QuestionHey Dan, thanks for the great response.
After further discussion on the z31.com forum, I came across some really intesting information. its at http://www.tsscc.org/images/handling.pdf
"I will discuss springs and swaybars together. Springs and swaybars work in tandem with each other during a cars transition and steady state handling (see Appendix A). Both affect body roll of the car as well as weight transfer. A stiffer bar can often be put on a car to keep body roll in check, especially if the springs are soft. Conversely, stiff
springs can be used to control body roll and smaller sway bars used with them. Which is better and why do you want to control body roll? I prefer having stiff springs and a smaller sway bar than the reverse. This is because a swaybar effectively makes the
suspension on that end of the car dependent (instead of independent). This means, in order to control body roll, a sway bar will tend to lift the inside wheel in a corner, making what happens on one side of the car dependent on the other. By using springs to control most of the roll, you keep the suspensio n more independent from side to side. The reason
you want to control roll is that body roll is a significant factor in weight transfer. While you do want to have some weight transfer (this is because a tire grips better laterally with more vertical load), at the same time too much weight transfer decreases vertical load on
the inside tire, making the outside tire do more work to keep your car turned. Cars that roll little are best."
This is good because my car has bad understeer in slow second gear or first gear corners, and by have a stiffer rear spings it might elimiate this problem.. But it might also give me more oversteer which i have lots of at higher speeds (high rpm in second gear, never had to switch to third in autocross).
So I think my next investment will be for rear springs and shocks.. But then again I will have to spend 400 bucks for new tires. I am thinking about gettting the Yokohama AVS ES100 or the Kumho ectra 711. I think they are the best bang for hte buck in performace tires. I wish I could send you picks of my car, but this site doesn't allow it.
After changing my rear brake pads yesturday and bleeding my brake fluid, I noticed my rear tires are wearing in a very interesting way. The inside and middle of the tires are worn completly bald almost, while the outside of the tire has tread left. I'm sure i don't have to much negative camber, but it probably has to do with my suspension and body roll putting a bigger amount of camber onto my rear wheels. My front tires by the way are still surprisenly in good shape for worn tires.
A problem I didn't tell you about before is that my car is rusting fron underneath, which is a reason i don't want to put much money into this car anyways. I wish I could just find a Turbo Z like a 240 or another 300 in good condition, with good parts already installed or good stock.
Any sujestions or comments?
Sincerely
Marcel Irnie (irnieracing@hotmail.com)
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Followup To
Question -
Hi there Dan
I currently own a 84 300zx n/a, and have been interested in racing all my life. I am 19 and just finished 2 years of university. I have been improving my driving techniques in the last 2 years very much, and I raced my first autocross just 2 days ago with it. Unfortunilty I'm making no money at this time, so my cars suspension is shit. My car has lots of body roll and forward back roll like a boat. But dispite this negatives, I can still drive my car really fast and drift the corners once my tires give way. I was only 10 seconds slower then the fastests cars on the track. (WRX STI, corvettes, integras, mazda speed turbo miatas,etc.. all with race tires. I by the way was using my worn out Dunlop street tires.
What is a affordable way to stop my car from swaying? I just installed some gabriel stut cartiges up front,(helped alittle). If i took the stabalizer bars off of a turbo 300 would the thicker bars help? Poly. bushings are very expensive so i don't want to get those. I am also thinking of finding used turbo 300 springs, but if i do that i think i will need shocks that are made for those turbo springs.
I am very interested in autoracing, and my life goal is obviously to become a professional racer, or maybe a stunt driver in movies, since I already have a Fine arts dilploma in video production.
Answer -
Hi Marcel:
You can spend about $2000.00 on suspension mods, but you have started with the shocks. Next, do install the heavier sway bars (proper name is anti-roll bar) both front AND rear. This will stop the body roll. The front to rear pitching is another problem, and may be best solved by reducing the car's weight. remove the spare, jack, passenger seat, carpeting, especially anything in the rear area, and when you can afford it, the urethane bushings. After this is done, you can consider stiffer springs.
