Resto-mod Manta in USA

sawguy · October 27, 2020

Early in 2020 I was looking for a car project and was searching for a early to mid 70's Capri. I ran into this running 74 Opel Manta ad on Racing Junk. I really wanted a Capri but, every time I looked at this ad I felt a challenge as you don't see Mantas very often. The car was in Aberdeen, MD....a long way from Mesa, AZ so going to look at the car was not happening as Covid-19 was hitting. I asked the owner, Jason, to send me lots of pictures. After quite a few phone calls, I pulled the trigger and used an Escrow service to make the money transfer (easy for both of us) and hired an auto haul service to deliver the car to me.

Originally, I was going to resto-mod a Capri using modern (2000ish) running gear, suspension etc. from a 4 cly BMW E36 or a RX 7/8 or Miata or ? Once I received the Manta, I figured the Miata was the way to go because of the after market parts, support and how inexpensive they are.

The car arrives and I take it around the block. Its the 70's all over again! Long clutch travel, noisy, smelly, sloppy steering and those analog switches. I miss those days.

Son & daughter in law test drive New grandson making his claim to the car

Soon after all the test drives, my son (RJ) and I start the process of documenting all the issues with the car and created a couple of videos of the engine running. The plan is to sell the Manta's front and rear suspension, running gear and anything else I won't be using. I was surprised by was how little rust was in the car, considering it came from the East Coast.

Within days of receiving the car, RJ and I disassembled the car, except for the body, chrome and glass. We started the process of finding and documenting the datum points, along with the center of the car.

I have never done something as challenging as this before, so this will be a big learning experience along with pushing my skillsets.

I purchased rear and front subframes from a wrecked NB Miata. The subframes were missing some parts but the control arms and knuckles were still intact, which will help us in understanding where the tires are going to hang. Another key was to use all of the mounting points for the suspension, shocks, steering rack as much a possible to minimize any changing any of the Miata geometry.

So now it gets real; figuring out how to put a independent rear suspension where there once lived a live axle.

Live Axle Independent

After numerous trails and errors, I realized the only way this Miata subframe would fit was to cut a BIG hole where the Live Axle once was, this included the frame. Not having done this before I searched the internet for ideas and best practices. I came up with a plan to support the rear of the car with auxiliary stands and welding in supports.

After that it was all about making room for the subframe and creating a frame to hold it in place. I went back to the wrecked NB Miata and cut out the rear frame area that interfaced with the subframe. Then I sectioned these frames so that I could insert and weld some 2x2 square tubing. By doing this I did not have to re-invent the frame studs and bolt hole that mounts the subframe.

Miata rear frame cut and section

2"x2" square tubing inserted into the sectioned Miata frame. Mock up of frame connecting the mid section to the rear of the car.

New frame tack welded and subframe in place to test fit and check for clearance.

Another view

A view from under the car and look.... the motor, trans and front subframe are just sitting there waiting patiently.

Mounting the shock top mount to the frame just like it was and in the same position as it was in the Miata. Now it's time to close up the holes.

Starting the process of filling the holes and adding more bracing to the frame.

As you can see there is a big hole where the spare tire holder use to be. I took it out because when you look from the back of the car it looked goofy with this bulge hanging down.

In the process of filling the hole I recycled some of the metal I had cut out of the car as the piece already had the rounded shape.

Test fit of the Miata wheels and tires. they will probably need to go up about another inch, so I will need to do some work to the fenders. The plan is to try a fender roller, if that doesn't work, I will have to use some fender flares. More on that later.

One thing I want to come clean on......those are not my welds! I hired a young guy, Derek, who is a fabricator/welder to help me with the critical areas (where the welds need to be better then what I can do). He is also helping me with the fabrication.

The hole is nearly filled. Once completed, I will prime and seam seal the bottom of the car AFTER the welds are smoothed out

By accident we made a battery box, this was not planned!.

