LocostUSA.com

Hi all,

Although I have not yet completed my current car project, I have already been planning the next one. After taking inspiration from the Midlana, my next car will be a scratch built mid-engine sports car. The design of my Midix has several key differences from the Midlana. In addition to some aesthetic differences that I wanted, I have designed my car to allow it to be used for as much daily driving as possible. Over the last few years, I have been putting together content to plan out the build, and I recently decided to turn this content into a website, which I have just launched:

https://midixsportscar.wordpress.com

Below are my CAD renderings of what the car will look like.

Due to time and space constraints, I do not plan on starting this build for a number of years, but I wanted to plan it out anyways well in advance.

Any feedback is welcome!

_________________
Photo gallery of my completed Locost:
https://plus.google.com/photos/10397358 ... banner=pwa

Interesting. You might want to run some type of "torque box" structure through the console area to stiffen the chassis. And raise the sides of the chassis up as high as you're comfortable with. GM did those two things to the C4 Corvette chassis, which still isn't the stiffest chassis around, but your roll cage can help with that.

Flip side, there were a lot of kit cars that got along just fine with a VW floorpan and some flexible fiberglass bodywork bolted to it...

Hi TRX, thanks for your feedback.

Good suggestion regarding the torque box through the center section. I had planned to add a tall tunnel structure through the cockpit section (similar to a Locost) to serve this purpose. I hadn't got around to adding them in the CAD model of the frame yet.

I had also thought about how tall I could make the sides of the frame that run underneath the door opening, but I suspect that I can't go much higher without making it difficult to get into and out of the car. As you mentioned, the roll cage should help quite a bit with keeping the frame from flexing.

_________________
Photo gallery of my completed Locost:
https://plus.google.com/photos/10397358 ... banner=pwa

Update: I did a lot more CAD modeling of the frame details recently.

_________________
Photo gallery of my completed Locost:
https://plus.google.com/photos/10397358 ... banner=pwa

Think triangles, everywhere. Take what you did at the backend panel and do the same for the rest of the chassis.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Instead of a pinto/M2 IFS, I recommend that you use an IFS and firewall mounted rack from the same make/model/year donor supplying the IRS and drivetrain. This solves many problems. If it helps, you can use the IRS subframe to make a reverse jig to create the LCAPs.

It appears the desired tank location prevents you from fitting tubes directly between the front LCAPs and rear subframe attachment. These tubes should also run diagonally or at least a split X frame.

Instead of a transverse fuel tank, make use of the tunnel with a long skinny tank with the filler at the rear with an elbow to connect the filler to the B pillar. A fiero is a perfect example. Use a couple bolt-in 12x24 aluminum plates (1/4 to 3/8 nutserts in the rails on 3 inch spacing) across the bottom of the tank to tie the lower chassis rails together and also supports and protects the tank.

I see a lot of offsets for secondary loads instead of straight lines between nodes for primary structure.

Also consider “cowl shake” where the base of the windshield can move laterally over the floor rails from torsional loads like going over railroad crossings at an angle other than perpendicular to the rails or one wheel over a pot hole.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Thanks Kurt, I will add some more triangulation to the frame.


Thanks for the feedback. Can you elaborate on why you recommend using the IFS and rear-steer rack from the same make/model/year donor, and what problems you think it will solve? The donor car will come with MacPherson strut front suspension. I am going to run a double wishbone setup in the front. if I sourced a second set of the same knuckles for the front (because the original knuckles from the donor car will be in the back), I would need to adapt the MacPherson strut knuckles to work in a double wishbone setup. Why not just buy Mustang II spindles already designed for a double wishbone setup? Also, I don't want to have power steering, so I would need to modify/depower the donor rack. Why not just buy a readily available Mustang II manual rack?

When you say to use the IRS subframe to make a reverse jig to create the LCAPs, I assume that you mean to use the front subframe from the donor car to reverse jig the lower control arm pickup locations. Note that I plan on bolting the entire donor car front subframe under the rear of my frame, so it will already have the correct mounting points for the donor lower control arms that will be reused (similar to the DF Goblin).


Although there is no driveshaft running through the tunnel, it will still be fairly crowded to run the shift linkage, brake lines, clutch line, coolant tubes and wiring from the front to back. I'll stick with the transverse placement like Kurt has in the Midlana, which makes use of the otherwise unused wedge-shaped pocket between the passenger compartment and the engine.

