Here's a quickie web page showing the progress of the Tube Chassis Car build...

A few years ago I saw an image of a VW powered tube chassis car that kinda stuck with me... I wanted to build a car to highlight my Suspension products, and slowly things are coming together.

Here is a photo of the car that caught my eye and got my mind working on figuring out how to build one... It is VW powered... air cooled, and the front suspension is VW.




I began by creating a few CAD drawings to layout the frame, wheelbase and a few other points of interest.




This simple 2D drawing was then turned into a SolidWorks drawings / rendering.
An important aspect of the frame is the rounded frame rails. Here are a few simple renderings of the frame rails and tires scaled to proper size. Frame rails are 2" OD. Tires are approximately 26" OD.











Physical Layout

Making the frame rails was an iterative process that began with using thin-wall PVC. The ( approximately ) 2" OD PVC was too stiff to work with... so I bought some blue swimming noodles. The noodles were too flexible and didn't support their weight. The next step was to insert some 3/4" PVC inside the noodles to give them some rigidity. This worked very well.
Once the noodles were placed and their location was verified visually, measurements were taken as points of interest - like the firewall, the front axle, etc. Using these blue noodles was really the key to setting up the locations of the frame rails. With all of the CAD drawings, etc... it still comes down to "what looks right".
Here are a few photos showing various placements of the blue noodles.








I don't have a good image of the blue noodles in their correct locations, but hopefully the photo below gives the right idea of the path from PVC to noodles to PVC and ultimately to the DOM tubing that was used. The image below ( front view of the car ) shows the bent EMT on the passenger's side and the blue noodle on the driver's side.



Since the noodles would not hold their shape, I needed another lightweight material to bend and use as a template for the ultimate DOM frame rails.
EMT is a lightweight round tube used for electrical conduit. It is available in 10 foot lengths at Home Depot or Lowes. Below I will describe how the EMT was easily bent... no expensive rollers or bending tools necessary for this step.

The EMT is placed in a vice to hold it steady and marks are made every 6 inches to indicate the cut lines.



The EMT is placed in the chop saw and cuts are made about 3/4 of the way through the material.



I marked the chop saw blade guard with a sharpie after the first cut and verified that the chop saw made all subsequent cuts to the same depth. This approach leads to a more uniform bend of the 10 foot length. The arrow indicates the mark on the blade guard.



Once the cuts are made, you can bend the EMT tube to your desired radius. You may have to enlist the help of a friend, a truck bumper or a vice to hold one end in place as you bend it... be creative. Here is a shot of the two frame rails next to each other to verify the bend radius is the same for both. This may take a couple of tries, and in my case, a second round of notches to the EMT.



Here is a close-up view of the bent EMT... notice the slight buckling where the notches are. Since this is only to be used as a template, these imperfections are tolerable.


Now that the bend radius is known, the next step is to get 2" DOM tube bent to the same radius. The upper and lower frame rails on each side run parallel to each other. They are about 8 or 9 feet each. Tubing is generally sold in 20 foot lengths, so I purchased 2 lengths of DOM Tubing 0.90" wall thickness.
A local shop had a roller to bend the 2" DOM. After about an hour we were able to bend the 20 foot lengths to match our EMT template.



With the frame rails positioned, the seating location was determined... yes, that's me in the driver's seat. The goofy look on my face is apparent... the engine noises cannot be captured in a photo.




With various wood beams and round rods in strategic places, the frame rails are placed for general overall appearance evaluation.




It would be nice to have a shop the size one of those high end TV studios, but at least this chassis table is level and easily adaptable to setting up the chassis.




The red arrows indicate the wood props that hold the frame rails in place. The original mechanical drawing provided the height above ground at various locations of the frame from the front to the rear of the chassis. Using this information, I marked and cut out holes or slots for the frame rails. This simple approach let you position the frame rails easily. Also note the wood under the seats. This was the very first piece made for the car.



The car was built from the inside out. The width of the frame rails was determined by positioning the seats with me in one seat and another 6 foot 215 lbs guy in the other seat. Since I wanted to actually be comfortable while driving this car, I took this inside-out approach vs. building the car and then trying to squeeze everything into it once the frame was complete.




The frame is located along with the front and rear tires... The roll bar hoops are clamped into place as a first guess at their location. Note the large rectangular tube at the front. This ties the left and right frame rails together as well as functioning as the upper shock mounts and front suspension crossmember mount. This could have been more elegant, but after trying a few different options, this was the most direct solution.



Note the markings ( red arrow ) on the rectangular tube showing the upper shock mounting locations.



This is a good shot to show the overall view of the frame in its initial layout. Note the penetration of the round frame rails into the rectangular tubing that makes up the frame of the firewall behind the seats. Also note the various jacks, blocks, clamps, etc... holding everything in place. This allows for fine tuning, measuring, measuring, measuring - did I mention measuring? to make sure all things are in their proper location prior to tack welding.



