Black Mirage Build Diary

[Manta22]

I've posted my build diary on the Yahoo Manta Group website but some folks have had difficulties in seeing the photos there. I'll post in parallel here and hopefully it will be easier to navigate this site.

Briefly, long go I bought an unassembled Manta Mirage kit from a local fellow with the idea of building it into a dual- purpose street/track car. The build started off in that direction but I soon realized that the compromises necessary would result in an overweight, uncompetitive track car and a totally unsuitable street machine. About that time I attended Speed Week at Bonneville for the first time and decided that this Mirage was going to be built to SCTA (Southern California Timing Association) rules. A few car shows might be the only other option.

I'll attach a couple of pictures that show the general idea and also a few details.

[Manta22]

In August I assembled the car in its still- unfinished state and trailered it up to Bonneville to get it looked over by the SCTA tech inspector. This way I could find out if there were any problems and then have time to remedy them as the build finished. No such luck-- Speed Week was completely rained out; there was 6" of water covering the salt flats. I found a couple of inspectors who gave it a quick look but that was all. As they say "That's racing".<br><br type="_moz">

[Manta22]

SCTA rules require a very sturdy roll cage as well as on- board fire extinguishers, parachute, race tires, etc. I added a full roll cage and after all the welding was finished I had the bare chassis sandblasted. Next was a two- part zinc chromate epoxy primer followed by a topcoat of two- part polyurethane isocyanate resin.

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[Manta22]

To enclose the cockpit and add stiffness and strength to the tube chassis, I riveted on aluminum panels of 0.063" 7075-T6 with A256 and Monel 5/32" dia. Cherry and Huck rivets. These are very high strength fasteners that require a hydraulic rivet gun; pulling them with a hand tool is out of the question. Cleco skin fasteners were used as temporary clamps to fasten the panels to the chassis tubes while drilling holes and then pulling the rivets. The two- part zinc chromate epoxy primer was used on all the aluminum panels.

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[Manta22]

The driver's view photo was taken before the top roll cage tubes were added and a titanium sheet was riveted across.

[Manta22]

I'm using a Porsche G50-01 transaxle, inverted so that the car goes forward. The adapter, flywheel, and clutch are Kennedy Engineered Products. The shifter is a rod type with Thompson ball- bushings and Apex u-joints.

Rear uprights are Porsche 996 and the rear calipers and rotors are from the front of a Porsche 928 S4. I had the rear hubs re-drilled to convert the original 130mm bolt circle metric threaded holes to a 5 stud on a 5" bolt circle ("5 on 5") pattern so that I could use Bassett circle track racing wheels. The new studs are coarse thread 5/8" -- a standard in circle track racing but using a different taper lug nut.

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[Manta22]

These are the 5/8" wheel studs from ARP. The rounded nose makes slipping on the 1" (across the flats) lug nuts easy and the long unthreaded section holds the nut straight so that it can't be cross- threaded.

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[Jerry]

I like it!

It has a look influenced by an Apachi helicopter or something, Cool. :-)

I think there are 5 Mantas within 150 miles of Willow Springs Calif.
That would be a fun race if we can all get them finished.


Looks like you have a lot of hours into that frame.

[Manta22]

422Thanks, Jerry-- beaucoup hours is right!

There was a Manta get together at Laguna Seca around 1979. Someone named "Leo" at Manta Cars took this picture:

[Sulley]

I love these build threads. Thanks for posting over here as well. If you or anyone has any issues navigating this site please let me know.

I've started a Manta reunion thread here:
http://mantacarsforum.com/showthread.php/2774-Manta-Reunion

I would be in for a reunion at some point. I don't want to hi-jack this thread so I'll post on the other thread about my thoughts on the reunion.

[Blueovalz]

422Thanks, Jerry-- beaucoup hours is right!

There was a Manta get together at Laguna Seca around 1979. Someone named "Leo" at Manta Cars took this picture:

Neil, could you post this photo in another forum as well? Perhaps in the original photos section? I love this photo, but think it will get "lost" in this string for those looking for vintage photos.

Terry

[Manta22]

Terry;

Yes, I will post it and a few others in the original photos section- good suggestion, thanks.

[Manta22]

I still don't know if I'll really need a fan to cool the radiator but I thought that now is the time to fabricate one- just in case. I decided to use an array of six small 12V fans and this made it necessary to cut 6" holes in my aluminum shroud. I made a circular gizmo out of 5/16 aluminum plate. on one end I drilled a 3/8" hole for a pivot bolt and 3" away from that I drilled a 7/16" hole that fits my rinky-dink Harbor Freight plasma cutter. The arc distance is set by a stack of 3/8" washers. After the pivot bolt is fastened to a center hole, the torch is placed into the 7/16" hole and the arc is run around the pivot. Voila! a nice big hole is cut out.

