Tandem seater, T bucket inspired

360° animations and more pictures, going back years: http://www.eternalmachinery.com/ecar/

I'm very interested in feedback / suggestions.

Take a T bucket, remove the bucket body, add two seats straddling the drive shaft, add a very simple minimal body, replace the ladder frame with a space frame. 

My goal is a very fun near daily driver.  No plans to race anything competitively, but I'd have to try drag street nights and autocrossing occasionally.

Yes, it's snug.  I'm planning to mock it up to verify my girlfriend and I fit, and I can see, before building.  I really like the idea of the symmetry / balance of sitting in the middle.  Not having to make front suspension uneven to compensate for uneven weight = traction on the rear tires to get it to go straight when mashing the throttle, with such a light car.

I'm planning to weld everything myself, which should be neat, since I've never welded.  So step one is buy a welder and practice a lot.  Which welder should I buy?  I realize this is a very ambitious project, likely to take years, and less ambitious projects often are not completed.  I'm up for doing it wrong the first time.  I got time. 

I've tried to balance the weight of the engine, driver, gas, and battery, between the axles, with equal size tires all around, in hopes of being able to turn well. 

I'm thinking third generation Chevy Camaro donor, manual transmission.  305 (5.0L), and T5 transmission (plus an LSD eventually).  Because I think this would be way less expensive than a 350 and T56, and I think this should give me plenty of power to weight.  Others have guessed 1500 pounds total weight (id' like more guesses), 10 pounds per hp seems great, and 150 hp seems easy to get out of a 305.  My Honda CBR1100XX is 563 pounds wet and 164 horse power = 3.4 pounds per hp, which I think gives me a good appreciation of "it's more fun to drive a slow car fast than to drive a fast car slow".  I'm not complaining, I'm very thankful I get to have this bike, but I also like getting to open the throttle more often.  I had great fun wringing the crap out of my first car, an '88 Tempo.  My '98 M3 is 14 pounds per hp, and fun.

I'm planning to remove the ECM and replace the carb and distributor with ones that don't need the ECM.  Because I've had enough electrical problems, and would like to try mechanical ones for a change.  Same reason I'm not going for an LS engine.

I'm planning to use square tube for the frame.  The model is based on 1.375" = 3.4cm wide tube, which came from the SCCA roll cage requirement for cars up to 1700 pounds with round tube.  I'd like to know what square tube is as strong as round tube that wide (0.080" wall thickness).  It looks like my motor mount situation should be similar enough to locosts that I should be able to get away with 1" square tube (two tubes per side supporting the motor mounts, one straight, one diagonal brace). 

I think the type of welding I want to do is TIG?

Live rear axle (from donor), dual wishbone + push rod front, fabricating the wishbones, push rods, etc., myself.  I'm not excited about calculating roll centers.  Hopefully using all the knuckles/spindles and brakes from the donor.  Mounting fenders to the knuckles via existing (dust cover?) bolt holes.  Would it be a terrible idea to use a single coilover for the front suspension?  Push rods -> rockers -> single coilover, equivalent to a perfectly solid sway bar?

I live in New Hampshire, and I'm planning to register this as a reconstructed / homemade vehicle.  Which requires fenders and bumpers and a front license plate.  And, if I understand correctly, at least a 20 year old engine to get rid of the electronics (OBD) requirements.  Still working out what I want to do about bumpers, maybe Model T style, interested in suggestions (the exact requirements seem to be undefined, and extremely minimal).

New Hampshire law is here: http://www.gencourt.state.nh.us/rules/state_agencies/saf-c3200.html

Probably typical T bucket exhaust.  "Classic T-bucket headers" look about right.  They're a few inches too wide, so maybe I'll get them unfinished, cut, and re-weld them, then have them coated?

Shoebox problem of space frame design:  A shoebox is structurally sound until you take the lid off.  The top of the box with the lid off is similar to the un-triangulated rectangle that often occurs around the people.  I'm thinking of trying to solve this problem with gussets, resulting in an oval shaped hole for the people, around shoulder height. The inside edge of those gussets is shown in blue in my models.  I'm curious why I haven't found others doing this.

I do my rendering in blender, which is free.  I wish solidworks wasn't $4,000. 

I live in Pelham NH, if you'd like a hand wrenching or whatever some time, I'd like to get to know more people who do these things.  I'm about 40 minutes North of greater Boston, which I go to all the time.  And let me know if you hear of a good donor?

I think I want to get in and out of the car by hinging the canopy at the firewall, and putting the back seam at the rear roll bar.  Also hinge the hood at the firewall, and make the top and sides of the body forward of the firewall all one piece (except for a bit around the wishbones) for easy access under the hood.  Complete flat bottom for the whole car?  I'm planning to add a transmission tunnel, of course, not in the model yet.

