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Home brew road racer

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Old 12-17-2011, 06:10 PM
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Home brew road racer

This thread is to chronicle the transformation of a very tired 83 Z28 into a very capable track day road racer with acceptable street manners. Even though most of this thread is about suspension modifications almost everything has been designed and fabricated by myself using little more than standard hand and power tools found in most home work shops. I hope you'll follow along and offer tips and advice as I'll be the first to admit that I am not an expert at any of this.

The car is an 83 Z that I bought after it had been wrecked. It was hit hard on the left side from the front wheel forward to the point that the frame horns ahead of the k-member were pushed to the right enough to put a small crease in the right front fender. A local body shop pulled the frame back square and the only parts I gad to replace were the left front fender, spindle and strut. I drove the car for a couple hundred miles but it smoked like a stove. A compression check revealed all the cylinders were less than 120 psi and a few were in the low 80s.




I have always wanted to build a track day car and think the third gen Camaros are one of the best looking cars GM ever made. They do however have some designed-in shortcomings that require correcting if any type of serious performance use is considered. The engine/ drivetrain in these cars is wimpy at best. The poor structural rigidity of the unibody is notorious and the front and rear suspensions are limited in their adjustablity and weight transfer.

3rd gens are very nose heavy. I was able to scale my car before I started on the project and total weight was 3208 lbs. This is with a/c. 700r4, full interior and the factory spare and jack. Front to rear was a perfect 60/40 split with 1900 on the front and 1308 on the rear. 3200 lbs isn't excessive for a street car or even a dedicated race car but the 60/40 split isn't good for either one.
This is something that I will try to correct when making the modifications buy trying to move as much weight to the rear half of the car.

This is a complete car make over where every major component will be modified or replaced with a a better component with much emphasis given to the suspension, drive train and unibody/chassis. To keep everything in its place and get repeatable, consistent measurements I designed and built the ramps the car is on. The ramps are 12ft long and 17in wide and the height is adjustable from 5in to 15in, to 20in. The ramps can be raised and lowered together one end at a time using a single 2 ton floor jack. I made movable plates that could slide along the ramps and special stands that bolt to the wheel studs to locate the axle/spindle wheel positions.
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Old 12-17-2011, 06:13 PM
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Re: Home brew road racer

I guess the photos didn't stick. I'll try again.
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Old 12-17-2011, 06:34 PM
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Re: Home brew road racer

This thread is to chronicle the transformation of a very tired 83 Z28 into a very capable track day road racer with acceptable street manners. Even though most of this thread is about suspension modifications almost everything has been designed and fabricated by myself using little more than standard hand and power tools found in most home work shops. I hope you'll follow along and offer tips and advice as I'll be the first to admit that I am not an expert at any of this.

The car is an 83 Z that I bought after it had been wrecked. It was hit hard on the left side from the front wheel forward to the point that the frame horns ahead of the k-member were pushed to the right enough to put a small crease in the right front fender. A local body shop pulled the frame back square and the only parts I gad to replace were the left front fender, spindle and strut. I drove the car for a couple hundred miles but it smoked like a stove. A compression check revealed all the cylinders were less than 120 psi and a few were in the low 80s.
Attached Thumbnails Home brew road racer-83-camaro-001.jpg   Home brew road racer-83-camaro-067.jpg  
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Old 12-17-2011, 06:40 PM
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Re: Home brew road racer

I have always wanted to build a track day car and think the third gen Camaros are one of the best looking cars GM ever made. They do however have some designed-in shortcomings that require correcting if any type of serious performance use is considered. The engine/ drivetrain in these cars is wimpy at best. The poor structural rigidity of the unibody is notorious and the front and rear suspensions are limited in their adjustablity and weight transfer.

3rd gens are very nose heavy. I was able to scale my car before I started on the project and total weight was 3208 lbs. This is with a/c. 700r4, full interior and the factory spare and jack. Front to rear was a perfect 60/40 split with 1900 on the front and 1308 on the rear. 3200 lbs isn't excessive for a street car or even a dedicated race car but the 60/40 split isn't good for either one.
This is something that I will try to correct when making the modifications buy trying to move as much weight to the rear half of the car.

This is a complete car make over where every major component will be modified or replaced with a a better component with much emphasis given to the suspension, drive train and unibody/chassis. To keep everything in its place and get repeatable, consistent measurements I designed and built the ramps the car is on. The ramps are 12ft long and 17in wide and the height is adjustable from 5in to 15in, to 20in. The ramps can be raised and lowered together one end at a time using a single 2 ton floor jack. I made movable plates that could slide along the ramps and special stands that bolt to the wheel studs to locate the axle/spindle wheel positions.
Attached Thumbnails Home brew road racer-83-camaro-014.jpg   Home brew road racer-83-camaro-015.jpg   Home brew road racer-83-camaro-012.jpg  
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Old 12-17-2011, 06:42 PM
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Re: Home brew road racer

This looks like a promising thread! I look forward to seeing the transformation.
-Phil
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Old 12-17-2011, 07:55 PM
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Re: Home brew road racer

The basic plan was to stiffen the chassis and provide solid mounting points for the suspension. With this in mind I decided to start at the rear of the car and do the replace the rear axle and suspension. I wanted to do away with the torque arm as it limits the choices on rear axles available and all are very costly. I also am a big fan of 3 link rears for their simplicity and wide range of adjustment. The criteria I was looking for in a rear end was some thing that was available from a wrecking yard, preferably with a posi and disc brakes and having a width between the 3rd and 4th gen axles. I seriously considered the 4th gen as they're a bolt in and the torque arm mount can easily be adapted to mount the upper third link. The often maligned 7.6 diff doesn't concern me much since this is a road race car and I won't be doing 5000 rpm launches at the drag strip. I have built and raced short track stock cars with the 7.5 in the metric monte carlos for several years and never once broke an axle or buzzed the teeth off a ring gear.

