LocostUSA.com

Hey guys,

I've been devouring all the information on this site for about 2 weeks now after I got the bug to build my own car; and I've decided to get some input to my ideas. My past experience is with 70s era muscle car builds/restorations but I have the itch to do something which includes a little more engineering and creativity (By day I am a mechanical engineer, fresh into the auto industry). In college I got the opportunity to run the Baja team where we designed and built an offroad vehicle for the SAE competition. I liked the design and build aspect, plus there's nothing like driving something you built. To me, designing and building a functional machine is one of the most gratifying projects you could ever do....but thats just me

Anyway, after reading much of the info here I have developed some design criteria for my project. Please feel free to interject and correct me if i'm heading in the wrong direction, afterall I am a noobie. With that said, I'm looking to build a very small, lightweight car tuned for road courses. It will be a street car, something that can rip up the "Tail of the Dragon" or roads like that ......weight target is 1220lbs, track width 52" front and rear or possbily 53" in the rear (have done much research on determining the perfect track width, yada yada input welcome ) Wheelbase around 85" giving a 1.63 wheelbase-track width ratio. It will be a two seater (side by side), open wheeled in the front, covered rear suspension (similiar to, but much cooler than the Crysler Prowler) I am planning on using MX5 front and rear uprights, hayabusa 1340cc I4 (200hp, 220lb wet) powerplant w/ the 6 speed sequential gearbox, and an FSAE style rear LSD for the rear IRS. I would like to run 185 R13 in the front, 215 R13s in the rear.

Currently I am in the front suspension design process and I am looking for input or techniques to determine control arm length and pick-up points on the chassis. Seems these cars can be as compliated as you want to make them and although I am a young engineer and want to learn A LOT, I dont want to over analyze every aspect of this car. In addition, what do you guys think of a pushrod style front suspension? I've see many implimentation of it here on the site, just wondering if those that have done it think its worth it.....sure looks cool! and gives better suspension performance, but I'm not sure if I want to spend 1000 hrs designing a system in CAD since I do not have a chassis built yet to try things on. I do have CATIA V5 that I am planning on using for design purposes and I would like a full vehicle model when I'm done.

Thanks in advance for your time & input!

-Lance
Vehicle City Flint Michigan

Depending on what you want to use as your constraints, a couple of different strategies for front suspension design start to appear. If you want to use an unmodified steering rack, picking the rack, uprights, tire diameters, roll center characteristics and camber curves should pretty much define the geometry in one plane. That also allows some freedom in the second plane for placement of the actual chassis pick-ups. Alternatively, you could start with a desired roll center characteristics and camper curves and then use your chosen uprights and tires to define the rest of the front end in plane. the second option gives more freedom, but also tends to imply more fabrication will be needed for a more custom design.

Personally, I love technology and simple, elegant solutions to design problems. I also tend to like cool technology just for the sake of it being cool technology. One thing I constantly find myself doing, is re-thinking a number of the details in my build as I get closer to actually building something, and then working hard to eliminate the unnecessary complexities. Building (in my case rebuilding) a car from pretty much scratch is going to be a long, hard and complicated process. Every step I can take to simplify the process without compromising my end performance goals makes that job easier. It's very easy to get sucked into "I need this cool feature because ..." as you're pulling the car together in your head. However there have been quite a few of those features that I have later decided were not really necessary, and especially not necessary as part of "getting it up and running". Some of those features may creep back in, but only after the car is on the track, and I have decided that they will improve my enjoyment and/or performance in the car.

Or more elegantly put, "Simplify and add lightness".

Thanks for the reply! I feel like the only way to tackle such a huge project is to make a list of everything that needs to be determined and designed and break it into smaller manageable chucks. THen attack each of these chucks in a logical way trying to simply as you go. Your two methods that you provided helped me understand the need to determine my plan for the rack earlier than I had anticipated. I am planning on using a manual rack, or i suppose a depowered one. I'm not real sure if I want to try and modify a rack....with that said I guess I have to find either a production rack. (Which non-powered racks are you guys using for such a narrow track width?) or get a custom one made. Are there any companies that provide "locost" custom steering racks? The only such supplier I am aware of is Woodward steering. Since I am using the MX5 spindle, should I try and maintain the same rack length of the miata or wont that matter? Is there a way to calculate the tierod lengths needed to provide the tight turn circle I want?

The best suggestion I can offer is hitting the suspension books: Competition Car Suspension by Allan Staniforth, Tune to Win by Carroll Smith and finally Race Car Vehicle Dynamics by by Milliken and Milliken. The first two will get you to the point where you should be able to answer most of of your suspension design questions, the last covers just about everything else. There are other books as well, but these three combined do a pretty good job of covering suspension at the level we seem to need.

As for modifying a rack, it has been done; you can find examples in the build logs. Keeping the rack and uprights from the same donor should help add some predictability to the final car's steering behavior unless you change the relative height or for/aft placement of the rack.

