LocostUSA.com

I'm debating over frame choices for my Locost. I want something well-documented, and this is not really competitive car so 100lb of weight is less important than being able to get it together with less fabrication work. for some reason I'm having trouble finding details on what fits the Miata drivetrain the best. I know I read it at some point, but I'm lost now...

Could anyone give me Miata-build specifc information about frame choice? I'm planning a 1.8L NA with Miata IRS, tranny, and spindles. FI is on the roadmap, but a standard book frame should handle 250 whp with a decent diff mount, from what I've read, so that's probably not an issue. What about fitment and such? Being able to buy bodywork is a big deal for me, too. Precise tube-frame fabrication is my kind of thing, but I don't like bending sheet metal or molding fiberglass.

EDIT: It's not sexy, but I am considering swapping the Miata rear subframe and PPF (probably with modifications) and just using the rear control arms. It's not visible like the front, and although it will cost me some weight it will speed things up a lot. I can always make a tube-frame replacement down the road, but of course I'm then limited since I'll have fabbed the frame to fit a the stock parts. Then again, the nice thing about steel if that you can just cut and weld and it's as good as new...

Coveland does, see this...

http://www.coveland.com/motorsports/index.cfm?ID=69#top

If you want a well documented miata build, buy Keith's book, and buy the Coveland chassis. The Coveland chassis is designed directly from a similar CMC chassis like Keith used for his build.

Here is Keith's website:
http://cheapsportscar.net/
link to buy book here:
http://cheapsportscar.net/buy.php

If you do a search on this site, you will find more information.

--
Brian

I've heard the Coveland Miata chassis is also a "book" (Ron Champion's) sized frame fwiw.

Bear in mind that you will have to lengthen your wheelbase a bit (4-5") to fit the rear subframe in if you choose to go that route.

I'm in the process of building a Miata based locost with a book chassis. I plan on going FI too since that way I don't have to build a long tube header.

People have used the miata rear subframe with success, but I am going to make my own IRS setup. I am attempting to duplicate the Maita rear subframe's suspension geometry where it is possible. Features that aren't possible or practical to duplicate I will borrow from the chassis our friends at CMC designed.

I would also recommend Kieth's book if you are building a Miata based car. The pics alone are worth it.

_________________
He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

Both books are in the mail. I've read pretty much every thread on the site regarding Miata donors already, so I've got a good idea of what's been done - but the build pages I found left out details about what they started with.

chetcpo, I've been following your build. It looks nice, but is a bit more than I want to do right now. Are the upper spring mounts and associated tubes all to book spec, or did you relocate them according to Miata dimentions?

When you say I need to lengthen the wheelbase to fit the subframe, is that because the front of the subframe is so far ahead of the axle centerline? Mark Rivera's build looks to keep the axle pretty far forward, no?

I'm actually debating on doing this with my mustang donor car. Literally dropping the front and rear subframes on the floor, complete, and mating them to the chassis when I build it. I don't see why it'd need to be any longer, just weld the subframe to the chassis, wherever you see fit. Obviously that's a little over simplified, but honestly, why make it any harder than it needs to be? This is a project car, locost at that, and my donor car already has a newer, completely adjustable suspension that I'd prefer to take advantage of.

Well actually not so much. His wheelbase is 7.5" longer than Kieth's CMC chassis according to the C&D article. Granted he used a +442 chassis, so four of those inches don't count. The problem is that the cockpit area of the seven is so low that the bottom of it actually sits below the diff and lower control arm. This makes it so the only way to get the factory rear subframe and control arms to fit is either to move the cockpit area of the car up about 5" (rediculous) or move the subframe back behind it, increasing the wheelbase by about 4".

I don't think it is any huge handicap to have the longer wheelbase, but I'll bet you'd notice the difference if you slalomed them both at an autocross. Mark's build also came out over 200 lbs heavier than Kieth's, but it's likely most of that was the FI bits.


As for the spring and suspension hookup locations you ask about in my build they haven't been established yet, but no they won't be in exactly the same place as the book plans. Once I get it sorted out I would be happy to share what I did with anyone who wants to know. If you aren't comfortable blazing your own trail you might want to just buy a Coveland Miata chassis and Control arms and be done with it. That way you would at least know that you were getting a tried and true product. Truth be known it isn't that much more expensive. (I'd estimate about $1800 more)

_________________
He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

I am very temped my their chassis - $2700 for the square-tube with control arms, right? How is the diff mounting on it? I know the CMC chassis had lousy supports for the rear end, hopefully that's been resolved. I think I'm going to call them up and chat. They're local (4 hrs away) which is nice, too...

On the other hand I've done Formula SAE and the cutting and welding doesn't worry me much. I'm actually looking forward to something as simple as this - highly triangulated .032 wall chromoly round tubes are horrible to fit and weld.

I agree it is a pretty good deal. If I wasn't strapped for cash I'd have gone that route. They have reportedly resolved the issues with the diff mount.

_________________
He is a wise man who does not grieve for the things which he has not, but rejoices for those which he has.

You should go a little extra for their DOM chassis. It is quite robust!

--
Brian