I searched through several catalogs that listed replacement axle shafts and tried to match up something that was close to the 3rd and 4th gens. What i came up with was the 8.6 axle assembly from the S10 ZR2. I've seen this mentioned a couple times on TGO but the general consensus from the responders was that it wasn't much different from the 7.5 and not worth the bother. Boy were they wrong!

The ZR2 axle is the same 8.6 axle assembly found in any 88 and up 1/2 ton GM pickup truck that GM modified to fit under the S10. These modifications consisted of shortening the overall length and making axles with the 5 x 4.75 bolt pattern instead of the larger 5 x 5 truck pattern. It is 1.5 inches longer axle flange to axle flange than the 3rd gen and has only the two leaf spring perches welded to the axle tubes. The ZR2 axles only came with 3.73 gears, a posi, disc brakes, and 30 spline axles. I bought mine over the web and paid $350.00 including the truck freight. I couldn't upgrade one component on my stock 7.5, 3.23 posi, drum brake axle for that amount.

The only disappointment I had was that they gutted the internal e-brake unit. I new I would have to get calipers and probably rotors but the e-brake stuff is a little harder to come by.

Here is what the ZR2 really is.
Attached Thumbnails Home brew road racer-83-camaro-010.jpg   Home brew road racer-83-camaro-027.jpg   Home brew road racer-83-camaro-035.jpg  
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Old 12-17-2011, 08:45 PM
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Re: Home brew road racer

i hope the thread is well received. I've been a rather casual member of TGO for a while now. Posted a few pics of my son's 84 Berlinetta that we built from a gutted shell but basically read and did a lot of research. Like most forums there is a ton of misinformation out there and maybe I can help correct a few mistruths with pictures and fact. The ZR2 rear axle swap is one of those.

I have a 40 year background in mechanics and automotive parts sales so I'm no novice. But Im not an engineer with CAD/CAM at my disposal or a racecar mechanic working at a fully equipped fab shop. There have been several outstanding builds posted over the last couple of years but almost without exception the the equipment and technology available for the build was far beyond what the typical guy at home has at his disposal. The most high tech tool in my garage is a Lincoln Pro Mig 135 110v welder. I want to show what can be accomplished on a budget, with pretty much common hand and power tools.

Planning is a big part of it. I have had this car since 2005, built the garage in 2007, the ramps in 2010. I spent many hours designing what looks to be very simple ramps. I even made a full size mock up in wood to find any problems that weren't apparent in my drawings. I went through many design changes and mock ups before I cut my first piece of steel. It starts with an idea, then some rough sketches, scale drawings on graph paper. a scale size or full size model and in the case of the ramps many many full size jigs, fixtures and patterns.

I hope you enjoy the thread and everybody please feel free to comment, question and critique.
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Old 12-17-2011, 09:40 PM
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Re: Home brew road racer

I live in northeast OH where cars rust out in a matter of a few years, but the 83 is from SC and is pretty solid. It is also almost completely original and unmolested for a beater. It still had the oem dual mufflers, tailpipes, heat shields,etc. Other than some replacement rear shocks and a welded-in cat the bottom of the car was vintage 83.

Pics of the bottom of the car show some of the 3rd gens design short comings when it comes to high performance modifications and or driving. The torque arm, drive shaft and exhaust mid pipe all have to pass through a very narrow trans tunnel. Because of the floor pan design there is no room to run dual exhaust and even running long tube headers and a custom y-pipe is a major project requiring custom trans crossmembers and other fabrication. I've look at over a hundred post on dual exhaust and few of them really have adequate ground clearance.

The 15.5 gallon fuel tank mostly sits above the rear axle center line. Not only do you have to totally disassemble the back of the car to get it out, its also the wrong place to put a 95lb block of weight if your looking for improved handling.

Also if you are lowering the car to close the gap between the top of the wheel opening and the tire you have to cut up the inner sub frame around the spring area to clear the axle tube and sway bar mount. The lca angle is pointing down to the front so relocation brackets are needed.
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Old 12-17-2011, 10:08 PM
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Re: Home brew road racer

Modifications to the back of the car are going to include replacing the stock 7.5 axle with the ZR2 8.6 axle assembly, designing and building an adjustable 3 link suspension and panhard bar, installing adjustable coilovers and installing a 15 gallon fuel cell behind the rear axle.