You should probably also track down the suggested books thread and find some recommendations for chassis design and general car fabrication. What seem to be small details really have the potential make your build stand out or leave you feeling like you could have done something better. All the reading seems like an excess of preparation, but if you have done that reading, you will find yourself understanding why you agree or disagree with almost any general aspect of a build you are reviewing. Or if not, a new topic to either review or gain more knowledge about.

The build logs are your friends; read everything. Dig through them and take notes. Then go back to the books again. The logs cover a wide range of builds and engineering styles; some will probably make you cringe, others will be truly inspirational. There are very few build logs that don't provide a chance to improve your final product by evaluating what you see in a log you are reading.

Forget the bike engine, get a 'real' motor that won't drive you crazy after the first hour.

Read up on the Stalker as I would go for an American V6 but each to his own.

hi having my car sorta complete, give you my 2 cents.
think about what you are going to do with in when done, daily driver, just a fast toy..
car engines are cheap an strong, heavy too. my ecotec bare is 330 lb
bike engine will take more engineering to get a long lived , practical drive line. pushing 1200 lb through that little clutch.
building a front suspension.. bump steer , camber control , some ackerman, are probably the most important on the street . just check for any binding, interference, though it whole travel and a little beyond.
get your seat, sit in it, place your pedals , steering wheel, shifter right where you want, build around that.
i am still exploring my car, but not much i would go back a change so far. even hot weather testing in the last few days has been good,.

Erioshi: Took your advice and bought the first book on your list. I have heard many others suggest this book so I figured it would be a good read. Thanks for the advice!

I too had doubts about throwing a motorcycle engine, used to pushing a 500lb bike into a 1200lb car, but the Caterhams seems to do it just fine. Trust me I am an american muscle enthusiast but there is something about a high revving exotic sounding car has always captivated me. Since I'm designing my own car.....figured I'd make it everything i want and light and nible is what I want. Unfortunately that is everything an American Muscle car is not so i don't feel to morally juxtaposed using a bike engine. Originally i did look into the de-stroke V8s which make incredible power, but they are much too expensive for me.

Anyone aware of a particular thread where locost suspension design is detailed from start to finish?
--Thanks guys, keep the info coming

Id put a car engine in a car,one thing overlooked is that while the car itself may weigh 1300 lbs you and your mate are going to add another 400 plus when you jump in..so your looking at 1500 to 1700 no matter what,thats alot of work for an engine designed for 600 lbs,i have gone with a nissan vq35hr v6 all aluminum ,revs to 7500 and makes 306 stock ,its the same weight as a zetec and you will never need more power ,just another opinion
Wayne-o

wayne-o: Definately understand where your coming from......what engine options are out there then? I want something thats all aluminum, revs high, and makes over 200hp. Needs to be very light! Suggestions welcome.

i dont know how light they are but what about:

1.built up honda b16
2.built b18a,b,c vtec
3.built f20b
4.stock f20-f22c
5.k20-k24 i-vtec

i know the new k' series are suppose to be lighter than the b series and 200hp capable while the type r b16 or b16 built will rev to 9k rpm

K24:
Engine + exhaust manifold + alternator + starter = 283 lbs. This does not include the flywheel or clutch (I had neither), nor engine mounts. The 5-speed transmission weighs 87 lbs + 10 lbs for the intermediate shaft, for a total of 381 lbs. Figure 8 lbs for an aluminum flywheel and maybe 15 lbs for the clutch, so the grand total is 403 lbs,

200hp is stock. 250hp is doable, but 300hp NA is very very expensive. Turbo, only your wallet is the limit.

Thanks for the specs! Thats why I have a hard time going to a car engine....the hayabusa is 220lb ready to run with a radiator, including the 6 speed gearbox and makes 200hp. Only thing needed is a reversing gearbox...and as far as the weight comparison goes: 1200lb + 2 passengers is still only 600lbs more than the bike + 2 passengers. I'm not to worried about the bike engine....I need help with the suspension design

Nah, it does need to be worried about, a BEC vs car engine is apples to oranges. I HIGHLY recommend finding someone in your area who owns a BEC and getting a ride, which should make or break your love affair. Make sure to take it on the freeway for five miles at constant speed and see what it's like to cruise at 6000 rpm. A BEC is much like owning a sportbike itself, it's a blast but gets tiring after an hour or two.

As was said, take the time and make a list of requirements. Unless it's a track-only car, as in: autocross, the bike engine advantages disappear in a hurry. However, if after driving for miles at constant speed on the freeway you still love it, have at it!

I can definitely appreciate where your coming from....I'll put some more thought into it. Also with the car set-up I dont have to worry about the diff, mounting, ect....since it's all packaged in. Does the FWD powertrain your using in your build (I checked out your site) have an LSD? That is a necessity for me....also, what wheel sizes are those in the pic on your site?

Yes it has one but it's aftermarket - Quaife. Wheels are 17s, 7" front, 9" rear.

I'm not trying to talk you out of using a bike engine, I'm just saying to make sure that it's what you really want. That's why it's a very good idea to get a ride in a BEC before deciding.