Thinking dangeouse thoughts, a Terrapin style single seater

[Adrian]

OK, I have no ideas if I’m really going to build something or not, but here goes with the history and questions. Warning, if you’re going to sit and plow through this I recommend grabbing a beer, a sandwich and finding a comfortable chair. My initial thoughts are long and rambling.

Let’s start with the background. I’ve wanted a 7 since I started attended British kit cars shows in the early 80’s with my dad. I lusted after Dutton’s, then the pre lit Westfield’s. Then in the mid 80’s I got an early edition of Staniforth’s of the ‘Race and Rally car source book’ The one with the case history of the 79-81 split chassis Gould Terrapin for those familiar with the book, and was smitten with the idea of building a single seater. As time progressed while still in the UK the financial reality just wasn’t there for either a 7 or a race car. I did run an old Davrian mkVI kit car for several years as my daily driver. That was fun when your eyes were the level of a Triumph Spitfires door handle! In 94 I moved to the US, I thought for 6-12 months, but somehow 17 years later I’m still here I’m a Citizen, married with kids and not going back! On an early trip ‘home’ I visited Westfield, Dax, Ginetta, OMS and Jedi who made small 500cc race cars. I was all set to order a Westfield when I decided to stay in the US permanently and bought a Mustang instead. Since then I had a series of fun cars for the road, autocross and even a season of road racing that would make heating your house by burning $100 bills in the fire place look like a good economy. I got Ron Chapman’s book when it first came out and daydreamed on and off about a 7 again. Then I got married, had kids and sold the toys, temporarily of course……NOT. Now several years later I’m on the verge (next year I hope) of having the time and a few spare $’s to rub together to play with cars again.

[Adrian]

So now I’m considering do I buy a project car (another Miata or an E30, 944 or Saab 900Turbo) or do I finally take the plunge and build a ‘Locost’. I decided long ago that a 7 isn’t for me anymore. Long gone are the days where driving the Davrian as an only car made total sense to me. These days ride, comfort, NVH and oh, yes, not becoming a pancake are far more important than the thrill of a tiny open car, especially in Michigan where some of the pot holes could swallow a ‘7’ whole never to be seen again. So If I’m going to build something it’s going to be a pure ‘race’ car. By race car I really mean a fun autocross car and track day vehicle that could be used in time trials or even hillclimbs (I started off doing sprints and hillclimbs in the UK before I moved here). Fun and safety is more important than competiveness. Having seen the lengths people go to in terms of effort and $$’s to win a bragging rights for missing some cones, I’m really not interested in seriously competing again. Back when I autocrossed every weekend I was a solid top 10% on PAX at a local level, but solid bottom 5% at a national level. And that was when a set of Koni’s, a front stay bar and two sets of BFG R1’s (costing less than $300 a set) was national level prep in autocross. Truth be told with lots of practice I’m solid midfield fodder at best, so why kill myself trying to have ‘the best’ car out there. Instead enjoy the journey.

So what would I build? Two options:

The first and less likely would be a Clubman’s / Mallock style car using a 1.6L Miata engine and box, RX7 GSL-SE LSD rear axle with 4 link and a panhard rod. 1.6L Miata front uprights etc.

The second, and more likely that I’ll expand on in my next ramble (yes there’s more of this diatribe coming) is a single seater in the style of the Staniforth's original Terrapin using a transverse engine and FWD gearbox. The primary candidates are a Focus with a 2.0L Zetec, an older Escort GT with a 1.8L, An Escort ZX2 with a Zetec, but the Mazda gearbox or possibly a late 80’s Ford Laser/Mercury Tracer with a B6. I would then plan on using the whole engine, gearbox and driveshaft’s with either the original FWD uprights/hubs, or in the case of the Mazda based offerings I think I could use Miata rear uprights as I ASSUME the driveshaft’s would have the same splines and fit the Miata units. The biggest issue with the Focus is I don’t believe that 13” wheels will fit over the stock brakes so that would be more work.

The thing is where to start with a possible design, especially as I haven’t decided to take the plunge. I’ve got a huge amount of ideas in my head that I need to get down on paper (well pixels). First to sort them out and second, every decision needs to be made for a reason and be defensible, not ‘just because’. So, if anyone is looking at this and cares enough. I’ll start with my assumptions in the next post and provide my thoughts and justifications for them. I’m looking for feedback so please, please, if anything I suggest looks wrong, sounds wrong or is wrong, let me know. I need the feedback.

[Adrian]

OK, thoughts and justifications of the layout:

1. Simplicity. To make this even manageable it needs to be as simple as possible. That means it’s also cheap and has a possibility of being finished before I retire!

