Track car design I've been working on

Over the last year decided to teach myself fusion 360 to help with my interest in designing my own track car.  Car is designed around a ZF8hp paired with some sort of chevy ls style engine, likely a iron block LQ# which is why ive stretched the front to bring that weight towards the center and rearward of the front contact patch. This is mostly due to ease of finding these, cost, durability and banging through 8 gears is just so sweet. I tried to add elements of tunability to the car through principals learned in books by seward and smith, various adjustments like the spacers that allow wishbone attachment to vertically move +- 1 inch to adjust roll/instantaneous centers for example. The frame isnt currently validated with FEA  like the aero hasnt been validated with CFD, (aero like the infinity wing is currently for funsies and like everything is subject to change.) I like the idea of an 8-1 collecter with equal length stepped headers (steps not pictured) for the sound even tho theyre likely a little less efficient that a really good tri y or something. The bellcranks are currently at a 2:1 at 30 degree pushrods, currently 3 inches wheel travel. Heave spring for eventual aero development. Played around with a few body design ideas but i need to keep drawing and coming up with a body shape/ style i like

Track 78"

Wheelbase 100"

estimated weight, not sure. probably similar to something like an ultima so like 1000-1200 kg? 

The reason I want to build a car vs just buying a track ready car which would be easier simpler and far cheaper, is the challenge and enjoyment of making something from scratch. I have welding and machining/ fabricating pre reqs from previous jobs and people in my life that can assist me luckily. Slowly working away, hoping to start in 2/3 years (currently building a house) so ive got time to continue refining/ redesigning etc. The car isnt for any class or designed to meet any stats. It'll be a garage queen for the winter and hopefully do 8-12 track days/ time attacks a year if i can get out. 

Looking for some constructive criticism 

This is insanely awesome.

Please, please, PLEASE follow through.

If I could just make one suggestion (I know ... everyone's a critic, right?)

As long as you're starting from a clean-sheet, might as well design the cage to fit around modern full-containment seats. From the images, it doesn't look like there's enough clearance around the head/shoulders to fit one.

My gut feeling is that the exhaust is going to cook a lot of things, and clearance is going to be fun as the exhaust expands with heat.  I've seen stainless exhausts grow an inch in length over the length of a car, you're going to have to account for that.

On that note, while you're adapting to a weird transmission anyway, why not just adapt to an Audi transaxle and go mid engined.  You have to route coolant to the front but that generates less heat than routing exhaust to the rear.

I like short wheelbase vehicles but 100" seems short for the amount of speed this may be able to generate, dependent on what your intended tracks are.

In reply to LanEvo :

Thank you very much

The cockpit is probably bigger than it seems. The seat itself is 34 inches tall and 4.5 inches off the floor, its an random model i got of grab cad a long time ago as a place holder that i scaled up to be the same size as a seat like this The seats for the winners - P 1300 GT (recaro-automotive.com) I believe this is what you mean

Ive hummed and hawed multiple times over the height as well as the angles on how the roll cage sides affect the shoulder width, the windshield here is modeled off dimensions from a corvette forum of a c7, so im not entirely sure what windshield ill be using and theres room to move it around. Id like a proper glass windshield as it would be nice to potentially hold the door open for street legality over some sort of lexan with coatings or whatever is used... Im pretty large, 6'4 and 230 and i dont want to be miserable in this thing. I think as is it should be pretty roomy as far as race cars go. The model here is scaled here to 6'4 

My only suggestion would be a cage that meets FIA specification or stronger. Not whatever this homegrown design is. 

Are you using known running gear? Its one thing to draw something up in cad, but if you want to be able to build it you should make sure you are modeling specific parts.

z31maniac said:

My only suggestion would be a cage that meets FIA specification or stronger. Not whatever this homegrown design is. 

Along those lines be sure to figure out exactly what you want to do with the car and make sure that's possible. A lot of track day and TT organizations aren't super friendly to non-production car based vehicles, and the few that are will probably have some fairly specific safety requirements. It'd be a real shame to go to all this effort and expense just to find you can't actually do anything with the car.

Really cool design and rendering but the frame's a mess. Lots of unreinforced bends (tubes only like loads along their axes - if they're bent compressive loads like to bend them further) and long/thin rectangles that'll parallelogram easily without putting much load on the tubes. 

