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Learning how to build Lotus Seven replicas...together!
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PostPosted: November 19, 2007, 11:09 am 
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Joined: July 17, 2006, 3:09 pm
Posts: 271
Location: Holly, MI
This car is not a Locost design, but I am trying to make it as low cost as possible. I have made a few posts before, but to refresh everyone I am making a two seat, mid engine car for the track only. It will use a LSx engine mated to a Corvette C5 transaxle directly. The powertrain will be long, but it's much cheaper than a Porsche transaxle and stronger than an Audi box. All the suspension pieces will be pure Corvette.

On to the pics. First are some of the screenshots from the CAD model. After that are some of the pics from this weekend. I have made the lower cockpit outline using 1.5x3x.120 rectangular tubing. All the round tubing is 1.5x0.090 DOM. I am also utilizng sections of the Corvette frame in the rear so I didn't have to make the suspension mounts. Enjoy:

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Last edited by BB69 on January 2, 2008, 2:51 pm, edited 1 time in total.

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 Post subject: length
PostPosted: November 19, 2007, 11:00 pm 
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Joined: December 2, 2006, 7:17 am
Posts: 88
what's the length from the front of the engine to driveline/rearside of diff?
always wondered, does this bolt up to the rear without the torque tube?


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PostPosted: November 20, 2007, 12:14 am 
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Location: Charleston, WV
Wow, that's gonna be insane. :shock:

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PostPosted: November 20, 2007, 12:44 am 
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Joined: October 16, 2007, 8:53 pm
Posts: 135
Location: Lyle, WA
Interesting project. What’s the wheel base and track width? What are you going to do for the body? It’s kind hard to tell from the pics – are those solid motor mounts?


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PostPosted: November 20, 2007, 7:36 am 
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Location: Holly, MI
The overall length of the engine/tranaxle package is about 54". That is without any accessories on the front. The distance to the axle centerline is about 47". It all bolts up if you use the correct bellhousing. I found a guy over at pro-touring.com that did this for his Corvair. More recently, I found a kit car company that is using this powertrain for a Corvette GTP replica. The name is Mongoose Motorsports. I am supposed to visit them and take some pics of their car to get some ideas about how they packaged their design.

I expect the car to come in around 2000 lbs. A base LS1 engine makes 350HP, and I will probably add a cam and custome tune to get to about 400HP. I think that will be more than enough to make a good track car.

The wheelbase is my biggest concern right now. When I first laid everything out, it was close to 120". After talking with the guys at Mongoose, their wheelbase is 107". I talked with a guy that drives for them, and he confirmed the cockpit is pretty cramped. I moved some things around, and I think I can get mine down to 110-115". It's going to be long, but I like to compare it to an F1 car, which has a wheelbase of something like 125". :) The track width will be stock Corvette, 61-62" depending on the size tires I end up with.


I don't plan on doing anything for a body at the moment. There will be sheetmetal closeout panels and firewalls though. The engine is mounted hard to the frame the way it sits. This car will be strictly for track use, so I am going for stiffness over comfort.
Thanks for the interest.
Ken


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 Post subject: axles
PostPosted: November 20, 2007, 7:55 am 
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Joined: December 2, 2006, 7:17 am
Posts: 88
I wonder how much you can "cheat" the wheelbase by moving the rear hubs forward of the axle line and putting some angle into the cvs?


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 Post subject: Re: axles
PostPosted: November 20, 2007, 9:30 am 
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Location: Holly, MI
tigris wrote:
I wonder how much you can "cheat" the wheelbase by moving the rear hubs forward of the axle line and putting some angle into the cvs?


The guy I got the idea from is doing just that. He said a friend made him some CV joints that allow 2" of offset. I decided to use the aluminum subframe from the Corvette, so my locating points are pretty much locked in. I could move them and fabricate some new mounts, but that would defeat the purpose of using the subframe and the Vette frame rails. I guess I just determined it was better to save myself the hassle of making mounts than save 2".

The idea is definitely doable, and if I ever build another version I might go that route. It would depend on how the car handles.

Thanks
Ken


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PostPosted: November 20, 2007, 9:44 am 
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Location: Holly, MI
Here is another idea someone came up with to solve a similar problem:

http://www.gt40s.com/forum/gt40-tech-po ... ansmission

Ken


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PostPosted: November 20, 2007, 2:03 pm 
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Joined: December 5, 2006, 10:42 pm
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Location: Metro Detoit
Ken,

Who bent your cage? I'm thinking I want a ful cage on my Locost but I don't want to buy the stuff to bend it myself. I hope to get back to work on my locost so I can come out with 3BR for a track day or two this year.

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PostPosted: November 20, 2007, 3:13 pm 
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Location: Holly, MI
jmanz6 wrote:
Ken,

Who bent your cage? I'm thinking I want a ful cage on my Locost but I don't want to buy the stuff to bend it myself. I hope to get back to work on my locost so I can come out with 3BR for a track day or two this year.