2. To keep it simple that means the use as many standard unmodified components as possible. Hence the use of the standard driveshaft’s (which will dictate track width), uprights etc. Yes I could reduce unsprung mass by fabbing uprights etc, but that’s a no no to my simplicity, time or cost rules.

3. Ditto the suspension. I would use outboard springs and shocks. Yes aero, unsprung mass and rising rate would be better/easier with push rod suspension, but that is a whole magnitude increase in complexity. Outboard springs and shocks need one attachment on the lower wishbone and one on the chassis side. Two brackets and you’re done. Pushrods need an attachment on the wishbone, a pivot on the chassis, a chassis mount for the shock plus the actual bellcrank itself which involves several pieces of material, three bearings etc. This massively increases fab time and cost. There is one possible get out clause to this that I’ll come to later.

4. Why transverse not longitudinal? Simplicity and cost. FWD drivetrains are common and cheap. Both the B6/BP and Zetec family of engine have been produced in massive numbers and are cheap and plentiful as well as having a significant aftermarket for cheap parts, and massive enthusiast followings for knowledge. All are iron blocked and relatively heavy which is a down side. The Focus/Zetec has the possibility to upgrade as a unit to the all alloy Duratech which is lighter, but not yet as cheap/plentiful in FWD form. The newer 1.6L Duratec Ti-VCT from the Fiesta is too new to be cheap. The newer engines also have far greater electronic issues to overcome. The intention would be to use the full injection and ECU from the donor car (obviously with a thrifted cut down loom). Also LSD’s are cheap (relatively) for the MTX 75 gearbox on the Focus, there are LSD’s available for the Mazda box, but I’m not as familiar with them. An LSD would be a later addition.

5. Why Ford/Mazda not something from Honda or the evil empire (Toyota). Well my pay check has a little blue oval at the top with the letters F O R D inside it. Nuff said? Yes we sold Mazda, but the cars I’m talking about were all from the era where Ford and Mazda initially cooperated or Ford was a majority owner and they all came with Ford badges on the front so it’s in the family as far as I’m concerned. Yes the 4AGE is a great little engine and if a rusted out Mk I MR2 fell into my lap for pennies I’d probably use that and Honda seem to make great lightweight powerful engines, so if I could find something cheap enough I might cheat here too. I’ll ask questions about power plants in a separate thread over in the Engines and drivetrains forum.


So, next post let’s try and define and defend some hard points.

[Adrian]

1. Rear track. This is the defining dimension as by my rules it will be dictated by the FWD donor vehicle. Using the Focus that would be 58.8”, using the Escort GT or ZX2 that would be 56.5”.

2. Wheel base. This is defined by intended use, rules and the track wheel base ratio. The only rules I’d have to worry about is B mod, which has a minimum of 80”. Considering I need to fit into this thing and potentially drive it on tracks as well that’s way too short. My gut feel was 90-92” which is about 6-8” short than a Formula Ford, but they are longitudinal mount not transverse. Then I apply the standard rule of thumb of a track wheel base ration of 1:1.6 and lo it would come out as 90.4” for the Escort and 94” for the Focus. So gut feel is right in line with physics. I love it when a plan comes together. The exact wheel base would be refined based on packaging and how reclined the driver would be. My tendency would to be towards slightly shorter if a compromise is needed not longer. My thinking there is with a transverse engine and box, the polar moment is going to be higher than with a longitudinal engine as the mass is located closer to the rear wheels.

3. Roll center height. Now I don’t see this as being supercritical in its actual height above ground. I think with the layout and style of the car the C of G is going to be very low. The only negative impact on C of G is going to be the transverse engine trans combo which will be relatively high and possibly worse give a steep C of G axis, up towards the rear. Obviously I don’t want it too high for jacking reasons and I don’t want it below ground as that would lead to the need for very stiff springs. I’m thinking 0-2” in the front with the rear at 3-4” This is something I definitely want input on. I’m also concerned about the roll axis inclination. With the high rear C of G, do I need a higher rear roll center and steeper R.A.I?

