Gents,
After much discussion with the wife, I have recieved the green light to proceed with building my homemade performance sports car. The primary goals are to keep the build cheap (and I mean cheap), reasonably light, and sturdy. My approach to car is to use ALOT of the components which I already have, and make purchases very sparingly.
In terms of my background, I work as a mechanical engineer at an engine performance and development company in Texas (doing engine testing, in-cylinder pressure data gathering/analysis, engine calibrations, etc...), 4 years experience in FSAE (for 3 cars), and 1 year of Mini Baja. ~4 years of Virginia region SCCA Autocross (DP, and SM class) and past Nissan mechanic, and long time bicycle mechanic (8 bike shops).
Sadly, this engineering desk job is deminishing my fabrication skills, and many moons have passed since I wrote codes for CNC machining for FSAE parts. And consequently, I'd like to keep this build caveman simple.
Goals:
1300 lbs
265ish hp
(4.9 lbs/hp)
$2,000 budget
I've decided to build a Middy Lotus 7-ish car powered by a 2L B18 engine, using a 1990 Acura Integra front subframe and suspension members, and a NA miata front subframe and front suspension members.
Weightwise, this may be challenging as:
front subframe: 16lbs
Pass side sub frame: 28.3lbs
rear subframe: 20lbs
driver side subframe: 31.7lbs
Subtotal: 96lbs
The front and rear subframes will be joined with four mild steel 2"x3" rectagular tubing above the subframes (3" sides placed vertically), and two 1"x1" square tubing below the subframes, which will form the spine of the car. Mild steel AISI 1020 intended (4130 is simply out of the budget, and I don't intend on approaching the yeild strength of the cheap 1020 stuff, and Youngs' Modulus is the same for 1020 and 4130). I'll be using my old faithful Lincoln SPT-135 MIG welder with Argon/CO2 shielding gas mix. Sorry, no showcar TIG work here.
I already have a 1-3/4" dia round tube main roll hoop from AISI 1020 with a triangulated rear X-brace (which is way overbuilt and intented for a 2500lb car), which will tie into the chassis in six locations:
X2 Roll hoop to Lower (Primary) Frame rail spine
X2 Roll hoop to chassis waist
X2 Rear X brace to upper shock tower/upper A-arm mount
weight: 68.5 lbs
The 2"x3" longitudinal rectangular lower box members will be in bending, and the upper 1"x1" square tubing from the roll hoop forward will be in compression. Rearward of the integra subframe, a removeable triangulated X-brace will tie the upper control arm pickup points, ala aerial At-om inspired. I intend to keep the car forward of the roll hoop very much Lotus 7-inspired.
With regards to vehicular motivation: Honda B series.
Why use a Honda B18? Simple. I've poured a foolish amount of money into building my 85mm bore B18A1 with Darton Sleeves, 12.5:1 CR JE Pistons, Manley 4340 Rods, Skunk2 Pro3 Cams, Skunk2 Pro valvesprings, Skunk2 titanium retainers, Skunk2 Pro intake manifold, match ported head, 76mm throttle body, yada yada yada, blah blah blah... In short, it revs to 9.5k, has measily torque, and makes ~265hp at the wheels.
For the transmission, likewise, more money was foolishly spent on a cable type GSR YS1 short ratio transmission with 4.4 final drive, rebuilt with sychrotech internals, an MFactory Multi-plate clutch pack adjustable 1-way LSD. For middy usage, I understand I will need to modify the transmission end of shifter linkage into a J-shape, with a U-joint on the selector shaft input.
Why an Acura Integra front subframe and suspension members? Primarily because this would save me alot of fabrication time and money, as the suspension geometry is already figured out, as lower control arm/radius rod, and upper wishbone have very good camber control, very little bump steer, and a VERY large Factor of Safety built into the design. The outboard pickup point on the upright is located outside and above the tire, which isnt very conducive to compact suspension packaging. I intend on cutting the upright/knuckle as far needed to clear the 16" wheel, and then cut a vertical 3/4" slot into middle to accomodate a spherical rod end bearing from the upper control arm. No fancy push rod suspension for the rear, just direct actuation from the factory LCA.
Why a NA miata front subframe, suspension arms, and steering rack? The miata already has very well sorted geometry and camber curves. Also the miata subframe and suspension designed to support a 2000+lb car, thus factor of safety for a 1500lb car will go up. More or less, the same reasons as mentioned above.
The current issue I see with using the front miata suspension/subframe, is that the factory upper shock mount is placed upwards and outboard. The two solutions I see are the following:
Use a very short shock body, and attack the upper shock pickup point in between the upper wishbone arm. (Essentially use a motorcycle rear spring/damper). Pros: Simple and reduced number of components. Cons: cost of new springs/dampers.
