A locost style track car, Car9

[horizenjob]

Is there a COM member that could measure the width of a Miata steering rack for me? I need to know the center to center width of the rack pivots or inner tie rod ends? I would like to include the Miata rack and also front spindles as options in my frame diagrams.

I got good news the other day. The developer of the bodywork pictured above called me after just finding my frame work in the last week and said he would like to adopt it. So he will work with me to make sure my frame fits his Lola replica and also will make Lotus Seven style bodywork to fit my frame. I am encouraged someone is going to build special nose and scuttle pieces. So there will be 2 choices for this car, a Seven style and a sports racer.

[962porsche]

you may want to check out flaming river steering racks . i have installed many over the years they are a very good rack and for a good price . they offer many deferent sizes and styles to pick from . they also offer any other steering part to also go with there racks so you can build the hole steering system from one place new at a low cost .

[horizenjob]

I did use measurements from Flaming River for the Mustang style rack in the drawings now. It's just that I would like to at least know the Miata rack dimension before I really nail down the dimensions of the front bulkhead.

When building a Locost and using a Miata donor, people usually have to cut down the Miata rack. It would be nice not to have to do that. My frame is a few inches wider at the steering rack so it might work.

There's a related problem though. I didn't realize how narrow a car a Miata is. Someone told me it might not be possible or easy to run the trailing arms in the rear. I put Subaru and Ford IRS parts in the drawings, but didn't realize the Miata track is 3"-4" narrower. So I need to find wider compatible halfshafts or axles or wheels available in much different offsets for front and rear. If anyone has ideas don't hold back because it will be even more fun watching me trying to put this together.

[962porsche]

let me ask you ?
why are you not picking some thing like Heidt's rear ends to use with this car ?
right now i'm working on installing one of there rears in a chassis . they sell every thing you need for the rear ends from were the power goes in from the drive shaft to were the wheels bolt on lug nuts . they have inboard brakes for unsprung weight and can handle big HP and TORK numbers .
i don't think the cost was that bad at 7K BECAUSE YOU GET EVERY PART needed to do the installs .
for many of the chassis i build i will try and use there products , winters performance , speedway engineering and so on. 1st for the added plus of the use of having quick change rear ends . that way the car can be geared for the track they are running at .

[brucesallen]

I did use measurements from Flaming River for the Mustang style rack in the drawings now. It's just that I would like to at least know the Miata rack dimension before I really nail down the dimensions of the front bulkhead.

When building a Locost and using a Miata donor, people usually have to cut down the Miata rack. It would be nice not to have to do that. My frame is a few inches wider at the steering rack so it might work.

There's a related problem though. I didn't realize how narrow a car a Miata is. Someone told me it might not be possible or easy to run the trailing arms in the rear. I put Subaru and Ford IRS parts in the drawings, but didn't realize the Miata track is 3"-4" narrower. So I need to find wider compatible halfshafts or axles or wheels available in much different offsets for front and rear. If anyone has ideas don't hold back because it will be even more fun watching me trying to put this together.

My Lotary 7 uses the rear subframe, double wishbone IRS and Torsen Diff from the third gen RX7. Has worked great but if you are not putting in 300+ hp you may not want the weight.

[962porsche]

most if the CO's that i have used like winters also offer rears that are lighter for cars not running high HP and Tork numbers .
if i remember right this chassis is being built to fit a V8 motor ?
one thing about chassis building is you really have to pick the drive line and stick to it for the hole design . if you build it light for say a 4 cylinder then it will not hold up over time if you drop in a higher HP / tork motor like a V8 and if you build it for a V8 then the chassis will have uneeded weight for a lighter HP / tork motor .
when a chassis is designed it's not only the 3 axis if suspension that has to be designed into the chassis it's also the HP & Tork that has to be added into it as well . on a lower tork and HP numbered drive line it's not a big deal but on a high HP & TORK drive line it's a must to design thows number into it as well .
this maybe why i came up with such deferent tork loads and number than marcus is ??

[horizenjob]

You guys have good points and comments. It will take me a little while to collect some thoughts and write a good answer.

I am fixing up my model after making some changes. Finally actually making room for useful items like a fuel cell and the rear coilovers. Also have simplified the front and floor and taken out maybe a dozen tubes.

[horizenjob]

Sorry I'm slow on posting here. Still working hard at it and making good progress.

I did some work in the FEA program and found that you can build a square tube version of this chassis to the same weight and stiffness. It would not have an integrated spec roll cage for wheel to wheel racing but would still have the roll hoops for rollover and rear end protection. Square tube would make for a quicker and easier build though. I used 1.25" square tube for the chassis rails and 1" square tube for the diagonals on the side of the car. These were 16 gauge tubes.

