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Old 08-18-2009, 05:34 PM   #1
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Default Miata based Locost build

The goal for this project was originally to build the car for $1000 or less, but after looking at locostusa.com for several weeks, I have decided this is not reasonable. I need the car to be safe and fun, so I have revised my budget. I will be building the entire car for less than the cost of a BEGi series 1 turbo kit. As of now, that figure is $3,089. The car could be built for $2000, but this thing will take over a year to build and I think that extra $1000 will turn fomr something fun to drive, into an absolute riot.

My goal is to have the car around 1250 lbs and about 200 whp.

Donor car: 1996 R package that I bought for $1200. I have slowly sold most of the parts that I don't need, and will more than likely come out with everything needed for free after selling everything. Already has some decent looking, semi-light, wheels. I will probably keep them unless I come across some Kosei K1 on the cheap.

Parts already purchased:
Tires: 205/50/15 Toyo RA1 on clearance for $80/tire: $345 w/tax
ECU: MS built by Braineack. I may know mechanical things well, but electrical stuff like soldering intimidates the hell out of me. $425
Turbo: T25 bought off of ebay a year ago for cheap but never used. Great condition and no shaft play. $82 shipped

The metal to make this is surprisingly cheap. 16ga 1"X1" in 20' sections is only $14 from my local metal yard. It will take around 100' of it to make just the frame, so about $70 for the frame metal. 4' X 8' sheet aluminium is $42 for 12ga for the floor, and only $23 for 16 ga for interior. I need to go back for another quote soon, becasue I know how much metal prices fluctuate.

This thread will be updated whenever anything happens and I will be taking pictures along the way. I will probably start soemthing over at locostusa.com too in a couple months if anyone is interested.
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Old 08-18-2009, 05:43 PM   #2
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Designing your own frame or did you buy plans? Using miata suspension or making your own a-arms? Pics of potential finished product? Sounds like a great build, can't wait for the flury of pics.
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Old 08-18-2009, 05:51 PM   #3
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You going to use the IRS?

I have the unkown pickup point dimensions. You won't find them anywhere on the net. I had promised to post up some drawings there, but sold the project and never got back to it. This could be my motivation to get them done.

Here's my build log.

http://www.locostusa.com/forums/view...ein%27s#p27239

If you read it, it has been sold twice now so not much progress other than a nice crop of rust. The car is in Dallas now. I'm sure that you can get a look at it.

I'm going to build another one. Still working on that S2000 that is now stuck in a farmer's shed. If I can pick it up for $2000 I'm doing it.
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Old 08-18-2009, 05:53 PM   #4
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The frame will be what is called the "book" frame. It is the frame designed by Ron Chapman in his book "how to build a sports car for $250". It will have slight variations to accomidate the rear subframe or the miata. I will use stock type suspension for the rear, but the front will be a new coilover setup.

The awesome thing is that the plans are available online for free and there is a ton of support behind this. The end result will be a Lotus 7 type car. It will look a little more rough around the edges, but I think I will ok with that.
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Old 08-18-2009, 05:56 PM   #5
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Quote:
Originally Posted by Stein View Post
You going to use the IRS?

I have the unkown pickup point dimensions. You won't find them anywhere on the net. I had promised to post up some drawings there, but sold the project and never got back to it. This could be my motivation to get them done.
That would be amazing and would cut down on my searching immensly. I need to know how high off the bottom of the frame the mount needs to be for the rear subframe and the shock tops. All I can find in the drawings are people who have done a direct diff mount and custom coil over.
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Old 08-18-2009, 05:57 PM   #6
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Quote:
Originally Posted by rharris19 View Post
The frame will be what is called the "book" frame. It is the frame designed by Ron Chapman in his book "how to build a sports car for $250". It will have slight variations to accomidate the rear subframe or the miata. I will use stock type suspension for the rear, but the front will be a new coilover setup.
I would seriously consider a +442 frame. My next one will be a +442. The Miata motor does fit a book frame but it is TIGHT due to the huge IM.

Plus, a book frame only allows for 17" inside for the seats. Tough to find seats to fit unless you go with a Kirkey 15.5 or 16.5 drag seat. The whole frame is only 44" wide, so 42" inside the tubes, minus the tranny/driveshaft tunnel.
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Old 08-18-2009, 06:00 PM   #7
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Quote:
Originally Posted by rharris19 View Post
That would be amazing and would cut down on my searching immensly. I need to know how high off the bottom of the frame the mount needs to be for the rear subframe and the shock tops. All I can find in the drawings are people who have done a direct diff mount and custom coil over.
I did a direct mount. Didn't use the subframe. Take a look at my build thread. Lots of pics on what I did.

