LocostUSA.com

Hello fellow constructors,

Better start this extremely non-traditional build log in the traditional manner - been a long time lurker here and big fan of some very clever and cost effective construction. I don't think there is a better forum for automotive creativity and "bang for the buck-id-ness" than this one.

I start this log hoping that the project will serve as entertainment and not as the title suggests a descent into madness, although given the scope of what I am building, the latter seems likely on first pass. I have however been working on this project for 25 years so have a few things pretty much ironed out planwise and will be constructing over the next 5 years as the paychecks allow.

Currently the car exists only in CAD models and a smattering of parts, and I would appreciate any advice or info to help flesh out the detail.

Build location - Auckland, New Zealand

Stage 1 - Design Approval from the NZ LVVTA so that the car can be road registered - currently working on this now - COMPLETED AUG 2021

Stage 2 - Test Mule - a track only steel space frame setup very much like BB69's track monster (which served as huge inspration for this build, thanks Ken) which will allow me to prove out this odd setup in a safe environment. The car's name is Patience for obvious reasons. The test cycle will be thrash, break, fix, repeat.

Stage 3 - road car development - intend to use the demonstrator to form a syndicate of likeminded nutters who can share the costs of building the moulds and making the carbon fibre panel work.

Stage 4 - Fully Electric version - since the rear subframe is removeable there is future scope for a fully electric version once the Tesla motor and battery packs get cost effective, using same chassis and body panels.

The car has a 3 seat configuration with driver in the middle - some may call it a Mclaren F1 replica but its more like my hommage to a design I respect but cannot (and would not want to) afford. I am going to thrash this thing. I prefer the "just raced 24hrs at Le mans" look over concours, especially as it is "not a real one".

Engine - there isn't one - there's two. Mounted amidships transversely. I am pairing up 3.5L V6's from the 8th Gen Honda Accord (the ones with variable cylinder management) - because they are $3/Hp here and I get 540 HP & 500 ftlb torque with stock honda reliability (OK, so the VCM's are not super reliable if you drive them on ECO mode all the time, but NZ roads are mostly curves so that is not a big issue here). They have headifolds which makes my exhaust system simpler to fabricate. With a bit of tweaking these motors can put out 350 Hp each, so power to weight should be good using 2.

ECU - Speeduino - an open source DIY engine management system that uses Tuner Studio as per a megasquirt setup. Because I have 2 independant engines I must run 2 ECU's.

Clutch - Stock Accord Dual mass flywheels for the test mule - jury is out on drivetrain harmonics so real track testing will be informative.

TBox - a custom made transfer box that has 2 pinions (in constant mesh with a common crown wheel) that allows the unsynchronised engines to both feed power into the transaxle at a 1 to 1 ratio. I intend to run on only one engine for economy on long runs and keeping under the speed limit, with full power only a clutch dump and "on the fly" crash start away. There is only one starter motor so the primary engine has to be fired up before the secondary can be engaged.

Transaxle - Corvette C6 6 speed - TR6060 ideally a 2009-2013 MM6. I know this forum has a hot topic on the best transaxle for a middy, but I cannot afford to build a longitudinal V12 with a transverse manual gearbox - so I am building a transverse V12 with a longitudinal gearbox. If the tbox turns out to be a failure I can fall back to a semi-conventional layout and bolt the V6 onto the end of the transaxle and twin turbo it (plus I will have a spare motor!)

Suspension and brakes - C6 Z51 front and rear knees - all stock GM spindles, hubs, brakes and control arms.

Tires - 265/35/18 front & 305/30/19 rear - likely to be Kumho Ecsta V720's

Steering - Porsche 911 rack - its the only "road car" sourced rack that has a central perpendicular pinion that I have found - although it is too narrow as stock so jury is out on how to modifiy it to make the front suspension work without bump steer.

Frame - 4130 tubing with engine and trans on an easily removed subframe (see the TBFR test protocol above) - makes it simple to get road worthiness if its a steel frame, not enough composite car manufacturing locally to consider that as an option. I am adding weight due to some of these design decisions but these decisions also help keep the total cost lower and within my means.

Glazing - polycarbonate for the mule, custom made glazing for the road version (real windshields are apparently 15K GBP - umm - no thanks!).

Target weight = 1300 KG (2866 lbs) as shown is calculated at 1050 kg dry and distribution is 43F/57R.



Attached are some early Cad renders to give you an idea of the layout.

Cheers,
Marcus.