Her are some pictures of the car before any work was done, getting the location of the stock rear axle located on the ramps, and the stock ZR2 set in place for a trial fit. You can see how the movable plates and axle stands allowed me to remove the original axle and install the ZR2 in the exact same location. The axle stands move in and out in a channel keeping the axle centered as the original but adjusting for the extra width of the ZR2. It worked just like I had hoped it would. Its great when a plan comes together!
Attached Thumbnails Home brew road racer-83-camaro-007.jpg   Home brew road racer-83-camaro-023.jpg   Home brew road racer-83-camaro-042.jpg  
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Old 12-17-2011, 10:22 PM
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Re: Home brew road racer

Following also.......
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Old 12-17-2011, 10:40 PM
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Re: Home brew road racer

One thing I didn't point out in the last post is that the car is sitting at factory ride height. The distance to the bottom of the rocker gfx is 9 3/4 inches. You'll notice in the picture of the stock diff that the bottom of the brake drum is just about even with the bottom of the rocker. The gap between the tire and top of the wheel opening was about 3 inches with distance from the top of the wheel opening to the ramp at 28 7/8. I've set the targeted distance to the top of the wheel opening at 26 inches and will be running a 25.5 to 25.7 tall tire.

Even with the body at stock height there is only about 4 1/2 inches between the top of the axle and the snubber mount. to lower the body 3 inches is going to require some serious metal work to the rear sub frames. Thats ok because mini tubs were also part of the plan. I mentioned the diameter of the tire i'm using but the actual size is 275/40R17 on 17 x 9 wheels with 6 inches of back space. I am hoping to get enough space to fit a 295 or even a 305 tire on the rear for track outings and use the 275 on the street.

Here are some pics of the stock tire and wheel on the ZR2 axle.
Attached Thumbnails Home brew road racer-83-camaro-043.jpg   Home brew road racer-83-camaro-046.jpg   Home brew road racer-83-camaro-045.jpg  
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Old 12-17-2011, 11:56 PM
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Re: Home brew road racer

Originally Posted by 83RDRACR View Post
3rd gens are very nose heavy. I was able to scale my car before I started on the project and total weight was 3208 lbs.
Don't forget when you scale a car, you must have driver weight behind the wheel for an accurate weight. Adding that 170+ pounds to the left side of the car can really throw that scale weight off. Scaling also isn't just front to rear. All 4 corner weights need to be taken for a side to side scale.

Although my car isn't designed for road racing, it's still nose heavy and with a good suspension setup, it doesn't stop me from carrying the front end past the 60' mark.
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Old 12-18-2011, 12:02 AM
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Re: Home brew road racer

Originally Posted by 83RDRACR View Post
..... the tire i'm using but the actual size is 275/40R17 on 17 x 9 wheels with 6 inches of back space. I am hoping to get enough space to fit a 295 or even a 305 tire on the rear for track outings and use the 275 on the street.

Here are some pics of the stock tire and wheel on the ZR2 axle.
To run those tires sizes on the ZR2 wider than stock rear axle, you won't need to mini tub it.

Last edited by BlackenedBird; 12-18-2011 at 12:20 AM. Reason: typo fixed
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Old 12-23-2011, 02:20 PM
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Re: Home brew road racer

Originally Posted by AlkyIROC View Post
Don't forget when you scale a car, you must have driver weight behind the wheel for an accurate weight. Adding that 170+ pounds to the left side of the car can really throw that scale weight off. Scaling also isn't just front to rear. All 4 corner weights need to be taken for a side to side scale.

Although my car isn't designed for road racing, it's still nose heavy and with a good suspension setup, it doesn't stop me from carrying the front end past the 60' mark.
Good point about the driver being in the car. I scaled it without the driver for the sake of comparison from stock configuration to my modified car. Final scaling with the driver will be done after the car is mostly complete.

As for the rear traction issue the stock suspension can be helped out with the LCA relocation brackets. I would assume your car is a 4 link with a good amount of anti squat dialed in. the steep upward angle of the lca's force the body up and the axle down on acceleration but that same angle creates a ton of roll steer when the body leans in a corner.

The 3 link I designed is very adjustable from 0% to about 80% anti squat and will probably run it at 10% for street and open track duty. I also made the lca's as long as possible with the center to center distance at 23.5in. compared to 19in. stock. This will also help reduce roll steer.
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Old 12-23-2011, 02:32 PM
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Re: Home brew road racer

Originally Posted by BlackenedBird View Post
To run those tires sizes on the ZR2 wider than stock rear axle, you won't need to mini tub it.
Here are a couple shots of the 17x9 wheel on the ZR2 axle with it centered under the car. Remember the ZR2 is only 3/4 in. wider per side than the stock 3rd gen axle. As you can see I'm about as far out as I can go and clear the wheel lip when cornering. The inside clearance is a little tight around the bump stop area and would require some trimming and reinforcement. A 17 x 11 wheel with 7 or 7.5 back space won't clear without a mini tub. My 3 link is going to require me to remove the factory rear subframe to at least the rear axle center line so mini tubs were in the initial plan.
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Old 12-23-2011, 06:32 PM
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Re: Home brew road racer

My mods include some major floor and frame mods but the following pics show how well the ZR2 axle matches up with the stock lca locations. It would be easy to use the stock brackets from the 7.5 axle or premade bracket for rod ends for more tire clearance.
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Old 12-23-2011, 06:51 PM
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Re: Home brew road racer

Because I wanted to use the longest possible lca, cutting out the factory frame brackets and part of the rear floor was required. I started with just removing about a foot wide section as I wanted to keep as much of the rear sheet metal intact. My plans were to make a 2x4 rear crossmember to locate the front of the lca's and provide a strong base for the main hoop of the roll cage.