I'll give a +1 to ensuring it meets cage & seat requirements for what you want to do, other than that the only thing that jumps out at me is the wheels looking pretty small, what size are those? The best selection of tires is now in 19s and 18s so that's the diameter you should aim for, and with this much power and downforce you should be looking at 11"+ wide wheels with a square setup for ease of maintenance/rotations.

smichers said:

In reply to LanEvo :

Thank you very much

 

The cockpit is probably bigger than it seems. The seat itself is 34 inches tall and 4.5 inches off the floor, its an random model i got of grab cad a long time ago as a place holder that i scaled up to be the same size as a seat like this The seats for the winners - P 1300 GT (recaro-automotive.com) I believe this is what you mean

 

Ive hummed and hawed multiple times over the height as well as the angles on how the roll cage sides affect the shoulder width, the windshield here is modeled off dimensions from a corvette forum of a c7, so im not entirely sure what windshield ill be using and theres room to move it around. Id like a proper glass windshield as it would be nice to potentially hold the door open for street legality over some sort of lexan with coatings or whatever is used... Im pretty large, 6'4 and 230 and i dont want to be miserable in this thing. I think as is it should be pretty roomy as far as race cars go. The model here is scaled here to 6'4 

 

That's not passing the broomstick test, you'll need to sit lower or raise the cage.

Even if the cage didn't look like it was intended to bend easily - and that one does, with all the tubes that connect unsupported to the middle of other tubes instead of meeting at common joints - if you are in a situation where you need a cage, the cage WILL deform.  And seat belts are amazingly elastic no matter how tight you wear them.

I second the fact that you need to base the cage exactly on your desired organizations cage specs.  They won't let something far afield on track.   FIA is probably an excellent fall back/catchall.  

For track width do you actually mean a 78" track width or do you mean a OA axle width of 78".  A 78" track width would be like 90+" wide with a 12+" tire.  

My LMP360 is 73" overall which is the same (+/- 1") as a actual LMP car.  I could see your aero getting out around the 85-90" range but that is a WIDE car.  

Don't be surprised if your weight ends up substantially above 1000kg.  Your not making a small car and unless substantial parts of it are Carbon it's just really hard to wind up <2500lbs.  Which is absolutely fine, imagine a Z06 -700lbs.  It's going to be crazy.  

The concept looks great, do some structural refinement, ask lots of questions and keep after it.  

Not sure how to multiquote/ one post per hour unfortunately so ill try and address everything as one. thanks for the feedback thus far

Did some reading of article 253 and about fia roll cages. Made a mock up that i believe should fit their criteria and edge me closer to a better frame. Both hoops are single pieces, radius bend of 4x on 2" pipe, (might end up eventually with 1 3/4 or 1 7/8, not sure atm). i think ive read docol r8 is the best. not sure what thickness for this diameter tubing but id go over what i need. Raised it up a few inches so theres more headroom. 

The track is Atlantic motorsports park so its a slow and technical track Radical SR3 Atlantic Motorsports Park (youtube.com). A year ago i contacted one of the event organizers that does track day events and racing and they said a scratch build would be fine as long as it passes their safety. Ill do some follow up and find their rules, for the interim ill approach with FIA rules. 

In terms of the track thats to the center of the contact patch, she thick lmao. Looking back at some older iterations they're 70-72" and i think it was just width creep for that widebody look lol. I'll work on 72" for this frame as its quite wide with 10-12 inch tires and i believe theirs room to spare/ i can bring the heave spring in within a width that doesnt require adding a extension to the shock i would use. 

wheels are 19 front and rear. Its modeled 10 front, 12 back, 25" tire. 

Doing my best to model things 1:1 with the irl counterparts through techincal drawings, and in other cases where im lucky enough to get models from them like the tilton oil pump ive got there, or some of the hardware and bearings that mcmaster carr has on their site. 

Going to do more reading tomorrow

still needs the rear strut

ignore the assymetry of not doing the other side yet lol 

not sure if anti intrusion bars are missing on the front hoop...

In reply to smichers :

Wow I guess those wheels just look small compared to the rest of the car! Putting 19x12s up front as well should be good.

Pete. (l33t FS) said:

On that note, while you're adapting to a weird transmission anyway, why not just adapt to an Audi transaxle and go mid engined.  You have to route coolant to the front but that generates less heat than routing exhaust to the rear.

Ive thought a lot about a mid engine, im open minded to it. I just know im likely spending more with a transaxle tax, especially if i want something comparable like the pdk (which funny enough uses the same turbo lamik or htc tcu's) which would likely end up 2-3x the cost... still a wonderful transmission. I could probably get a 6 speed manual at a similar cost when you factor in the driveshaft and third member much easier than the pdk... Next is sourcing, and finding one in the country to avoid any import taxes or brokerage bullE36 M3 as much as i can or at least state side to minimize shipping. Ive looked at other new options like hewland, sadev mendeola. All more than i realistically want to pay, though ive seen some used deals on sites like racecarsdirect but again most are in europe... Mind you time is on my side, i can shop around for a while...