I tried to point out the X bracing behind the firewall. 1 1/4" OD round tubing 0.120" wall thickness is indicated with the light green highlights. It is difficult to see the X brace among all of the other tubes, but hopefully this photo tells the story.
Another thing to point out... If there are any symmetric components used ( like to sheet metal floor ) be sure to mark a line down the center. This helps with alignment. Also, the milky surface appearance of all the sheet metal used is due to the layer of Ospho sprayed on all pieces used. It is far easier to coat the sheet metal prior to installation. Ospho prevents rust and does not affect welding like paint or primer would.




The floor is braced with 1" x 1" square steel tubing as indicated by the green lines below. These will later be tied into the lower round frame rails.



The driver's side view of the floor shows the gap between the floor and the lower frame rail. This area will be filled with sheet metal.





The chassis is coming together. The firewall behind the seats and the floor are 16G steel. The floor is reinforced with 1" x 1" square steel tubing ( 16G )



Here is a closeup of the rectangular tube, the central tunnel, floor, side panels, etc.



The front suspension crossmember, spindles, steering rack and steering column were all taken from a Pontiac Fiero. The tubular upper and lower control arms are available from Held Motorsports. This is their Wide Track Sport Front Suspension.





With the suspension in place, the steering column is held up to its approximate mounting location. The green circles indicate the locations of the mounting bolts.





The green rectangle highlights the steering column mount. This column is a GM unit ( from a Fiero ). This unit was chosen because it matched the front suspension, eliminated the need for difficult ignition, turn signals, horn and other wiring.



The steering column is in place along with the front suspension.


another shot of the steering and front suspension.





The lower side panels ( 16G sheet metal ) are welded into place. The floor is reinforced with 1" square tubing. Also note the 3/4" square tube "tunnel" that runs down the middle of the chassis. This boxed tunnel will serve to mount the shifter as well as route the shifter cable or shift rod along with electrical lines, hydraulic lines and anything else that needs to run front to rear and be protected.
The tunnel will either be covered with aluminum panels or fiberglass.



Here's a nice shot of the roll bars welded in place with 10G tabs attaching the round hoops (  1 1/2" OD DOM .120" wall tubing ). You can also see the reinforced floor and tunnel running from the firewall to the front suspension crossmember. The image is off-center so it doesn't show the true symmetry of the components.



Notice the green circle. This is a triangular brace designed to tie the firewall to each of the strut towers. The rear mounts place the bolts in shear, but the front mount is a male / female socket and receiver held together with a 3/8" bolt. The bolt is under very little stress as the socket / receiver keeps the brace from moving fore / aft or left / right.



The rear portion of the chassis is shown below. With no suspension in place, you can easily see the triangular bracing that ties the firewall to the upper and lower frame rails.



Another view of the rear shows the triangulated bracing. The green frame members are 1 1/2" square tubing .120" wall thickness and the orange pieces are 1 1/2" round tubing 0.90" wall thickness.







Rear Suspension

My inital design incorporated a mid-engine cradle to mount the VW engine / transaxle. The transaxle, engine block and even the exhaust were ok, but the passenger's side cylinder head interfered with one of the structural mounts... rather than redesign this product, I decided to go with rear struts. Additionally, I decided against the VW engine and opted for a Mazda Rotary engine ( 13B ) from an RX7. The engine install pics may be found below.



I decided on using a strut style rear suspension. The image below shows a scaled sketch of the rear frame member and the struts, spindles, etc.





In order to keep the chassis at proper ride height, aluminum blocks are placed to bear the load of the chassis. This keeps the chassis in place as other components are added, removed, modified, etc... This photo shows the rear bracing prior to the final location of the suspension components. Also, you will note the firewall cross bracing.



The rear strut towers were fab'd from 10G steel. The box was made by bending the corners at 90 degrees. There were some funny angles to deal with to get the correct pitch of the strut tower which is based on the required camber setting for the strut.



The rear structural piece is made from 10G sheet metal. It is reinforced with 1" x 1" square steel tubing. The square steel tubing is indicated with green lines. Also note the dimpling of the round holes. This smoothes the round holes inner edges for a better look, but also stiffens the entire piece.



After making / using the dimpling dies, I found out that these dies are available in a variety of sizes. The dies shown below were made by a local machinist. After positioning the dies on the sheet metal hole, they are compressed... then removed - the dimpled hole remains as a result.








The finished look of the "inward" dimple is shown below. This is the rear view of the vehicle.



... and the view from the other side... note the square steel tubing used to reinforce the 10G sheet metal.




After a few choices in double A-arm suspensions were tried, I settled on using Fiero knuckles and rear struts. The struts shown in the photo are mock-ups that are set at ride height. Using charged struts would not be practical for initial setup since the light weight of the chassis would not be enough to keep the strut compressed.



This passenger's side rear strut oustide view shows the bracing clamped into place. Also note the upper strut tower.





It's a rolling chassis!!!
This view shows the VW transaxle in its initial location. This empty case is much easier to maneuver than one filled with gears.




Here's a closeup of the driver's side lower control arm spindle and coilover strut.



Tuning the rear struts is easily done with a twist of the knob on top of the strut. The knob sets the dampening of the strut from soft to firm. The adjustment knob is circled in green.