I also decided to secure the body to the ramps to 1, support the body and 2, keep it from moving so that all future measurements were consistent. I cut some 2x3 tubing for stands and tack welded them to the rocker pinch weld and welded them to the ramps. This holds the body at the factory ride height of 9 3/4 inches.
Attached Thumbnails Home brew road racer-83-camaro-054.jpg   Home brew road racer-83-camaro-057.jpg   Home brew road racer-83-camaro-062.jpg  
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Old 12-23-2011, 07:11 PM
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Re: Home brew road racer

The sheetmetal that makes up the inner surface of the rocker is incredibly thin. I miked a section of it at .028" and that includes the paint on both sides! In order to weld the crossmember to the inner rocker I had to increase the thickness of the steel at the weld area by using 6 x 6 x .125 steel plates. My Pro 135 welder wanted to burn through the thin metal of the rocker when it was at a heat setting high enough to burn into the thicker plate. To solve this I first welded slightly larger pieces of .060 sheet steel to the rockers and then welded the .125 plates to the .060 sheet steel.

There is a real nice thread from a Candian member who chronicled the the install of a full backhalf and 4 link done by Sandales Performance. I used the pictures from that thread to guide me in design and placement of my crossmember and lca front brackets. I don't have a TIG welder so mine isn't quite as pretty but it is very solid.
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Old 12-23-2011, 07:34 PM
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Re: Home brew road racer

Facinating stuff....I intend on following.

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Old 12-23-2011, 07:39 PM
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Re: Home brew road racer

even though i measured twice, actually 4 or 5 times, when it came time to mark the tubing for the crossmember I mistakenly marked the cut at 54 3/16 instead of 54 7/16 so my crossmember was 1/4" short. After kicking myself a few times I cut the crossmember in half since i would be cutting out the center anyway for the drive shaft to pass through, and fit into the car. I kept it straight and true by tack welding 1/8" angle iron to the bottom of it. i ran a string from the pinion flange to the transmission tailshaft and was a little surprised at just how much the drivesfaft runs off-center in the tunnel.
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Old 12-23-2011, 08:18 PM
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Re: Home brew road racer

The next next step was to figure out just where to place the front lca brackets on the crossmember. although I'm not big on body work and customizing I want the exhaust to exit through the rocker panel behind the door. I am going to raise the front floor pan so that I can tuck the exhaust up flush with the bottom of the pinch weld and also I think it looks cool. It also is going to dictate where the lca's mount. I made some scale drawings on graph paper based on the mufflers I want to run and came up with a distance of 9" in from the point where the crossmember meets the rocker. I marked this on the crossmember and with some string and a small square transfered the point to the rear axle.

I took the axle from the car and cut all the brackets off the axle tubes. Having already graphed out my rear suspension design I knew I wanted my rear axle lca mounting point to be 7 inches below the axle center line. i looked in various catalogs and came across some brackets from Allstar Performance that I thought would work. The only problem with using these premaid brackets was that the ZR2 axle has 2 5/8 dia axle tubes and all the brackets are made for 3". I solved this problem by splitting a section of 2 3/4 od tubing with a 3/16 wall thickness and hammer forming it to conform to the 2 5/8 od of the axle. i clamped the 2 halves around the axle tube with hose clamps and tacked them together at the bottom leaving a gap at the top. Now I had a 3" tube to weld my premade brackets to.

By leaving the hose clamps on I could position the brackets both laterally along the tube and radially around the tube so as to square and plumb.
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Old 12-23-2011, 08:42 PM
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Re: Home brew road racer

With all the fabrication your doing including the table you build to build the car on, it certainly looks like you have the skills to build your own LCA mounts instead of buying some.
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Old 12-23-2011, 09:48 PM
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Re: Home brew road racer

With the axle back under the car it was apparent that most of the back seat sheet metal would need to be cut away. I cut away everything up to the start of the flat area over the rear axle. Because I knew I was going to mini tub the car I cut the inner fenderwells out also. To simulate the coil overs that also mount to the lca axle brackets I fabbed up a simple shock using 1/2" I bolts. Knowing the space I had to work with let me pick out a QA1 coil over with a median ride height of 15 1/2". I made my shock substitutes to this dimension and tack welded an upper mount.

The axle brackets are actually backwards and swapped side for side as I wanted the shock to be as close to the wheel as possible for better control. The brackets were designed to place the shock behind the axle but I didn't want to run into interference problems with the panhard bar.

Now that I had a clear shot to the crossmember from the rear axle I could fab up the lca's and the front brackets. The lca's are a combination of 19", 3/4 swedged steel tubes from Allstar and QA1 XM chromemoly rod ends. center to center is 23 1/2". For the front brackets I used Comp Engineering 4 link brackets. These are one piece brackets designed to mount both the lower and upper arms on a 4 link drag car set up. I cut them up and fitted them to the front crossmember making sure that the position of the lca could be changed without readjusting the length of the rod.
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Old 12-23-2011, 10:14 PM
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Re: Home brew road racer

Originally Posted by BlackenedBird View Post
With all the fabrication your doing including the table you build to build the car on, it certainly looks like you have the skills to build your own LCA mounts instead of buying some.
Skill, maybe, but to take all the measurements, make some mockups, and then transfer everything to metal takes a lot of time and I have to worry about making both sides identical. Also I'm working with a chop saw, a 4 1/2" cut off wheel, and a sawzall, there is no plasma cutter or operating cutting torch here. The brackets that I found fit my design almost to a "T", all I had to do was drill the bottom hole where the lca would actually mount.
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Old 12-24-2011, 01:47 PM
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Re: Home brew road racer

Where in northeast Ohio are you? I live in Cleveland and have a few ideas of my own maybe we can get together some time and work on the cars.
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Old 12-26-2011, 10:39 PM
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Re: Home brew road racer

With the the lca's in place the next step was to mount the 3rd link. With my target ride height 3 inches lower than stock there isn't a lot a room above the differential so my top mount can't extend much higher than the top of the diff if I want to get 3 to 4 inches of clearance above it.