While the hole in the rear is being worked on, I decided to start on the front end. Using the Miata subframe and control arms I started the process of centering the tire to the fender opening. The orange strap is to hold the control arms at the ride height of the Miata.

The Miata tires and wheels are 23.3" od 205/45ZR16, the Manta tires and wheels are 23.2" od 185/70 HR 13. So the tire height is really not much different. Before blowing the Manta apart I compared "key" (datum) dims with what was in the manual. From the center of the axle to the fender lip its 14" with the stock Manta tires.

I had to cut the rear of subframe to get the thing into the car and it doesn't look good. I am not at the right ride height yet and the rear lower control arm pivot is crashing into the frame!

Found another "crash point", this time on the upper control arm. I will have to notch the frame to take care of this. Had to cut the rear of the lower control arm to get around the rear pivot hitting the Manta frame. The plan will be to move the rear pivot closer to the front pivot.

Marking the subframe mounting holes on to the Manta frame. Notice the Miata subframe mounting location is WIDER then the Manta frame!!! Also for the control arms to be at the same relationship as they were in the Miata, the subframe is adjusted so that it is not parallel with the Manta frame. This because the Manta frame is not parallel with the ground.

To solve these two challenges I used some 3x3x0.250 inch angle Iron as a interface between the subframe and frame. The angle Iron is bolted in for now but once the suspension is squared to the frame and motor placement is found it will be welded to the frame. The angle Iron will also be reinforced at the ends.

This is the Miata upper shock mount for the front suspension located in the Manta fender at the same distance, angle and relationship to the lower control arm as it was in the Miata. Even though the Manta gauge of metal is pretty thick some reinforcement will be done in this area.

Testing the fit of the front strut/shock assy.

h0tr0dder_uk · October 27, 2020

check out my mates miata / manta project.

Jessopia74 · October 27, 2020

Interesting stuff with suspension setup. It's funny as I have been looking at the rear axle of the Mazda mx5 (miata) for Ascona A setup. But the front does make some sense to use too.

Plenty of good tuning options for the 1.8 engine too.

sawguy · October 27, 2020

Hi hotrodder uk thanks for the link on your buddies build. Wish I had seen it before, I could learn a thing or two.

sawguy · October 27, 2020

After looking/studying the Miata subframe, the Manta frame, the engine, the exhaust, and where to locate the rear pivot point for the lower control, I realized this thing was going to be too restrictive. I did some internet searching and found a company (V8 Roadsters) who makes Miata subframes for fitting V8"s or other motors going into a Miata. I ordered it without the motor mounts attach so I could attach my own, once I come up with best fit of motor in the car.

After receiving the subframe I modified it by removing the rear pivot mounting points and shorting the rear of it to fit the Manta. The great thing about this subframe is that the rails that are parallel to the ground, fit between the Manta frame rails. Also this subframe is going to make it easier to get access to things on the engine and to run the exhaust.

Next I had to figure out how much of the rear (the lower control arm) to cut off.

Yep that looks like enough.

A little bit here and little bit there

.

DONE

IT FITS AND WORKS WITHOUT HITTING ANYTHING! 😅 I also notched the frame were the upper control arm hits, all good.

Secured the rear of the new subframe to the same location as where the original Manta subframe was secured. This is also a great datum point to use when I was squaring the new subframe to the Manta fram

Jessopia74 · October 27, 2020

Great info, would they not make you a frame that married up to the original points on the rails?

sawguy · October 27, 2020

Did not ask, don't want the project to stall. Also trying to do this on a thin budget.

sawguy · November 6, 2020

Now it's on to the steering

All holes are filled in the back of the car. I need to prime the metal, seam seal the welds and then paint. Then I will be ready to finally install the rear subframe for what I hope is the LAST time.

The plan is to use the Miata steering column, this will give me options with accessories controls (switches). The Miata column is shorter so some modification to the mounting had to be done as well as getting the column shaft to interface with the Miata rack. I could have used the Miata steering shaft but it presented some challenges in shortening it.