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Discussion Starter #1 (Edited)
Mid-engine K24 project, Midlana

Been on K20.org for a long time and finally noticed this sub-forum, doh.

I built a mid-engine H22-powered carbon-shell tube-frame Mini several years ago called Kimini. It turned out too nice to beat up on-track so design started on a new project.

Background:
The term Locost is a play on words, formed from "Lotus Super Seven" and "low-cost." The Super Seven was designed in the 1950s as the ultimate sports car, very small and light. At around 1200lbs, it didn't take much power to get it moving and the low weight allowed it to beat many much faster cars (think: original Cobras!) on road racing circuits.



Typical of the time, the car was front-engine, rear-drive. While original Seven's are very expensive, Caterham still makes new ones, and there are also many kits with a lot of people building them from scratch, which is where the Locost name comes from.

Builders today typically use rotary, Miata, Ford I4s, or GM V6s, but they all have one thing in common: they're all front-engine rear-drive drivetrains, and that's where Midlana comes in.

Midlana is a modern (re)interpretation of a Lotus Super 7, but mid-engine. A book is being written in parallel which will contain plans. Once the car's done and has gone through shakedown testing, the book will be available soon after. [7/2014 update: the book is available, see site!] Depending upon drivetrain, you can have Atom-beating performance at 1/4 the cost.



I wanted to build a Locost,but update it with what's available today, mostly because front-engine-rear-drive powertrains are very limited. FWD transverse drivetrains are the prodominate powertrain so it makes sense to use one - but in a mid-engine configuration. To do so, the passenger compartment is moved forward to make room for the ex-FWD drivetrain to fit behind the seats.

What drivetrain to use? Having built a mid-engine Mini (Kimini) I'm somewhat familiar with Honda engines, having used the Prelude H22A1 dead-stock. For Midlana though, I wanted to use the latest and greatest Honda power plant, and always wanted to own at least one turbo car, so to make a long story short:


  • 2004 CRV K24A1 block
    ERL sleeves
    Coated CP pistons with gas jets
    Pauter rods, EDM oil holes
    TSX head
    RSX-S cams
    Baffled Mugen oil pan
    RRC intake
    Custom exhaust
    Twin-scroll GT3071R [now a GTX3576R]
    Ebay intercooler
    Two 38mm Tial wastegates
    Engine built by Drag Cartel

    Competition Clutch twin-disc
    Base RSX 5-sp with LSD, straight-cut gears, dog-engagement
    DSS axles
    Kpro ECU
    Target hp: ??? whp on 91 octane [currently 400-500 whp depending upon dyno]
    Expected wet weight, no driver, 1650lbs
    Theoretical performance: 0-60 2.5 sec, 10.7 sec quarter
    Steet driving and trackday events
And finally, the name, MidLana.:"Mid" because it's mid-engine, and "Lana" is our granddaughter's name. It sounds a bit like "Katana", a Japanese sword, and since both this car and Lana are part Japanese, it fits. I like the sound of it and it's unique on the Interweb, so there you go.

The car isn't a pipe dream, here it is in 2010:



And done (2013)

 

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That's an awesome project you've got going there! I'm very excited to follow your build process. I really appreciate all of your updates on your website. Hopefully you won't mind if I use some of your ideas for my own build.

PS Nikos just added this section a few days ago. I for one am very happy that he did.
 

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Your Kimini website has always been an excellent resource when i have contemplated the thought of building a semi affordable track car. I am so glad you are undertaking the challenge of doing a basic Locost approach for a mid-engine platform.

I am curious though.. On your chassis design are you going with a large diameter CNC bent tubing like the atom or just a basic square tubing space frame? While i LOVE simplicity and affordability i don't believe even for a track day car i could stand to drive something that resembled a go cart like the traditional locost space frame. The subtlety of the of large diameter tubing just seems to give a car with no body work some character.

Any ideas on which uprights your going to use? Factory piece or custom units? I'd give anything for some basic cad skills to draw up some designs..One for a nasty track car and one for a super aerodynamic commuter trike to use for an EV platform or small diesel.
 

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Discussion Starter #7
The chassis is mostly 1.5" OD tubing, with half as many tubes as a Locost yet with twice the torsional rigidity.

The only CNC-bent tubes are the main and windscreen hoop. I agree that the Atom layout looks nice, but it's more money to get all those tubes bent and many builders have a very small budget.

Uprights are Miata all around for cost and sourcing reasons. Custom axles (which are always needed due to differing track widths) handle the spline change going from the Miata uprights to the drivetrain.

All this information, and more, is on the website.
 

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Discussion Starter #9 (Edited)
The K24A1 was disassembled last Sunday, having served its purpose during mockup and it's time to start thinking about it being built up.

For no logical reason whatsoever I've decided I want to turbo it; 400 hp in a 1600lbs car is something that just has to be done. Yes I know a supercharger seems more proper, but I had a supercharged car and wasn't impressed with the top-end performance. Plus, a 1600 lb car can't use huge low-end torque anyway. Boost-by-gear will keep the tires from being totally shredded.

Anyway, it was disassembled so piston pin offset could be measured, something that seemingly no one on earth knows - 0.0325" BTW - so the pistons can be ordered.