I'm curious what I'd need to do different to meet SCCA cage requirements, not because I'm planning to race, but because I might as well try to build a decent cage if I'm close: "No alternate roll hoop will be considered unless
it contains a main hoop having a minimum tubing size of 1.375” x .080” wall thickness. The roll bar
must be capable of withstanding the following stress loading applied simultaneously to the top of the
roll bar: 1.5 (X) laterally, 5.5 (X) longitudinally in both the fore and aft directions, and 7.5 (X) vertically,
where (X) = the minimum weight of the car."

If you don't already know about Lotus Sevens or their home built versions known as Locost Sevens, you should do some research on those. The space frame looks to be half built to your design. Ambitious project!

Seems very roughly to me like you have over-specificity in some decisions, and not enough in others.

I think hanging around here and over at locostusa.com is likely to give you a bunch of useful info. You might also look into some related books. I like Allan Staniforth's "Race and Rally Car Sourcebook" for an intro to a lot of concepts. Your front suspension description sounds to me like the opposite of a perfectly solid sway bar, as it would have zero resistance to roll (unless topped out, the car can roll without further compressing the spring). If you're not excited about suspension calcs, I'd avoid reinventing the wheel (and I'd be very thorough and careful in borrowing a preinvented wheel).

305s and 350s are both so dirt cheap as to make it not worth pondering a 305; my secondhand impression is that they're worse with no upside, even in cost. I also think you might expand your search, though it is hard to beat a small block Chevy for cheap, easy power. You don't need a T56 for a 350. 

I don't think you can make the seating that... cozy, and still have it safe. Remember that each person needs enough seat structure to locate them firmly, and with safety in mind, it's hard to imagine not using highback seats (with headrest, that is). You'd have the passenger having to get their legs around the driver's seat, and that's going to be awkward, and make for a great deal of difficulty in ingress/egress. Also, I challenge anyone to be accurate with throttle and brake inputs with that leg placement :)

Anyhow, I'm no expert; that's just the first pile off the top of my head... Good luck with the project!

Looks interesting, but ergonomics are going to be a big challenge unless some changes are made. As mentioned above, the seating looks way to snug to fit 2 people and having the shifter right between your legs and inline with the steering wheel is going to be awkward to shift. Are you planning on having both the throttle and brake pedal on the right side of the transmission and the clutch pedal on the left side of the transmission?

Yup.  I'd love a scale top down diagram of a T5 transmission so I could accurately model it and see about pedal fit.  I realize I might have to widen the car for this.  (I've seen scale diagrams with measurements from the sides, which is where the shifter and drive shaft placement came from.) 

Short of that I figure I'll buy the donor and take the measurements / mock it up myself.

If anybody has a T5 and feels like taking a few width measurements, I'd appreciate that very much.  Front and back of the bell housing would be most important.

Edit: Width at the joint between the main case and extension housing would also be great (I didn't know those terms - for the two large outside parts other than the bell housing).

I have a feeling from your model that the shift lever for the T5 would be in a very uncomfortable position for the driver. That said I love the idea and think it's looks cool. I do somewhat question the in line seating as above. 

I think you'd be doing yourself a disservice to pick the 305 just based on it being cheap. This is going to cost you several thousand dollars at least and years of your time - there's no reason to pick an anemic engine just to save a few hundred bucks. If you really want a v8 there are all sorts of good options out there, some of them the same price or only slightly more than a 305. As mentioned even a 350 would be a better choice and would probably not cost any more.

Myself, with a 1500lb weight, I'd rather have either a modern 4 cylinder or something similarly lightweight. You could even do something wild like a Toyota 1uz-fe v8 and a Nissan manual trans but that starts to push the bounds of low budget due to the price of the transmission adapter pieces. An aluminum 5.3 LS v8 would be cheap and would provide far more power at a lower weight than the 305. An Infiniti / Nissan VH45DE would be fun, too; 4.5 liter aluminum v8 with 270hp and engine donors are available super cheap. (Infiniti Q45.) I know a manual will bolt up but I don't remember which one.

I like the tandem idea but like you said you might need to do some measuring and mockup to come up with something that works.

dculberson: Can any of those be run without electronics (ECM / ECU / EFI)?

Stampie said:

I have a feeling from your model that the shift lever for the T5 would be in a very uncomfortable position for the driver. That said I love the idea and think it's looks cool. I do somewhat question the in line seating as above. 

The passenger also looks to be in a very uncomfortable position for the driver

i also would prefer not to be straddling spinny bits in the event of u joint failure

The F-body shifter is pretty far back on a T5. The S10 one moves it closer to the firewall. Still the seating looks pretty intimate both with the mechanical bits as well as the passenger.

Darxus said:

dculberson: Can any of those be run without electronics (ECM / ECU / EFI)?

 

Any of them can be run without EFI but ignition will require a computer as none of those have any provisions for a distributor. The LS platform (4.8, 5.3....)has lots of aftermarket support for bolting on a carb if that is what you want to do. If you are planning a junk yard v8 there is usually zero price difference between a 305 and a 350, and a running example without too many miles or mysterious noises is usually not much cheaper than a complete 4.8 with accessories, wiring and computer. Also keep in mind that any 350 or 305 you're likely to find used is more than likely going to be a smog era truck engine that is all out of poop by 4500 rpm. 