4. For the front geometry I would go about it as follows.

a. Start with Miata, or whatever front upright I end up using. Locate where the lower ball joint would be located with the intended tires (I’ll come to those next) and track (See above). Then locate the inner wishbone as dictated by the chassis width (probably 20” plus the bracket) but at the same height as the outer. That gives me a plane X long, parallel to the ground.

b. Draw a line from the contact patch, through the desired roll center height (Start with 1” above ground then work from there as needed) to intersect with the LCA plane.

c. The upper wishbone outer is located in the same way as the lower, the inner would be located by drawing a line from there to intersect where the LCA and roll center line intersect.

d. Start with a UCA around 80% the length of the lower and see where the camber curve comes out.

e. Adjust as necessary

f. I would like to have very long swing arm lengths to help reduce roll center migration and to minimize scrub of the tires and they go through jounce and rebound.

5. For the rear I would follow basically the same process once I’d finished the front. Starting with whatever the final RC height came out at the front I’d start around 1” higher (Do I need a great roll center inclination, especially given the high rear CofG with the transvers engine?) I would also aim for a greater camber gain in the rear as there is no camber gain due to steering. Both upper and lower wishbones would have to be shorter due to engine packaging. This will also lead to greater roll center migration Is this an issue?

6. Bump and rebound. I’m thinking for now, with my target 2” ground clearance I’d aim for 1” bump and 2” rebound. That would allow for increasing ride height if needed.

7. Wheel frequencies, not sure right now, I’ll need to look into that. Suggestions?

8. Shocks, I’d want to keep cheap and off the shelf. I know motorcycle shocks seem popular and they might work depending on what I need for wheel frequencies. The issue I see is most M/C shocks only seem to have 1.5 – 1.75” travel which doesn’t sound enough to me. This is where I said I might cheat on my no inboard suspension. Some of them seem to come with a rocker already built, so it becomes much easier. The ratio seems to be around 1.9 – 2.0, so the 1.5” stroke suddenly becomes 3” which is what I was looking for. The next question becomes, is my desired wheel frequency (Which I have no idea on) close to the spring rate that would result, or close to it so I could swap springs and still be in the working range of the shock damping. This all sounds a little tenuous to me. Assuming I stay with outboard suspension, at the front I imagine I’d end up with something around 45° inclination of the shock which also needs to be factored in. At the rear I think I could get much closer to vertical due to the wider rear chassis, shorter wishbones etc. I also I assume I’d end up with some kind of minimal bodywork back there so aero would be less of an issue.

9. Caster and KPI, I’m open to suggestions, but would probably go with the stock Miata value.

10. Now wheels and tires are obviously key to defining the location of the spindle. My initial thougths were to use either FF1600 or FF2000 autocross sizes as B and C Mod is a popular classes and cast offs should be cheap. Checking on the Hoosier site shows that FF1600 fronts are 21” diameter and FF2000 fronts are 20.8” diameter, that’s only 0.1” difference in radius so no problem switching between the two. FF1600 rears are 22.6” diameter and FF2000 rears are 22.4” so again no issue in swapping. I then thought that I could possible use cheaper R comp DOT tires as well so again I went looking. In 13” R comps there’s a 205/60 at 22.8” and a 225/45 at 20.9. That’s awkward as the narrower tire is the larger diameter, not what I need. Then looking in 15” there’s 205/50 at 22.8” and a 225/45 at 22.9” That could work depending on my front ride height and camber curve. It’s just a though.

11. Initially wheels would be cheap steel (Diamond, Aero or similar) 13x6 fronts and rear for FF1600 tires or 13x8 for FF2000 rears. Yes they are heavy, but several D Mod ‘7’s seem to use them to good effect. Ditto if I went for the 15” DOT R comps.

12. Steering rack, that’s something that I think my life would be easier by getting a single seater or small buggy rack. I’d use that so I could set the tie rod length to be proportional to the difference between the upper and lower wishbones and set the height for zero bump steer. This is one issue I see with the Miata uprights, I’d love to have the steering arm at the same height as the upper wishbone so a)bump steer would be easy to calculate and b) the steering column would be above my toes making pedal access (heel and toeing) easier.

13. Steering column. I’m assuming just a straight steel bar. Do single seaters have a collapsible column? If so I would imagine an outer tube with a very close tolerance inner rod. The inner rod would have a long flat machined in it with set screws through the outer. This concerns me though. Again this is something I need advice on. The lower joint would be a UJ to suit the rack. The upper would be supported from a Heim joint.

14. The chassis from the roll hoop forward is relatively easy. Its job is to locate the suspension pick-ups, steering gear, my fat arse etc then tie it together with maximum triangulation and minimum number of tubes. From here back it’s a little trickier. The engine/trans is going to be wide for a single seater so the main chassis ‘rails’ will have to kick out. I’d plan on having the rear roll bar stays spreading out and locating near the rear shock pick up points. I imagine I’ll need a removable cross member across this point to facilitate engine removal. I’d probably plan on a diagonal across the rear as well, also removable. I’m concerned that the top of the engine bay would still be too open and flexible. I can picture all this, I guess I need to make some sketches.