The block will be sleeved, the Pauter rods are on-hand, 9:1 coated CP pistons are on order, the K20 baffled pan awaits, along with the K20 oil pump and GTX3576 turbo [upgraded in 2014]. Both the intake and exhaust will be custom. Basically the engine's being built as if it'll be handling 600 hp but since it's to run on 91 pump gas, it'll probably be around 400 hp. Since trackday events are in its future, having the margin is a good idea.

Instead of filling this up with pictures you can check out the latest progress at: http://www.midlana.com/Diaries/Current/

The manuscript is coming along - yes, there will be a book on how to build one. If you get interested enough to consider building your own, check out the forum at http://www.midlana.com/forum/ (You have to register to see the other 90% of the site.)
 

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I followed your projects at lowcostusa.. Very impressed and I also liked the videos.

What is the total cost for material to build the rolling chassis without the powertrain?
 

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Discussion Starter #11
What is the total cost for material to build the rolling chassis without the powertrain?
That's a number I will have to provide in the book, but right now it's a guess. It very much depends how crazy you go on the parts. For example:

1. Seats, from free to $1200 each.
2. Dash instruments, none(!) to $3000 for a full Motec setup.
3. Gas tank, $100 for a self-built aluminum one, to $2500 for a true custom fuel-cell.
4. Shocks, $250 - $2000 each.
5. Axles, depends on power level, $400-850.
6. Wheels and tires can range from nearly free, using the Miata donor parts, up to... well, you know.

The actual steel and aluminum in the chassis is under $1000. Miata donor parts (uprights, steering, and a few odds and ends) will be from $100-400 depending where they're sourced, Craig's list on the one end, to a botique-style wrecking yard at the other.

If you have a spare Honda drivetrain sitting around that can save a ton right there, especially if it's running with a KPro.
 

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Discussion Starter #13 (Edited)
They're custom, which isn't a big deal since you're already welding the chassis together!

The best thing to do is go to the forum and read the FAQ; I have a ton of info in there.
 

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Discussion Starter #14
Pistons are being coated now and once they're here it's time to start the build. Still need a gasket set, and that raises a question of which head gasket to get, one that fits the K24A1 block, or one that fits the K24A2 head, or maybe it doesn't matter. I asked on the Engine Building forum and have received contradictory answer, lol. Probably doesn't matter - but it might - there's too much on the line to guess.
 

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Good luck. I know I told you turbo was going to be too much for the light chassis but Im interested to see if you can make it work. Nice stuff so far.
Is the chassis together yet? Thread needs pics!
 

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Discussion Starter #16
There's lots of pictures on the website and on the forum there are two other cars going together.

I plan to run boost-by-gear and RWD helps a lot, too. The 400hp value is the design-to number, not where I'll be running it.
 

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Discussion Starter #17
Looks like an engine builder has been located. He offered to port the head which I have to research to find out if it's worthwhile. Lower boost is good but it's hard to tell how much it'll drop and if it's worth the money. I'll post who's doing the build after it's in-process.
 

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Discussion Starter #18
Had a long vacation and got a ton done on the chassis. Also, the coated pistons arrived from Swain and everything was handed to Jeremy at Drag Cartel for the build - yes I finally chose a builder. He'll be providing pictures and though it's nothing special, it is to me!
 

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Discussion Starter #20
A few people have asked why I'm not using a Rotrex supercharger and am going turbo.

While some people clearly have Rotrex religion (almost annoyingly), call me skeptical. The centrifugal compressor used in the Rotrex works the same way as the compressor in a turbos. This means the claimed "linear boost with rpm" is Marketing Speak. The amount of air a centrifugal compressors moves is not proportional with rpm - it's by the square of the rpm. If you get 5 psi at 3000 rpm, it'll attempt to produce 20 psi (4x) at 6000 (2x the rpm.) There are two ways to deal with this, using a big unit that never reaches too high a boost but has no bottom end, or a smaller unit that provides boost down low but overheats the air higher and/or needs a blow-off valve. Regardless what people claim, the Rotrex unit has not rewritten physical laws.

Also, a turbo does well at quieting down both the exhaust and intake of an engine, something that's becoming a big deal at tracks where noise is a problem. The Rotrex will make the engine louder by effectively raising the compression. Yes, a better muffler can be used, but still.

Finally, there's the following hypothetical case:

We build two identical cars, one with a turbocharger and the other with a centrifugal supercharger. Both produce identical power and both cars have a 10 lb wastegate.

In neutral, rev both engines to 3000 rpm and note the boost. The supercharger’s boost is 10 psi due to being related solely to engine speed and because the throttle is nearly closed (because it’s in neutral with no load.)

The turbocharger’s boost will be very low because the engine is producing little exhaust pressure and because the throttle is nearly closed.

Now apply a load by driving both cars up a step hill, still at 3000 rpm. Turbocharger boost will be 10 psi because the engine is burning a lot of fuel and the throttle is wide open. The supercharger boost will be far less, perhaps 5 psi, because the boost is based upon crank speed and the open throttle decreases the measured boost.

Because of the rpm squared issue, the centrifugal supercharger, at low rpm, is producing very little boost. Either it must be geared to spin faster at low rpm or the engine rpm must be increased until the compressor impeller gets to its “sweat spot” and produces full boost. If it geared to spin fast enough to produce full boost at low rpm, at higher rpm it is severely heating the intake charge.

I may change my mind someday but for now I'm not convinced any belt-driven centrifugal supercharger is "all that."
 
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