I think once you flesh this design out, you will find that you need a very long cockpit/passenger compartment. Unless you're proposing the passenger is actually sitting on your lap and doesn't mind the steering wheel in their face and you reach around them. Otherwise the passenger will need to be behind you. And if you're sitting on their lap that moves the wheel and pedals in relation to your seating position and if there is a passenger or not. This leads to the only way to have a tandem arrangement is two individual seats. The passenger is now sitting on top of the rear axle and the driver on top of the transmission.

Having driven a Caterham Seven with your butt only 4-6" off of the ground it was great! Riding the transmission puts you up rather high. You might want to consider going with an automatic to get rid of the crotch shifter because you have to consider the space between the shifter and the wheel and still being able to operate both effectively. That pushes the shifter way down and the steering wheel up and now the base of the windshield (scuttle) is getting quite high.

This just brings back the elegance of the Lotus Seven. If you want a tandem design I think you should focus less on laying the passengers down, and more about upright comfort.

Look at the relationship of the shifter, wheel, driver, and the ground in a Lotus/Caterham/Locost Seven. Then consider your design and what your criteria are for nailing down actual dimensions.

http://www.carmagazine.co.uk/features/car-culture/60-years-of-the-seven-lotus-and-caterhams-kit-car-through-the-ages/

The Elio* design is based on tandem seating arrangement and they get around the pesky 'sitting on the drivetrain' by using a front wheel drive layout. You could do a tandem seating with the engine in mid-ship or rear engined. That could get the tandem better suited for more comfort.

*The Elio is still vaporware, by the way.

You have some interesting ideas.  The devil always lives in the details.  Think pedal placement.  Exhaust routing.  Driveshaft.  In addition to all the "check out the Seven" comments, I'd like to add: Check our Legends cars and Mallocks. 

A Legends car is a single seater, but could provide some inspiration for chassis design and packaging.  I'd look a their driveshaft arrangement and avoid siting on top of it.

Similarly, the Mallock is like a center seated Seven.

In terms of CAD - check out Autodesk Fusion 360.  It's pretty powerful and a real CAD/CAM system.  Can do FEA powered by NASTRAN.  And it's free for enthusiasts.

Design on!

Ace and Gary approved!  

In reply to RossD: Yup, 9.9" from the bottom of the oil pan (not counting drain bolt) to the top of the drive shaft, in a third gen Camaro.  Dry sump wouldn't gain me much, due to the clutch / crank.

Yeah, I realize I might end up needing to have the people more upright. 

I had an automatic once.  Not doing that again.

I keep forgetting to mention 1920's Indy 500 cars probably look closest to what I want that I've seen.  The Mercedes W25 Rennlimousine even had a roof, although only one seat, and wasn't an Indy car.

Some of the 20's Indy cars also did front wheel drive, for the same reasons, very successfully.  I'm not willing to do that either.

I don't think it would be worthwhile to me if I can't get tandem seating.

The Elio is mentioned on my page I linked to.  Locosts / sevens are also a great reference, I mentioned them in my post.

I've modeled all kinds of things over the years, including moving a transverse front wheel drive to the rear, using a FSAE / DSR style rear motorcycle engine, classic VW bug style rear engine + transaxle (VW transaxles are weak, Getrags are expensive, although a lot less than they were, Corvettes' are long....), a couple types of reverse trikes, motorcycles, all on the page I linked to.

I am willing to make the car taller and wider, I admit the current dimensions are optimistic.  And I realize that it might not work out at all. 

I do really appreciate all the suggestions / criticisms. 

I need to look into what tandem seaters others have built lately. 

Auburn Imp. Single seater. Individual belt to each rear wheel. They had this all figured out 105 years ago.

I love T buckets and wish you good luck with your build.  I lived in NH for 20 years and have gone through the NH registration process a few times.

Here is a picture of my T bucket build in progress.  It's been on hold as I've been building a Cheetah inspired car. 

I built the space frame.  C4 Corvette suspension bolts in. The engine pictured is a 305.  I purchased it for, I think around $400.  It has vortec heads, aftermarket pistons, a mild cam, air gap intake and 4 barrel carb.  I drove the car it was pulled from. The guy was putting an LS engine in his Camaro.

The transmission is 4 speed Richmond.

I made the body out of foam then put a couple layers of fiberglass over it.  I wanted a hot rod that was cheap to build and had good handling.  I'm going to finish it as soon as my Cheetah done.

Here is another car that I built and registered in NH.  It was inspected and registered as a street rod.  Fenders and front plate were not required. This was about 12 years ago.  The rules might have changed.

I built an aluminum tub. C5 corvette cradles bolted to it.  It runs an LS6 and the vette transaxle.  I shortened the torque tube and moved the engine rearward by 23 inches. This car is the best handling car that I've ever driven.  It's also the car that was the hardest to drive at speed limits.  I made the fiberglass panels. 

Have fun planning and building!