_________________
Photo gallery of my completed Locost:
https://plus.google.com/photos/10397358 ... banner=pwa

Happy to elaborate. I assume the donor will be rear steer. By adapting ‘70s ford suspension to whatever your late model fwd donor will be, you are creating extra work and expense. Using the donor suspension on the front and rear with matching wheels solves wheel offset, scrub, hub centric wheel pilot rear versus lug centric front, track width, reduces braking balance issues due to differences in brake rotor size, caliper bore, pad swept area, allows for similar or same geo for the front and rear, you are already making UCA adapters for the rear so it is easy to make two more, you can probably reuse the front sway bar as is, and there is no need for brake line adapters from sae to metric. The donor rack width should work with your UCA conversion by adjusting the height. Adapting has a snow-ball effect on your effort and wallet. Probably don’t want to carry an sae and metric lug wrench or two different spare tires either, but you could further adapt the pinto ifs to work with the donor compatible lugs and wheels but not the scrub created in the process without custom length balljoint pins for rebuildable race joints. The pinto has a good bit of scrub as-is but it has been used a great deal and it has very strong aftermarket support. Why pay extra to fit something that will need further adaptation to work with what is in front of you and is not as good as what came on the donor?

The missing chassis rails I described go through the area behind the seats to connect to the rear subframe front attachment. However, you can still place a fuel tank there if it is small enough and/or the chassis tubes are removable. All those things don’t have to go through the tunnel. Wiring and shift cables are usually above the floor/tunnel. If this is going to be a backbone chassis (I see no torque tubes near the rockers like an elise), then the tunnel should be much larger in height and width.

Just another person with an opinion.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Thanks for the feedback.

Although it will likely be more expensive to use a Mustang II front suspension compared to using a second set of front knuckles, I think that it will be less work than adapting the factory knuckles for double wishbone and depowering the factory steering rack. Also note that on most FWD knuckles, the CV axle and nut needs to be in place to secure the hub to the wheel bearing. Because of which, using a second set of front knuckles means that I would also need to source a second set of CV axles and disassemble them so that I could install the outer portion of the axles to secure the hubs to the wheel bearings.

Regarding hub centric vs lug centric, most aftermarket wheels have centerbores large enough to accommodate multiple hub diameters (hence the availability of hub centering rings), so I just need to select wheels with centerbores large enough to accomodate the front and rear hubs.

Since I plan on using aftermarket brake master cylinders, I can select the bore sizes of the front and rear master cylinders independently (and/or adjust the brake pedal balance bar) to work with whatever size rotors and calipers are on each end, so there is no need to have the front and rear rotors and calipers the same size.

It is not uncommon for factory cars to have different width/offset wheels on the front compared to the back, but they don’t carry two different spare wheels. The spare wheel is there just to prevent you from being stranded, so it doesn’t have to be the same size as the regular wheels. In fact, most space saver spare wheels are much different width/offset compared to the regular wheels. All of this is moot though, because like the Midlana and most Locosts, I don’t plan on carrying a spare wheel, so I also don’t need to carry a lug wrench, let alone two different ones.

Having the door openings large enough to make it easy to get into and out of the car limits how tall I can make the rocker panel tubes but I may be able to make them a bit higher than what I have shown, to add a bit more rigidity. Also, I have since made some updates to the model with additional triangulation, including the center tunnel. I will post an updated screen shot once I get a bit more done on it.

Thanks

_________________
Photo gallery of my completed Locost:
https://plus.google.com/photos/10397358 ... banner=pwa

Thanks for the explanation, but I am well aware of all these things. I stand by my reccomendation and there certainly is no need to defend your position, but I appreciate your replies.

I will add that when buying salvage yard fwd suspension assemblies, they use a torch whenever it saves time. The old axles are of no value except for the weight in scrap so they simply pop them out of the transmission or cut them with a torch between the joints and include them with the spindles. That is typical in the USA. Can't say for BC.

I look forward to reading about whatever you build.

I just joined Kurt's site to see what all the fuss is about. Not sure why I didn't when he started it. Probably because I am not building a middy?

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Good to see you survived the holidays and are progressing.

I've been working on modeling the rear suspension. As shown below, my plan was to remove the factory strut from the knuckle and fabricate an adapter that bolts to the factory knuckle. The adapter would provide a lower mount for the rear shock, and pivot points for an upper control arm to convert to double wishbone suspension. The upper control arm would connect to the adapter using two rods ends, which could be threaded into or out of the upper control arm to set the static camber and toe.