I've owned a 280 Z, and 4 280 ZXs, but the 300 ZX suspension was so poor that I never bought one. You will need to stiffen the rear springs sometime, but look around for other options. Many race parts companies offer replacement springs. You will have to visit a chassis specialist, explain your situation (financial) and ask for help. You'll have to remove one rear spring to have it tested for it's rate, then try to find one of the same length, with about 25 % more stiffness.
When you go for rear shocks, get adjustable racing shocks and set them for maximum rebound. This will stop some of the pitching, and help with braking. Stiffer springs in the front will also help, as will racing shocks that are set for maximum bump (0pposite of the rears.)
I'm impressed that you got within 10 seconds of the Subie WRX, those little guys are really something, I've seen them beat 700 horsepower Camaros in road races, purely by out handling them.
Auto crossing is a good way to start toward a pro career, If you've heard of Randy Pobst, he started in autoX about 15 years ago, and has done a lot of amateur racing in my region of SCCA (Central Florida). It's important to know though that he spent a LOT of time marketing himself and took some pretty shakey drives before he finally landed the deal with Porsche. In the meantime, he never missed an opportunity to race, and was lucky to marry a gal that was totally supportive, and a hell of a driver in her own right.
I would suggest that you not ponder series like Formula One, CART, or IRL just yet, usually those guys come from mountains of wealth, and they started in go karts when they were 6 years old ! Think in terms of the Speedvision Cup, The GT series, Touring car Series, etc. and work in that direction. There you have a chance. It also wouldn't hurt to add an engineering degree (automotive of course) to your resume. It's another 4 years, and a LOT of math, but you can do it, it just takes work.
Best of luck in your persuit, When you get on the podium at Sebring , mention my name.
Dan Liddy
Sarasota, Florida.
AnswerHi again Marcel:
Your car has a semi-trailing arm rear suspension developed by Porsche in the mid 50's. It didn't work then, so they sold the idea to BMW who couldn't make it work. Eventually the Japs copied it, and used it on the Datsun 510 (that what my race cars are.) And- - - -well, it still didn't work. So Datsun/Nissan built the 240/260 Z cars with a straight perpendicular "A" arm on the rear which worked beautifully though it was mushy. This worked so well from 1971 'til 1978 that they discontinued it !!, and built the first 280 ZX models with the same semi-trailing arm arrange ment from the 50s'. Guess what- - - it STILL doesn't work. The only solution is to stiffen it up in a big way, which requires stiffening of the front as well.
Your rear tire wear is typical of the 300 ZX cars because they squat so much under acceleration. The solution is to relocate the upper suspension pick up points forward by about 4 inches. Hardly practical. The other solution is to stiffen hell out of it. The stiffening is going to loosen the rear noticeably. You might try reducing your rear tire pressure by about 2 pounds , see what happens.
My personal experience tells me that it's better to use roll stiffness from anti roll bars, than stiff springs. Your understeer on corner entry is the bane of all street cars, they're designed for it. Correcting is is sometimes a major challenge. One thing to ponder is getting as much weight off the front as possible, concentrating on the driver's side which will be as much as 200 Lb. heavier than the passenger's side. Move the battery to the trunk area, as far back as you can get it. Get a fibreglass hood, bumper, and front fenders (yep- - -$$$$) Install a header to save weight and gain performance. Change the front to a coil over (saves weight in springs).
The rust problem is something to look at carefully. Is it the floor pans?, or the framework? Both can be repaired, and it's a lot of unpleasant, dirty work. I took 4 years of welding instruction at the local vo-tech when I started racing, it's been a godsend, and all my race pals depend on me for it. Somehow, I also developed a talent for panel beating (racing in Improved Touring probably) and I get my share of that too. I'd think long and hard before I switched cars. A 2nd generation Mazda RX-7 will beat the pants off a Z car though. I drive one on the street, and it's a lot more comfortable .
You should try to get a copy of the book: "Hot To Make Your Car Handle" by Fred Puhn, your bookstore might have it, or they can order it for you- - -it's invaluable, and only about $15.00. You will learn a LOT from it, be sure to read it at least twice.
Finally, to speed this up, you may write me directly at "DanL5454@AOL.com" I try to answer mail daily and would be happy to offer more help if you should need it.
Again, good luck
Dan Liddy