Using graph paper drawings I determined that the top mount on the differential should be about 20 inches from the ground. The bar will be horizontal at this height and will be adjustable downwards at the front to allow for more anti-squat adjustment without having to resort to setting the lca's at steep upward angles. At a height of 20 inches the upper link mount has to nearly lay on top of the differential case.

It took a little head scratching, several designs and drawings but I finally came up with what I think is a fairly efficient design. The front mount is mounted on top of the rear rear drive shaft loop that is mounted into the rear crosmember.. I had a local weld shop bend the hoop out of .125 wall 1 3/4 dia tubing with a tight radius that gave me about 6' inside the legs, perfect for a 3" driveshaft to pass through. The rear mount is also heavy wall 1 3/4 tube that I welded to brackets that I made. Not knowing just where the tubing would attach to the brackets I left the brackets a little long. I'll cut and profile them when everything is in place.

The actual rear mounting brackets for the rod took a lot of thought and several poster board cutouts to come up with the final design. These brackets and the multi-hole front brackets for the top link were made from leftovers from the four link brackets that I made the front lca mounts out of. Also, like the front lca brackets the top link position can be moved from hole to hole without having to adjust the rod length.

You'll notice that the actual tube for the top link has been cut and spliced back together. I wanted all the links in the rear to be the same length so I only need to keep one spare on hand. The lca's are made from 19" tubes and When I went to do the top all they had was a 21". I cut it to length and pressed a 3" long piece of tubing inside and pressed the two pieces together leaving a very slight gap between the two halves and welded them back together making sure I had good penetration in the inner and outer tubing. I also drilled 4 holes in each half and plug welded the inner tube to the outer. It is probably stronger at the weld than the original tube but I will get the correct one made up and keep this for a spare.
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Old 01-01-2012, 09:58 AM
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Re: Home brew road racer

i am really liking the creativity (s10 rearend cheaper than a 9") to get it done you have got my attention in this build looking forward to progress!
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Old 01-01-2012, 10:51 AM
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Re: Home brew road racer

After I had the upper and lower control arms mounted I raised and lowered the axle housing through its travel several times to make sure the geometry of the arms didn't cause any binding. It moved very smooth and at least visually the pinion angle didn't appear to change much.

With the arms located it was time to move on to the coil over mounts. For the best suspension control you want them both located as close to the wheel as possible. When I located the rear axle I had the shock location vertical much like factory. The coil overs however forced me to tip the shock in about 10 degrees to make sure the ere would be no interference with the tire and the coil over spring.

I had to make an upper frame section that would tie into the existing subframe above the rear axle and then connect that to the 2x4 crossmember that ran between the rocker panels. The height of the inside of the boxed area above the factory spring perch turned out to be a very convenient 3". I drew up plans for a top frame that consisted of two short frame extensions that would tie into the factory sub frame and a lateral section that would connect the two rails together at the front.

While I was planning out the design of the rear frame I had the good fortune to come across a fair amount of 2x3 x .125 mild steel rectangular tubing. A local, semi pro body builder was selling off some of his weight lifting equipment at a yard sale. One of the items was a large squat rack. The tubing from that rack is what the rear frame and future SFC's wil be made of. Like I said at the beginning this build is in a budget.
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Old 01-01-2012, 11:45 AM
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Re: Home brew road racer

man thats some good info on that zr2 rear. i wonder how well it holds up to high hp applications. probably a lot better than the stock 10 bolt. i look forward to seeing where this build goes.
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Old 01-01-2012, 09:30 PM
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Re: Home brew road racer

Originally Posted by travis401 View Post
man thats some good info on that zr2 rear. i wonder how well it holds up to high hp applications. probably a lot better than the stock 10 bolt. i look forward to seeing where this build goes.
The 8.6 from the ZR2 or any 88 and up 1/2 ton GM pickup is actually an improved version of the old 8.5 rear end. I think it has larger OD carrier bearings. It takes the same posi units and gear sets as the 8.5. The best improvement you can make to this or any GM axle is to replace the factory crush sleeve with a solid pinion spacer. Even though a standard crush sleeve can take a few hundred lb/ft of torque to set the initial pinion bearing preload (usually rated as inch pounds of drag) it takes much less to continue to collapse the crush sleeve. Think of crushing a pop can. Repeated hard launches with high HP cars with sticky tires can actually over crush the sleeve and allow the pinion to move for and aft a little with disastrous results.
The latest issue of Car Craft magazine ,March 2012, has an article about this very modification.