However, given the width of the transverse drivetrain, there does not appear to be much room for the upper control arm, which is why I have it shown as being very short. I haven't run the numbers yet, but I suspect that this very short upper control arm will cause issues with overly aggressive camber gain as the suspension compresses. Given these issues, I'm considering just using the factory MacPherson strut setup (similar to the DF Goblin) rather than trying to convert to double wishbone.

Let me know if you have any feedback.

_________________
Photo gallery of my completed Locost:
https://plus.google.com/photos/10397358 ... banner=pwa

You can still have good camber gain by sufficient aft offset of the forward UCAP cl that clears the drivetrain and falls on a line parallel to a line through the UBJ cl and the opposite side LBJ cl to setup a reasonable VSA. Maximize the distance between the UCAPs of the UCA for stability by extending the aft UCAP to the back of the chassis.

Fitting a single UBJ will allow you to reduce the offset of having a second ubj further forward.
If you want to fit longer coilovers with a lower cg and don’t extra links or need to raise the UBJ along the KPI to improve clearance to the forward UCAP, build an offset rocker UCA that places the coilovers behind the engine. This requires either a traditional style UCA with an extra link for the coilover attachment where the UBJ and coilover ends can be connected directly over the top of the UCAP axis or a tube of adequate cross section and wall thickness to cope with the torsion loads and not buckle.

I like the idea of ball bearings versus bushings or needles because the ball bearings have a greater radial cross section to take up the difference between a reasonable size for a clamp bolt and spacer versus a reasonable cross section for the pivot tube loaded in torsion while keeping it light and reasonable in cost for material and machining.

I posted a drawing of a rocker on ccrunners Berkeley but his loads are half as much and the available space for a rocker is probably a third of the space you have.

An easier option to all of this would be to keep the original struts but cut the seats to fit standard coilover springs and use a rod end and rod to replace the rack for toe adjustment. There are a number of chinese adjustable coilover kits on ebay for around $50 that could be used if you make a new upper seat. The included seat was plastic on the set I used and skinny G used on the firefly build. If you can’t find a universal spring with the right ID for your needs and the kit springs are too stiff, cross reference to an oem spring is an option and usually cheaper since they usually come in pairs. I recall applications ranging from less than 3 inches to a common 5 inch ID.

If you'd like a drawing for the general idea, post a view from behind the left rear tire looking down and forward at the left rear corner.

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Looks like you will have enough room for a traditional (yet offset) rocker instead of the extra expense and complication of a torque tube rocker. Here is the general idea.

What is it they say about pics vs. words?

_________________
Miata UBJ: ES-2074R('70s maz pickup)
Ford IFS viewtopic.php?f=5&t=13225&p=134742
Simple Spring select viewtopic.php?f=5&t=11815
LxWxHt
360LA 442E: 134.5x46x15
Lotus7:115x39x7.25
Tiger Avon:114x40x13.3-12.6
Champion/Book:114x42x11
Gibbs/Haynes:122x42x14
VoDou:113x44x14
McSorley 442:122x46x14
Collins 241:127x46x12

Thanks for the continued feedback, much appreciated. Cost and simplicity are big driving factors, so the thought of just reusing the struts and modifying them with cheap slip-on coilover sleeves and aftermarket springs is really appealing. This company has a pretty good selection of different sizes:

https://www.a1racing.com/coil-over-conversion-kits.aspx

One of the potential issues with this solution is that I was planning using the rear rotors from the Civic donor car on the front (now rear) knuckles, and making a custom adapter bracket to allow the rear calipers from the donor Civic, which incorporate the parking brake, to bolt to the Civic front (now rear) knuckles. In order to do this, I was planning on swapping the knuckles left to right in the Midix. This will allow the rear calipers from the donor to be mounted towards the rear of the car, as they are in the donor Civic, to maintain the brake line and parking brake cable routing direction as used on the donor Civic. This should hopefully allow me to reuse the factory parking brake cables from the donor car, with straightforward cable routing. However, doing this will now make the steering arms on the knuckles point forward instead of backwards, so I won't be able to simply replace the steering rack with fixed rod and rod ends for the toe control, as the new forward placement of the faux rack might interfere with the engine/transmission. Without the actual parts in hand though, it's difficult to say for sure how much of an issue this will be.

The inboard rocker setup that you sketched out looks pretty slick. I'll work on modeling up both solutions on my CAD design to see how they look.

_________________
Photo gallery of my completed Locost:
https://plus.google.com/photos/10397358 ... banner=pwa