15. Reading the GCR (9.4.5) it appears that the front and rear hoops plus side brace between the two can be 1.0 x 0.080” seamless, It might be easier to use 1.375 x .08”. It looks like the hoops have to extend to the ground, although I’m unsure if they sit on the chassis rails or go all the way to the floor level.

16. For the floor, bulkhead at the roll hoop plane, the front of the chassis and the plane of the pedals/master cylinder I was thinking of welded or brazed in 18swg steel shear panels rather than alloy paneling and triangulation. The reason for this is twofold. 1. You need something there anyway, but if you go for alloy paneling you still need to triangulate those areas, with a steel shear panel you do away with those tubes so I doubt it would end up much if any heavier. 2. Steel on the bottom give greater protection to the soft squidgy bit inside and increased abrasion resistance compared to alloy. The sides would be traditional riveted on alloy paneling.

17. As the heavy engine is going to be offset to the right, I’d place the battery and radiator on the left to counter that. This would be a balancing act and I’d imagine final placement would be decided once partly built so I can check weight and F/R Vs. L/R balance. I’d want them as far back as possible to help the cross weights, but as far forward as possible to prevent a too rearward C of G. Advice?

18. For the fuel tank I’m imagining a small fuel cell right behind the driver in front of the engine. When I say a fuel cell I’m talking a small (5 gal?) circle track cell not an FIA cell due to cost.

19. I’ve got some mental thoughts on upper bodywork, but that’s not important for now. Other than I imagine a plan shape somewhat like an old Brabham BT52 due to the wide engine and rear placement of the radiator etc. I was wondering about a full width/length under tray though to help the aero, this would be alloy not steel like the floor, supported by guy wires from the upper chassis rail to prevent it collapsing.

20. Aero. Initially nothing, later the possibility for front and rear wings. This will affect wheel frequencies and rate so has to be born in mind, especially with my concerns over M/C shocks.

Thoughts? Have I lost the plot or do I have the basics of an idea?

That’s about where I am right now. Please provide feedback, I have a thick skin.

[GonzoRacer]

Good morning Adrian-
Welcome to the forum. You've got an interesting discussion going there, although a bit one-sided so far. I think you can find other folks have followed some of the same paths you are considering, especially in the area of using a FWD/transvers driveline behind the cockpit for a middie. Look through the various builder's logs, you'll find lots of answers. There's even some fool building a "Mallock" type car with a Ford V8.

Meanwhile, to take up one small part of your discussion:

The biggest issue with the Focus is I don’t believe that 13” wheels will fit over the stock brakes [snip]

The thing is where to start with a possible design, especially as I haven’t decided to take the plunge.

You've got the answer to your question right there, although kinda hidden. The design of the chassis is dependent on the design of the suspension, which is dependent on the design of the hubs, which is dependent on the wheel/tire combination you're gonna use. There's at least a dozen ways to approach this problem, but I'd suggest picking a tire diameter that puts the hubs at a height you want to work with and work outwards from there. You can try to fit the wheels of your setup to the brakes on hand, or use the wheels on hand and get brakes to fit them. The "Locost" solution would be to use the brakes AND the wheels from the donor...

Clear as mud? Are you totally confused? Hearing whirring sounds in your head? Good, my work here is finished...

JD Kemp

*EDIT* Why is it that I never see my typo's until after I post???

[Adrian]

Good morning Adrian-

You've got the answer to your question right there, although kinda hidden. The design of the chassis is dependent on the design of the suspension, which is dependent on the design of the hubs, which is dependent on the wheel/tire combination you're gonna use. There's at least a dozen ways to approach this problem, but I'd suggest picking a tire diameter that puts the hubs at a height you want to work with and work outwards from there. You can try to fit the wheels of your setup to the brakes on hand, or use the wheels on hand and get brakes to fit them. The "Locost" solution would be to use the brakes AND the wheels from the donor...

Clear as mud? Are you totally confused? Hearing whirring sounds in your head? Good, my work here is finished...

JD Kemp

*EDIT* Why is it that I never see my typo's until after I post???

Thanks. Yes, I've kind of got that hidden in there. Essentialy aiming for FF slicks that's dictating a 13 x 6 / 8 wheels with a front diameter of 21" and a rear diameter of 22.5". The possibility of running 15" R comps would be a bonus, but 13" is a given.