The fan panel is almost finished; I still need to run the wires to the barrier strip. I did the usual 2- part zinc chromate primer and assembled the ribs with 1/8" Avex rivets.

Regards, Neil Tucson, AZ

[Blueovalz]

Now you can stage you cooling!

[Manta22]

I ran into town to run a few errands, one being to take advantage of a heat gun on sale at HF for $8.99. My old Ideal heat gun finally burned out the heating element. It was a POS and not repairable so I junked it and, most conveniently, the HF sale came up at the right time for me. Out of desperation yesterday I tried my wife's hair dryer on the shrink tubing but it would barely affect it.

I finished wiring all the fans on my panel and they all work. http://www.landracing.com/forum/Smileys/default/cheesy.gif

Regards, Neil Tucson, AZ

[Manta22]

The panel is mounted with the same 1/4"-28 bolts that fit through vibration mounts into nut plates on the underside of the radiator support tubing.

This shows how it is mounted.

Regards, Neil Tucson, AZ

[Jerry]

It is easy to see you are doing amazing work !

[Sulley]

What are the advantages of using the 6 individual units? Is that more for Bonneville than other events?

[Manta22]

Sulley;

The main reason I used the six small fans rather than one large one is that the large fan simply didn't fit. Its shroud was too high to it under the sloping nose of a Mirage. The photo shows how high it was.

The six fans actually covered a larger area of the radiator than the single large fan.

[Manta22]

Another very tiny step forward; I have added a push- pull control cable to actuate my battery cut-off switch. I didn't like my original idea so I re- did it. This cable runs forward to the nose. On the right side of the radiator air inlet there will be a small handle to shut off the battery by a pull, which rotates the arm and moves the switch to the "OFF" position. The thing is a trial assembly right now so there is no nut on the rod end bearing thru bolt. I'll clean it up and finish it with primer before final assembly.

The arm is made out of 1/2" 6061-T6 plate. If I can find a threaded handle it will save me from having to make one. Rubber- lined 3/8" clamps secure the control cable to the chassis.

[Sulley]

How are you routing your cooling lines?

[Manta22]

Sulley;

I had originally planned to route one line back through the right side of the cockpit but now I think I'll route both lines around the inside the left side pod. The right side pod contains my fuel cell so no lines can run through there but the left side pod has only two fire extinguishers hanging from the top cover so the two lines should fit OK.

[Manta22]

I was afraid that this might happen.

I searched the internet for a pull knob that would be suitable for my battery cut-off cable, a push- pull control cable with ends threaded 10-32. No luck, so I made one out of 1/2" 6061-T6 aluminum plate. Nothing fancy- I cut it out with a hacksaw, dressed it up on a belt sander and then tapped it 10-32. I had a can of self-etching primer so I tried that after soaking it in a phosphoric acid solution. The topcoat of red should make it visible to the emergency crew. I designed it so that it could be pulled by a person wearing gloves.

Regards, Neil Tucson, AZ

[Blueovalz]

1/2" with a hacksaw...I'm impressed, ahhh in the red handle I mean.

[Manta22]

1/2" with a hacksaw...I'm impressed, ahhh in the red handle I mean.

It is an Armstrong hacksaw, Terry.

[Manta22]

I placed my battery in the required box and padded it with slabs of polyethylene foam to cushion it from vibration. It is a closed-cell foam so it doesn't absorb liquid. I added a blue poly rope around the battery so I can use it as a grab handle to easily lift the battery out of its box. It is the biggest battery Costco had that would fit into this box.

The box is now placed into its fixture and clamped into place in the passenger's foot well. I still need to install a few more cover bolts.

Regards, Neil Tucson, AZ

[Sulley]

Battery box looks good.

[Manta22]

Today was a fairly productive day. I marked the access panel cut-out on the left fiberglass side pod cover with blue tape, removed it from the chassis and cut out the panel. I drilled two starting holes in the bottom side to insert a "body saw" (pneumatic HF tool) and cut two radiused corners and then realized that the blade was too dull to cut much more. A search turned up no spare blades so I switched to a fine-tooth (32 TPI) saber saw for the straight cuts. I had to revert to the body saw to cut the two other corners since the saber saw wouldn't turn a tight radius.

As I had it up on sawhorses anyway, I sanded the cut edges smooth and then fabricated a bottom air skirt for that side (driver's side) from 1" x 0.065" 7075-T6 aluminum angle. The pieces I had were all too short so I had to make it in two pieces with a splice panel made from the same stuff. It was necessary to trim both legs shorter and put a small radius on the outside edge so the splice would lay flat The angle is made with an inside radius, not a sharp edge. I'll shoot zinc chromate primer later when I do the skirt for the passenger side.