Welcome. I skimmed through your post and don't see anything regarding fabrication of the shell. That alone can consume an enormous amount of time and is very messy, so if you're willing to consider it, look into starting with an existing shell. That decision alone can save literally years of work.

Regarding the drivetrain, think long and hard about that, about what it's going to take in both time and resources to make it reliable. Ask yourself, do you want to build a car, or develop an engine - they are two different things. Might I suggest a turbo V6 (to keep weight down), or go with a boring V8 until you get it on the road, and THEN start on the twin V6 as a side project. This way you have something on the street while that's going on.

_________________
Midlana book: Build this mid-engine Locost!, http://midlana.com/stuff/book/
Kimini book: Designing mid-engine cars using FWD drivetrains
Both available from https://www.lulu.com/

Mumble - mumble - cough, (BMW or Jag V12 with SC/Turbos).
Or maybe two v6's in a W arrangement and a more conventional transaxle.
I have seen this done with SBC's so other engines should not be much harder.
Maybe two of those odd little narrow VW 6's a'la Bugatti?
In any case I hope you have a very deep pile of cash under your mattress!

_________________
If I must be a one-man PC free zone, so be it!

Thanks for the sage advice Kurt, I truly appreciate your viewpoint, experience and comments.

Twin turbo V6 is certainly a sensible path, a lot of manufacturers have gone that way for good reason, trouble is I prefer big capacity naturally aspirated engines - which are expensive and heavy. Using the twin V6 concept means I get the plentiful supply of cheap lightweight die cast engines. The gearbox development could be a deep rabbit hole - but I am going full "Road not taken" by Robert Frost here.

Unfortunately the v8 option doesn't fit - with a 107" wheelbase it is half way through the drivers seat (pic below). Conventional transaxles like the audi and porsche will stick too far out the rear - like a lotus europa and I am trying to bring the centre of mass forward as much as possible.

Using the transverse engines I have designed a gap through which the front bank exhausts pass, but crucially the standard corvette gearshifter linkage is also retained, something I have never seen in any mid engined setup. The shifting will be very direct and "like a rifle bolt".

Thanks Richard, the W combo is a good one and was one of my first iterations. In engineering most things have been tried and forgotten - I got some of my ideas from projects such as the link below;
https://oldmachinepress.com/2017/04/20/ ... ft-engine/

Unfortunately my wife found that pile of cash and it's long gone, but through career planning I am a mechanical engineer working in the protoyping department of an investment casting foundry with full use of a Co-ordinate measuring machine, 3D printers for making patterns up to 120 Kg in aluminium or High strength Low alloy steels (and some shiny high alloy ones too!) , a large 3 axis and small 5 axis CNC mill and a small unused router which is going to be configured into a car sized gantry to carve the mould plug. If it wasn't for work commitments I would have finished the car years ago but a recent health scare has kicked me up the backside to sieze the day and stop dreaming and get busy.

I didn't know how to respond to this thread at first... Thought to myself "that is a HUGE bite to chew"



This gave me faith- you would need access to that kind of equipment in order to get a project of this magnitude completed.

Do they have any job openings for another Mech E? I wouldn't mind moving to NZ... I'm already an Australian Citizen, makes it a little easier

Consider Docol R8 if you can get it. It's stronger than 4130, and is more forgiving to tig/mig weld.

4130 works great when OA welded, or when it can be heat treated. I know it's used a lot, but I'm not a fan of using the stuff in working part of a motorsports chassis. Lots of failures. One spot cools a little too quickly and suddenly you've got a critical joint made of glass.

Mild steel is also worth considering, if you're not building for a particular race or racing class where 20 extra pounds could make you a loser.

_________________
Aedifico ergo sum.

Thanks for the info Graveyard, I had never come across Docol R8 before - I now have more homework!

Glad to see your V2 build is getting so close to moving under its own power, your workmanship is superb and the design is looking really well balanced asthetically. Very inspiring, you are doing true solid modelling.

Any chance you know the length and diameter of the input shaft for the transaxle? I have not been able to find that info anywhere on the internet, the tremec datasheets only list the non-corvette configurations. I was told they are are the same as the other chevy input shafts but the photos look different.



Sorry bud, just took on a graduate and he is working out really well, so unless I retire or he leaves....

