74_5.0L_Z

As far as the Woodward racks go, I think you can change the ratio just by getting a different pinion. I just went from the stock 260Z rack which had a gain of 1.59 in / rev to the stock 240Z rack which has 1.81 in / rev. The effort increase wasn't terrible, and the increased rack speed was noticible. Next I was planning to get the Woodward 2.09 in / rev (22 inches center to center) rack and install it without power steering. Then as funds permit I am going to add an electric power assist column. With a rack that is too long, all you can do is raise/ lower the rack or ends to get yourself on the right side of the bump steer curve. If you have bump steer, you want the front tires to toe out on bump and in on droop. Unfortunately, the slope of the bump steer curve is almost entirely dependent on the center to center length of the rack.

3D Kinematics analysis of the S30 suspension shows that minimizing bump steer requires a rack with a center to center distance shorter that what came from the factory. Any rack longer than 24.25 inches center to center will make bump steer worse. For what I want from my car (autocross), minimizing bump steer is a priority. While power steering would be nice, bump steer and rack speed are more important to me. I have my eye on a custom Woodward steering rack that will be about 22 inches center to center.

First, cool work on the rack. I hadn't considered modifying the length of an existing rack. I just measured up a 240Z rack for the purposes of modeling the front suspension kinematics. To do so, I disassembled a couple of spare racks that I have and measured their component parts using calipers and a tape measure. I even cut apart an inner tie rod to measure the ball diameter. Then adding up all of the measurements, I was able to determine that the center to center distance was between 24.2 and 24.3 inches. My measurements agree with yours but I can't specify the accuracy beyond one decimal point. It sounds like you have access to better measuring equipment than I do. Did you use a CMM for your measurements? Also, the stock rack has a total of 4.78" (2.390 each direction from center) of travel unless the factory limiters are removed. From my kinematic analysis of my front suspension, if I were to replace the stock rack with something different, I would buy or make one that was between 22 and 23 inches center to center.

I have a friend who owns the company that makes the Brunton Stalkers. The Brunton M-Spec cars come with LS Engines and have side pipe exhaust. The sound of his cars is very nice, and well below the SCCA dB limit. He uses catalytic converters in line with the mufflers to keep the exhaust quiet. If you give him a call (Scott Minehart), he can tell you which mufflers and cats he uses. http://stalkercars.com/ Here is his car on track.

Cary, I did run limiters on the front for a while just to keep the springs from getting loose when I jacked it up. I've since raised the front just enough to no longer need them. Clark, I am not having either an understeer or oversteer problem. The car pretty much goes where I point it. It just takes more slip angle to make it change direction. I am still not used to the Bias ply slicks. The car always feels at the limit of traction (even when its not). I am slower on the bias ply than on the radials. I may get used to them and get faster after a bit more time, but I plan to go back to radials. So, I probably won't spend much effort trying to perfect this set-up until I am back on radials.

The car could use more droop in the rear. Unfortunately, way back when I sectioned my rear struts, I shortened them too much. I have a couple of options to get some of that droop travel back. 1. Lower the rear. I can lower it about 1/2 inch before the spring loses all pre-load at full droop. Unfortunately, that gets me really close to rubbing the inside if the wheel well at full bump. 2. Add an aluminum spacer between the rear camber plate and strut tower to lower the camber plate mounting relative to the body. Then also perform option 1 but lower the spring farther. 3. Get some new rear strut housings and start over.

I started with the tires in the 18 to 20 psi range and the tire temperatures seemed to indicate that was the correct pressure. Unfortunately, the car felt like it was falling over all the time and the tires were rolling under pretty badly. So, contrary to the tire temps, I started adding pressure until the car felt more stable. I've got the car down to 2580 full of fuel with me in it. I have 610 lbs on the right front and 638 lbs on the left front.

Yes, I am experiencing the same problem that I spoke of earlier. This was a really tight course where you had to brake pretty hard and then turn pretty tight. I am trying to decide what I want to do to settle the car down. Currently, I have 500 lb/in front springs, 425 lb/in rear springs, 20mm front sway bar, no rear sway bar, and Koni 8610-1437race struts all around. The front suspension has the following static settings: camber: -1.8 caster: 6.3 toe: 1/8" out front roll center on the ground or maybe slightly below The rear suspension has the following settings: camber: -1.2 toe: 1/8" in The rear roll center is about 2.5 inches above ground. Tires: AVON 10.5/23.0-15 Cross Ply Slick (A11 compound) all around 22 psi rear / 27 psi front Wheels 15x10 with 5.25" back space mounted with no spacers. This gives me about 2 inches of scrub radius. I have no droop limiters on the car at the moment (except the struts themselves). The car really pitches around more on the bias ply tires than it did on the Hoosier A6 tires I was running. The tire itself seems to deform much more. When driving, I do not notice the tires lifting (front or rear). When these tires are done, I plan to go back to a radial. I am thinking about lowering the rear roll center, raising the front roll center, softening the rear springs, or adding a stiffer front sway bar.