I'll post a few pictures of the skirt and how it will be fastened to the chassis. The fiberglass will be sandwiched between the skirt and the chassis brackets.

Next will be deciding on how I'll fasten the access panel to the side pod fiberglass. Among other things, this panel will allow inspectors to check the fire bottle certs, etc.

[Manta22]

The side pod fiberglass is not very thick so it is not very stiff along the long cut edges. To prevent oil canning at high speed I thought it would be prudent to stiffen those edges with some of the same 7075-T6 1"x1" 0.065 angle that I used to fabricate the side skirt. They are drilled now and Cleco'ed in place in this photo. I shot some primer on them so I'll need to wait until tomorrow to rivet them on. I left space on each end to install self- ejecting Dzus fasteners.

34 more holes drilled. When someone asks, I think I can say "I built the hole thing."

[Blueovalz]

Neil,

I've finally received a fire suppression system. Any suggestions on where to mount the nozzles? I know it sounds like an obvious question, but I've never had any experience with an AFFF system, and have no idea how far out the foam exits the nozzles, nor the impact of adding multiple nozzles to the efficacy of the system. I assume that with the 6 supplied nozzles, there is still sufficient flow through a small ~1/4" tube to ensure sufficient flow and pressure to all six simultaneously. Any suggestions or advice?

Terry

[Manta22]

Good ol' Aircraft Spruce came through today with the longer Avex rivets that I had ordered so I was able to install the stiffener ribs in my sidepod access panel. I used blue goop to seal the joints to keep as much salt, debris, and water out as possible. Maybe tomorrow the Dzus tabs will arrive and I can put in those self-ejecting spring plates.

[Manta22]

UPS delivered my order of Gates Power Grip hose clamps yesterday and I installed a couple of them to see how they worked. These clamps are easy to install- crush the cardboard form and slip the clamp off, slide it over the tube/hose joint and use a heat gun to shrink it in place.

I'm impressed by how tight these clamps get. One advantage over worm drive or T-bolt clamps is that you won't slice off any skin with these. Nice for tight places where your hands need to work.

Regards, Neil Tucson, AZ

[Blueovalz]

I would guess that if you don't have a lot of room, 360º around the tube for uniform shrinking, a clamp would be better in those really tight places.

[Manta22]

Today I finished the coolant lines on the right side. They pass by the outside of the fuel tank support and will just fit under the fiberglass side pod. The hard line is 304 SS with both T-bolt clamps and Gates Power Grip shrink collars.

Regards, Neil Tucson, AZ

[Jerry]

Looks good. It looks like you will be done pretty soon.

[Manta22]

I mounted a brake proportioning control valve this morning. Maybe I can even out the F & R braking effort on salt, maybe not-- we'll see. The main high speed braking will be from a 'chute but I'd like to have a back-up. On the X-Mile events the brakes should be very effective but I'll use the 'chute as required.

I'd prefer to mount this control where it would be accessible from the cockpit but there was no good place for it without interfering with a quick bail- out. I don't want my fire suit catching on this knob (or anything else).

I drilled 1/4" holes in the side pod top panel and put in four 10-32 UNF stainless steel Rivnuts for the Phillips head titanium screws. The neat aluminum bracket was a piece of aircraft surplus that I bought a long time ago with the idea that it would be useful some day.

Regards, Neil Tucson, AZ

[Manta22]

All my brake line is now plumbed as is the hydraulic clutch line. I used terne plated steel Bundy tubing- 3/16" brake & 1/4" clutch.

I installed a set of Performance Friction Carbon Metallic brake pads this afternoon. The big rear calipers & rotors are from a Porsche 928 S4 front brakes.

Regards, Neil Tucson, AZ

[Blueovalz]

At least the color is agreeable and matching! :)

[Sulley]

Not sure what kind of fluid you are planning to use but I use Motul 660 on my track car.

[Manta22]

Not sure what kind of fluid you are planning to use but I use Motul 660 on my track car.

Thanks, Sulley. I'll keep that in mind.

Regards, Neil Tucson, AZ

[Manta22]

I ordered caterpillar grommets from Aircraft Spruce and tried putting it around a hole in a gusset where my oil pressure tubing passes through; the stuff is easy to install and it fits on tight. I'll order more for use around places where gusset edges might benefit from softer edges.

Regards, Neil Tucson, AZ

[Manta22]

My fuel cell is now installed in the right side pod and most of the Avex rivets are installed in the panel; I need to temporarily remove a couple of things to get access to the remaining rivet holes.

