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Learning how to build Lotus Seven replicas...together!
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PostPosted: September 29, 2020, 2:02 pm 
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Joined: September 29, 2020, 12:39 pm
Posts: 1
Hello, all. New member here, at Kinetic Vehicle’s recommendation.
After a too-long layoff my build project is back on the front burner. Here’s the deets:

OBJECTIVE - A late ‘60s – early ‘70s mid-engine sports racer tribute; picture a beefy Lotus 23
o Most tubing will be 1.5” OD, both square and seamless. The tubing I have on-hand is 0.090” wall; heavy, I know – I got this spec years ago from the Ultima GT site and went with it. I’ll be using it in the chassis bottom plane and the cockpit inner wall, with lighter gauge material for the rest
o Torsion boxes around the cockpit
o Integrated roll cage

INTENDED USE: spirited road driving and timed events, maybe track days and hill climbs. The goal is getting around corners as fast and as safely as possible rather than a big top-end numbers

STYLING - the 1966 Alfa Romeo Tipo 33 Periscopica is the primary styling influence
 Lotus Elise windscreen
 Styling cues I’d like to add:
• Chassis visible through windshield like the Birdcage Maserati
• Cut-out front wheel arches like the McLaren M8 (You guys must know – what are these called?)

I’m more interested in how something works than what it looks like so I’m planning minimal bodywork with much of the chassis exposed, especially the rear. On that, I love the look of a short front overhang and a large rear. Ahem. I’m using a 2004 Subaru Impreza (NA) transaxle which to my eyes is kinda long. I’m planning on building structure aft of the transaxle mounts for crash protection, rear deck support and taillight mounts

I have the Collins and McDonough book on the Tipo 33, which contains nice contour drawings. When the time comes I’m hoping to engage an Industrial Design student from a local university to model the body, integrate the Elise windscreen and stretch it over the chassis, then use the final model to build a body buck

BASIC DIMENSIONS
 I like the size and presence of the Lotus Esprit so I’m using its 60” track and 96” wheelbase as my baseline
 180 hp to 200 hp from a hopped-up Alfa Romeo 2 liter twin-cam with ported heads, hotter cams and a Megasquirt or similar system controlling fuel and spark
 1,600 lb wet with driver
 40/60 front/rear weight distribution

SUSPENSION - Modified NA Miata suspension geometry and widened steering
o Track widened to ~60 in. via longer control arms, retaining the upper/lower length ratio
o Stock roll center will hopefully be retained by relocating inboard upper suspension pickup – picture the arc traced by the upper inboard pickup pivoting downwards slightly around the upper ball joint
o Twin trailing link independent rear suspension like that on the Lotus 49 and others of the era; the Miata rear upright is perfectly architected for this layout.
>> Unknown #1 – Still haven’t nailed fabrication details for the clevis that links the trailing arm to the upright – any recommendations most welcome
o Preserving steering rack location as on the stock subframe to retain bump steer characteristics
>> Unknown #2 – Recommendations on fittings to lengthen the steering tie rods would be greatly appreciated
o 15” wheels, 50-series tires, 7” wide front and 9” wide rear
o Miata big brake kit so no power brakes, or power steering

I want to use a screw-in lower ball joint like that on aftermarket Mustang II parts. I think this will allow me to get the lower coil-over mount closer to the ball joint than with the OEM part. As a result I have a pair of brand-new OEM NA ball joints for sale…
>> Unknown #3 – the lower ball joint taper and how difficult it may be to find a screw-in part with same?

POWERTRAIN - Alfa Romeo 2L twin cam mated to a 2004 Subaru Impreza transaxle.
>> Unknown #4 – Recommendations on custom half-shafts with Subaru front inboard/Miata rear outboard splines would be greatly appreciated
o Work on measuring for the adapter plate is in progress. Kennedy Engineering has agreed to sell me “half” an adapter plate drilled and tapped for the transaxle with engine side "left blank." I will also ask them to locate the transaxle input shaft with a drilled hole
o Ported cylinder head by Norman Racing Group
o 45 mm Weber DCOE look-alike ITBs and trumpets and a Megasquirt or similar system controlling fuel and spark
>> Unknown #5 – setting up the aftermarket ECU

UNKNOWNS - where to begin? The biggest ones are:
- How much suspension travel is reasonable?
- Is it the coil-over that constrains suspension travel?
- Suspension frequency? Hello?

