Classic HorsePower Scratch GT40

[Devin]

Hey Y’all (West Texas lingo for “everyone”)

Long time lurker/dreamer/collector of various parts here. I’m finally at that stage in life where I had to commit to getting started on this adventure or move on to other life goals & priorities.

My experience over the last 35+ years has been primarily with Mustangs, Porsches, BMWs, and Cobras amoung various other muscle cars and trucks from the 1940s to the 80s. The GT-40 was my “unicorn” and have begun the build to make it a reality.

After weighing budget, time and my experience, I have chosen to truly make this 40 a custom build to fit me as a taller (6’1”) individual yet make it as true to the original look (to the untrained eye) for the major key features of the car.

After acquiring the major body shells (some almost 20yrs ago), front, rear clamshells, roof/spider skins, door skins, sill covers, and dash. After committing to a custom build vs buying a manufactured kit, I’m sourcing things as I go along and face dimensional & fabrication challenges but that is the “fun” of a custom build to me,

Devin
Abilene, TX

 

[Devin]

For my chassis, I’ve committed to the ActivePower/ Corvette C-5 suspension design for ease of domestic US parts and maintenance. With that being said, I’ve varied from the standard AP chassis in several ways for added interior room and to meld the various previously sourced body parts.

The following is a summary of what I’m envisioning the final specs:

- 2” longer wheelbase with added 2” between interior leg space & engine bay room
- SBF (289-347ci) carbureted with Porsche Boxster S (6 sped)
- 15” BRM or Halibrand replica wheels (or 17 if not practical)
- LHD with center shift (Boxster cable system)
- Traditional black low tech interior with AC (Texas heat!)

With all that being said, I am new to TIG welding but have years of MIG welding, ASE certificates in brakes & suspension, and have access to an Aero/Mech Engineer for sanity check on design & materials.

I started with chassis welding in October and here are the first stages of my build.

 

[Devin]

More TIG welding and fab for the suspensions pieces...had a local metal shop CNC cut the mounting brackets & sheet metal plates according to plans. Of course they never just fit the first time even though everything is “within spec” of dimensions so a few more hours of thought and work are always the rule for custom building.

 

[Terry Oxandale]

Hi Devin. Welcome to the site. Sounds like you've got a good start on what you want to do. Please continue with the build photos, and good luck on you project.

 

[Udo]

Hi, your panels look pretty much like mine did. Enjoy grinding and lamination work

 

[Devin]

Mostly finished up initial welding (need some more seams done on rotisserie) of the main chassis and suspension mounts. Need upper mounts of the rear shocks but will wait until I have those in hand to get the angle correct.

Also reworked the drivers fuel pod to enable the installation of Tornado fuel tanks...need to do the same to the passenger side (right) next. Relearned a valuable lesson to have the parts in hand before final welding. As we all know, no two replica manufactures dimensions are the same...my first attempt at the fuel pod was about 1/4” too narrow but more critical was that the height of the tank was 3/4” taller than my planned space which would be the lowest point of the car...not acceptable. Cut and replaced the side bar of the pod from 1.5” square to 3/4” square. Yes, less strength (not completely necessary in that area) and side impact protection however I added 3 additional cross braces for added strength. More diagonal bracing will be added in multiple areas once on the rotisserie as well.

 

[Devin]

Finally got the chassis off of the welding table for the first time and mounted to a rotisserie.

Funny thing is that I inherited this homemade rotisserie with a past Austin Mini restoration and stored it away for several years. Thought it might work so I brought it out to measure and see if I could modify it...all I needed was to relocate the mounts and figure out how to attach to the chassis!

Once mounted, it’s top heavy (of course) so will have to work out a counterweight to assist in rotating it but for now welding on the underside is a luxury.

 

[Joe]

Looks great

 

[Markus]

Mmmmh, GT40 drive train and Mini body?
;-)

 

[Devin]

Been a busy couple weeks here at Classic Horsepower garage.

Had to make emergency trip back to KS but decided it was the right time to help my dad’s forever best friend dig out his 65 Galaxie 500XL (390FE) after its 40+yr hibernation in a barn. Needless to say I’m reviving it back to life so will take some time away from the GT40 build but am determined to keep making small progress weekly.

Here’s the 68-72 Sprite/Midget steering rack I just got and it’s mounting on my scratch chassis. Sorry forgot who here suggested the muffler/pipe clamps but looks like they will work like a champ with raising them from the mounting surface with a 1/8” plate spacer!

Figured out the old BMW wheels from my son-in-laws car will work the same as the Corvette lug pattern and will serve temp duty until body is somewhat mounted for a custom rim order. So think getting it on its feet might be next after welding the rear upper coilover mount.