If you don't want the 6061-T6 to crack when you bend it you have to ensure that the inside bend radius is at least 2.5 times the thickness of the sheet. So, if that is .125 thick sheet, you need a .375 radius. If you anneal the material in the region of the bend before you bend it then you can get away with a tighter bend (approximately 1.5 time the thickness).

I like how you blended in a rear spoiler to the quarter panels. What spoiler is that?

I have the Subtle Z kit (modified) on my car and I have plenty of space for 275/35-15 Hoosier A6 and Avon 23x10.5-15 Tires on 15x10 wheels with 5.25 inch backspace.

Just an aside: The Ford engine family that included 221, 260, 289, 302 (5.0L), and 351W all have 90 degree angles between their banks. It would be more appropriate and correct to refer to these as Windsor engines and not 60 degree engines.

Mike, Midwest Control sells adjusters like the ones that you made: http://www.midwestcontrol.com/series.php?id=194

Caster has some really good benefits on our cars and also causes some problems. First the good: With our front struts we have a large Steering Axis inclination (SAI). With factory settings, the cars have very little caster. So, with the factory settings the outside front wheel first tends slightly toward negative camber when the wheels are barely turned and then swings toward positive camber as the wheel is turned further. Similarly, the inside wheel will slightly gain positive camber as the wheel is turned. Ideally, the outside wheel would gain a lot of negative camber and the inside wheel would gain a lot of positive camber as the wheel is turned. Adding caster helps the camber gain a bunch. On my car I have 6.4 degrees of caster and -1.8 degrees of static camber. When I steer the front wheels 5.7 degrees, my outside front wheel gain negative camber so that it has -2.35 degrees, and the inside front wheel gains positive camber to -1.1 degrees. This change in caster is before the outside wheel compresses and the outside wheel droops. The changes in caster from strut compression / extension will add to that from turning. The change gets really significant for tight turns. If I steer my front wheels by 30 degrees(essentially full lock) the outside wheel goes to -2.9 degrees camber and the inside wheel goes to +3.9 degrees of camber. It has been shown that having caster about half of the SAI give pretty good caster gains with turn of the wheels. So, for our cars 6-7 degrees is the rule of thumb. Now the bad: Adding a bunch of caster causes problems. First, it causes the weight jacking / de-wedging problem that I talked about earlier. The combination of caster and SAI combine to cause the front spindle to swing on an arc. Adding caster tilts the steering axis back toward the fire wall. The tilt of the axis from caster causes the spindle to rise on the outside tire and fall on the inside tire. So, the SAI and Caster effects are additive (but in a non-linear kind of way). The large SAI and caster magnify the rise and fall of the spindle pin. If we could get an SAI of lets say 5 degrees and run a caster of 2.5 degrees, we would get the same level of caster gain as we do with our struts and 6-7 degrees of caster. However, the low SAI spindle would have much less weight jacking associated. Unfortunately, strut cars need large SAI for wheel clearance. The only way to get low SAI like I propose is to convert to a SLA set-up. On a strut car the weight jacking can be minimized by running the smallest scrub radius possible. Theoretically, a zero scrub radius car would not have any weight jacking from the steering effects discussed here. Next, adding static caster increases caster gain. If the strut had no caster and the lower control arm were parallel to the ground, the strut would maintain zero caster for all of its travel. As you add caster by tilting the strut back toward the firewall, bump travel will cause the caster to increase. The more it is tilted back, the faster the caster will increase for a given bump motion. On my car, I have raised the TC rod 0.5 inches and run 6.4 degrees of caster at ride height. One inch of bump increases my caster to 6.9 degrees. The problem with the caster gain is bump steer. The caster gain causes the outer tie rod to rise relative to the steering rack. If the rack is in the stock position, then this rise of the outer tie rod end causes the virtual length of the tie rod to shorten. This causes toe in on bump, and we all know that toe in on bump is a very bad thing. The problem of bump steer can be mitigated a little by raising the rack or by adding the bump steer extension to the outer tie rod ends. But that is a Band-Aid and not the best solution. I have found that I can almost completely eliminate the bump steer in the front end (for my current set-up) by going with a much shorter rack (~22 inches center to center of the inner rod ends).

I will postulate that the lifting of the inside rear wheel is caused by the combination of the following: 1. The 14 degree SAI and ~ 7 degree caster cause the outside tire to rise relative to the body and the inside tire to drop relative to the body. This takes weight off the inside rear. You can see how much this de-wedges the car in even a static situation if you have some turn-plates and wheel scales. 2. Large scrub radius. This exacerbates the problems caused by problem 1. The larger the scrub radius, the more the outside wheel will rise and the more the inside tire will drop. 3. Super stiff springs. This magnifies the problems caused by 1 and 2 above. So what is happening is that you are entering the corner and transferring weight to the outside front tire, which as you turn is rising relative to the body. Meanwhile, the inside front tire is dropping relative to the body. Essentially, the car tips about the diagonal line connecting the inside front to the outside rear. If the rear tire does not have much droop available, then it will be lifted off the ground. I know from your build that you have super stiff springs, lots of caster, and HUGE scrub radius.

