johnc

From my own experience testing my 240Z with below and above ground roll centers (yes, I did back to back testing at Buttonwillow but not exactly for roll center positioning). Keeping the roll centers above ground made the car more responsive at turn in and the car would take and hold a line in high speed corners (above 80mph). It was easier and more predictable to drive at the limit. With below ground roll centers lap times were the same and sometimes a bit better then the above ground roll centers because the lower speed corners could be driven a bit harder. But, the high speed corners were scary. Even after adjusting out much of the bumpsteer the car was darty and less predictable above 80mph. The car lost compliance and bumps that would normally be absorbed by the springs were now being transmitted into the sprung mass and affecting the chassis. Not a big deal at low speeds but very unnerving at high speeds. The below ground roll centers would work for a qualifying lap but I'd bet a lot of money that you couldn't run a race without going off the track or wrecking. This testing was done to see how I could get the front and rear suspension of my car past the "no change in suspension mounting points rule" for the SCCAs SM2 class while running 26" tall tires with an under 5" ride height. Take what I posted for what its worth. I wasn't a specific test of roll center location because other changes were involved, but the testing revealed enough to make the conclusions I did above. I ended up just using 25mm bumpsteer spacers, 25.2" tall tires, and a little higher ride height.

Race Car Vehicle Dynamics doesn't tell folks what to do to make their car handle better. In that respect it is often a big disappointment. What the book has attempted to do is describe vehicle dynamics in a fairly understandable way. Its just a step below a full-on engineering treatise (which was all that was available before this book was published). Treat it like a college reference book. The kind of reference that was boring as hell reading and made you certain that college would never teach you anything practical, but years later you kept referring back to when trying to understand some "practical" problem like, "Should my roll center be higher or lower?"

If there was a way to take the ECU and the whole ONSTAR communication system out of the car and put it in a washing machine on the spin cycle...

BS. It says nothing of the sort. As with all suspension types they discuss in detail in Chapter 17 they give the benefits and drawbacks of each. And MacPherson struts are basically a SLA suspension design with an infinately long upper arm (sometimes referred to as a slider). They state the obvious regarding the infinately long upper arm, "This is one of the major compromises of the strut type suspension, especially for performance applications." (page 632) The Millikens make similar, and correct, judgements about all suspension designs discussed. Now, knowing that MacPherson struts are a form of SLA suspension, most of the discussion regarding SLA suspensions also apply including the discusion of instant centers, roll centers, degrees of freedom, motion path, camber curves, anti dive, squat, wheel path, caster change, wheel loads, etc.

Nope. Didn't see a message but I'll check again in a bit.

This gets to a fundamental problem I see with a lot of modified cars: preparation. Once a person decides to start modifying their vehicle, they assume the responsibility of designer, engineer, chief mechanic, and driver. You may not be able to perform all of those roles, but you are responsible for them regardless of who actually performs the work. This vehicle is now your creation and you must get very intimate with it. Think of it as a prototype that is being tested for the first time. Inspect everything regularly and replace parts that are suspect. Is there a bolt head with one corner slightly nicked from a wrench? Replace it. Is that washer no longer flat? Replace it. Is this crossmember so dirty that I wouldn't be able to see a hairline crack radiating out from a hole? Clean it and inspect it. Is that lug nut a little hard to thread on at first? Replace the nut and the stud. I don't know what this cracked vacum line does? Figure it out and replace it. I see a lot of people who really only assume the role of driver of their highly modified cars. I usually won't even go for a ride with them.

A well designed part going from perfectly fine condition to complete failure from one load is actually pretty rare. What happens more often is a crack developing at a stress riser as a result of a load applied. The crack begins propgating through the part following the path of least resistance. This propogation starts at a very slow rate (it probably took a long time for the crack to start in the first place). Each load applied to the crack will increase the rate of propogation and the size of the crack. Then, maybe months later, yet another load is applied and the rate of propogation pushed the crack beyond the tensile strength of the remaining uncracked material. The part then fails. The failure appears to us as something that happened suddenly, but the part separating into two pieces actually took a long time to occur. We were just ignorant of everything until we heard the bang. 200hp ITS 240Z races cars can break stub axles and they are often replaced ona regular schedule. Stub axles used in road racing tend to separate at the fusion weld where the flange meets the stub axle. This is due to the cyclical lateral loads (over 1.1G) experienced on a race track. Also, large rear toe-in number can contribute to failure.

If you're asking these kinds of questions, you should buy Race Car Vehicle Dynamics by the Millikens. Chapter 17 Suspension Geometry will answer your questions and a section in 17.5 titled: Front Suspension Design, MacPherson Struts has everything you are looking for.

If you are able to lift your foot off the throttle in a long corner and not spin, you're still a little ways from the limits of the car. A 240Z at the limit will spin if you lift off the throttle. Its not a snap spin or anything mean, but the back end will lose traction from the weight transfer forward and you better be ready to catch it and reapply some power. Again, go to an autocross or an open track day and learn what the car feels like at the limit.

The EMI Racing plates mount to the underside of the strut tower. The flat face in the picture is pulled up hard against to top of the strut tower by the two mounting bolts. If the monoballs are mounted correctly they shouldn't rattle unless: 1. The nuts on the shock shaft have backed out. 2. The wrong monoball spacers are used and the nuts bottom on the shock shaft itself. 3. The car has been bottomed heavily and there are no bump stops on the car. 4. The suspension has topped out hard and there are no droop limiters in the shock or on the suspension. The monoballs are not designed to take suspension load, thats what the upper spring perch is for.