Use a pushrod and bellcrank setup, and place the dampers within the front subframe. Pros: adjustable rideheight by varying rod length by not removing damper travel. Reduced polar moment of inertia in roll. Adjustable installation ratio by virtue of bellcrank design. Can still use current springs/dampers. Cons: Increased overall weight and complexity. Increased packaging difficulties with radiator and spring/dampers. Increased fabrication time. More suspension analysis and design required--Adams, Optimum K, etc...
Shape of the Car/Body:
I would like to place two small motorcycle radiators (in series) (or a Griffen 19"x22"x3" radiator) within the front subframe, followed by a 10 gallon fuel cell rearward of the front subframe, followed by my optima battery.
Essentially, replicate front and middle dimensions generally speaking, of the Lotus 7, with the beautiful long slender bonnet, however with a battery and longitudinal fuel cell, in place of where a longitudinally mounted rover engine would have traditionally been. I plan on trying my best to copy the shape and paintjob of a caterham r500.
Attachment:
IMG_3655.JPG
The nosecone would be standard issue Lotus 7. The goal for the car is to NOT have high placed tubes forward of the main roll hoop, with the upper waist of the chassis barely chest high whilst the driver is seated. car will have no windshield, no roof, no doors. The bodywork behind the rear subframe would quickly terminate at a sharp angle. The seating placement would be more forward than a traditional Lotus 7, thus to maintain the slender bonnet style the wheelbase would be slightly increased. This is not necessarily a bad thing, as a ~6" longer wheelbase would be more conducive to stability, and a slender and centered longitudinally placed fuel cell would aid in transitional handling.
I would like to run 1.75" dia aluminum tubing within the longitudinal 2"x3" frame rails, with 90 degree bulkhead fittings at the frame enterances and exits.
To itemize the components that I already have, and components which I would need to purchase:
Currently have:
Acura Integra subframe
Acura Integra front suspension arms
Eibach Springs/ Koni/tokico Dampers
Honda B-series engine (Complete w/wiring harness, manifolds, ECU, starter)
B-series transmission (Complete w/ clutch cable)
Clutchmasters Kevlar Clutch w/ heavy duty pressure plate
Integra Type R flywheel
B-series shift linkages, and shift lever w/knob
Acura Integra pedals (top swing)
Left and Right axles w/ halfshafts
left and right knuckes
Wilwood Dynalite 4-piston brake kit w/ 12.2" rotors, and Aluminum hats
1-3/4" dia Main Roll Hoop (AISI 1020) w/ rear X-brace, and lateral member for harnesses
Kosei K1 16x8" wheels
Yokohama A048 tires 225/45R16
Momo Start Seat
Momo steering wheel
Simpson 5pt harness
Optima Red Top battery w/battery box and 20 ft of battery leads
OEM integra fuel pump and fuel lines
To buy:
Miata front subframe
Miata front suspension arms w/knuckles
Miata steering rack and tie rods
Miata steering shaft
(Miata parts total: $600)
Wilwood Caliper bracket for NA Miata knuckles ($100)
Aluminum Sheet for body panels: ($250)
60 ft of 2"x3" tubing AISI 1020 ($200)
100 ft of 1"x"1 AISI 1020 ($100)
20 ft of 1.75" diameter 6061-T6 aluminum tubing ($40)
Griffen 19"x22"x3" radiator ($173)
X2 Spherical Bearing rod ends (1/2" ID) ($30)
X4 Yamaha R6 Shocks used: $200
brake lines ($150)
fuel lines ($100)
Headlights, turn signals, brake lights, horn ($100)
side mirrors, rearview mirror ($50)
RCI Fuel Cell 8 gal: $90
http://www.summitracing.com/parts/bob-10993/overview/Also, out of curiosity, as well as trying to be somewhat considerate of the weight of each of the parts, I've weighed the parts which I've cannibalized from the integra:
Roll Bar: 68.5
Wheel/tire: 37.3 (x4 149.2)
front subframe: 16
Pass sub frame: 28.3
rear subframe: 20
driver side subframe: 31.7
Subtotal: 96
radiator: 11
wilwood dynalite caliper: 4.1 (x2 8.2)
wilwood 12.2" rotor and hat: 10 (x2)
optima red top battery: 33.3
pass side axle: 14
drivers side axle: 14
steering column: 8.9
steering rack: 23.4
upright, upper arm, lower arm, and radius rod: 30.6 (x2 61.2)
master cylinder: 2.2
brake booster: 8.5
pedal box assembly: 9.9
header: 17
exhaust muffler: 20.6
seat and bracket: 25.7
steering wheel and adapter 3
seat belts: 4.7
koni shock +eibach spring+fork: 11.8 (x2 23.6)
tokico shock + eiback spring: 10.6 (x2 21.2)
shifter linkages +knob: 6
intake arm: 3.7
catch can +hoses: 5.7
Engine/Trans: 350lbs (est)
subtotal: 1009.5 lbs
I'll try to post pics of the madness once I start cutting metal.
-Andrew