Mid Engine Suspension Research: Considering Miata Parts

First post here.  Hope it goes well.

First, a little introduction: I have been building cars and doing welding and fabrication for about twenty years now.  I was on hold for a while due to life circumstances, but I'm getting back to business.  

I really want my next project to be a mid engine conversion.  I had long wanted a mid engine car, specifically to convert a front engine car to mid engine, but then I worked at Midwest-Bayless for three years converting Fiat X1/9s to Acura K20 powertrains.  That experience convinced me that I had to build something mid engine for myself.  

Anyway, the reason for the post starts meow.  I would like to borrow somebody else's suspension engineering, as I am aware that much science is required to make a mid engine car be more than a smoky donut machine.  

I had a chance to look at NA Miata suspension (yes, actually a first time experience for me) and found the suspension to be remarkably self-contained and swap-friendly, especially the rear with its flat and horizontal mounting surface.  I would like to borrow somebody else's engineering in order to save time and effort and to help prevent failure and disappointment.  So now, the questions:

1) Does anybody here know about anybody using Miata suspension to make a mid engine car?

2) Do longer aftermarket suspension arms exist?  I would like to widen the track of the car, and can build to suit, but existing solutions have the virtue of already existing.

3) Is there a particular reason why I should not be considering Miata suspension?

I would think that a FWD car would be a better choice. They tend to be pretty self-contained as well. I suspect that you'd have a hard time packaging the Miata rear subframe with an engine/trans in close proximity.

There is a wide track kit available from Paco Motorsports, but it's aimed at offroad use (!) and may not suit your needs. Keep in mind that lengthening the arms will likely change the suspension geometry somewhat so you'd be moving away from the "someone else's engineering" parameter.

Now you have to tell us more about the Fiats with the K20s. It's the rules.

Is your plan to stuff something like the VW Type 3 gearbox into the Miata rear cradle and then fab up some axles? Might be better to steal the entire Type 3 structure and stick it in the back of  what you are building.

What are you building?

Here is a build thread to inspire you. Very Grassroots aproach to this game. Sadly I think the builder has abandoned the project for lack of a race venue.

http://forum.retro-rides.org/thread/202888/audi-a3-mid-engine-v8?page=6

Pete

Keith, this is an Audi longitudinal engine layout.  The rear subframe would probably require some work to clear the middle part of the transmission, but the engine will be out of the way.  Also, I wouldn't mind jigging up and building a whole new subframe to the factory hard points if that were required for clearance.  

Building a wider subframe would also be a way to preserve factory geometry while achieving a wider track.  I could make an expandable jig and build a wider one or section and widen the factory units.  But if wider control arms move upper and lower points directly out by the same amount top and bottom, I would expect the only change in geometry to be slightly less camber change during compression.  

Using front suspension in the rear seems to be an easy recipe for a smoky donut machine, but I really want to avoid that.  My plan up to the point that I discovered Miata parts was to use on-hand Audi 4000 Quattro rear strut housings and build suitable control arms.  That idea would still work fine, but the idea of having real aftermarket support for suspension upgrades has become very appealing; I can find respectable Miata full coilover systems for less than the cost of the components to build my own using Audi housings as a starting point.  

As for the K20 X1/9s, what would you like to know?  A 220 HP engine that revs to 8K completely transformed the X.  The factory engine and trans are garbage.  The shift linkage was made of wet spaghetti.  I built a cable linkage that made it feel like your right hand was reaching into the transmission to change gears.  

In reply to NOHOME :

VW Fox, Audi 01E FWD from Europe, and an Audi I5T, either 10V or 20V depending on the over vibe I choose to go for.  

Other than Miata parts, my plan has been Audi 4000Q uprights and arms built to suit connecting to a tube frame also built to suit.  

Keith Tanner said:

I would think that a FWD car would be a better choice. They tend to be pretty self-contained as well. I suspect that you'd have a hard time packaging the Miata rear subframe with an engine/trans in close proximity.

There is a wide track kit available from Paco Motorsports, but it's aimed at offroad use (!) and may not suit your needs. Keep in mind that lengthening the arms will likely change the suspension geometry somewhat so you'd be moving away from the "someone else's engineering" parameter.

Now you have to tell us more about the Fiats with the K20s. It's the rules.

I was going to say something similar. Does an RSX still have a double-wishbone upfront, or had it moved to MacStrut at that point. It seems like just grabbing a full FWD unit (engine/transmission/subframe/etc) would be much easier, fab wise, than reinventing the wheel. So to speak.

2nd. I also want to here about these Fiats with K20s!

I'd be tempted to steal the Miata mount points and just build my own subframe. I did just that on my LS-powered MGB. My biggest concern with moving any points or extending the arms would be changes in roll center behavior, which is a big factor in the Miata's handling in my opinion. Depending on how wide you want your track to be and what you want for tire width, you may want to do it all with wheels instead. There's a lot we don't know here.

I'm sure the Fiats were transformed, but do you have any pictures? Overall weight? Did you have 100% function of all accessories like AC and gauges?

RSX is Mac strut

It will be easier to do with a FWD drivetrain mounted in the middle.  I think that is essentially what Toyota did with the MR2, and they have a team of engineers and a boatload of dough at their disposal.  I think that is what Fiat did with the X 1/9 too.