Cheers,
Marcus

A couple of big milestones were reached yesterday.
1) Managed to get Solidworks to behave while doing complex surfacing and have replicated some of the outer door skin - below are photos of the CAD and first 1/10th scale print

2) All four corners of C6 Z51 corvette brakes and suspension arrived after 2 months on the slow boat from long beach - now I can move onto accurate suspension models and progress into the chassis detailing proper. Updates may be sporadic for a while.

Render of progress;

Today has been a long time coming - I have been trying different approaches attempting to model the nose accurately for about 10 years - even though it is still not smooth enough I am 95% there - I could correct the errors with bondo in the real world.

Sweet Progress! Looking forward to seeing more. What are you using to model the suspension geometry? I've been using susprog3D. If you're keeping the stock control arms, you can set up susprog so that the arms and spindle geometry are fixed and than move around your roll center, ride height, and instantaneous center to get minimal roll center migration.

This is why I am building my car the way I am - It is sad to me that these cars become so "precious" that people don't risk driving them anymore, according to Mclaren only 5 of the F1's are being used regularly - the rest are investments locked away.

https://www.youtube.com/watch?v=haVCTy8mfsQ

You don't need the biggest horsepower numbers to make fun things happen, just stick to original design brief as much as possible - which was lightweight, unassisted driver interface and a big capacity naturally aspirated V12.

Rocan,
Suspension arm pickup points on the chassis are next on my list after modelling the spindles - I have the stock corvette co-ordinates but got them off the internet so trust them 0% and will be verifying the "best" position for the stock suspension components. I am making a road car so it will have compromises towards that end in spring rates etc.

In the next iteration i.e. the racing version of this car I expect to use something like the 3.7l honda V6's dry sumped and dropped as low as possible in the subframe since I can have a larger offset from the transaxle input axis due to the fact that the pinions could be hypoid design. The road version I am building first uses spiral bevels with zero offset so that they are symmetrical and therefore interchangeable. My theory is if I have a spare part on the shelf it won't break on the car. A hypoid offset will make the gear set even more expensive as it will require 2 different pinions.

cheers,
Marcus

Would really appreciate some help getting these critical dimensions for the 2008-2013 MY C6 corvette MM6 6 speed manual transmission. There are none of these available locally and can't find anything on the internet. Time to sign up over at the corvette forum I think.


Thanks!

Spent a few hours at pick-a-part today, have found a suitable steering column, swithgear and Nardi leather steering wheel for the meagre sum of $70 NZD (45 USD) - currently CAD modelling it into the final assembly.


Turns out I should have taken the tape measure with me - the standard subaru steering shaft is too long - but a grinder has fixed that. Now I have also have some MX5 and honda civic parts to "reconfigure" to make a frankenstein steering column that meets code requirements.

I love it.

Let me know what dimensions you need from the transaxle, and I will see what I can do. I started at TREMEC earlier this year, so I should be able to dig up some numbers.

Thanks for the shout out as well.

Ken

Thanks Ken, I really appreciate having your view on the project. Any info you can provide will be absolute gold.

I have been searching for the input shaft info for years, but corvette details are thin on the internet, even more so in NZ where C6 model parts are like chicken teeth - everyone has them installed in their cars.

I am at a critical point in the Tbox design, since I would really like to finalise the stress calcs and design of the custom spiral bevel pinions and crown wheel and all the associated bellhousings and the Tbox pumpkin. To do that I need to know the dimensions (and tolerances ideally) for the input shaft of a standard TR6060 MM6 transmission - as shown in the A, B C dims in the post above. I intend to make the TBOX accept a standard transmission. I did consider saving some wheelbase inches by using a custom input shaft, but now prefer the idea of "plug and play" with all the major components "off the shelf" where possible. By running the engines transverse they snug up nicely to the trans and I have a fair few inches of fore aft freedom as to the centerline of the engines vs the transaxle front plane. I want to minimise weight where possible, but also want to position the engines forward, yet not so much that the headers of the front banks roasting my kidneys! Having the standard input shaft length will freeze some critical positions in the layout.

Also am I correct that the spline form on the input shaft is a 26 spline involute form on a 1-1/8" Pitch circle. The MM6 input shaft will need to slide inside the crownwheel shaft so I will need to wirecut or broach the female spline form.

I also have quite a challenge making the oil seal between the "wet" pinion and crown lubrication system and the "dry" input shaft. I am hoping high pressure moly grease will resist fretting on the splines however 500ftlb of torque will windup the input shaft by a certain angle so some fretting will be expected.



I am looking forward to posting an image of my track monster in the same situation!

Cheers,
Marcus.