track the car, so it needs to be good for higher speeds.
5C31DA9A-A994-4C56-A497-17AE8245AAE0.jpeg
 
Nice.
What number are you going to stick on those "big'a-spicy-meatball'as "?
#46. It's the year my dad was born...and explains why his dream car was the GT40; he was in his 20's when the GT40 came out, and was also racing SCCA in California, so he knew of Shelby and many of the others too.

*Glad I choose the big Meatballs...cause it covers more of my paint imperfections :) (I had continual issues w/ debris landing in the clear coat...so i've got lots of buffing/polishing to fix it)
 
Top