I konw if I use Miata uprights I can package the brakes in 13" wheels no issue. The problem is, assuming the Zetec/MTX 75 is the most likely engine combo, would Focus driveshafts fit the splines of the Miata hubs? I'll measure the splines on some Focus driveshafts this weekend and post to see if by some 10,000,000: miricle they would fit Miata hubs.

To complicate matter further, I just happen to have a set of SVT Focus front hubs and driveshafts, but no brakes. So the real Q is, is there a bolt on caliper and off the shelf rotor that will bolt to the Focus hub and fit a 13" wheel?

BTW, I love your Mallockfor a couple of years now. I love the green

[Tom17]

Sorry I don't have anything constructive to say as I have not even started my build yet, but...

I just wanted to say welcome fellow "Brit over 'ere". Enjoy your stay! I've been reading, lurking & occasionally posting for a couple of years now, love the place!

Tom...

[Adrian]

Sorry I don't have anything constructive to say as I have not even started my build yet, but...

I just wanted to say welcome fellow "Brit over 'ere". Enjoy your stay! I've been reading, lurking & occasionally posting for a couple of years now, love the place!

Tom...

Thanks

[Adrian]

I mentioned Terrapin's, I think most people here are familiar with them. There's another transverse engined single seater that I loved watching in the 80's. Van Diemen built a class of car call 'Formula First' starting around 85 or 86 for a one make series. The concept of that was basically the front half of an outboard suspended FF1600, with a Fiesta XR2 carb fed CVH 1.6L engine and transmission at the rear. This is the car/series that Ben Collins that the ex Stig got started in. They produced frantic action packed racing. Sometime in the early 90's they changed the body work, then it died out. Most of the cars moved over to Scandinavia for a new one make championship called Formula Basic that is still running. Here are some chassis pictures I've trolled up from the Internet.

EEerrr, how do I post pictures from my hard drive??

[GonzoRacer]

EEerrr, how do I post pictures from my hard drive??

Look below where you type the message, there's a line of small text that says

If you wish to attach one or more files enter the details below.

And below that is the label "Filename", a blank space and a button that says "Browse". Click that button and navigate to the picture you want, click it and Bob's your uncle!

Thanks for the kind words regarding my Mallock build. This group has been great support, info, and guidance during the process. We've also uncovered several otherwise normal-acting guys who have a rather strong streak of insanity just beneath the surface. (And we know who you are, Marcus!)

[Adrian]

OK, I figured out how to upload pics. Please note these are all from here. http://formulabasic.com/ I realise they are all probably copyrighted so I've edited to link to them rather than upload them to here.

This is what a Formula First/Basic looks like.



Front chassis shot without bodywork



Rear engine bay



I can't imagine why I wanted this one here?

[Adrian]

I've found this picture here on the Locost forums for dimensions of the Ford Zetec, but I can't find anything on the MTX 75 box. Does anyone have one?

[Driven5]

A few drivetrain notes: The Miata uses 26/26 (inboard/outboard) spline axles. Both the Zetec and Duratec Foci use 26/25 spline axles. The Escort ZX2 uses 26/26 spline axles. And the Escort GT uses "24+2 Blanks"/26 spline axles. So it's at least possible one of the Escort's axles might plug into the Miata hubs and work...Maybe. The focus axles will not, although I suppose there is a slim chance the Miata stubs/axles could plug into the MTX75.

Also to upgrade the Focus Zetec drivetrain to a Duratec you'll need to replace the transmission as well, since they don't share a bellhousing pattern. And while the Zetec engines do run a little cheaper than the Duratec engines, for the nominal overall price difference I would strongly consider just starting off with the Duratec if planning to go the MTX75 route.

Will also try to provide some input to your boldened questions later.

[KB58]

I suggest doing some more thinking and reading before buying parts, since, well, you're still kind of "all over the place." You might want to check out my Kimini book; though it's a two-seater, it does use an OEM transverse FWD assembly behind the seats (and yes, I own Allan Staniforth's book, too.) I'm currently working on a new project and book which is basically a Locost with a transverse FWD lump behind the seats, but since you're doing a track car, the Kimini book's probably better suited. Best of luck - and do lots of planning!

[Adrian]

I suggest doing some more thinking and reading before buying parts.......!

Oh yes, I'm a long way from even considering shelling out my hard earned! That's why I'm here, trying to get help with organizing my thoughts and see what is really practical. It's funny, you can read and think you understand what's needed, then you try and organize the possibilty of actualy doing it in your mind and it's suddenly not so clear. I'm really looking for real world advice as to what is really needed and what will work with suspension geometry.