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oldtin
oldtin Dork
2/18/11 10:12 p.m.

OK mechanical gods - thinking of a cycle car type of project - in my head it looks like an amilcar c6. What's the lightest diff/straight axle you can think of?

tincetti
tincetti New Reader
2/18/11 10:18 p.m.

The Model T speedster of my dreams uses a narrowed 105 series Alfa Romeo rear axle. Can some one help with a pic ?

m4ff3w
m4ff3w SuperDork
2/18/11 10:40 p.m.

aussiesmg
aussiesmg SuperDork
2/18/11 11:34 p.m.

I used one of these on my RX3 with a BP 13B 4 port making around 250 hp, it is light, strong worm drive style, center housing is aluminum, the axles tubes are sheet metal (which you can tweak to gain negative camber BTW), the diff is very light and the GTV2000 version has beefy bearings, it is an LSD which can raise the amount with shims and has disc brakes albeit with tiny pads. I adapted larger calipers to the stock 11" solid rotors

Good choice IMHO

modernbeat
modernbeat HalfDork
2/19/11 12:03 a.m.

Speedway engineering.

Speedway Engineering

The champion's choice, this specifically engineered unit is for smaller, lighter racecars. The Mini Stock Quick Change is the smaller version of our best-selling Super Max.

Features: > Aluminum 4 lug hubs (5-lug hubs also available) > ARP 1/2"-20 quick start studs (T or 3.5" available) > Aluminum rotor adapters to fit any brake package > Gundrilled premium axles standard > 3-inch OD .120" wall Chrome-moly tubes > Snouts are 4140 heat treated steel, heli-arc welded into position > Heat-treated lower shaft > 4.11 ring and pinion > Standard Spicer yoke > Aluminum 28 spline spool standard > Optional- Detroit Locker

Benefits: > NEW - Rear end pump retrofit kit available > Uses standard 6 spline change gears (Midget) > Aluminum hubs machined for back mounted rotor adapter

kb58
kb58 Reader
2/19/11 12:14 a.m.

A Datsun 1200 axle is a real lightweight and would work great assuming you aren't running high power.

DrBoost
DrBoost SuperDork
2/19/11 6:55 a.m.

I don't think a solid axle comes much lighter than this

tincetti
tincetti New Reader
2/19/11 7:10 a.m.

In reply to m4ff3w:

I guess I should of specified a pic of a CLEAN one

minimac
minimac SuperDork
2/19/11 9:11 a.m.

An old timer I knew from West-by-God-Virginia used the front end off of VW Bugs(old ones) for the front of his sprint car. He claimed they were strong, light, easy to fix, and cheap. I'd think any early(70s-80s) Toyota, Mazda, or Datsun/Nissan rear would be more than adequate.

Dr. Hess
Dr. Hess SuperDork
2/19/11 10:12 a.m.

I've got a Starlet axle under my work bench. Gearing is high, should be just right for a bike engine. I have ~$25 in it. You can have it for that. Pick up in NW AR.

Javelin
Javelin SuperDork
2/19/11 10:33 a.m.

SA/FB Mazda RX-7 is one of the lightest and narrowest solid axles that you can get with discs and an LSD.

dculberson
dculberson Reader
2/19/11 11:41 a.m.
tincetti wrote: In reply to m4ff3w: I guess I should of specified a pic of a CLEAN one

Your choice - one that's actually been in use or a clean one. It is Italian, after all.

modernbeat
modernbeat HalfDork
2/19/11 12:01 p.m.
Javelin wrote: SA/FB Mazda RX-7 is one of the lightest and narrowest solid axles that you can get with discs and an LSD.

Yes, but not as light as the Speedway I posted. Here's the modified RX7 axle in my old Seven.

erohslc
erohslc Reader
2/19/11 12:17 p.m.

I like the horizontal Watt's link. Many folks don't even realize such a thing is possible. Another Watt's trick is to mount the bell crank to the chassis, and connect the links to the ends of the axle housing.

Carter

DILYSI Dave
DILYSI Dave SuperDork
2/19/11 12:44 p.m.

FYI on Watt's Links - In traffic the other day i was stunned to see one under the dodge durango I was following. Turns out they came that way. So there might be a junkyard watt's setup out there for someone.

