Lo-cost 101 (how do I make a cool Caterham replica?)

Zomby woof wrote:

kevlarcorolla wrote: Sorry can't seem to attach the link,Search "home built,bike engined autox toy".

Here's the link. http://grassrootsmotorsports.com/forum/grm/home-builtbike-engined-autox-toy/39878/page1/ Kevlar, your car has me inspired. I've been looking at it for months. My retirement project was going to be a tube chassis kit car, probably a Becks Spyder, but I like the look of your car so much, I might actually use the look for my own version. Probably Swift GT powered, of course. Thanks Mike,I think the 13b would make an excellant choice for a road based home built-with boost of course. Back to the shop,the "other" pretty much home built car needs to get finished-ice racing starts next weekend and I have so much to do.

geek49203 wrote: Just to lend some perspective here, the new 2012 Indycar will weigh about 1380 pounds total, of which at least 212 pounds will be in the motor (rumor has it that the current motors in testing are closer to 250). The new motors (2.2L) are supposed to be making about 575 hp. Now... without getting into the typical flame wars that have surrounded Indycar for decades (or being accused of being off-topic on my first post here), let me suggest that perhaps trying for sub-1000 pounds with car motors (assuming 200 hp or more?) is a great engineering exercise, perhaps it won't be "locost" and maybe just a bit much for a fun drive?

I think you hit it there, bud. Welcome to GRM.

I think the assumption that you'd need 200 out of a car motor is a bit on the high side. You don't need that much power to make 'em work. We have the DP-modified V8 Atom in town, and he's almost exactly as fast around our local track as Brandon in his R1-powered sub-1000 lb Locost - and the Atom has Hoosiers versus Nittos on the Locost.

Ah- you shouldn't be so modest- it was your (much heavier) car that Burt Levy compared favorably to a supercharged (300 claimed HP) Atom if I recall correctly?

And yours put down ~140 to the wheels if I recall?

Yeah, my 1250 lb car with 148 hp at the wheels was better than a supercharged "300 hp" Atom according to Burt. Faster, too. But he also noted at the Atom was fresh out of the box and not set up properly, and it turns out that "300 hp" in Atom-speak means about 225. The DP V8 car was properly sorted, which is why it's a better comparison.

Hey guys, I had been looking into a lowcost type car before I picked up my current project. way back on page 3 some guys were talking about subaru engines. This is what I'm putting in the back of my project so I thought I'd offer some info. the block is right at 30 inches wide, so I don't know how that would fit in the front of one of these. Howerver, the transmission options are wide open. Especially if you wanted to do a mid engine car. Look into the high end sand rail world and tons of those guys run subaru's mid engine bolted up to a vw, porsche or mendeola transaxle. they are cheap cheap hp. Right now you can get a twin turbo ej20 for $600.

zombie locust goodness!

Salanis wrote: I haven't heard about too many Nissan (240sx or Z-car) or BMW based Locosts, although I don't see why either of those wouldn't work.

Bad ideas. Baaaaad ideas. I know where there is a 240Z that has mostly biodegraded.

The neat thing about the 240Z is that the rear suspension is mostly self contained. There are no longitudinal links, just an H-shaped control arm and struts. Should be easy to package lengthwise, and make a simple yet stiff central tunnel based frame instead of a perimeter frame since ALL suspension/acceleration/deceleration loads will be going in through the middle.

Of course, an L24 would be all wrong for this, it would have to be a rotary with a 48 DHLA, because I have one of those.

One potential issue with a BMW-based Locost is the way the engine is slanted, so they tend to take up a lot more room than the usual upright engine and the engine cover ends up wider than the way a 7's is. Everything can kinda snow-ball from there and cn mess up the overall proportions.

Occasionally, I think I should build a Locost out of my 1800ES drivetrain. Wouldn't be the first, but in many ways it would be a fairly straight-forward build.

You know.... could instead use a Miata transmission/PPF/diff behind that rotary, reduce a lot of frame strength required since the engine and transmission would be supported at the ends, no loading in the middle...

I hate it when my brain starts working, sometimes.

(The original Lotus 7 weighed 975lb with an all iron engine. Shooting for sub-1000lb with a modern drivetrain is not a bad thing)

This thread has some staying power. One thing to keep in mind is that reported weights are much like fish stories and tend to leave out driver weight and all liquids.

I haven't visited this thread in a while and my mid-engine Midlana has been on the road for several years now. There's a book with complete plans and everything you need to build your own at www.midlana.com. It's an alternative to front-engine drivetrains and allows using widely-available FWD drivetrains mounted mid-engine.

Anyone built a v6 midlana yet? I'm thinking supercharged 3800....

Knurled wrote: You know.... could instead use a Miata transmission/PPF/diff behind that rotary, reduce a lot of frame strength required since the engine and transmission would be supported at the ends, no loading in the middle...

You'd need to fab your own PPF, the factory one is way too long. A Seven engine is set so far back that even in a +442 chassis with a Miata donor the driveshaft is about half the length of a Miata's.