The subframe is heavy and tough to get in place, plus the geometry is less than ideal. But, using the subframe is cheap and quick.
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Old 08-18-2009, 06:07 PM   #8
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This is gonna be awesome

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Old 08-18-2009, 06:17 PM   #9
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So the miata rear has no trouble with the +442? I thought it would for some reason. I see what you were talking about with the rear pickup. I may just end up doing that. It doesn't look overly difficult, especialy in comparison with the rest of the build.
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Old 08-18-2009, 06:41 PM   #10
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Originally Posted by rharris19 View Post
So the miata rear has no trouble with the +442? I thought it would for some reason. I see what you were talking about with the rear pickup. I may just end up doing that. It doesn't look overly difficult, especialy in comparison with the rest of the build.
It will be close and you need to measure. IIRC, track is stock track is 55" so it really depends on what wheel offset you plan to run. I do know that there were no problems with the book frame and a stock wheel offset.
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Old 08-22-2009, 10:45 PM   #11
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If you need any dimensions off anything I have a partially finished CMC chassis build in storage. It's Miata front and solid axle (Rx-7) rear though so some dimension in the rear will be different for you.
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Old 08-23-2009, 05:36 PM   #12
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Don't fall into the single donor trap. The Miata has a great drivetrain for a Locost, but by substituting a few parts, you can make it better, and the build easier.

Instead of the Miata diff carrier (the cast iron part, not the aluminum part) use one from an FC RX7. The snout is longer and it's easier to use when you don't have a PPF. Instead of the Miata spindles, use Chevette/Fiero spindles. They're slightly smaller and make it much easier to use standard A-arms and position the steering rack easier than the Miata parts that require the rack to be so low it interferes with the lower A-arm unless you make it an L-arm like the OEM Miata arm.

If you make it RHD, you have some extra freedom to position the steering column where you want without the exhaust interfering. Consider going to pushrod suspension up front for even more A-arm freedom and getting a 1:1 wheel to shock ratio.

There are LOTS of pics of my old bike engined Locost on the LocostUSA forum. Gene Young built it and put a lot of thought into the suspension design.
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Old 08-23-2009, 06:58 PM   #13
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Subscribing.
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Old 08-23-2009, 07:13 PM   #14
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Awesome guys. I truely appreciate the help.
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Old 08-25-2009, 02:09 AM   #15
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Quote:
Originally Posted by modernbeat View Post
Don't fall into the single donor trap. The Miata has a great drivetrain for a Locost, but by substituting a few parts, you can make it better, and the build easier.

Instead of the Miata diff carrier (the cast iron part, not the aluminum part) use one from an FC RX7. The snout is longer and it's easier to use when you don't have a PPF. Instead of the Miata spindles, use Chevette/Fiero spindles. They're slightly smaller and make it much easier to use standard A-arms and position the steering rack easier than the Miata parts that require the rack to be so low it interferes with the lower A-arm unless you make it an L-arm like the OEM Miata arm.

If you make it RHD, you have some extra freedom to position the steering column where you want without the exhaust interfering. Consider going to pushrod suspension up front for even more A-arm freedom and getting a 1:1 wheel to shock ratio.

There are LOTS of pics of my old bike engined Locost on the LocostUSA forum. Gene Young built it and put a lot of thought into the suspension design.
Some of this I agree with, particularly the "one donor" comment. My car has Miata spindles with no issues. I suspect CMC arms to be slightly different than book arms as I had no problems whatever getting good aligment on the steering rack, plus I used a Coleman race rack, not a Miata rack... it's narrower than a Miatas. I'm running an FB RX-7 rear end, Toyota 4AGE/T50 engine/trans, Triumph GT6 steering column, and an MGB e-brake lever, so mine is quite a mutt. While the one donor thing can make things simpler to one degree or another, some times I think it makes you get lazy and use what you have rather than what will work best.

Making it RHD sort of solves one (somewhat non) issue and gives you a different one. RHD puts the column past the intake mani/oil filter area, which depending on how high the OP needs the wheel to be could be just as problematic. Putting the column past the exhaust isn't difficult, it just takes a couple u-joints and a little more time planning. As far as pushrod or rocker A-arms go, they look neat, you can play with rising rate linkages until your head explodes, but IMHO you don't gain much but a little less unsprung weight and a lot of engineering time to make it work right. I'll also add that NONE of the race cars I work on have a 1:1 motion ratio (ok except for the Elva Courier racer that has a solid axle). I mostly work on vintage F1/F2/Can Am/FIA sports racers from the 60s up into the 80's that were designed by some of the best in the book. If they didn't see a need to do it, I can't imagine a Locost will see much benefit from it.

I don't mean to be adversarial here in any way... just sharing another point of view to be helpful.
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