There is a kit that takes a V-6 honda drivetrain and mounts it amidships.  Might be a good base, or at least a starting point.  Maybe that 818 kit that uses Subie parts could give you some guidance, or point you the right direction anyway.   I think there also was an article in GRM mag about a guy who made a midengine car out of a 4 banger civic, if I remember right.

You're thinking of Midlana.

Since the Audi engine came in a FWD package, I'd start by looking there. Motor mounts and everything!

In reply to Toebra :

Those engineers knew that they also had to make some compromises.  So...

Which Civic was famous for it's double A arm front suspension?

I have an X1/9 I've been bench building for a while, and Immediately thought of miata parts. 

Observations- 

The front suspension is wonky for a mid engine, if you want to use the front subframe. Just long, and front steer doesn't help packaging. 

As stated, the rear is self contained, but also not good for a longitudinal mid engine. I suspect, if widened enough, a reverse engineered subframe could be golden in your application, but then, what do you do fro front suspension? 

I settled on 85ish MR2 suspension, and plan to adapt it to the X1/9 shell. 

The cars you built are Awesome! This leads me to believe my advice has limited usefulness.

This guy's guidance, on the other hand, as previously stated is golden.  https://midlana.com/

Also, check this out.http://www.locostusa.com/forums/viewtopic.php?f=36&t=14452

The only one i can think of is the mid engine rotary miata built by Randy Zimmer.

In reply to alfadriver :

the pre RSX flavor, EG I think.  Like 1993 through maybe 2000, was not just the front.  Upper and lower arms, front and rear.  Had a 1998 Integra GSR sedan with that setup that I still miss.

Keith Tanner said:I'm sure the Fiats were transformed, but do you have any pictures?

*CONSPICUOUSLY LOUD COUGH**

You might take a look at a RX8 if you want wider.   

I don't know if my Audi transaxle will fit into the rear, or shall I say how much mod/fab it will take, but it was my plan for my mid-engine GT6 project,

rx8 rear suspension with transaxle, and rx8 front suspension.

Maybe you can figure it out first so i can follow your lead for my project.

Otherwise, I am also doing a mid-engine Corvair, and I used a 944 front and rear suspension,

and well there is also the 914 suspension.

In reply to Toebra :

That is definitely not what FIAT did on the X.  The X1/9 rear suspension was designed specifically for rear end duty and was shared only with the Scorpion.  

In reply to wheelsmithy :

The recipient car is already front steer, and I think due to the longitudinal FWD nature of the car, space may be limited to make it rear steer anyway.  

In reply to Knurled. :

Thank you for sharing those!  That one was sent to western Canada, and was my particular favorite.  

In reply to Keith Tanner :

Two cars had functioning AC.  I used two different Japanese AC compressors on the two AC equipped cars and made a bracket that mounted the compressor in the RSX's original power steering pump location.  

Speedo and tach were Marshall units that were integrated into the factory cluster.  I did not do that part.  The owner of the company subbed that work out to a customer of his in exchange for FIAT parts.  

nimblemotorsports said:

You might take a look at a RX8 if you want wider.   

I don't know if my Audi transaxle will fit into the rear, or shall I say how much mod/fab it will take, but it was my plan for my mid-engine GT6 project,

rx8 rear suspension with transaxle, and rx8 front suspension.

RX8 is also NC Miata. They're set up to go a little toe out in the rear on turn-in to make the nose really pointy - which might be a little too exciting on a low polar moment midengined car. FYI.

Thanks for the pics, Knurled. That Fiat is all full of Honda. 

Been searching for a solid X1/9 to do this to for my next project car...... Had an X1/9 in my early 20's, was an amazingly light, great handling car with out a lick of power...... this should solve that problem!

In reply to Keith Tanner :

And that isn't the supercharged one.  Or was it turbo? I forgot.

It seems like the Miata suspension idea may not be for the best.  

I could just go back to the original plan of using Audi 4000q rear housings (basically a modified 5000 front housing with an arm for toe control) and Audi 5000 turbo front housings and building control arms to locate them where I want them to be for my desired audaciously wide track.  

If I do that, the next question is: what undesired effects might come from cutting the strut tube free of the knuckle (Audi 5000 housing shown below) and angling the tube inward 3-4" at the top?  I will need to do this to keep the strut mounts between the fenders instead of disappearing under them.  I expect such a move to cause more compression induced negative camber at all four corners and more caster angle in the front.  I don't know the math to determine the safe limit for such a modification.  

Just here to also say I love x19s with different motivation.

Here's mine (admittedly not moving along very fast):

https://grassrootsmotorsports.com/forum/build-projects-and-project-cars/fiat-x19-bike-engine-challenge-build/122836/page1/

In reply to gastungstenarc :

Have you looked at what solutions the mid-engined cars that use Audi transaxles have done?

Strut based suspension is always a compromise and can work "fine" within a narrow range of movement, its main advantages are in packaging and cost, both of which are important in mass produced vehicles, not necessarily for purpose built performance vehicles.

I might consider looking at other solutions, like some of the CUV/SUVs that have some very neat, self-contained IRS solutions with longer arms and optional AWD (aka RWD) solutions, common bolt patterns and decent sized brakes.