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Old 10-09-2013, 07:29 AM
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Graham08 Graham08 is offline
Master Fabricator
Join Date: May 2006
Location: Iron Station, NC
Posts: 1,800
Pavement Sprint Car Build

I've hinted at the existence of this project for quite a while, but never done a full blown build thread because there wasn't much building going on. Now that I'm working on it again, I'm going to start from the beginning with a proper build thread.

This build has unfortunately taken way too long. I started designing the car back in 2006, but building a couple customer cars, a move, building a new shop, and life in general have gotten in the way. Recently, I've started buying parts and reworking the design, so I figure it's time to start this thread to document where I'm at, and where I'm going.

Starting from the beginning, I had spent a season driving my previous sprint car against supermodifieds in the Midwest Supermodified Association back in 2004. I had zero previous driving experience, so the learning curve was extremely steep. I finally got up to reasonable speed, and proceeded to wad the car up like tinfoil at Mansfield Speedway.

Because the old car was a converted dirt car, it was heavy and not particularly stiff. It also had some rear suspension geometry gremlins that I needed to take care of. With the damage done in the crash, I figured it would be easier to start over, so the old car was scrapped.

When I started designing this car, my primary focus was on weight, stiffness, and a wide rear spring base. To that end, the plan has always been to run manual rack and pinion steering, which led to cantilever coil overs on the front end to package the rack. This also allowed the frame to be really short in the front, with the axle, rockers, and coils all mounted out in front of the frame.

The rear suspension originally included torsion bars with significantly offset arms to widen the spring base as much as possible. This is one thing that is changing as I work on the car because I don't want the headache of custom torsion bars, plus you're limited on spring rate by the diameter of standard bars (going to non-standard diameters gets expensive real quick).

With all that said, here are some pictures from the original construction process.

Unlike most "conventional" sprint cars, which are built as two sides in jigs, that are joined together with crossmembers and a motor plate, this car was built from the bottom up. This is a shot of the main rails and crossmembers from front to rear.

The frame table is my dad's. It consists of a large I-beam and square tube crossmembers. We made jigs to better locate the tubes in the front K-member and rear torsion tubes.

Here is a better shot of the front K-member. This car is built with the max allowable offset (4"). In this shot it looks a little goofy because the K-member is offset to the right so the cantilevers are centered on the track width. The centerline of the frame ends up offset 4" to the left of the center of the track width.

Here is the original configuration of the rear torsion tubes. I had originally planned to run 26" by 1-1/8" bars to get the possible rates higher than you can get with 30" long bars.

Here is another shot of the frame while the build was in progress. This is different from conventional construction because it has a main hoop in the cage, rather than some crossmembers that tie the two sides of the frame together. I feel like this gives the cage a little more structural integrity...but the normal way of doing things is also plenty strong.

This is the front of the frame while the build was in process. The front axle will eventually be located ahead of where the top rails bend downward.

I'll continue to add to this thread over the next few days to get caught up to the present time.
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