Locost (Caterham/Lotus 7 replica) build

[zieg]

I keep telling people it's a kit car but that's not really true. Most kit cars you buy the frame and bolt things onto it. In the case of the Locost, you buy a book that contains the plans and other information to build the chassis. Then you ignore most of what it says about the suspension and design your own.

I've been fascinated by these things after riding in them at local autox events, and decided to build one over the winter. Many people take years to complete these things, but I'm being very aggressive and want mine done by the spring so I can race it and sell my RX8.

So, step one is usually plan. Found a 3d model of the chassis already made, then started modeling the suspension components. I wanted to use a live axle for the simplicity (Could go IRS later on) and I really wanted the same wheel bolt pattern on all four corners. So many people have mixed patterns because they use different donor cars for the front and rear. I also wanted front and rear disc brakes that were at least meant to work together at some point. So what does a guy do? Get creative. Sourced a 7.5" rear end out of a Ford Ranger, then narrowed it by having the long side cut down and grabbing another passenger side axle (the short side) to use on the now-shortened driver side axle. This gives me the correct track width and puts the pinion flange in essentially the center of the car. For the front spindles, I went SN95 Mustang. Why? Same bolt pattern, center bore, and SN95 Mustang rear disc brakes can be adapted to the Ranger axle with little fuss. But the SN95 uses a mcpherson strut! How TF do you plan to adapt that to work with a double wishbone suspension? Easy. Upper balljoint adapters!










Okay, great. What about the engine? I really want a bike engine. Driving the RX8 has me loving high RPM engines, and a sequential transmission would be super cool. So the obvious choice is a Hayabusa engine, until you realize how much they cost and the fact that you need a dry sump system if you plan to put it in a car. Pass. Next best choice? Yamaha R1. They can be had cheap, are reliable, and all you need to do for oiling is add some oil pan baffles and install an accusump. So I bought the whole bike, parted it out, kept the engine and all electronics and indeed it did end up being reasonably cheap.

Kind of funny buying a bike when you don't have your license, have never been within 5 feet of a bike before, and immediately proceed to tear it down.




Okay, time to start building the frame. The first thing I had to do was make a very sturdy, flat, build table. 2 sheets of 3/4 MDF, steel studs in between to make a ghetto torsion box, everything glued and screwed, complete with leveling feet and topped off with a skin of 16ga sheet metal for a good welding ground and the ability to tack things down. I have no idea what I'm going to do with this thing after this project is done, it must weigh nearly 300 lbs.



Limit of 5 attachments? Damnit!

[zieg]

So anyway, fast forward a few days and I have this:



This is as of today. I've taken the week off work (entirely with banked hours I might add....) and have been working to get as much of the frame done as possible. And this is why I just posted another thread saying I need a tubing bender, because I need it to finish off the rear section of the frame, lol.

Speaking of vacations, know how some people like to post a pic of their legs on the beach or whatever? Well I couldn't resist having a seat in the frame and since I am on vacation in a sense...




I also happen to have another chassis that's already built, but I can't use for a number of irrelevant reasons. However when I ordered my fiberglass panels, windshield, some suspension parts, seats etc I did to a little mockup just for fun:




So yeah, that's where I'm at now, and over the next few months I will hopefully make some wicked progress! Stay tuned..

[Twin_Cam_Turbo]

Ah I wondered what you were building for next year so early. What’s your target weight going to be? Are you going to jump through the hoops to try and get it registered for street use like Duane tried with his Borkin a few years ago?

[zieg]

Target weight should be 1400 lbs or less. I will take a slight weight penalty for having a passenger seat and yes, the parts to make it street legal. But I really enjoy being able to share an experience, so a passenger seat is a must for me. For making it street legal, Bill R. gave me some great advice and I'm hopeful the process won't be too terrible.

Along with the rest of the bike electronics, I also kept the headlights. The low beams are HID, and they have DOT markings on them. I plan to experiment with molding them into the nosecone to look sort of like a Donkervoort. If that doesn't turn out I will be going for the traditional bugeye housings.

A Donkervoort for reference:

[Sentry]

R1 engine and sequential trans will be mental, these things haul ass with even a 1.6 miata donor.

[Twin_Cam_Turbo]

Sub 1400lbs is a good target, puts you really close to a proper Caterham/Lotus with the narrowbody and is lighter than most kits. I think Bill said his with the 302 weighs 1900lbs or something. Good call on the passenger seat, we found it’s actually faster with a passenger because the extra weight really helps get heat into the tires despite the weight penalty which is noticeable under acceleration.

[zieg]

Yeah, and it balances out the car. My frame is smaller than Bill's though. 2 inches shorter, 2 inches narrower and 1 inch lower if I recall.

Frame is essentially done now, but I still need to bend this fking tube. I bought the 12 ton tube 'bender' from PA today but it's kind of a pos, can't get a good bend out of it and the dies are way too big for their claimed size. Hmm...