I would have them water jetted or cut out on a mill. If you do have them plasma cut, then make sure you clean up the edges. The plasma cut can leave a rough edge that can create stress risers.

Those look great. How much do they weigh?

Both configurations will be equivalent as far as bump steer, roll center and camber gain are concerned. For kinematics, all that matters is the distance between the centers of the suspension attach points. The different configurations will cause different bending moments on the dog-bone. However, with the use of the improved dogleg, I don't think you will have a problem in either configuration.

That's interesting. I had three different 240Z racks and two 260Z racks, and all the ones that I have encountered had interchangeable inner tie rod ends (though there are at least two types). I would be interested to see the rack style that you turned in as a core. I just finished replacing the 260Z rack in my car with one from a 240Z. During the process, I had both racks apart on the bench for comparison and measurement. Here were the main differences: The 240Z rack is 2.3 lbs lighter than the later racks. The 240Z rack is faster. The gain on the 260Z rack was 1.59 in/rev of the pinion and the 240Z gain was 1.8125 in/rev. With the 240Z rack, the steering ratio is 15.8 to 1 and with the 260Z rack the overall steering ratio is 17.8 to 1 (assuming 4.5 inch steering arms). All of the later racks that I have encountered have been the slow (1.59 in/rev) style, and all of the 240Z racks have been the faster (1.8125 in/rev) style. I would be interested to know if anyone has a newer 260Z / 280Z rack that has a faster gain than I have posted. If so, what is the gain of the rack, and what year did it come from?

The inner tie rod ends for the 240Z, 260Z, and 280Z are all interchangeable.

What do the fasteners that attached that to the LCA look like? Did the rear bolt and washer bend? Can you post a picture?

As you stated, with the control arms mounted in the stock position, the arm angles forward as you add caster. The angle of the arm away from perpendicular (as seen from above) creates a virtually shorter control arm. The virtual shortening of the LCA reduces the amount of static camber that you can achieve with camber plates. You can correct that to some degree by shimming the inboard side of the LCA as far forward as the stock cross member will allow. Even with the spherical bearings on the inboard side of the LCA and the pivot shimmed as far forward as possible, you will start to get forward angles on the LCA after about 5 degrees of caster. I fought that problem for a while and decided to do something about it. I made a custom front cross member that moves the mounting point of the LCAs forward but keeps the fore/aft position of the rack constant.

The heim at the frame connection of the TC rod is not enough. Here is a simple experiment to prove the point: With the strut assembly removed and the car properly supported, 1. Install the LCA and TC rod on the car and make the bolted connection between the two. There will be a certain length for the TC rod that will allow you to install the two bolts connecting the TC rod to the LCA. 2. Lengthen the TC rod one inch. As you do you will start to feel resistance as the TC rod connection to the LCA tries to rotate (but can't). 3. Now remove one of the two bolts that connect the TC rod to the LCA. If you are able to remove this bolt at all without damage then try to reinsert it (the holes will not be properly aligned). I am running 6.5 - 7 degrees of caster on my set-up with no problems.

There is a major problem with the design of the TTT TC rods: The end where the TTT TC rod bolts to the LCA is welded. That means that the angle between the LCA and the TC rod is fixed. The TC rod, LCA, and the frame between the connections of the LCA and TC rod form a triangle and each of the three legs of the triangle is rigid. The angles between the three legs of this triangle is governed by the Law of Cosines that states the following: A^2 + B^2 -2AB cos(theta) = C^2 where A is the length of the TC rod from the frame to the LCA connection point, B is the length of the LCA between the inner pivot and the TC rod connection point, C is the distance between the TC rod connection to the frame and the LCA connection to the cross member, and theta is the angle between the LCA and the TC rod. Rearranging the equation given above, cos(theta) =( A^2 + B^2 - C^2) / 2AB. In other words, as the TC rod length changes, the angle between the LCA and the TC rod also changes. If the connection is rigid (as in the TTT TC rod) then either the bolted connection between the LCA and TC rod must have enough slop to accommodate the angle change, or the rod itself must bend. Either of these options is unacceptable. It should also be clear at this point that the only successful design for an adjustable front LCA / TC rod assembly allows for the deformation of the triangle. The connection between the LCA and TC is a pin joint that allows the angle between them to change but also keeps them in the same plane. The connection between the frame and the TC rod and the cross member and the LCA must either be very compliant (rubber) or a spherical bearing. Rigid bushings at either the TC rod or in the end of the LCA will cause binding and prevent proper adjustment.

Regardless of the clevis that you use, I would make the attaching bracket to the control arm with a little more material around the hole and around the bend plane. Attached is a link with the drawing used to make my bracket. Mine was made using 1020 mild steel, but you could step up to 4130 for more yield strength. http://forums.hybridz.org/topic/41611-tc-rod-pivot-relocation-bad-dog-subframe-connectors-slotted-crossmember/page-6