 

[DaveC]

Have you looked at suspension geometry with regards to bump steer? You may want to temporarily mount that rack with tack welds, get the a-arms mounted, and see if the bump steer would benefit from moving the rack up or down, although up looks tight there. That being, if it's just a street cruiser, I wouldn't get too worked up about bump steer.

 

[Devin]

Have you looked at suspension geometry with regards to bump steer? You may want to temporarily mount that rack with tack welds, get the a-arms mounted, and see if the bump steer would benefit from moving the rack up or down, although up looks tight there. That being, if it's just a street cruiser, I wouldn't get too worked up about bump steer.

I’ve been referring to other AP build pics here and going with how is appears how theirs have been mount (mostly to the top of the cavity). Yes I have tack welded it just in case there need to be readjustment for bump steer but also plan on using variable spacing with the end links since the corvette tie rods are metric and the steering rack is SAE 5/8”-18 threaded.

 

[Ian Anderson]

Mmmmh, GT40 drive train and Mini body?
;-)

Like this?

Mini GTD V8 pick up: Spotted

Want something truly silly for a Sunday afternoon? How about a Mini with a V8 in it...

www.pistonheads.com

Ian

 

[Brian]

The tie rods are a moot point. The corvette upright steering arm have the big end of the taper on the bottom intending the tie rod to be below the arm. With this rack location, you have to use an adapter and a heim above the arm. Since you're already forced to ditch the oem tie rod, you can correct bumpsteer with the spacer between the upright and the heim.

 

[Devin]

The tie rods are a moot point. The corvette upright steering arm have the big end of the taper on the bottom intending the tie rod to be below the arm. With this rack location, you have to use an adapter and a heim above the arm. Since you're already forced to ditch the oem tie rod, you can correct bumpsteer with the spacer between the upright and the heim.

Brian, do you have a pic and/or part# of what folks are using for the heim “adaptor”?

 

[Brian]

It's something Chris provided. It's just a bolt and a cone shaped spacer. I have a more solid idea for my permanent solution, stay tuned and I'll share.

It'll be a tapered sleeve with a slit that fills the void you would have if you just stuck a bolt with a washer in the hole. I'll slit it on one side so as the bolt is tightened, the cone is pulled in to the taper of the arm chucking the bolt like a collet. Then a machined to size conical spacer to brace the bolt against the bending forces of steering.

I'll try to get you a pic of what was supplied in the next few days. Where you are now, a cheese grade bolt and piece of tubing will suffice for mock ups.

 

[Devin]

It’s been a while since my last update...

Got “distracted” from the ‘40 project with a life long family friend’s 1965 Ford Galaxie 500XL Hardtop. It was parked in a barn back in the 1970’s with 54k miles due to a smoking #7 cylinder. Needless to say, I had to pull the engine and do a complete rebuild on the 390FE. Boy did I learn a lot of FE particular lessons & technical specifics along the way...may be useful for a future FE powered GT40??

Well back to this project.

I finally bought a media blasting cabinet and reconditioned my C5/6 suspension pieces by glass beading and then light sanding to get back some shine to the aluminum. Also installed new ball joints, wheel bearings and Prothane bushings. It was a lot of work but well worth doing it right now and having it all ready once the chassis is complete and powder coated...besides, one of the wheel bearings was almost frozen so needed it easy to roll to move it around the shop.

Was also able to mount the rear suspension and coilover stocks to tack the upper mounts into place in prep for getting it on all four wheels in the near future for the next phase of the project...body mounting. Once on the ground, I’ll be giving it a good four wheel alignment on my Hunter machine to make sure I’m working with a good base for the wheel openings and mounting locations. Also need to finish up the steering rack & rod end solution to the front uprights.

 

[Devin]

Got it off the rotisserie and on its four feet this weekend. Next is getting the chassis on the alignment machine to get things square and placed for a good reference during body shell mounting, followed by steering shaft mounting

 

[Devin]

More progress on scratch build 40.

Was able to get it on the alignment rack and dial it in at set ride height (with wooden shocks) with good results and a bit more adjustable if negative camber is needed later.

After achieving a square foundation, I mocked up everything to locate the FFR GTM windshield and rear bulkhead. With the supposed original spider splash molds...I had to section and re-curve the windshield base to match the one I have. After that I was able to bond the bottom support piece to the sectioned top piece with 3M panel bond adhesive and prep for fiberglass & epoxy work.

The rear bulkhead upper support bar which I thought could be straight (using 1.5” square tubing) ended up being a bit too low for the window opening so had to section into more of an arc for better curvature to match the roof line.

Next will be fabrication of the rear legs of the bulkhead roll bar.

 

[Devin]

Bulkhead window & engine access panel framed.

Question to those with completed cars…how often do you all need to remove and get access to the front of the engine via the cockpit? I have both drive on 4 post and 2 post lifts so thinking once the car is completed I should only need to do that when/if a water pump or maybe alternator/fan belt needs servicing??

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