The frame is mostly done now. I need to draw in some diff and fuel cell mountings next.

My Lotary 7 uses the rear subframe, double wishbone IRS and Torsen Diff from the third gen RX7. Has worked great but if you are not putting in 300+ hp you may not want the weight.

That's a good solution. For this car I expect the V8s to put out that much power. I am hoping to attract other builders to this design so there is a lot of effort up front going into the drawings and thinking out the suspension. This would not be economical for a single car.

A goal here is to provide a chassis that has the adjustability you see on some oval track cars. This will allow for different levels of power and different choices in running gear. There are Ford and Subaru rear end parts in the drawings now. I am seeing some of the compromises inherent in this and will probably spec out some custom fabricated uprights one of these days, probably using off the shelf sealed hubs.

So Bruce, I am going to need a test driver one of these days. You have experience in formula cars, which I value, and also a seven type roadster. Interested? Anyone else?

why are you not picking some thing like Heidt's rear ends to use with this car ? i don't think the cost was that bad at 7K BECAUSE YOU GET EVERY PART needed to do the installs . winters performance , speedway engineering and so on. 1st for the added plus of the use of having quick change rear ends . that way the car can be geared for the track they are running at .

I'm not sure I have a really quick or short answer to this. Some issues would be cost, weight and geometry. I also made a choice to avoid using a half shaft as a suspension member. That doesn't mean someone couldn't use one of these. With an expected weight of 1500 lbs. for Car9 with a V8 and 1200 lbs. with an I4 that rear end is huge overkill. There isn't that much torque available at the rear wheels.

I do like the speedway engineering mini quickchange rear ends. Those would be nice. I wouldn't mind drawing one of those in, it hasn't been a choice yet of the first people to express interest in building one of these though.

In board brakes are a big plus, really one of the main significant advantages of running IRS.

I haven't really itemized a list yet, but it seems to me you could build an entire Car9 for $7k. Obviously you can always spend more, but that $7k should get someone a genuinely fast car. I am hoping to make a case that it makes more sense to run something like this, which is faster and more responsive to the driver then any street car, and not risk those expensive and compromised street machines at the track. Those street cars are nice and fancy pieces of equipment, don't get me wrong on that, but they carry one or two thousand pounds of extra stuff around. That gives them a lot of inertia which makes them feel clumsy and slide forever when a driver loses control.

[962porsche]

there are some many benefits to inboard brakes . the 1st and for most would be unsprung weight . but you would also have the benefits of more flexibility of wheel fitment . there is also the fact that your not putting any tork on your suspension as it would in the same way as outboard braking systems do . it also allows the wheels to follow the contour of the road better .

there is a big deferents in the way a chassis will handle the HP and tork of a small displacement motor .
if you build a chassis for that then in most cases it will not like a bigger / higher tork motor .
if you build a chassis for a big tork motor and drop a small motor in the car the chassis will have to much weight to use the power of a smaller motor to it's fullest . were if you drop a high tork motor in a light weight chassis there are many draw backs to that . a chassis really needs to be designed and built for a certain tork and HP range . more so for the tork range . you can have a motor that puts out say 400 hp but if it is only putting out 250 torks than the chassis is not going to notice much .but if your using a motor that is say putting out the same 400 HP and then about the same torks number of say 400 tork the chassis will have undue flex .
i could get into the hole thing about what hp is and what tork is . but a quick summery is tork is what gets you off the line and up to speed and hp is what maintains it .
over the years i have had to add strenght to chassis because the customer has added motors to the cars with greater tork numbers .

[horizenjob]

I am used to the idea of inboard brakes. I wonder how much trouble they are when trying to fit a nice diffuser for aero though. This car has trailing radius rods for the rear suspension to handle the acceleration/deceleration loads so the torque of the outboard brakes is very directly and well taken care of. This is a reason I like the traditional trailing arm setup from the 60's - 70's. It will also allow very easy adjustment of anti-lift in braking because there are multiple mounting holes for the front of those trailing arms.

I understand your concern about the frame being designed for small and big motors. So the drawings do include different running gear, a Subaru IRS for smaller motors and Ford IRS for bigger motors. There is some compromise in the frame being able to handle either size engine, but it is covered by things like the minimum requirements for roll cage tubing and also providing a level of safety. Another factor is the light weight providing a limit to the amount of torque or horsepower that can actually be put to the ground before the wheels spin.

In the end the compromises in the frame to support both sizes of motor may not amount to more then 10 pounds, It's a little hard to say and we can discuss this in more particular either now or when this work is closer to actual metal.