Another upgrade would be to install an aftermarket aluminum diff cover that has the load bolts that preload the carrier bearing caps. Add in a set of C-clip eliminators and a set of aftermarket axles and I don't see why an 8.6 couldn't handle 500hp at the flywheel.

The 8.6 axles are in every 1/2 ton GM truck built since 1988 both 2WD and 4x4 models with the 4x4's having a 6 bolt lug pattern. These axles are dirt cheap in the bone yards and many come with posi's and taller gear ratios. They are a bit long but if you have the axle tubes cut down you can replace the bearing ends with 9" ford ends and do away with the c-clips and/or the c-clip eliminators.
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Old 01-01-2012, 10:08 PM
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Re: Home brew road racer

The last group of pictures I posted shows the shocks moved in 4" from the outer edge of the frame rail. After reinstalling the wheels and remeasuring I only had to move the shocks in 1 3/4" with a shock angle of about 8 degrees. This is much closer to what I had envisioned.

I used some more of the weight bench tubing to make the frame kick-ups that connect the new crossmember to the new upper frame section. Even though I didn't plan for it, the inside dimension of the rectangular tubing fit snugly over the front lca mounts. This allowed me to support the crossmember at the exact location of the front lac mounts where all of the forward force of the axle gets transmitted to.

I laid a piece of tubing across the upper and lower frames and used the digital level to find the angle (about 37*) and transferred that to the tubing and cut it off inthe chop saw. I left it a little long and snuck up on the final length and angle so as to get a tight as fit as possible.
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Old 01-01-2012, 10:26 PM
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Re: Home brew road racer

The fitment at both ends was better than I could have hoped for. This is critical as the majority of the rear weight of the car will be carried by these two kick-up rails and the down tubes from the main roll bar hoop.

It's when things work out this well that I feel like the project is going to be a success and that all my designs, drawings and simple graph paper blue prints were worth the effort. I know what I want the car to be when I am done and when I plan the modifications, even though they are very extensive and complicated, I try to keep the construction as simple as possible and within the limitations of my skills, equipment and financial constraints.

This makes me feel good.
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Old 01-03-2012, 08:15 AM
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Re: Home brew road racer

You got me thinking of doing a zr2 swap but i am wondering if you can take a few more measurements to post. After hrs of surfing the s10 pages i found the 2wd and 4wd and zr2 axles are all different in 04? they made a 2wd zr2 and i dont know if that is the same as the 4wd zr2.
On my stock third gen housing i measured 56" backing plate to backing plate added 2 inches for bearing and axle (estimated i have no axles in my old housing) to come to aprox. 60" wms to wms (wheel mounting surface ). If i add the 3/4" inches you said added to each side that would be 63" wms to wms.
I found two different post one said it was 63" wms and the other said 65" wms
could you measure backing plate to backing plate and wms to wms and add these #'s to the post
4th gen rear aprox. 65" wmp to wmp (took a close guess car in storage cant access very well

Last edited by tealrs; 01-03-2012 at 11:36 AM.
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Old 01-03-2012, 01:26 PM
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Re: Home brew road racer

DAM this car is turning out amazing. How did you build those ramps as I would kill for a set of those. Cant wait to see future updates, keep it up man
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Old 01-10-2012, 07:49 AM
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Re: Home brew road racer

Originally Posted by tealrs View Post
You got me thinking of doing a zr2 swap but i am wondering if you can take a few more measurements to post. After hrs of surfing the s10 pages i found the 2wd and 4wd and zr2 axles are all different in 04? they made a 2wd zr2 and i dont know if that is the same as the 4wd zr2.
On my stock third gen housing i measured 56" backing plate to backing plate added 2 inches for bearing and axle (estimated i have no axles in my old housing) to come to aprox. 60" wms to wms (wheel mounting surface ). If i add the 3/4" inches you said added to each side that would be 63" wms to wms.
I found two different post one said it was 63" wms and the other said 65" wms
could you measure backing plate to backing plate and wms to wms and add these #'s to the post
4th gen rear aprox. 65" wmp to wmp (took a close guess car in storage cant access very well
I checked my notes and the WMS as measured on my stock 7.5 axle was 61 1/4". The ZR2 measured 62 1/2 so only 1 1/4" longer than stock, not 1 1/2 as I stated earlier. These measurements were taken without rotors or brake drums. As for a different axle in 2wd or 4wd all I can say is that the Superior Axle replacement axle catalog I have only list one set so I have to assume that both are the same.
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Old 01-10-2012, 08:19 AM
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Re: Home brew road racer

Originally Posted by 6SIX6 View Post
DAM this car is turning out amazing. How did you build those ramps as I would kill for a set of those. Cant wait to see future updates, keep it up man
The ramps are a critical part of this build as I am using them as a chassis jig to locate and center the front and rear suspensions and keep any measurements consistent over time. Once the car is finished I can use the stands for routine maintenance and repair work for all of my vehicles.

They consumed over a year of my time in design and construction. The ramp itself was pretty straight forward but the stands went through several designs. One of things I wanted from the ramps was height adjustability. These adjust from 4.5" laying flat on the ground, to 15" like in the photos, to a max of 20" If I flip the stands up. My first design that took months to perfect utilized two 1/4 sheet steel boxes that fit inside each other, pivoted on different centers and locked in place with a simple through rod. The main reason for the design was it gave a wide stable base and the steel boxes could be laser cut and formed at the local weld shop, leaving me with minimal welding and fitting. After going as far as building a full scale mock up in wood and drawing up a set of full size blueprints to give the guys at the weld shop the estimate to make 4 of the box stands was over $700.00 not including the ramps.

