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Learning how to build Lotus Seven replicas...together!
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PostPosted: August 1, 2012, 7:34 pm 
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http://www.roadrunnerracing.net/the-roadrunner-sr2.html

There's not a lot of photos on their site - I stole these from their Facebook page.

Nice huh!!



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PostPosted: August 1, 2012, 11:47 pm 
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It's interesting, from both a ratio and strength perspective, that they're backing it up with the 7" Miata differential.

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PostPosted: August 2, 2012, 12:19 am 
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Driven5 wrote:
It's interesting, from both a ratio and strength perspective, that they're backing it up with the 7" Miata differential.



That almost is oxymoronic. Can the Miata diff take that kind of torque? I guess it doesn't matter, the tires will light up long before the pumpkin is subjected to anything close to 200 pound*ft.

Also notice the diagonal braces that go across the in-board CV's; there's a lot of triangulation going on back there. The cockpit/roll cage looks like it was designed by someone other than the whomever did the rest of the car.

I bet that thing hauls a$$ and takes no prisoners. (pun intended)

Tom

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PostPosted: August 2, 2012, 8:19 am 
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I realize there's a huge engine in the way, but does the engine bay look sorta flimsy to anyone else?


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PostPosted: August 2, 2012, 8:22 am 
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Driven5 wrote:
It's interesting, from both a ratio and strength perspective, that they're backing it up with the 7" Miata differential.


You mean that a 1700 pound car with a high output v8 motor might not need a 4:10 rear end? Unless of course it was participating in a tractor pull, or being used in a rail yard to tow around locomotives?

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PostPosted: August 2, 2012, 8:48 am 
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schwac2 wrote:
I realize there's a huge engine in the way, but does the engine bay look sorta flimsy to anyone else?


I'm amazed how lightweight the front control arms look. :shock: Then factor in the monsterous engine.... :!:

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PostPosted: August 2, 2012, 9:07 am 
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I'm amazed how lightweight the front control arms look.


Agreed! And the flanges they attach to as well. It appears the upper front mounts are single shear, "tabs" welded on the frame tube.

The cars are right-hand drive, and have the "bolted thru the frame rail" style shoulder harness mount that's common in the UK. If we assume these cars passed the MOT inspection there, perhaps they're much more solid than they appear. :?

Standard disclaimer: "I ain't no engineer!"
:cheers:

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PostPosted: August 2, 2012, 9:34 am 
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It appears the upper front mounts are single shear, "tabs" welded on the frame tube.
I had to do some searching. Thier website is new and looks like a startup-on-a-shoestring site with a lot of links and stuff not working well. Their facbook page shows a frame with double shear mounts. Plus photos of a frame in a garage, presumably their first manufacturing location...... :?:

Interesting construction on the upper caontrol arms out at the BJ adjustment. They added two perpendicular 1" long tubes just to mount the longer tubes?

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PostPosted: August 2, 2012, 11:41 am 
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Off Road SHO wrote:
Can the Miata diff take that kind of torque? I guess it doesn't matter, the tires will light up long before the pumpkin is subjected to anything close to 200 pound*ft.
Between the reduced weight and the likely traction limitations, I'm sure it will work...Now whether that's measured by individual feet or thousands of miles, is anybodys guess. :wink:


geek49203 wrote:
You mean that a 1700 pound car with a high output v8 motor might not need a 4:10 rear end? Unless of course it was participating in a tractor pull, or being used in a rail yard to tow around locomotives?
Yeah, something like that. Of course it also depends a bit on what exactly they're using for a transmission, rear tire size (diameter), and rev limit.

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Last edited by Driven5 on August 2, 2012, 11:52 am, edited 1 time in total.

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PostPosted: August 2, 2012, 11:49 am 
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You guys do know Ultralite is working on the same thing don't you? I haven't talked to him in a while, but I'd expect his is further along or better tested anyway.

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PostPosted: August 2, 2012, 12:24 pm 
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crafty wrote:
Nice huh!!
If you couldn't tell by now, critiquing other peoples and companies designs is one of the most popular pastimes on this site. :mrgreen:


rx7locost wrote:
Interesting construction on the upper caontrol arms out at the BJ adjustment. They added two perpendicular 1" long tubes just to mount the longer tubes?
Trying to avoid making any blind assumptions on strength, I figure that it's probably a concession to manufacturability. Two issues arrising from the angle of the arms are the sharply acute angle to weld and the extra length required on the camber adjustment tube that could be problematic to its design/functionality. I can't say that it's necessarily any worse than the bent ends commonly used which aleviate the acute angle and provide clearance around the coilover. However the design is different enough than what's proven to work for such applications, that it would make me a little uneasy...That general feeling of uncertainty is extended to the lower control arm and the way that the pushrod loads into it as well. But for all I know, they have the analysis and/or testing to back up the strength and use of these design.

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PostPosted: August 2, 2012, 9:43 pm 
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just goes to show that doing a cad and all that stress analisis is good at reducing tubes as well as adding them.

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PostPosted: August 2, 2012, 10:19 pm 
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schwac2 wrote:
I realize there's a huge engine in the way, but does the engine bay look sorta flimsy to anyone else?
You're right, it does. The upper rail specifically does seem to be missing the longitudinal triangulating tube that analysis generally shows to add a decent bit of strength...And the conundrum they face is that the output of that huge engine makes it all that much more important. Maybe they've done something we can't see well to make up for any lost strength from eliminating tubes from the traditional design.

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PostPosted: August 2, 2012, 10:38 pm 
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Driven5 wrote:
Maybe they've done something we can't see well to make up for any lost strength from eliminating tubes from the traditional design.


Engine as a stressed member?

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PostPosted: August 10, 2012, 6:55 am 
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Brunton Automotive has been offering the LS engines in their Stalkers. Very fast!

http://www.bruntonauto.com/

Scott


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