[962porsche]

i would not think the inboard brakes would interfere with a rear diffuser . most of the one i have installed on cars the rear end housing is bigger and hangs lower than the brake rotors do .
you don't want a diffuser to be angled more than 14 dergrees max 12 is best . but for aero to work and work at it's best you have to take the dimensions of the under side of the chassis and then you can come up with the dimensions of the diffuser size and angle .
when it comes to tires that the person is going to pick will have allot to do with how the hole car will work .
if the car is designed for say a performance street tire and they slap on a set of full slicks shocks and spring rates will change greatly even going from a R compond tire to a full slick offers greater traction

[horizenjob]

David, I want to thank you for your efforts checking in on this thread and the comments you make. I have just gone thru the thread again to understand this

on a lower tork and HP numbered drive line it's not a big deal but on a high HP & TORK drive line it's a must to design thows number into it as well .
this maybe why i came up with such deferent tork loads and number than marcus is ??

So first I want to say I think I misunderstood you at the beginning when you said you built a model and tried some changes. I thought you meant this was for your own space frame project (mid-engine maybe?) but now think it was for this car. So thanks for all that effort. I think I have landed up doing many of your changes, but perhaps would have done so quicker if I had understood you correctly sooner! I will put up another picture and address some of your earlier comments later today or tomorrow.

I was looking thru this thread to understand your comments about the numbers but didn't find it. I do remember something about this though. So I will work through a bit using the 400 torque number you mention above. Torque and horsepower sort of work out to be the same by the time you get thru the gear reductions to the tire contact patch. Different for things like motor and diff mounts though.

With 400 torque at the crankshaft and 1:1 reduction ( 4th gear ) you get 400 going into the diff thru 3:1 reduction gives 1200 torque split between rear wheels. So 600 torque at each wheel. Say the car is 1700 lbs. wet with driver on the track. I hope for rear weight bias 55%, so rear wheels have 935 pounds total. Say that gives 500 pounds per rear wheel. The force available at the tire contact is the weight times the tire friction. Then times the height of the tire to the hub to make foot - pounds. The tire friction is probably 1 for good tires and 1.2 for good slicks and more for the best or qualifying style slicks.

For street tires, 500 pounds times 1 tire friction is 500. With 24" diameter that is 12" radius or 1 foot giving 500 foot pounds of traction. Even in a straight line in good conditions 400 engine torque in fourth gear ( 600 per wheel after the differential ) will burn rubber in this car. Perhaps over 100 MPH. On New Hampshire track I think this would be so scary on the oval turns or climbing the hill that it would not add up to being a fast car. When cornering with a limited slip it would likely easily break the rear loose.

[962porsche]

i did do a scale model of your design . the deflection of the modelings material is the same as it would be in full scale .

[brucesallen]

CALLS FOR BIG WINGS!

[horizenjob]

CALLS FOR BIG WINGS!

I am putting an option in the drawings for a tall front hoop / windshield support / deer protector. It would look great with a sprint car sized huge wing on top then. Imagine the size of the COM logo you could run with.

i did do a scale model of your design.

I remember you were concerned about the yaw flex in the front of the frame and I think that is well fixed with the bracing now on the top and bottom of the engine compartment. I'll include a current picture below. The changes from the last picture are that the very front bulkhead has bee removed and the wishbones face backwards now. The bulkhead that takes the cornering loads and carries the steering rack and coilover mounts remains unchanged. The front wheel location is also the same. There have been small adjustments to the rear of the frame to make space for the fuel cell and to comfortably accomodate the Lola style bodywork and the drivers elbow.

Got some very good news the other day. The builder of the Lola style bodywork contacted me, he had been unaware of my project with Car9. He had his own effort to provide a redesigned Locost frame for his car. After going thru my thread on LocostUSA, he has decided to use this work instead as a default frame. We have been working together to make sure the bodywork and frame are well suited to each other. In the Car9 drawings there is now an option for a "Frame-Lalo" which relocates some tubes under the driver's elbow upwards a bit to make it comfortable. That tube nows goes to the rear top of where the doors are or would be and there is a shelf in the bodywork to rest your arm on.

It's time to move on to the suspension and final running gear work. There remains some work on the frame and I will list some items here. If you guys think of things I should still fix up or have forgotten they will be added to the list. When these issues are cleaned up we will get to a revision 1 of the frame.

Car9 frame items:
- I started drawing in the inner seatbelt mount, need to finish that.
- gas tank mounting, maybe both above and behind diff ( votes here? ).
- diff rear support and diff mounting angle ( Miata diff drawing? )
- firewall sheet metal
- optional tall front hoop for windshield


Jack at Kinetic Vehicles is a great guy to work with and I am encouraged by his positive feedback and adoption of this work.With more people contributing to this design, I think it can only be improved.