Wally
Wally SuperDork
2/19/11 2:26 p.m.

If space is an issue and you need a fair amount of travel you may want to look into a Jacobs Ladder instead of a watts linkage: http://www.spitzracing.com/index_files/Page724.htm

oldtin
oldtin Dork
2/19/11 4:39 p.m.

In reply to Dr. Hess:

That sounds like the ticket. Now I just need to figure out the GRM relay to Chicago. I'm thinking bike engine 75ish hp and keeping the weight under 600.

The speedway axle looks cool, but I'm guessing it's a titch more than $25

erohslc
erohslc Reader
2/19/11 6:57 p.m.

In reply to DILYSI Dave: Yes, Watt's link is also used on the PT Cruiser rear beam. It's an interesting variant in that the the top link is shorter than the bottom link.

http://chrysler.thenetlab.net/pt-cruiser/perform/feature5.html

It works OK tho', because the ratio of top linkage length to bellcrank length is same for top and bottom pieces.

Carter

Keith
Keith SuperDork
2/19/11 9:55 p.m.
modernbeat wrote:
Javelin wrote: SA/FB Mazda RX-7 is one of the lightest and narrowest solid axles that you can get with discs and an LSD.
Yes, but not as light as the Speedway I posted. Here's the modified RX7 axle in my old Seven.

Now that, ladies and gentlemen, is one low polar moment. Awesome.

I'd never considered a horizontal Watts linkage. But it would work, wouldn't it? You'd be limited in vertical travel and roll by the misalignment range of your rod ends, but unless they're really short (or your travel is really big) that's not really a problem.

Dr. Hess
Dr. Hess SuperDork
2/19/11 9:58 p.m.

In reply to oldtin:

Well, PM me if you figger it out. Chi Town isn't that far from here. About a day's drive. I bought a Europa there.

peter
peter Reader
2/19/11 10:37 p.m.
Keith wrote: You'd be limited in vertical travel and roll by the misalignment range of your rod ends, but unless they're really short (or your travel is really big) that's not really a problem.

I'm pretty certain I'm out of my league here, but Modernbeat seems to have sidestepped some of that issue by having the rod ends 90 degrees to each other - the outboard rod ends are limited by misalignment in the fore-aft direction, and the inboard ends in the vertical direction.

Frikkin sweet.

Curmudgeon
Curmudgeon SuperDork
2/20/11 8:12 a.m.

I've seen Modernbeat's Watts link pic before, very nicely engineered! FWIW, that type of rod ends have around 17-18 deg of angularity available and assuming that everything starts out horizontal the links are long enough that bottoming is a very remote possibility.

I got two stupid questions about the (awesome) car: First, it seems to be bike powered. What motor was used? Second, was there a reason it was built RHD?

peter
peter Reader
2/20/11 9:35 a.m.
Curmudgeon wrote: Second, was there a reason it was built RHD?

IIRC it was because the layout of the bike engine necessitated it being located mostly on the left hand side of the car. The driver was put on the right hand side to balance that out.

Keith
Keith SuperDork
2/20/11 11:32 a.m.
peter wrote:
Keith wrote: You'd be limited in vertical travel and roll by the misalignment range of your rod ends, but unless they're really short (or your travel is really big) that's not really a problem.
I'm pretty certain I'm out of my league here, but Modernbeat seems to have sidestepped some of that issue by having the rod ends 90 degrees to each other - the outboard rod ends are limited by misalignment in the fore-aft direction, and the inboard ends in the vertical direction. Frikkin sweet.

That just means you're equally limited in both directions to the lower limit - both ends of the rod will see the same misalignment, so the ones that bottoms out first is your limit. But it's not an issue unless you're chasing more articulation than is required by most road cars.

modernbeat
modernbeat HalfDork
2/22/11 8:46 a.m.

The engine in the Seven is a late 90s Honda CBR1000. And yes, it's RHD because the engine is positioned left of center when the output flange is centered in the chassis. To balance out the weight (it IS a competition car) the driver was moved to the right.

Lots more detailed photos: http://grassrootsmotorsports.com/reader-rides/528/

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