351 in a Lotus (Locost) 7 - Suspension design help

[hssss]

351 powered Lotus (locost) 7
I am about to start building the chassis for a Locost 7. I have a concern for front & rear suspensions. One driving standard is the use of as many production parts as possible. The running gear collected so far is as follows:

351W roller eng dry sump
McLeod (?) 2 disk 7" clutch and flywheel
Lakewood scatter shield
Cobra T5 with Kirban shifter
Either 9 or 8.8 rear end
Cobra front PBRs with 13" rotors and rear MK VII with Cobra hydroboost
95R wheels front 9" 255-40-17 rear 10.5" 315-35-17

The chassis will be built with the tub area being basically a cage using 1.50x.0625 as well as the upper and lower rails. All other tubing will be 1.25x16 gauge. The floor, trans tunnel, firewall, and rear firewall will be 16 gauge steel perimeter and plug welded. I haven’t decided on the side or rear panels yet. the tub area will be coated with a light coating of Linex inside and out to further bond the panels and seal against rust. I have found a guy that will do the glass in carbon fiber.

The primary questions are about the suspensions. The original is a 50+ year old design intended for less than 100hp. What I've come up with is to use a 3 link rear, much the same as the 05+ Mustang, which will be easy to package but I am not sure of the relationships. If I use lower links of, say, 18" how long should the upper be? How far from the axle centerline should they be? Are they long enough? What should the angle of the upper be in relation to the lower? The springs will be on top of the axle using a dirt track style jacking assy for adjustability. The shocks will be mounted as nearly vertical as possible. Lateral location will be a Mumford link.

The front suspension will probably be either Mustang II or SN95 spindles with coil overs and fabled A arms generally following the Mustang II setup. The Mustang II has relatively short lower arms, approx 13", but it seems like they should be around 15". It seems like you would want a bit of rising caster and camber. This is beyond my ability to engineer. Has anyone worked up a Mustang II suspension for a tube frame optimized more for handling than just as a way to hang wheels on a car?
Any help/thoughts would be appreciated.

[Norm Peterson]

7's are neat little cars. A couple of the guys who have been coming out to Philly Region autocrosses have Caterhams (one guy drives his to the events, with his race tires in a custom rack that's pinned to the rollbar!), and I've had a few peeks at it all. Without having done any numbers, I get the impression that the front suspension is a falling rate arrangement, though I'm not sure why. You'll get negative camber gain as long as your upper arms are shorter than the lowers and the upper arm is inclined downward toward the chassis more steeply than the lower is (this is the general case; I'm not recommending downward-sloped lowers as a static arrangement). Positive caster gain usually comes along when anti-dive is built in. It's definitely worth a couple of iterations to see how much roll you're actually going to get with such a light, low vehicle and see what combinations of camber gain, static camber, and camber gain from caster plus steering you actually need to put the outside front at a small negative camber while cornering hard.

I think that for 18" rear lowers, about 13" for the upper. I'm not sure just how a Mumford link behaves, so I'm not even sure if 18" is what you want. As the lowers get shorter they tend to exaggerate the variation in rollsteer over the range of suspension movement if the PHB/Watts link pivot/Mumford link/woblink/whatever doesn't rise and fall at a compatible rate, and with a light powerful car I think you want the rollsteer to be stable (lift-throttle oversteer can be rather evil). Do the lowers have any plan view convergence?

FWIW, I think the Rotus replica of the Lotus 7 used 14 gauge for the more powerful engines (up to the Buick/Rover aluminum 215 CID V8 IIRC). 16 gauge just sounds too light for good durability with a 500 lb cast iron engine on board. You'll be under 5 lb/bhp and 5 lb/ft-lb and have plenty of rubber, so a few more lbs of structural frame material shouldn't affect the performance much. FWIW, I've toyed around with the notion of a 289 into a Sprite . . .

If this tangential discussion gets split off into a separate thread, fine by me.

Norm

[David Pozzi]

I created a new thread for this topic.

[hssss]

Norm Years ago I lived in Black Horse, NJ and worked in Philly. I stoped driving the 914 into Philly because just when I thought I had memorized where the POT HOLES were, they moved them. Years ago I had a bugeye that I enjoyed thoroughly but was painful to drive, Im 6"5" and at the time was about 200lb. I had a friend that had a bugeye named shagnasty, 30 years ago, that had a SBF in it. It had Sports car Blue Streaks, BIG, and was about cube shaped. That thing would take off nearly as fast sideways as forward, and after about 3 blocks you could smell burning tennys.
One of the nice things about this project is that for the most part it is a clean slate. The length of the rear LCA was just a number thrown out because I believe that is what will fit inside the rear fender, this couild be made longer by a mod to the fender or divorcing the fender from the body. The other possible option is using a J bar.
The front seems like, if grabbing numbers, upper A arm 15"x8" at rest paralell to the ground with the back frame mount .5 from the ground higher than the front. The upper 13"x8" with both pickup points equadistant to the ground and the frame location 1" below the upper ball joint center.
Springs should be used to hold the weight of the car and sway bars used to control chassis roll.

Here is the standard chassis I would be building a +663 (width/length/heighth)
https://static1.pt-content.com/images/noimg.gif
https://static1.pt-content.com/images/noimg.gif

[Lowend]

Look here
http://www.wcmultralite.com/

[hssss]

I believe Ultra lite is out of buisness, could very well be wrong. I remember seeing thier prototypes and assets on Ebay a while ago.

This build is intended to truly be locost. I have most of the running gear laying around originaly intended to go into a heavily modded 88 Mustang LX, partly to keep my 93 Cobra stock. After consideration, I'm retired so my toy car dosn't have to be nearly as practicle, and building the Lotus 7 wouldn't be much more trouble than the level of mods I had intended to do to the LX. Since it is a clean sheet I wouldn't have to make any where as many compromises with the LC7.

The steel for the frame should cost about $250 for steel and in the spirit of Locost the sheetmetal will be nearly free, comercial shelving for the floor/firewall/trans tunnel/bulkhead and billboard galvanized for the sides ($25 per sign). The Stalker which is probably closest adding thier costs shows a build of just under 15,00, the Ultralite starts at 34,750. I hope to have no more than 4,000 in the LC7 and at the same time learn a lot.