Planning stage on my home built autocrosser ....

..... Current spec sheet .....

..... Will be updated to reflect current plans .....

..... VERY early basic info at this point .....

..... Last updated 14 January, 2017 .....

Single Seat, Tube Frame chassis. Track/autocross only, NOT street legal. Target weight approximately 1,250lbs without driver.

Engine: Mid-Engine layout, currently favoring Toyota 4AGE.
Transmission: VW 002 or 091(4?) Transaxle.
Fuel Delivery: Megasquirt EFI or dual carbs.

Front Suspension: Unequal length A-Arms, or derivative of. Rear Suspension: Possibly DeDion tube? Not 100% sure yet.

Brakes: 4-wheel disk.

Steering: Rack and pinion, non-power. Front-steer spindles and rack.

Due to rules set, will require either fenders or a full body. Currently leaning towards full body, with radiator and possible intercooler mounted either side of the driver.

Size and Weight Calculations: Engine/Transmission 400-450lbs including ancillaries and cooling.
Wheels Tires: 100lbs

Wheelbase: 2700mm / 106.3"
Track Width: 1675mm / 66"

Do I have to wait for post 2?

Honestly, half the reason I'm doing this thread is just to keep some documentation somewhere in order to keep things under control. But I for some crazy reason want to build my own tube frame car for autocrossing, and potentially some track time if it doesn't try to kill me in the cones. Timeframe is to start construction AFTER I make my 2018 run in One-Lap with my MR2. So a year of research and planning. I'll be updating the first post in this thread with current specs and concepts, as a sort of summary, but I have nailed down a lot of what I want from the car so far.

First thing I could use some advice from the hive on is which books are worth looking at. I have my 'wish list' at Amazon filled with books that I want to but, but from those who have built a car in this manner, which have you found most useful?

I've also decided that I want a Mid-engine layout, because I feel it will work better with a single seat cockpit. I have zero need for a passenger or co-driver. So why add the extra weight and aerodynamic negatives of a two seat layout?

Anyway, time to get the first post updated with my initial planning layout of this car.

Stampie wrote: Do I have to wait for post 2?

Ok, now that was funny.

The answer depends on your skill level and what you consider your areas of weakness. For generic advice: The KiMini and Midlana builds are good. The Goblin build on here is nice as well. Other than that I would read every build I can find on the locostusa.com forum.

MrJoshua wrote: The answer depends on your skill level and what you consider your areas of weakness. For generic advice: The KiMini and Midlana builds are good. The Goblin build on here is nice as well. Other than that I would read every build I can find on the locostusa.com forum.

The main area I need to focus on is suspension geometries. The basic plan is to first identify the major components that are going to define the chassis geometry, locate those 'in space', and then go into the chassis design after that. I just am not good enough to do a full 3D modelling of the thing, but it won't be a problem at all to do a 1/12 or so scale model first.

What I really want to avoid is doing design during fabrication, I'd very much prefer to at least have a workable drawing package to starting building from. I know there will be modifications as things progress but it's a lot easier to do that on paper than in steel.

I read through the Goblin thread a few times, and really like how it progressed. I really considered buying a kit for quite a while. But the more I get involved with things, the more it's just not what I wanted from a build. I'm looking for something lower profiled and about 500 pounds lighter if possible.

And might as well address the biggest piece of this puzzle right away too..... Engine selection.

I am very much NOT locked into any particular engine. A lot of it will come down to cost and availability in my area. South Dakota, particularly in my part of it, is very focused on the 'Big Three'. A lot of Pontiac's around here of all things. Fair number of Toyota's, but most other Japanese manufacturers aren't well represented around here. European stuff is very rare. Lots of Harley's, very few sport bikes.

Been leaning toward either using the 4AGE that'll be coming out of my MR2 eventually, or perhaps grabbing one of the many beater Celica GT-S's around here to snag the 2ZZ, particularly if it comes with a 6 speed. But I am very open to suggestions on engines. I know there's a lot of love out there for the 1.6 Ecoboost's, but too new and probably too spendy. What about the Duratec's and Zetec's? Not sure on controlling with a Megasquirt.