Bound to happen. We've been lucky to have a reasonably priced race shock available to Z racers for a long time. Koni's replacement for the 8610-1149 is the 8610-1437RACE. It will physically fit in the Z strut tubes although the body is about .10" taller, the max length (at full rebound) is longer by .57" and the stroke is increased by .39". None of these changes are show stoppers and the increased stroke is a good thing. How much a strut is shorted for these shocks will be different then for the 1149s. But, the big question is valving... We're tryning to get a shock dyno graph and, unfortunately, the lastest Koni Motorsports catalog omits it.

Your choice of spring rates depends a lot on shocks available to control the springs. The non-adjustable Tokicos, Monroes, etc. are fine until you hit psring rates over 175. The Tokico Illumina is good 150 to maybe 250. The now discontinued Koni 8610-1149 is good from 250 to 350. There's also a Bilstien application that is comparable to the Koni but I don't know its part number. For spring rates over 350 you're looking at a custom setup. BTW... the most important question is: What do you intend to do witht eh car?

[picking nits] Camber plates don't really correct suspension dynamics. They just give you a greater range of camber adjustment and most plates now also allow a caster adjustment. The change (notice I did not say "correction") in suspension dynamics comes when camber and caster are moved to more appropriate settings based on how the car is used. The camber and caster settings I used on my track only 240Z made it a bitch to drive on anything but the smoothest of streets. Conversly, street caster and camber settings make a car more difficult to drive fast around a track. [/picking nits] Caster is adjusted with the EMI plates by bolting it to the strut tower using different combinations of the left and right mounting holes in the plates. Scroll up and look at the picture of the camber plates and focus on the plate in the lower left. Assume we've installed it exactly as oriented in the left front strut tower and you're looking down on the plate while leaning on the left front fender. Assume the mounting holes in the plate are numbered from 1 to 4, top to bottom and there's a left row of holes and a right row of holes. By mounting the camber plate using left hole 3 and right hole 2 you've rotated the camber plate clockwise. That pulls the upper spring perch and shock mount to the rear, thus increasing positive caster. If you needed more negative camber but didn't want to make a caster change (you actually will make a minor change to caster but its not significant) you would change the mounting to left hole 4 and right hole 3.

The second link was interesting until I got to this paragraph: Another member of the tin foil hat brigade.

Go to a local autocross and find out what the car's actual limit is. Unless you've spent some time on a track or at an autocross driving over the limit, what you're feeling might well be far from the rear end breaking loose. The mods you mention are fine but I think your tires have a sidewall that's a bit too short. For some reason, and I've talked with Hoosier, Kumho, Penske, and Koni reps, the 240/260/280 handles better with a sidewall aspect ratio not lower then 45. There's a level of compliance that a taller tire sidewall provides that the Z seems to need. You can compensate for it with double adjustable shocks. Without this compliance the Z tends to skate in the corners and people often confuse a skate problem with understeer or oversteer.

Geez! http://forums.hybridz.org/search.php?

Uuuhhh, 91326 is Northridge. If you drive for an hour you'll be at my shop in La Habra. http://www.betamotorsports.com

Just got back from Benchmark and the mold is all done. Stan will make a hood and I should have it next week. I'll take some pictures, post them on my web site, and update this thread. We will hit our $500 price target but that will be for a pin on race fiberglass hood with clear Gelcoated carbon fiber over the scoop and the rest of the hood in primer. FYI... Carbon Fiber pricing is expected to be over $20 per yard by this summer. That's double what it was last year. Stan's suppliers are blaming the huge increases in defense spending and the volumes of CF that Airbus is buying to make the 380.

Since you're eliminating the diagonal in the main hoop, put an X brace between the two rear braces going back to the strut towers. You have to have something keeping the main hoop from racking in case the car rolls hard onto one side. Right now, as built, an impact on the driver's rear corner of the roof can cause the main hoop above the shoulder bar to rack to one side. The X brace I mention is required in FIA legal race cages and should (but maybe won't) satisfy SCCA's main hoop diagonal requirement. The box design in the seatbelt retractor pockets is fine. An inspector will look at the weld where the main hoop goes through the plate and won't even care about the tube projecting into the retractor pocket. PLus, you now have a good jacking point! One of the reasons to build boxes that connect the cage to the chassis is to introduce loads into the cage as normal to the tubing as possible. Its better to have the legs of the main hoop perpendicular to a plate then have it welded into the plate at an angle. I wouldn't worry about connecting the front hoop tot he TC rod area. That whole front corner where the rocker, floor pan, and front frame rails come together is pretty strong and if you span those three areas with plate you'll effectively tie them together.

I sell the EMI Racing camber plates as Keith mentioned. $300 per end of the car. Here's a shot of the set were run on my 240Z for 8 years (sold them late last year for $125). You don't have to cut the strut towers and the design allows you to adjust caster in the front.

A strut is an upper suspension locating member that is typically a vertically oriented metal tube that is connected to the hub. A shock is a hydraulic device the dampens the motions of the suspension springs. On a McPhereson and Chapman Strut suspension the strut has a coil spring located around it and the spring sits on a lower spring perch attached to the strut. In addition, a shock is installed inside the hollow tube of the strut with the shock body clamped in the tube and the shock shaft is attached to the vehicle body at the upper spring perch.

Funny, the ROD lifted a front wheel on almost every corner.

Spend a lot of time using the search function. Your question has been answered many, many times here. Welcome and good luck! http://forums.hybridz.org/search.php?

Lots of threads have already covered this topic. http://forums.hybridz.org/search.php?

I don't know. The factory setup had the PCV valve on the lower tube you mention and the filtered air into the crankcase went into the engine via the cam cover. Maybe there's some kind of air flow deisgned into the crankcase itself? On my race engine I just ran hoses from both into a big, vented catch can.