(pretty sure the question that triggered this was 4 years ago...)

codrus wrote: You'd need to fab your own PPF, the factory one is way too long. A Seven engine is set so far back that even in a +442 chassis with a Miata donor the driveshaft is about half the length of a Miata's. (pretty sure the question that triggered this was 4 years ago...)

For someone thinking about building a frame out of 1x1 box tubing, and who has fabricated motor, trans, and rearend mounts for all manner of vehicles, shortening a PPF is absolutely trivial...

Knurled wrote:

codrus wrote: You'd need to fab your own PPF, the factory one is way too long. A Seven engine is set so far back that even in a +442 chassis with a Miata donor the driveshaft is about half the length of a Miata's. (pretty sure the question that triggered this was 4 years ago...)

For someone thinking about building a frame out of 1x1 box tubing, and who has fabricated motor, trans, and rearend mounts for all manner of vehicles, shortening a PPF is absolutely trivial...

Most Locost builders are using MIG and doing mild steel, the Miata PPF is aluminum and a PITA to weld. It's also pretty tricky to fit into the usual Locost driveshaft tunnels. Fitting it in the one I had would have required making the tunnel about 3-4 inches wider and a similar amount taller to have enough clearance around everything to actually install it.

In reply to Dusterbd13:

I really want to use a nissan vq. Even n/a they can put down some good power.

codrus wrote: Most Locost builders are using MIG and doing mild steel, the Miata PPF is aluminum and a PITA to weld. It's also pretty tricky to fit into the usual Locost driveshaft tunnels. Fitting it in the one I had would have required making the tunnel about 3-4 inches wider and a similar amount taller to have enough clearance around everything to actually install it.

I was thinking of just overlapping it and bolting it back together with four or six bolts. Do it as far away from the diff as is practical. Simple, effective, move on to the next problem.

I see the tunnel width as a good thing, give some elbow room I'm thinking of a central spine frame design anyway, you are going to need some width there to build good torsional strength. It doesn't need to be a bank vault, we're shooting for 1000lb so the tires will be small and light and the suspension will be fairly soft, but a little width is a lightweight way to get strength. Box the top and sides, bolt-on cover panel underneath, make the central tunnel a single formed tube.

It occurs to me that I'm describing a scratchbuilt 5/8-scale C5 Corvette without the transaxle.

The key is, actual Sevens had perimeter frame design because they were solid axle, the loads went into the chassis at the ends, so you put the chassis members out there. I'm thinking of a 240Z based suspension, which puts its loads into the chassis in the center, so the frame members should be in the center. In essence, the body can be as wide as it needs to be for interior room (to the limit of the track width), because its width is no longer dictated by the need to directly accomodate a rear axle's suspension links.

And here you will find me arguing in favor of an IRS over a solid axle, for the first and probably only time

In reply to Knurled:

One downside I can see to that is by concentrating the structure in the middle of the car, you lose some of the benefits of triangulation when the suspension mounting points are farther apart, thus requiring more material (and weight) for chassis strength.

The 240Z rear suspension concentrates all of its suspension loads into its subframe. That's the instigator of this idea. No loads go into the perimeter.

That's all there is to it.. with a PPF to take the diff loadings, all of the chassis loads go in through the little bit that the control arms mount to, fore-aft only. So the frame won't need to deal with bending loads, just tension and compression, which is a piece of cake for a straight tube mounted on-axis with those loads.

Cut the strut tubes off, make some simple tube A-arms, use motorcycle shocks, done.

Knurled wrote: (The original Lotus 7 weighed 975lb with an all iron engine. Shooting for sub-1000lb with a modern drivetrain is not a bad thing)

Given the fact that Alfa parts are all very light, one of the things that sometimes kept me up at night was using all of my spares to make a locost near 1000lb. Maybe even hybrid some techniques to stiffen an keep light....

I ran off and bought a Supra setup before thinking about brake size and tire fitment.

Im wont be able to fit 13" race stickys over the supra brakes.

I cant put smaller brakes on it to make clearance because it appears the upper ball joint will still be in the way.

Eh. 15x15 slicks solve this problem. Dirt track guys use that size, so they outta be cheap.

Oh! that makes me think of the G60 tires used on dirt modifieds.

Stock car pavement tires will be too hard, thats what the Banks guys were using (takeoffs from south sound speedway). They have switched to the G60 tire so they can get fresh rubber, they are faster than the pavement takeoffs. Pretty high minimum weight too (3300#).

I don't think those tires will be as sticky as the 13" tires used in EMod, also heavier (but street legal).

Im still hoping for a street legal EMod class...

You have to build the car around the tires, that determines how big your brakes can be and where your pickup points are on the frame to set chassis height. And also dictates what compromises you need to make for scrub and other geometry.

Taking all these things into consideration hurts my head, I'm convinced no matter what I build I will wind up cutting it up every winter (or sooner) to make changes until I am happy.

G60 may be what I'm thinking of. About 15 inches wide on a 15 inch wheel, 28ish tall? Have grooves/tread blocks all the way round.

Hoosier G60s

Those wide tires are either sprint car or late model dirt or Sprint/late model/super modified pavement tires.

The dirt tires come with a block pattern tread, pavement tires will be slicks.