Other unknowns as stated above:
 1. Rear suspension trailing link clevis on uprights
 2. Steering tie rod extensions
 3. Lower ball joint taper for Mustang II-style screw-in part
 4. Custom half-shafts
 5. Setting up the after-market ECU

LIBRARY – I’ve accumulated a decent chassis and suspension design library; I can post a list at a later date if there's interest
o I have the Kimini and Midlana books and looking forward to reusing as much as I can, especially the integral roll cage

Like many of you I’ve been dreaming of this build since I was a kid, drawing F1 cars since grade 4. What got it going, though, was finding a motorcycle-engined single seat chassis outside the mechanical engineering lab of a local college in the early ‘90s. In hindsight I think it may have been a Formula SAE build. I thought, I could build one of these, but it would have to be a two-seater and street legal. I started researching the build but wasn’t until 2007 that things got rolling when 1) I realized time was marching on and I needed to get it going, and 2) I moved into a place where I could finally build a workshop. I took a welding class at the regional voc/tech and started collecting tools while looking for a donor. MIT was the only school I could find in my area with an F-SAE team website so I emailed them, hoping I could arrange a shop visit and ask some questions. I really lucked out – the team leader invited me to actually work with them. This was late 2008 and I was recently out of work due to the economic crash and I ended up spending all of 2009 and early 2010 hanging with the team and helping on a couple of builds. They shared shop space with the solar racer team and other groups doing cool stuff like converting a 914 and various motorcycles to electric drive. Good times. And I’m still good friends with Josh, the team lead, who has provided a tremendous amount of assistance and advice.

My first thought for the build was a mid-engine space frame with a FWD transverse V6 drivetrain mounted longitudinally sending a half-shaft to each axle for an AWD setup. I dialed it back and decided on a VW Jetta because I wanted a longitudinal layout. I ditched that and went with a NA Miata + 914 transaxle so that I could steal all I could from the Locost world (what was that Picasso said?). After the transaxle proved way too much to rebuild I flipped it and bought a mildly totaled 2004 Subaru Impreza to steal from the Factory Five 818. After seeing their build using a Ford 4-cylinder Ecoboost I decided on the Alfa Romeo twin cam. It’s a really sweet engine, state-of-the-art circa 1954. It looks great uncovered, and I’m planning on either polishing or crinkle painting the cylinder head and leaving it and the ITBs exposed through the rear deck. It fits the classic sports racer tribute vibe well, and there’s a solid ecosystem for go-fast parts. Bonus: it sounds so good when wringing it out, especially with intake trumpets.

There you have it - hope it wasn't too long. I'm new to this discussion board thing so I hope I won't be too annoying. I do look forward to interacting with you.

And how to I create a signature? Here it is for now:

----------------
Complexity is my muse.


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PostPosted: September 30, 2020, 8:59 am 
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Joined: October 19, 2012, 9:25 pm
Posts: 3316
Location: Summerville, SC
Welcome to the funhouse

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OOPS I did it again
http://www.locostusa.com/forums/viewtopic.php?f=35&t=17496

Blood Sweat and Beers
http://www.locostusa.com/forums/viewtopic.php?f=35&t=15216


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PostPosted: September 30, 2020, 12:11 pm 
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Joined: July 17, 2008, 9:11 am
Posts: 5909
Location: West Chicago,IL
Welcome. It sounds like you have a plan. Now all it takes is some follow through. Start a build log when you start acquiring and or cutting/welding tubes.

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“Any suspension will work if you don’t let it.” - Colin Chapman

Visit my ongoing MGB Rustoration log: over HERE

Or my Wankel powered Locost log : over HERE


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PostPosted: September 30, 2020, 3:03 pm 
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Joined: April 23, 2019, 4:30 am
Posts: 176
Excellent project, looking forward to seeing how you style this, the goal sounds beautiful.

Since this is a locost project you may like to consider the speeduino ECU, it's an open source low buck option that is DIY, which is both its strength and weakness. If you keen on electronics it is very simple, if you prefer a plug and play maybe best to give it a miss. Uses Tunerstudio just as per the Megasquirt to set the firmware.

Welcome to the group, there is a lot of hard earned knowledge freely shared here.


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PostPosted: October 1, 2020, 1:03 am 
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Joined: March 19, 2011, 10:22 am
Posts: 2099
Location: Holden, Alberta, Canada
Welcome to the forum! As said, looks like you have a plan, that's a good thing. There's a bunch of very knowledgable people on this site, so you have excellent resources here.
Buy some steel and start glueing it together.
All the best on your build :cheers:

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Perry

'If man built it, man can fix it'
"No one ever told me I couldn't do it."
"If you can't build it safe, don't build it."

Perry's Locost Super Che7enette Build
Perry's TBird Based 5.0L Super 7 L.S.O.
Perry's S10 Super 7 The 3rd
Perry's 4th Build, The Topolino 500 (Little Mouse) Altered


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