Volvo P1800ES...kinda

So, this is where I am at with the rear. I got the back half of the Miata donor striped down to the bare essentials.

Two options at this point:

I can use the entire floor/bulkhead and gas-tank structure as it was designed by Mazda.This will save a ton of time with engineering fuel delivery, handbrake and transmission tunnel systems. The only real downside is that it will eliminate any hint of a backseat such as the P1800 has. Not that you would put people there, but its a P1800 feature. Part of this will be decided when I determine if the Miata fuel tank will fit under the P1800's raised rear deck; I THINK it will.

Other plan is to use only the minimal amount of Miata chassis structure so as to be able to mount the Miata rear suspension cradle. I would then keep the Volvo fuel tank and figure how to integrate a fuel pump.

There is a 7.3" difference between the Volvo and Miata wheelbases (Volvo is 96.5 and Miata is 89.2) What I am trying to picture in my mind is where the difference comes into play(and how its going to try and bite me).

My inclination at this point is to cut the roller-skate in half just in front of the handbrake mechanism. That means that the handbrake mechanism stays intact with the rear, and the front firewall,chassis and transmission tunnel moves forward. I suspect that the answer is going to require a cut that does not go straight across the car, but rather slices around the floor-pan so that the Miata seat mounts go forward with the firewall and floor, while the handbrake goes rearward with the rear bulkhead.

I can't help without tons more pics, but I imagine you have it taken care of. Keep the progress going!

Brian:

I use this build thread to talk things through in my head as much as to show others how crazy I am.

As it can be seen , this is an evolving project and I am having a lot of fun pulling pieces together to see what gels. I am fortunate in that I am not (overly) budget limited and the pace is more set by my capabilities as a designer fabricator and parts locator!

I lean towards keeping as much of the Miata pan intact as possible, for your reasons stated. The only time the back seat is up in the ex-g/f's 1800ES was at shows. The rest of the time it's folded down.

It's good the fuel filler is on the same side - that should be relatively easy to modify.

I also lean towards extending the pan in front of the hand brake assembly, but it would really depend on where the Miata firewall lines up with the ES firewall.

Ian F wrote: I lean towards keeping as much of the Miata pan intact as possible, for your reasons stated. The only time the back seat is up in the ex-g/f's 1800ES was at shows. The rest of the time it's folded down. It's good the fuel filler is on the same side - that should be relatively easy to modify. I also lean towards extending the pan in front of the hand brake assembly, but it would really depend on where the Miata firewall lines up with the ES firewall.

Ian:

You should have told me this could get complicated!

The firewall situation is interesting: If I measure back from the axle center line, the Miata MC could bolt right on to the face of the big hump where the Volvo MC bolts to.

But from there, things get a bit complicated in that the Miata has the wiper tray where the wiper blades and mechanism hide out. Mentally, I have not integrated this transition area into the equation.

The good news is that if I measure from the front axle center-line, back to where the steering wheel ataches to the hub, the Volvo and the Miata are pretty close. That means that I wont be driving from the backseat or with my head jammed up against the windscreen.

Yeah, the whole wiper/HVAC inlet assembly and getting those to make happy with the Volvo windshield and dash will be a challenge. On the plus side, I think the Miata and 1800 windshields are pretty close in both size and orientation. I think the Miata is tad larger/taller and laid back more. You might have to cut/tweak the arms to get a good arc.

Those are details, but the devil will be in the details with this build... I don't envy you there and it's the main reason why I ditched the idea. Sorting out those details would be more work than keeping the B20.

Ian:

You might be able to answer this one. The wipers on my MGB GT are so craptastic that I avoid driving the car is there is any chance that I will have to deal with rain. It's not that I am overprotective of the car, just that it sucks to the point of being dangerous in my mind.

Since there is the possibility that the HVAC will remain Volvo, what is it like to live with? I seem to recall that you were less than a fan for some reason?

In reply to NOHOME:

Heat works well.