Myself and two of my buddies did the bending. The bender is on loan from another friend, but he has allowed several people to use it. The guy that helped me get started with it bent up a roll cage and back half for his off-road Jeep and a rock crawler from scratch. He showed me how to set the bender up and made the first bend with me. Then, my other friend and I bent up the main hoop and top hoop this past Sat. I did the down tubes on my own. I only mention that because you can bend short pieces on your own, but not the long ones.

Here are some pics of the bender while we were using it. It is setup to mount in a trailer hitch receiver. It's a pain to get the truck level, but once you do, it works well. The only other problem is the tubing will hit the truck in some instances.

I can't speak for the owner of the bender, but we may be able to work something out. I am paying in beer for the bender rental. :D I am using a 1.5OD x 6" radius die right now. The Jeep guys have a 1.75OD die.

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PostPosted: December 3, 2007, 11:46 am 
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Joined: July 17, 2006, 3:09 pm
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Location: Holly, MI
I finally have some more CAD pics of the chassis. Right now, I am doing some research trying to figure out the most efficient use of tubing. When I say efficient, I want the chassis to be as stiff as possible, especially in torsion, for the lightest weight. The nice thing about US is it calculates the weight of the frame so I can keep track of how much the extra tubes are adding.

I found a link to a SAE paper on increasing the torsional stiffness of a NASCAR Cup car. It was done almost 10 years ago, but it's still relevant. When I read through the article, I realized the Cup car chassis is very similar to what I am designing. The paper analyzes every change they make for added stiffness and weight. It is serving as a great guide for me. Here is the link for anyone interested: http://www.ces.clemson.edu/%7Elonny/pub ... 983053.pdf

And, here are some pics of where I stand right now:

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In this configuration, the chassis weighs 173 lbs. I still need to add all the tubes connecting the main cockpit to the rear subframe; the side impact protection tubing; bracing for the front suspension area; cross-bracing for the lower frame rails in the cockpit; and the sheetmetal. I plan to make a single piece sheetmetal floor as well as front and rear firewalls. In addition to this, I am planning on bonding/welding sheetmetal between key tubes to make some vertical shear panels. From my research, these should add a fair amount of stiffness. I will try and get some pics of that this weekend.

On the side, I started making a balsa wood model of the chassis. I did this because I don't know how to use the FEA package on UG. It didn't take long to realize it will probably be easier to learn to use the FEA. So, that's what I am doing. It might take a while, but it will allow me to try a lot more ideas. The wife will be happy too, because there won't be balsa wood and glue all over the kitchen table.

Ken

PS. I am also documenting this build at my site. It has a little more background. http://www.3ballsracing.com/index.php?o ... 75&catid=3


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PostPosted: December 11, 2007, 2:53 am 
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BB69 wrote:
Here is another idea someone came up with to solve a similar problem:

http://www.gt40s.com/forum/gt40-tech-po ... ansmission

Ken


Pretty cool. The only problems I see with it are:

you lose about 5% of your power through the belts

and, that's a real maintenance item. You don't want one of those suckers let loose on you when you're putting the power down.


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PostPosted: January 2, 2008, 11:08 am 
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Joined: July 17, 2006, 3:09 pm
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Location: Holly, MI
Happy New Year to everyone. I used the new year as motivation to make some progress on the car. The two weeks previous to that were spent relaxing with family and friends. Now, it’s time to get back on track. Yesterday, I got two big things done. First, I moved the engine back about an inch on the motor mounts. The engine was just too close to the seat. I could have simply moved the seat further forward, but every time I move the seat forward, I reduce the legroom and the amount of room available to climb into the seat. Below, you can see the revised mounts. It wasn’t that much work, but I tossed the idea around in my head for a long time.

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The other major accomplishment was connecting the rear frame rail sections with the rest of the car. Once I made the decision to move the engine back, I figured I was all set to start connecting the pieces. I had a lot of plans to tie down the rear suspension and make sure it was all square to within millimeters. Then, I realized that GM doesn’t get it that close, and the main goal of this project is to actually get something on the track. So, I checked the rear frame rails to make sure they were straight and level, and started welding. I still have to attach the frame rails in a few more places, but at least now they don’t move too much. I will continue to check the position of the rear suspension as I add the other connections.

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A problem I was facing was how to attach the rear down bars to the frame rails. My chop saw would not cut the sharp angle easily. I had some cutoff pieces of rectangular tubing available, so I used them to mount the down bars. I still need to add some reinforcement, but I think it came out well.

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The Harbor Freight tubing notcher continues to do good work.

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With this done, I am now out of tubing. It’s time to head for the store and order some more so I can finish the rear section and start working on mounting the front suspension. While I am waiting on the tubing, I will try to get some more work done on the CAD model and FEA. I need to update the CAD model to reflect these down tubes as they are in a slightly different position.


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PostPosted: January 2, 2008, 2:30 pm 
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Joined: January 7, 2007, 3:24 pm
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Location: Visalia, Ca
Nice work on your tube fitting! I like the concept and your choice of drivetrain. I've been trying to figure out how to get that combo in a decent layout. Keep us posted.

Rod

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 Post subject: t56
PostPosted: February 10, 2008, 5:52 pm 
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Joined: December 2, 2006, 7:17 am
Posts: 88
Re-looking at this.Is that a t56 or auto?


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