The big hole in the rear is for a fire bottle. There are aluminum mounting clamps under the top panel.

Regards, Neil Tucson, AZ

[Jerry]

Can you show some pictures of your transaxle, rear brakes, rear suspension?

[Manta22]

Can you show some pictures of your transaxle, rear brakes, rear suspension?

Sure, Jerry. Some of the pictures are older as you can tell by the chassis not being painted, etc.

[Manta22]

More older photos:

[Jerry]

Built for speed !

Great work !

[Manta22]

I finished plumbing the fire extinguisher system, both for the cockpit and for the engine bay. I used 1/4" 3003 aluminum tubing- what a joy to work with compared to steel brake line! It forms easily and flares nicely.

In the cockpit the tubing runs under the instrument panel so I added some braided sleeving to make sure nothing could make accidental contact with a hot 12 volt terminal. I did the same thing where the tubing runs by an external charging/battery connector. Shrink tubing over the cut ends of the braided sleeve keep it in place and add a nice cosmetic touch.

I'll show a couple of pictures.

Regards, Neil Tucson, AZ

[Sulley]

Neil it is coming along really nicely!

[Jerry]

Are you taking it to a salt flat soon ?

[Manta22]

Are you taking it to a salt flat soon ?

Jerry;

That is a good question. Last year Speed Week was completely rained out. This year the salt was in such bad condition that there was not enough good salt surface to run on safely. Potash mining has slowly been destroying the salt flats and we are very angry at the Bureau Of Land Management for allowing this to happen. We are trying to publicize the problem to get a solution (no pun) in place.

California dry lakes racers have had a problem this year with El Mirage being too wet to race on. Maybe abandoned runways may be the future- who knows?

I'm busy right now getting my car ready for a big car show here in Tucson on the 17th of this month.

Regards, Neil Tucson, AZ

[lukifer]

Wow, the quality of this build looks amazing. I hope that I can put this kind of detail into my car when I start it.

[Manta22]

My original YouTube build diary had no narration, only some text titles, so it wasn't very helpful in telling the story of the details of my build so I re- edited it completely. Now it has a narration soundtrack so it may be a bit more interesting but it does run pretty long (about 56 minutes!) so grab a beer or two to watch the whole thing. Here it is:

https://www.youtube.com/watch?v=LFu8QfUVHlU
(https://www.youtube.com/watch?v=LFu8QfUVHlU)

[Manta22]

This is a video about my trip to Bonneville in 2018: https://www.youtube.com/watch?v=XUAYETAsdL0&t=1s

[davebivens]

Hey, thanks for sharing the video, lots of knowledge and ideas in there! Question, those thin seats that were in the car before you went full race with it, would you happen to know who made those?

[Manta22]

Those were the original fiberglass seat shells with vinyl upholstery supplied by Manta Cars, Dave.

My YouTube video about restoring Manta 2 might be helpful, too.

[Manta22]

I've been considering something to hold my driver's side gull-wing door in the raised position after I manually push it open. I have a support rod that can hold it open but I can't raise it from the driver's seat, only from the outside. Initially I thought about using a gas spring and may try one yet but I found another way to do the job.

A straight helical-wound spring has lots of stiffness in compression but if it is pushed sideways, it collapses rather easily. Some clever individual seized upon this principle to create a purely mechanical hold-open. I ordered an all-stainless spring assembly from a marine hardware company for about $20 and gave it a try. I had to remove the lower end attachment for my application and make a bracket that would fit without interference. I had a piece of 3/4" aluminum angle and mounted a floating nut plate in one leg to receive a 10-32 oddball fastener I had. This fastener fits through the lower spring loop end. Both end attachments are riveted in place, as is the nut plate. The nut plate needed small diameter rivets (a #40 hole) and I had a bag of that size Cherry rivets. They were slightly too long a grip length but since they only held the nut plate in place, I would go ahead and use them. The upper end uses 3/16" rivets into the door.

The spring holds the door up nicely and when I push the spring sideways slightly, it goes down. On the downside, the placement results in the curved spring hanging down further than I'd like. I may move it to the rear edge of the door if it won't interfere with my helmet.

One thing more- when working on fabricated parts, de-burr all holes and break sharp edges (this is just basic metalwork) but I recommend also radiusing all those square corners. The corners add no strength but they do add weight and they lie in wait for the unwary. If you've never gashed yourself on a sharp corner when working on your car, it's only a matter of time before you do. Use a belt sander to round off the corners and then break the edges with a file. It looks better, too.
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[davebivens]

Here's what I decided to go with, your doors might be heavier since it looks to be joined top/bottom so you'd probably have to move the mount further out on the door and you'd have to figure out the gas spring force, mine is working with a 30N but you may want more force I think.

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