Ventilation - marginal. There are two fresh-air vents from the cowl inlet into the interior activated by individual pull cables. Unfortunately, the cowl area tends to get heat-soaked by the engine bay, so even when moving the air coming through them is pretty warm. The door vent windows provide some relief when moving. Make sure the rear fender air-outlet vents are clear and functioning or you can get some severe buffeting with the windows open.

A/C (factory authorized, dealer-installed version) - also marginal. And apparently loud, since it hangs under the dash. It's also a 100% recirc set-up. Originally sized for the smaller interior volume of the coupe, it can struggle to cool the ES. Tinting the rear side windows and hatch is recommended.

The defroster is equally marginal since there is no provision to send A/C (dry) air to the dash vents. During drives in humid, wet conditions we generally resorted to sending air to the windshield and then having the vent windows on the doors open a bit to encourage some air flow. This sort of worked.

To be honest, I have some ideas about what I want to do, but haven't dug into the details yet. My rough plan #1 is to use an aftermarket HVAC unit from Vintage Air or similar adn then figure how to do some sort of fresh air/recirc option with a cabin filter. Rough plan #2 is to buy an Heater/EVAP set-up from a junk yard and use the parts to scratch-build something to fit under/through the dash. Either would have additional insulation from engine bay heat and fan noise.

In many ways, when you get used to modern cars, the HVAC systems in classic cars is really an achillis heel... Granted, I live in an area subject to wide temperature and humidity swings. It might not be so bad in Canada.

The ES wipers are better than my GT6 or Mini, but still pretty much suck compared to a modern car.

Its going to be interesting seeing where the firewall splice wants to line up and what bits stay from each car. Obviously the more Miata the better but that is easier said than done. Would be great if the entire Miata HVAC came for the ride.

"easier said than done" will probably sum up the entire project. As mentioned earlier, it's one thing to simply slap the ES body on the Miata pan in "GRM Challenge Car" fashion... it's quite another if the goal is a fully functioning car you can confidently give to your wife to drive.

No good will come of this! Stretch Miata anyone?

I feel like the magician who cuts the pretty girl in half and then has to put her back together.

I would love to know what seam sealer Mazda uses, while I hate removing it, it sure does the job.

The tub is beng split at the factory joint where the tunnel meets the rear bulkhead. By picking the spotwelds apart it will give me a more accurate panel shape to base measurements on.

I need to scrape some undercoat from below to find a corresponding split point for the frame section under the floor. It might be that it just gets cut.

Note that I am drilling right through the factory spotwelds rather than using a spot weld cutter. This is because I have given it some thought, and any new metal is going to be under the surface of the holes. This means I can go quite a bit faster and have fewer cling on bits from spot welds that are not quite drilled.

While I have not run into it yet, I hope that Mazda did not use any panel adhesives in this joint!

One thing that has come of this approach is that, for better or worse, the rear seats in the P1800 are gone. The Miata subframe will come right up to the front of the P1800's seat support/crossmember. The Miata fuel tank looks like it will hide under the rear deck without any issues....maybe!

All this is why I figured for an Opel GT the easiest answer would have been to strip the front and rear bodywork off the Miata and graft the Opel bits on each end.

oldopelguy wrote: All this is why I figured for an Opel GT the easiest answer would have been to strip the front and rear bodywork off the Miata and graft the Opel bits on each end.

That's sort of what one guy did with a Corvette/1800. He striped off the Vette panels and grafted on 1800 panels, widening and stretching to fit. It looks OK, although there's pretty much zero Volvo in the car - the drivetrain, entire interior and windshield are Chevy. Naturally, the 1800 crusties hate it...

TIMBER!

Houston, we have separation. And rear chassis deconstruction.

Methinks it is time for the sandblaster soon cause I am tired of eating rust flakes. I do so envy those who get to play with rust free cars! The good news is that I don't see much rust damage that will impact the project. Most of the rusty bits were going to come off anyways.

The result is a tidy rear suspension assembly ready to graft in to the Volvo. The level/straightegde is there to check that the front panel is a straight and defined surface that I can measure from for the upcoming graft. Course, I need to carve out a matching rectangular hole in the back of the Volvo... but how hard can that be?

