Well, I had done just about everything I could to the MR2. Anything else would have been cosmetic, and for a couple of other reasons, I just decided that what I really wanted was a Lotus 7 and the MR2 would never be one. I have wanted a Seven for over 25 years, but, dang, they have always been expensive. Ten grand for the kit when I started looking seriously at them in 1979. More like 20 grand today, plus your donor car. Then I came across this book,
and I was off. The 250 GBP price is a bit optimistic, but it can still be built for considerably less than $20K. Actually about as much as you want to spend and do yourself. Ron's son wanted a seven but could not afford one either, so Ron said, well, heck, we used to build these in the 50's, and I figure it should cost about 250 GBP, so he built one. Ron taught shop at a boarding school. Then a bunch of the kids at the boarding school built several and Ron wrote the book, errors and all. The rest is pretty much history.
So, I was off. You start off with some 1" square tubing. Of course, I wanted stainless steel for my frame because I like to work with stainless. That blew the 250 pounds right there. I probably could have bought enough carbon steel for about $50 for the frame, maybe less. On to the welding. I decided that having 160 HP in a car with a target weight of 1200 lbs would probably require a limited slip differential, and I wanted independent rear suspension, so I bought a LSD from a Supra. That means redesigning the rear end and suspension, which is taking some time. It took me two months to figure out where to put two tubes for the upper inner suspension mounts, but I developed a suspension model program in the process.
I am using the MR2 hubs and a five link setup. The 5 suspension arms are set up to resemble a conventional A arm suspension, with 1/2" rod ends on each end. I made the links themselves out of 3/4" 304 stainless tubing with inserts machined from a smaller size stainless, welded into each end, then drilled to the minor diameter of 1/2 x 20 threads, and threaded. The inside of each link is left hand thread so I can adjust the links easily.
I have come up with the LEU concept, or the Locost Equivalent Unit which equates to GBP 250 in whatever currency you have where you live. This makes it easier to relate to costs. For example, it might cost 10 LEU's to build a car in Oz, and ten LEU's in Arkansas. How much are those coilovers? One LEU each or four for a LEU? If only Argentina had adopted the LEU as a currency standard, they would not be in the trouble they have today.
OK, OK, I have finally broke down and taken some pictures:
The front end:
Papillon's Big Sister:
Some build notes:
The header is entirely made of 304 stainless. The flange is 3/8" 304 stainless. I took my OEM header down to a shop and they scanned it into Autocad. I was not haphpy with the results, so I took their file and re-did it until I was happy with it. Then they took the file and cut the flange out on a water-jet machine. No header kits/pre-made flanges exist for 20v motors. I doubt they exist for a 16v 4AGE either.
Here is a secret: "Sanitary Tubing" is used in the food processing industry. Arkansas is covered with chicken farms and processors, so we have a place locally that stocks everything for them. I used 1.5" OD, 16 ga, 304 stainless and polished inside and out. They also have mandrel made pre-bent 90's in 2 different radii and 45's too. Pre bent's are $12-18 ea, so I only bought 4 pre-bents of small radius and bent the rest out of about 10 ft of straight tubing by welding a cap on and filling it with sand then putting it on the pipe bender. The sanitary tubing is _much_ cheaper than what they try to sell for stainless header pre-bend pieces. If I had to do another, I would buy all pre-bends, even if I would need 12 instead of 4. For the collector, I took 4 pieces 4" long down to the muffler shop and had them expand the pieces to where they would fit over a standard 1.5" piece. Welded these together and made a little pyramid for the middle. Then cut the outer part out of a piece of 304 counter top I had laying around, bend/beat/heat and welded it on and added a piece of 2.25" 304 for the final output. As I said, I had the shop TIG the pieces together after I tacked them because after spending that much time on them, I wanted it to look real nice and their TIG welders do magic. I looked at a chicken processing ramp/tray they were working on and I had to look _real_ close to see it was welded and not bent.
The Fuel Cell is from Jaz Products, I designed it myself, based on their 8 gallon unit turned on it's side with fittings on the bottom for pickup and return. It fits Just Right. Total cost was about $160, delivered, and if you want one, call Jaz, ask for Brad and ask him for the Dr.Hess Locost Fuel Cell. He will know what you want. I figured it was going to be much easier than making my own. The 8 gallon size allows just enough room for a battery box next to it. No wasted space here, as you can see in the pic.
Modeling is one thing and having a design
goal is something totally different. Not
being an automotive engineer, the best I could do is to read Smith (RIP),
Stantiforth and talk to people that are automotive engineers.
Stantiforth's book had some nice pictures and a good historical
background, but was lacking in nuts-n-bolts stuff.
Smith had better nuts-n-bolts. Some
people have diss'ed Smith, but at least he wrote his knowledge down and shared
it with the world. Some F1 team
expert may have better ideas, but if he keeps them to himself so he can win,
the rest of us are not benifiting.
So, in suspension design, near as I can figger, the idea is to keep the
tire on the road. And you want to
keep it there at an angle that will maximize the adhesion between the tire and
the road. Smith has a chart
showing that the ideal angle is about -1 degree camber for the particular race
tire that was tested. Not being
able to find any other chart on any other tire, that is what I went with as a
design goal. Next up, you need to
design for a certain amount of roll in a corner.
It would be nice to build a car and then measure exactly how much roll
you have and then build the suspension, but my resources are kinda limited, so
I went through my archives of pictures of Sevens driven in anger on turns and
figured that about 1" of roll is about typical, so that is where I set my
bump design point. My design has
1" bump camber at -1.099 degree and 1" droop camber at +0.998
degree, giving about 1 degree negative with respect to the road.