[Tej.S]

Wow, that's awesome. Definitely subbing to this thread to see how this turns out.

[racerocco]

find a 1/2" conduit bender... same as 3/4" od tube. thats what i used on the last locost chassis i bent

[zieg]

Ok. Got the 6 ton bender from PA and it worked beautifully. Hopefully I can use it on the rollbar too, when the time comes.

First test bend:


Using my ghetto tubing notcher...


Perfect fit!



Just doing the tube diagonals down the sides of the frame now. After that's done the basic frame is essentially done. Next, I want to weld up the rear trailing arms and mounts, get the rear axle in there and then mount the engine. From there I can take measurements to have a driveshaft made. That'll be interesting. Going to have to go with a 2 pce for sure, and planning to put a cog on one of the fixed points so I can rig up a starter motor to use as a reverse gear. Any suggestions for where to have the driveshaft made?

[s_havinga]

Pat's Drive line or maybe Drive Products is where I would start.

[never]

Corey Dean at Driveline Specialties.

[94boosted]

Very cool Ryan, Sub'd

[zieg]

Heh, thanks.

Bought a couple books on suspension design to help work out how I want the roll center to look at various points, as well as a couple other bits and pieces. Welded up the trailing arms last night but can't really do anything tonight - handing out candy.







ACCUSUMP!




edit: books..

https://www.amazon.ca/gp/product/047...XNGGFN49&psc=1


https://www.amazon.ca/gp/product/184...VTCY4ISS&psc=1


Frame now:

[Buster]

Awesome!

Subscribed

[zieg]

Few minor things arrived.. New front hubs, and pads/rotors all around.


Been fiddling quite a bit with the suspension and steering geometry. Found a good place to get a custom rack built, so I have been working on the steering geometry too. Not quite ready to start welding yet, but so far the numbers are encouraging. 5" of rack travel will get me a very nice turning circle (still need to decide on a steering ratio though). Getting 4 degrees of caster with plenty of adjustment plus/minus. With 1deg of static camber, I am getting the outside to be at 0* in a hard turn, and the inside wheel has 1-2* of -ve camber. I think I can live with that. Added a bit of anti-dive, but might put a little more. I also had to put the rack slightly back of the centerline between steering pickups on the spindles, but that has a nice side bonus of, amazingly, basically perfect ackerman. And essentially no bump steer. So if anyone asks, I meant to do that......


Next step is to decide on wheel rates and spec out some shocks!

[legendboy]

Thread is delivering

Your using IV i see

[zieg]

Yup, using a combination of inventor and autocad for my whole suspension and I'm sure other things to come. Have access to the whole suite so why not.

Had a rough day at work today so decided to test fit my axle. Strongarmed the thing in there on my own. So far so good, I think. The trailing arms will be level with the car at ride height, I just didn't have any wood the correct thickness.




You can also see how I figured out the panhard rod. The chassis-side mount will be on the opposite frame rail. Hopefully that LCA bolt stud doesn't hit the frame at full droop. Don't think it will, but need to check. If it does, I will put a hole through the panhard bracket so I can feed the bolt in through that side. It's fully boxed so I'd have no concerns.




Really hoping to start on the front suspension soon. Though I may focus on getting the engine mounted first, because then I can get a driveshaft and build a tunnel for it.

[zieg]

Alright, it's been a while and I am starting to make progress again, so maybe an update will help me with motivation. This winter was not good to me. Too damn cold to work in the garage most of the time, and I've been dealing with some life stuff too. I really want this thing to hit the road this year, though.

Well I mounted the engine, that went fine:


Then I had to do this to my truck:


I also designed a two piece driveshaft with an Elite reverse box in the middle, built the tunnel (and as a side bonus, kept the tunnel narrow enough that the seats actually fit) and it looks okay:


Uh oh, the stupid buldge in the diff for the ABS sensor is hitting my beautiful tunnel!


Since ABS isn't even allowed in Dmod I figured no harm in eliminating the problem at the source. Still decided to modify the back of the tunnel a bit, which is why the diagonals are cut out:


I don't have a pic of the finished tunnel because it's not finished yet. But it won't take much longer now that I figured out a good way to do it.

Took a quick trip to Seattle where I saw this at a classic car show:


Finished up all the suspension parts and assembled them. Painted everything with POR-15, which seems like pretty good stuff to work with:


So far so good. Steering rack should be here next week.


Just got the shocks in today. Fronts fit very nicely:


Rears, I left the brackets off so I could verify that I am happy with the clearance before welding. Looks good:


And that's about where I'm at now. Once I finish up the back of the trans tunnel I plan to strip it all down again, flip the chassis to weld the undersides of the tubes on the bottom of the tunnel, then weld in the floorpan and firewalls. I will probably rivet the coverings on the tunnel. Pretty soon after that, it'll be a good time to sandblast and paint certain parts, while I start in on the fun stuff like wiring and brake lines. I'd say I'm about 40% done with 95% left to go?

[EK 2.0]

Man I am so following this!!