I worked on this the last few nights for a mid engine. Drastically different, brought the width in a bit. increased the wheelbase to like 105-110 depending on the transmission. 

not sure if wishbone brackets are comically large or not lmao, they do the job though

Rip it apart pls

Im thinking of bringing the front end down to allow a node in the center to attach the heave spring to without having to bring the bell cranks up too much (even if it has to go above the frame) whilst bringing the nose down overall. 

Oh, hell, when I think of Audi transaxles, they are downright common.  I am thinking of some late model A4/Q5 thing with the center differential welded up so you don't need anything connected to the rear output.  Many of the late model vehicles seem to be twin clutch if that tickles your fancy.

Pete. (l33t FS) said:

Oh, hell, when I think of Audi transaxles, they are downright common.  I am thinking of some late model A4/Q5 thing with the center differential welded up so you don't need anything connected to the rear output.  Many of the late model vehicles seem to be twin clutch if that tickles your fancy.

OK sick, ill take a look into what audi has to offer :) 

I don't like A-arm inboard mounts overlapping with feet.  I understand sometimes it has to happen.  On my build the arms appear to go Forward.  With the rear mount basically at the axle center line.  That way your feet can be behind the arms completely.   

Your suspension mounts are probably generous but it may be the lightest easiest way to accomplish the goals.  My rear subframe is built the same way with shear plates to mount the inboard pivots.  If probably is 2lbs heavier then tube only but it was much simpler to fabricate and fixture correctly because all the holes are just cut in a sheet.  You could have send cut send plasma them easily for near 100% accuracy.  

I know it might be a place holder but I would (and do) run longer front VSALs.  It looks like yours is like .75×TW which is what I typically run in the rear.  My fronts are more 1.75-2.0TW.   I find when you plot the camber curve <.75 is on the edge of exploding non linearly with travel and >2.0 you are really not gaining much camber stability but start to have more RC migration because the ratio of A-Arms length to VSAL starts to get pretty large.  Also in the rear much smaller starts to get really short vertical separation on the IBJs unless you are running high outer upper ball joints like modern Trucks with the ball joints above the wheels.  

Also I run a heave spring on my car.  I currently only have one on the front suspension and rely on the rear wheel rates.   It takes a fair amount of math to get all of the ride frequencies to work well and keep roll to a desired range.  I have managed it with my build without ARBs, however I have a Very low CG Height and tolerate quite high Ride Frequencies.   The heave spring does work during straight line but if is most effective under braking.  My Vmax is only about 130mph though id imagine it will become more important if Vmax rises.  

I can share my spreadsheet I used to develop my installation ratios.  I like to think of everything in ride frequencies that way it can be translated from vehicle to vehicle.  If you made your car have the same ride frequency as mine it would have higher Wheel Rates but Scaled by your Corner weight increase. 

Just ask questions and we can try to get your belcranks 90% right when you get there.

As far as chassis design goes, it can be summed up by, "Triangles everywhere."

kb58 said:

As far as chassis design goes, it can be summed up by, "Triangles everywhere."

Triangle man hates Particle man.

I've been resisting the urge to add my two cents worth to this thread, because that's what my opinion is worth. I've built exactly one tube chassis in my life, so bear that in mind. If you want to actually build a car and see track duty with it, simplify your design so you can build it. Reduce the chassis complexity by utilizing one straight tube rather than two tubes with a unnecessary joint, etc. A simple design is your friend.

While you're a bigger guy than me (5'10", 195 but with a long torso) I think you can readily keep the car lower than the 52" in your earlier post. My car is 48" to the top of the body and I could do at least two inches better with a do-over. Overall my car is smaller than what you proposed...92" wheelbase and about 69-70" to the outer edge of the rims. It's basically Miata track width , plus 10" rims. Seat is bolted to the floor. Here's me sitting in the car. There's lots of head room, even with a fairly vertical seat.

Because of the engine setback ( GM LM4), foot room is the only issue, but's it's an automatic so two pedals is all I had room for. It'll work. As for shoulder room, that Corolla shell is only 48" across at the shoulders, and that"s a common width for many small cars (my MINI, and Miata are the same). Also, keep in mind this is a Challenge car, so stuff isn't optimal, it's cheap. There's less than $150 in the chassis. If you decide to go rear engine follow nocones build thread for an excellent tutorial.