The triangular stands that I made do the same thing at minimal cost but I had to make many jigs and fixtures to be able to make 4 stands consisting of 8 pieces exactly the same. This included jigs to cut and shape the tubing to welding fixtures to align and hold the parts for welding. They came out real nice and work well but it was A LOT OF WORK!!!! There is about $700.00 worth of steel in the two ramps and stands.
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Old 01-10-2012, 08:47 AM
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Re: Home brew road racer

with the 3-link and coil overs roughed in I moved on to the 2x4 crossmember. In an earlier post I mentioned that I wanted to have the exhaust exit through the rocker between the door and the rear wheel well. To do this the exhaust pipe has to pass through the crossmember requiring a 3 1/2 id hole on each side for the exhaust tubing to go through. I had the weld shop cut two pieces of 4" od tubing with 1/4" wall 2 1/2 wide. This will give me a 1/4" lip on each side of the crossmember to weld to.

I drew out a picture of the floor area with the SFC's, trans tunnel and rear crossmember and then using the dimensions in the Magnaflow catalog I positioned the muffler to determine where I had to cut the hole in the crossmember.

Once that was located I fabbed up a jig to hold the crossmember to my drill press. Cutting a 4" hole in a piece of 2x4 tubing is not an easy task. My Craftsman drill press runs much to fast for a 4" holesaw so I had to come up with a step down idler pulley that I ended up making out of a couple of mower deck idler pulleys I got at the local Napa store. It's still a little fast but it got the job done with a lot of oil and a set of earplugs.

Here is the crossmember with the tubes welded in.
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Old 01-12-2012, 09:50 PM
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Re: Home brew road racer

I put the crossmember back in and resquared everything and tacked it back in place. I then pulled the rear kickups and upper frame section out clamped it to a bench and welded it up. I put it back in and tacked in place rechecked everything for squareness and fully welded the crossmember and kickups in place.

Once that was done I moved to the back of the axle to mock up a panhard bar mount. I decided that for strength it should be tied into the LCA brackets. I'm going to be using adjustable panhard brackets from Allstar and should allow me to lower the bar almost 7" below the axle centerline.
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Old 01-12-2012, 09:54 PM
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Re: Home brew road racer

Here are a few more pics of how I tied the upper frame to the factory rear sub frame.
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Old 01-14-2012, 12:29 AM
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Re: Home brew road racer

Originally Posted by 83RDRACR View Post
The ramps are a critical part of this build as I am using them as a chassis jig to locate and center the front and rear suspensions and keep any measurements consistent over time. Once the car is finished I can use the stands for routine maintenance and repair work for all of my vehicles.

They consumed over a year of my time in design and construction. The ramp itself was pretty straight forward but the stands went through several designs. One of things I wanted from the ramps was height adjustability. These adjust from 4.5" laying flat on the ground, to 15" like in the photos, to a max of 20" If I flip the stands up. My first design that took months to perfect utilized two 1/4 sheet steel boxes that fit inside each other, pivoted on different centers and locked in place with a simple through rod. The main reason for the design was it gave a wide stable base and the steel boxes could be laser cut and formed at the local weld shop, leaving me with minimal welding and fitting. After going as far as building a full scale mock up in wood and drawing up a set of full size blueprints to give the guys at the weld shop the estimate to make 4 of the box stands was over $700.00 not including the ramps.

The triangular stands that I made do the same thing at minimal cost but I had to make many jigs and fixtures to be able to make 4 stands consisting of 8 pieces exactly the same. This included jigs to cut and shape the tubing to welding fixtures to align and hold the parts for welding. They came out real nice and work well but it was A LOT OF WORK!!!! There is about $700.00 worth of steel in the two ramps and stands.
If you ever want to share your design let me know as Id like to make a set like that for my garage as its pretty small as it is and I wanted to make ramps to drive up on as I cant jack my car up in there. Keep up the awsome work man as it looks good
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Old 01-22-2012, 10:53 AM
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Re: Home brew road racer

The panhard bar mounts on both the axle housing and frame have to be able to handle lateral (side) loads that will exceed 2000lbs. My original plan was to mimic the factory design in length and position, just make it height adjustable. After sitting under the car with a tape measure, a level and a square for what seemed like hours I decided on different design.

The have a solid mount to the axle I will have to mount the axle side bracket to the left side lca mount. This will shorten the length of the panhard bar from the stock 43 1/2" to 36 1/2". I made a mock up of the panhard bar out of wood and started tacking pieces in place on the axle. besides the panhard bar being shorter in length than the stock piece I also moved it a little closer to the differential. This will reduce some of the leverage on the axle brackets and also give a little more room for a fuel cell behind the axle.
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Old 01-22-2012, 10:59 AM
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Re: Home brew road racer

a few more pics of the panhard bracket.
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Old 01-22-2012, 11:25 AM
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Re: Home brew road racer

The relocated panhard bracket sets directly below the left frame rail where the factory panhard cross brace bolted to. With the axle set at the desired ride height there was less than 3 inches of clearance between the two. This required cutting out more of the factory sub frame.