Not sure why...but I have this feeling of deja-vue! Not sure whats up with me and spliting cars in half!

NOHOME wrote: I do so envy those who get to play with rust free cars!

You started with a rust free car and then tore it apart!

I love this thread - I get more excited at seeing your progress than my own. Keep it going.

Forget the measure twice advice, measure a thousand time. And spend a lot of time figuring out HOW to measure!

With the rear Miata clip cut loose, it was time to start figuring out how the two want to mate and what kind of ride height I can get away with.

So, I made up these stands that have the same height as the 16" wheel with 205 55-16 tires. When the time comes to mount the suspension, these wheel jigs will be precisely located on the chassis rack so as to establish the 3D position of the parts. Assuming the tub is also square on the table, things should fall into place.

The other item that got set was the ride height.The car is sitting level on the sills at 6" ground clearance.This will JUST work with the fuel tank located in the stock Miata location.If I lower the car anymore, the tank will poke up through the flat cargo floor of the Volvo.

Still pondering if I want to give the car a 1/2" or so of rake. I can do it after with the coil-overss, but from a design standpoint, always best to design it in at the start.

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That ride height looks about perfect. I am not sure how the rake would work out.

i like level rockers. I also like even tire tuckage at both ends. so if the fronts are tucked a half inch, the rears should be. but it should also be pretty close to level.

the car looks good the way it is, but youre local. you have eyes from all angles. only you can make the decision.

I am liking what I see big time.

The wheel-wells both front and rear are going to need some minor clearancing, but nothing that worries me.

The next step is to project the dimensions of the Miata clip up into the Volvo and then make a matching hole. Figure I need to be withing about 1/8" accuracy.

Working on that.

In the meantime, I have the rear clip and components going off to sandblasting, so taking a break for a few weeks. Then I have a few scruffy corners on the Miata that I need to repair...welcome to the rust belt.

Off work this week, so trying to get some progress on the project.

Today I made a BIG hole in the back end.

Tomorrow's job is to get the Miata chunk into the hole and get some idea of just how much fun this is going to be to blend the two into a single structure. Feels good to turn the corner and start fitting stuff back on to the shell rather than cutting off!

Front to back these two clips should occupy the same space. The Miata needs to be narrowed 2" along the wheel-wells and widened 2" at the B-post.

Whenever I see threads where people have cut the floorpan out of a project, they make it sound like a walk in the park. This E36 M3 takes a lot of time and sweat to do!

The Miata clip and suspension parts are back from the sandblaster, so there should be some painting opportunities ahead.

And in case anyone is wondering why I am starting with the rear, it simply because I cant get anyone to buy the engine or gearbox out of the Miata donor, so its still mostly assembled.

Try posting the power train on the locost USA forum.

And its IN!

Looks right at home if you ask me.

Need to come back another 1/4" to line up with the Volvo wheelbase, or it need for me to not care if the wheelbase is 1/4" short. It's a bit of a fiddle to get that 1/4".

Still a ton of work to get it integrated structurally. But that's more "work" than problem.

I am pleased that my measurements worked out as expected. The wheeltubs and shock struts line up where they should.

Nice!

Cutting out floors is a mother. Welding the reproduction floors that almost fit is another pita. Nicewhen its done though. And if its not pperfect, the only two people that will know are you and the guy you ran over. I know one ain't gonna care.

Been picking away at the structural part of the install.There will be two structural attachment points at the B pillar.

These will attach to a 1/8" plate welded to the B post as a re-enforcement. All material is 1/8" wall. the lower frame extension is 2x6"

From the front I will plate the firewall plane up to the B post. This should provide a reasonable overkill factor for the structure.

The re-enforcing plates will get a trim and a few hole drilled for plug welds for best structural attachment. The plates are not yet welded in and will be trimmed along the lines. http://i1063.photobucket.com/albums/t520/NOHOME1/PEST/WP_20140816_007_zps6777adfe.jpg

Backside

I now need to spend another two hours (for the tenth time) making sure that the alignment of the Miata sub-frame is square and level within the Volvo. THEN I can weld in the Miata clip permanently.That will be a big milestone.