Being that light what is your planed power level? Even a light engine/trans combo will push 300lbs.

I agree with Mr Joshua that you need to go and read through a big pile of build threads on the locostusa forum.

If you're interested in a total weight of a thousand pounds without driver, then IMHO you want a motorcycle engine, not a car engine. This thread is a particularly interesting example of a BEC ('bike-engined car'): http://www.locostusa.com/forums/viewtopic.php?f=36&t=2142

As far as suspension is concerned, the easiest way is to take subframes with control arms off an existing car whose characteristics you like and attach them to your own chassis. I suspect that's unlikely to get you to your weight target, though, so another option is to carefully measure the geometry of an existing car and replicate the pickup points onto your own chassis. You can then either bolt on some donor control arms or build your own.

I'm not sure if you are near an Engineering School with a Formula SAE team...but I'd encourage you to check out those cars. They will have learned a lot of what you want to know and will be excited to share this knowledge with someone building a car for the same purpose that theirs are built for. I say this as someone who worked on FSAE cars in school and loved it.

If not nearby, I'm guessing there is lots of info on the web these days. We built our cars before social media ;).

Sounds neat and I hope it goes well for you!

My advice, having spent years studying, and having partially completed my compromised front suspension would be to buy a miata subframe, and build off that geometry. You can still do tubular A-arms,and your own subframe, just use the miata hard points. It is a known good design, and the details involved in designing a suspension can drive you crazy.

The above is an opinion, and worth exactly what you paid for it.

Trying to get sub 1000lbs is tough. At that point you are building something more similar to a formula car or amod car than a locost or Exocet. A lightweight engine is a must. So are light hubs, calipers, diff, shocks, etc. Amazingly enough I think that rules out most Miata parts.

I do think the Miata subframes are a crazy easy button for a midengine build. They mount on rails roughly 30" apart up top and IIRC 18" or so apart on the bottom. That's a 4 rail chassis that you can build with straight tubing and sit in the middle of. Put a bike engine or Subie engine behind you and go.

I agree that if you want to be 1000 lbs, an automotive engine is not your friend. I suggest that you take a look at the SCCA rules for Mod, Prepared and Street Modified classes and also take a look at the cars that compete at Solo Nationals, find something that really gets you excited then go in that direction. Build to the class you pick. The description of the car you want to build makes me think AMod is the class you are leaning towards. That's pretty hard core. Take a look at Street Modified, you can build amazing looking cars that can also be great for track days and even (maybe) street legal. Here's a photo gallery of the different classes: http://autoxpix.com/2016-scca-solo-national-championships/

loosecannon wrote: I agree that if you want to be 1000 lbs, an automotive engine is not your friend. I suggest that you take a look at the SCCA rules for Mod, Prepared and Street Modified classes and also take a look at the cars that compete at Solo Nationals, find something that really gets you excited then go in that direction. Build to the class you pick. The description of the car you want to build makes me think AMod is the class you are leaning towards. That's pretty hard core. Take a look at Street Modified, you can build amazing looking cars that can also be great for track days and even (maybe) street legal. Here's a photo gallery of the different classes: http://autoxpix.com/2016-scca-solo-national-championships/

I'm actually looking at NASA's TTU/TT1 class, which is wide open for the most part, and is all based on power to weight ratio with some modifiers for tires and chassis type. I'd like to stay just inside TT1 if possible. Figuring in all the applicable modifiers, my target is to keep the wt/hp ratio at right around 11:1 lbs per hp, including driver. Rules page was down for a few weeks while they were updating from 2016 to 2017, new rules appear to have just come out.

With around 150hp at the wheels gives me a target weight of 1650lbs, that includes @ 300lbs for driver, fluids, and fire suppression. So a dry weight of 1350lbs

Or, with 125hp at the wheel, gives me a dry weight limit of 1075 lbs.

-Hans

For what you have described, it sounds like a motorcycle engine is what you need.

Ian F wrote: For what you have described, it sounds like a motorcycle engine is what you need.

All depends on what I can find down the road. Kinda scarce around here in the sizes I'd be looking for.

Saturn LLO? but not sure about their transaxles.