At times I have questioned my decision to retain as much of the rear frame and trunk sheet metal as I could. The rear frame is constructed of three and sometimes four layers of various thickness sheet metal that are spot welded together. Each layer is painted and some are galvanized and makes it difficult to clean and weld. working around this has been very time consuming and requires stitch welding all the seams back together and plating sections with 1/8 sheet steel to retain the structural integrity of the frame.

Cutting the factory frame off just ahead of the storage well in the trunk and drilling out dozens of spot welds might be the better way to go. Then I could have welded in a complete frame over and behind the axle. Oh well I've made my choice and will have to live with it.

Here is the trimmed left rear frame rail.
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Old 01-22-2012, 11:46 AM
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Re: Home brew road racer

The right side panhard mount also required extensive trimming of the frame rail. once it was cut away I positioned the panhard bracket by welding it to the right side lca bracket with a piece of scrap steel making sure it was square and level with the left side. I bolted in the wooden panhard bar and used it to keep everything in line.

I cut out pieces of poster board to make templates for the sheet metal bracing which consisted of 4 pieces that provided a triangulated mount that I think will be able to handle the lateral forces. Like the factory setup, I will also employ a diagonal brace from the left side frame rail to the right side panhard mount.
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Old 01-23-2012, 01:40 PM
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Re: Home brew road racer

I am throughly enjoying this build! Keep up the great "home brew" work.
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Old 01-24-2012, 06:25 AM
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Re: Home brew road racer

Originally Posted by 83RDRACR View Post
I cut out pieces of poster board to make templates for the sheet metal bracing which consisted of 4 pieces that provided a triangulated mount that I think will be able to handle the lateral forces. Like the factory setup, I will also employ a diagonal brace from the left side frame rail to the right side panhard mount.
Give yourself the ability to attach the brace as close to the PHB mounting hole as practical, so that the brace will take most of the load axially and not much will end up trying to bend the post. I'd add a crossmember between the rails up at the other end of this brace, just to spread the brace force out. That 2000# lateral load sounds like it's only due to the expected cornering lateral g's, meaning that you should add a factor to cover for things like rolling over an FIA curb from time to time. A multiplier of 3 is probably sufficient.


I kind of like the idea of a jack-powered lift. I'm at the point where I'd really rather slowly lift the car up just once than slowly get myself up off the ground . . . again and again and again . . .



Edit - I just sent you a PM.


Norm

Last edited by Norm Peterson; 01-24-2012 at 07:24 AM.
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Old 01-28-2012, 02:26 PM
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Re: Home brew road racer

Norm, I've got you covered on the diagonal brace. i had one pair of 4-hole brackets left over from the cut up 4-link brackets that I made the front lca brackets from. I centered them above the axle side panhard rod and tacked them in place to the inner left frame rail. Because so much of the stock sub frame had been cut away and the right side panhard bracket is very long, the diagonal brace is at a fairly sharp angle when the panhard bar is in the lowest position. I think it will still provide good lateral support to the frame mount though.

The panhard bar and the diagonal brace are made from 1 1/4 hexagonal aluminum tubing from Allstar and the same QA1 3/4 rod ends that were used on the lca's. The diagonal brace has enough adjustment to its length that it can be positioned 1 1/2 above the panhard bar for the bottom 4 adjustment holes.
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Old 01-28-2012, 02:57 PM
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Re: Home brew road racer

The only thing left to figure out on the rear suspension was the swaybar. I originally planned to use the factory Z28 bar but when I went to fit it up the ends of the bar interfered with the coil overs. I still had the ZR2 swaybar that came with the rear end and discovered it fit perfectly if mounted upside down. The ZR2 had the bar looped over the top of the pinion and that would have interfered with the 3-link. Placed underneath the pinion it cleared everything and didn't hang too low. Even better the arms fit inside my frame kick ups like they were made for each other.

I fabbed up some adjustable swaybar links from some short pieces of heavy wall 5/8" tubing that I drilled out to 29/64 and tapped with a 1/2-20 tap. I got 4 RH 1/2-20 rod ends from Summit Racing and played with the length to get the sway bar centered. I then made the frame mounts from 3/4 id tubing and Allstar 1/2-13 threaded inserts. I also made the ends of the swaybar adjustable in length which can be used to slightly soften or stiffen the bar to help fine tune the suspension.
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Old 01-28-2012, 03:13 PM
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Re: Home brew road racer

Here are a few more pics of the sway bar mounts and the finished adjustable links.

I was concerned about lateral forces on the frame. It lacked any diagonal bracing and the back half of the car seemed like it was just hanging of the rear crossmember behind the seats. I came up with an idea to cross brace the kick ups but had to work around the upper third link. I am thinking of doing something like in the last picture.
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Old 02-01-2012, 11:53 AM
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Re: Home brew road racer

The lateral loads (and the torsion that generally accompanies them) comes into that large open rectangle at the rearward corners, so if it is at all possible to start your diagonal bracing from those corners do so.

I'm thinking along the lines of running between the upper rear corners down to outboard of the 3rd link chassis bracket on either side (far enough for bolt removal/installation, but no further than necessary), with diagonals from the vicinity of that 3rd link chassis bracket running laterally and downward on each side from out to where that main crossmember frames into the sill structure. I know it'll be tight going over the white longitudinal rail portions kick up, but you won't have to be using 2x4 tube for these braces either.


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