The koni coilover is shown prior to installation.




The image below shows the view from the driver's side rear with the newly installed Koni racing struts. I fabricated the strut housings and used the Koni single adjustable racing inserts.


... and a view of the passenger's side.


The view of the rear shows the prototype rear transmission mount. This simple MDF mount was used to set the proper height of the transaxle relative to the frame.
A steel mount will be made when all the dimensions are established. The shifter will likely be mounted to this rear mount, so I will wait until the installation of the shifter to finalize the rear mount design.



Nothing new here... I just like the angle of this shot.


Here is the front quarter view of the rolling chassis. The sheet metal has been painted with truck bed sound deadening paint. This undercoating is paintable and although I haven't decided on a color scheme yet, the sheet metal will likely be black or another dark color... the tubing will be a brigher color... time will tell.



The view from the front.


To get an idea of how the front will look with some body work, I stretched some nylon spandex across the front tubes. The goal is to leave as much of the tubing exposed to view as possible, but I will need to keep the road grime, dirt, bugs, etc. off of me and my passenger. The angled pieces are clamped into place to stretch the fabric. Turning this fabric into a body panel can be accomplished by spreading fiberglass resin on the nylon...



A closeup of the passenger's side showing the nylon stretched over the frame rails... Yes, those are 18" Cadillac Escalade rims on a little Nissan pickup truck in the background.



Updated on August 23, 2008

Kennedy Engineering is well-known for their adapters for mating a wide variety of  engines to VW, Porsche and Audi transaxles... as well as associated items like starters, pressure plates, clutch, throwout bearings, etc.

Here are a few shots of the Kennedy Engineering components.

Adapter Plate and Flywheel



Clutch, Pressure Plate and Starter

  


For initial test fitting of the rotary engine, I used portions of 13B, twin rotor engine. The front motor mounts are built into the face plate - which is lightweight. This piece is bolted to the forward engine iron and the rear engine iron is used - since that is the interface to the transaxle adapter plate.
The oil pan ties all of these pieces together, since the oil pan has number holes that attach to the various engine "slices" via tapped holes in the base of the engine components.

The following views show the engine adapter plate mounted to the rear of the engine. Studs ( not shown ) from the adapter plate fit the VW transaxle. By the way, the yellow thing hanging in the foreground is the Up / Down switch for the electic winch.

   



The engine is attached to the transaxle via the adapter plate - no clutch or pressure plate yet... This is just the initial fitment to figure out the engine and trans mounts.
The first two shots do not include the alternator bracket.






The bracket holding the water pump and alternator are installed to verify clearance. Since the VW transaxle shift cone sticks out the rear of the car, I'm trying to position the engine as far forward as possible.











I know... things are a bit cluttered with the wiring harness and ropes... I will move them out of the way when I install the final engine.
At that time, the photos will be more clear... I will also move the car outside and take some photos with better lighting.

The forward mount needs to be reworked to include some rubber or poly mounts... The current design is simply a flat plate to locate the engine properly relative to the rear subframe. I'm waiting on the final design for the front mount until I see where the accessories and other items end up. I want to make sure there are no clearance issues as well as incorporating any holes, mounts, etc... that other items may require. Best to incorporate any necessary items into one piece.



The original mount above was simple, but I wanted to have some rubber cushion between the engine and the rear portion of the frame. I accomplished this by using a 2" x 2" piece of 3/16" thick angle as shown below.



Here is a photo of the angle, the GM transmission mount and the flat plate sandwiched between the angle and the front of the mazda engine. The round tube frame rails are spaced 18" apart on center. Two transmission mounts are used - making for a wide base to absorb any torque made by the engine. The rectangular tubing base ( 1 1/2" x 3" ) will be welded to the round tube frame rails.






Installation of the assembled engine / trans / intake / carb / exhaust

The image below shows a test fit of a Racing Beat header. Too bad this header did not clear the passenger side axle or fit through the rear of the frame. A local shop will be fabricating a header using a Racing Beat manifold plate and stainless tubing.





Here is a side view of the exhaust manifold plate. This will serve as the header flange. The intake manifold is shown above the plate.





The adapter, pressure plate, clutch and flywheel are assembled with the help of an input shaft from another VW transaxle I had at the shop. This input shaft was used to keep things aligned during the tightening of all the bolts.



here's a shot of the clutch... again, you can see the shaft used to align the assembly.



Flywheel...



Kennedy Engineering adapter plate.



The transmission side of the rotary engine prior to attaching the adapter plate is shown below.




The images below show the clearancing of the VW trans mount. This is necessary to clear two of the bolt heads associated with the adapter. I used the VW trans mount along with a 1/4" thick plate to mount the trans to the frame rails. The large, 3/4" bolt is overkill for this application, but the hole in the VW trans normally reserved for the VW frame is slightly larger than 3/4", so it was an easy adaptation.





Adding the Carb, intake and air cleaner













Feel free to ask any questions / comments / suggestions.
thanks for looking.
dave@team321.com
Team321 LLC
Cocoa Beach FL