How do they measure HP? You are going to want limited slip and decent gear spacing. That might be hard to find in that HP range. The transmission might be your driving factor in what engine you choose.

I have this book. You should look for a copy. It might be a good place to start.

Zetecs well soon be reaching the point of trying to hoard parts to keep the engines running without breaking the bank. Ford had already stopped supplying some parts such as a fuel sensor on the fuel rail.

That said they are not hard to find at junk yards as there are always a plethora of them available... For now. I guess it comes down to the point of how far down the road are you looking?

More good news is that one of the bigger names I know of in Zetec tuning is focus power (aka turbo Tom) who has already tuned many of these engines for roughly 15, 16 years using sct. (No need for aftermarket ecu, yay!) He's already got his name attached to a couple back yard garage rally team winners/scca winners. Michel sperber is the scca winner.

Bad news to him is that he can be a bit eccentric like the old school parts guy kinda way.. He's a one man band afaik so getting a hold of him can be difficult over the phone. I've had much better luck through email strangely...

For duratec I think mountune makes engines ready to go and I think offers tunes on them as well. Or you could build your own and have someone else tune it.

MrJoshua wrote: How do they measure HP? You are going to want limited slip and decent gear spacing. That might be hard to find in that HP range. The transmission might be your driving factor in what engine you choose.

Dyno tested on a Dynojet only, for the official rules. The local group may take a different approach, they did mention without a dyno sheet I'd automatically get placed in the TTU classing.

-Hans

hhaase wrote: ...What I really want to avoid is doing design during fabrication, I'd very much prefer to at least have a workable drawing package to starting building from...

Check out midlana.com then, the book contains complete plans of a mid-engine car using Miata uprights and a drivetrain of your choice.

[edit] just read you're after getting under 1000 lbs. It's doable with a bike engine and very little in the way of safety (SCCA role cage). Midlana went for a balance of both so it doesn't qualify if your weight goal is cast in stone.

Your going to be TIG welding a lot of Chromemoly tube for this project. Is that something you are good with?

For suspension, I would be camped out on a Lotus Elise forum. I hear rumors that they upgrade and sell stuff reasonably cheap. Either get the cast-offs or find out what they are upgrading to.

Been following a Lotus Elan build over on retro-rides. This guy wants to build the worlds lightest and fastes Elan. When it comes to weight, the word "obsesive" does not quite capture his devotion.

Be prepared for some fabrication work once mentally committed to the church of light weight.

Knowing what I know about suspensions (enough to be dangerous) I would not attempt to design one without some sort of computer program to validate my thoughts. I think there are a few affordable options without going all the way to a Solidworks seat. Once again, Locost forum is your friend. Good news is that, being a race car, the suspension travel will be limited and esier to keep in the zone.

NOHOME wrote: Your going to be TIG welding a lot of Chromemoly tube for this project. Is that something you are good with? For suspension, I would be camped out on a Lotus Elise forum. I hear rumors that they upgrade and sell stuff reasonably cheap. Either get the cast-offs or find out what they are upgrading to. Been following a Lotus Elan build over on retro-rides. This guy wants to build the worlds lightest and fastes Elan. When it comes to weight, the word "obsesive" does not quite capture his devotion. Be prepared for some fabrication work once mentally committed to the church of light weight. Knowing what I know about suspensions (enough to be dangerous) I would not attempt to design one without some sort of computer program to validate my thoughts. I think there are a few affordable options without going all the way to a Solidworks seat. Once again, Locost forum is your friend. Good news is that, being a race car, the suspension travel will be limited and esier to keep in the zone.

I have a few friends and neighbors that weld for a living, so I'm mostly going to be sizing and preparing the material, and have them do the final welding. But I'm leaning toward DOM instead of 4130 just because of the process complexity with 4130.

And you guys are right, car engines are NOT my friend here. Looking at the center of gravity, any kind of FWD transaxle is going to put the engine too close to the rear axle. So it's either got to be something with a VW/Hewland style transaxle that pushes the motor forward, or a bike engine. And hooooo boy those Hewlands are spendy.

Makes me start thinking about going back to an air-cooled VW, which is what started this whole thinking process, when I was looking at Formula Vee's for autocross use. Either that or a wasserbox.