Which brings up the road. You
have to think in terms of "with respect to the road" and not with
respect to the chassis when you design these things.
Many don't. So that +1
degree of camber in droop with respect to the road translates to a -1 if you
look at the other side of the tire and the forces involved.
The outer wheel is "digging in" when that side of the chassis
is unloaded in a turn.
Smith says that it is best to not have your RC move around much.
My rear RC moves 0.09" in bump.
You want to minimize Scrub (sideways movement of the tire).
Mine is 0.1" in bump. My
RC position is at 3.4". It
was easier to achieve the design parameters at lower RC, but you don't want
too low, and you want the front RC lower than the rear.
Bump is more important than droop.
Think about it: Under bump
(wheel up), you have the wheel under load from the turn.
Under droop, your wheel is unloaded, so less force is transmitted to
the road through the tire.
There is no perfect suspension design.
They are all a compromise. You
give up RC height for scrub, etc. My
software went through billions of possible locations for the pivot points
before finding the one I have described.
I also did a design for Jim McSorley's front pivots but I think he
changed uprights and used something else. Also forgot which upright
that one was for. Front
suspension design begins with the same as an IRS, that is, camber curves,
scrub, etc., but then you have to add in King Pin Offset and more which will
effect the camber when the wheel is turned.
As I said above, Unbalancedengineering.com helped me a lot.
Jon Oellrich is a MR2 guy and on the lists.
We thought about marketing my software, but it is really a very unique
tool, and given the skills and knowledge required, it is probably better to
just use the tool on a consulting basis rather than sell it outright.
How many people understand what I just wrote?
If you bought a piece of software "to design my IRS", would
you know where to even begin? Now
maybe you have a starting idea.
Chopping the sump:
OK, with the motor in the frame at my 6" of ride height, the sump was about 3 to 4 inches below the frame, giving me not a whole lot of clearance. I don't think I could get out of my driveway, much less down the dirt road to pavement. So, the sump had to be shortened.
What I did was:
Some random thoughts and suggestions:
First off, you need to join the Yahoo group Locost_North_America. Then lurk and start going through archives. Pretty much every question you have is in the archives somewhere.
The Ultimate Locost depends on what you consider Ultimate. So, you want cheapest? LOwestCOST? Do a single donor from a Pinto someone gives you because it is currently lawn art. You want fastest? Probably a Hiyabusa if you keep the weight of everything else down. Also remember that the most HP does not always make you first around a track. You want to build a 1/4 mile drag car for showing up Civics at the stop light or a road racer? Have a goal as to exactly what kind of car you want.
Round v. square tubing? Well, not being an engineer, but having friends that are, I have put the question to them. The answer was that round tubing is better for building if you don't know where the load/impact is going to come from or if the load is torsional (think drive shaft) or pure compression, if I recall. Otherwise, square tubing is stiffer in the flex direction. It is also somewhat easier to work with using simple tools, i.e., not having a fancy mill set up for cutting the ends at specific angles like on American Chopper. Many Sevens are built with round tubing, many are built with square. Locosts use both. Adding "The Aussie Mods" helps the rigidity of the chassis a lot. Like twice as stiff or something, I forget the actual chassis torsional numbers, but in Oz, they have to actually test that to get them registered. Probably a law created by their equivalent of a Democrat. (jab jab)
The Seven (of any type) is as aerodynamic as a brick. Putting enhancing wings and other stuff is about like, as I read on other forums, lipstick on a pig or snow tires on a cruise ship. If you want aerodynamics, then build an Eleven, which is a Seven with a couple extra tubes and a pretty good aerodynamic body, especially considering the design is about 45 years old. A Seven is actually an Eleven with a couple less tubes and no aerodynamic body if you want to get technical. CMC kept showing previews of their Eleven body. I wonder where the molds went.
Solid Axle v. IRS: Go solid axle. I have an IRS setup I designed myself with help from an automotive engineer friend, and the extra work is tremendous. There are no off-the-shelf IRS designs to just borrow (not that they would necessarily be any good anyway), so you are basically on your own. Worth it? Probably not. Would I do it again? No. I did learn a lot doing it though.
"The Book" is more inspirational than educational. There are better plans out on the net, such as Jim McSorely's. The same design but without the errors in the book. I am not saying don't get the book, as it _is_ very inspirational. You can look at it and say, "dang, people with about the same skill set or less than me have built these things. I think it can be done. I think I can do it too." But you can probably get that inspiration from a night of Google-ing "Locost Seven." The book does stuff like (paraphrasing) "to make a nose cone, start with some fiberglass and start laying it up and stop when it looks like a nose cone," then shows a picture of an obviously store-bought nose cone cloned from an S2. But the BS was necessary to keep it under GBP250 by not blowing 1/3 the budget by taking out the Visa card and picking up the phone.
It's been a while since I updated this. I've been busy with other stuff, like the Esprit, the bikes, the 20v Rolla, rebuilding the 22R in my truck, MegaSquirting both of those, etc., and haven't had much time to work on the Seven. Anyway, after getting sort of caught up with the Esprit doing well, the 20v Rolla my current daily driver and Truck running well, I've been working on the Locost again. I added some 1" square tubing at the bottom of the frame at the sides of the sump as a sump guard and ground down the side welds to get ready for the body panels. I reinforced the back rail with some bracing, added a spare tire carrier, and made a roll bar. I had a local (sort of) race car shop bend up the hoop from 1-3/4 095 wall mild steel, then I cut it to fit and welded it to removable plates that bolt down. Here's a pic: Rollbar.