Auto Racing: 280ZX, polyurethane bushings, datsun 510

Question
QUESTION: Sir,

I am so happy to have stumbled into your excellent site, and have found in your prior advise some answers I needed.

I agree with you that a fellow just starting out racing,
and who likes Datsuns should avoid the ZX. Earlier models are easier to modify and find racing parts for.

I did not realize this when I started messing around in road race time trials here in California, with my 1981 280ZX turbo.

It has not been easy or cheap but little by little, the tubby old Z now gets around track quick enough to embarrass some very expensive and exotic machinery.

Unless you ask I will not bore you with all the mods I have done.

My question is a follow on to the coil over spring dialog you recently had with another fellow.

I am old school and would rather not resort to coil over unless I must. All that hacking and welding, just to find that something is too long or short and you beat it apart like that poor lad did.

Already have after market sway bars, springs, adjustable shocks, polyurethane bushings, and it all works fine, full race tires and by the way the car is never on the street as I trailer to the track.

The springs I am using are the stiffest I could find in the after market and as I recall are about 200 pounds per inch.

But still way to soft as the car hobby horses over the bumps. Was not aware until a buddy took video, and now I can feel it on the track.

Regarding 280ZX springs there are three things I wish to find out.
1.  Is there a company who will make me some very stiff springs which will install in the stock perches? If so is this okay?

2. How stiff is okay.  Am thinking about 300 pounds.

3. What about front to rear difference in stiffness?

Seems to me fairly equal would be okay but just had a chat with a very respected full race vintage Datsun 510 guy who claims he is running 800 pounds rear and 300 front.

How is that possible or good?

One final point, I assume if I got coil over at one end must do the same at both ends of the car.

Thanks for taking the time to consider my e-mail.

Art

ANSWER: Hi  Art:

You can put coil-over fronts on your ZX without distrubing the rear or converting it. Before you do the cutting and welding - - -MEASURE EVERYTHING- - - TWICE!!

The reason that the spring rate is so different from front ot back is because of leverage.  In the rear the stiffness of the spring is reduced by about half dut to the fact that the suspension design creates a negative fulcrum.  More spring is necessary, to accomplish the same amount of resistance.  I think your selection of 300's in the front may be pretty close, and the 800 rears too, though it would take a bit of experimentation.  Most of the stock car supply companies have a wide variety of 5" coil springs in different rates. They should fit your stock spring pan with little added work. go to
>> www.performancebodies.com << for a complete supply .  They're also fairly close to you , in Iowa.  Measure your free length before ordering though, you may have to fabricate some spacers. You can even run an assymetrical spring rate to compensate for your body weight which would help balance the car even further.

For mamximum handling you want to reduce body roll more than increase stiffness. Especially if you're racing on bumpy surfaces.  The suspension corners need to work for the car to handle.   With the after market sway bars , you are doing the right thing. The hobby horse action may be due to poor shock set up.  start at 50-50 and move either direction front and rear to see what helps.  I suggest you should set your rears to max rebound to reduce forward weight transfer under heavy breaking.

Feel free to write again is you need further help !

Good Luck
Dan Liddy
Sarasota, Florida

---------- FOLLOW-UP ----------

QUESTION: Dr. Dan,

Many thanks. Good suggestions.
I have Tokiko Illumnia adjustable shocks up front set for setting 6 which is max stiff.  Could only find Koni adjustables for the rear when I set the car up, and at first set those at mid setting but now all four shocks are at max stiff.

There must be something about the 510 geometry which allows or requires extreme spring rate of 800 pounds.

That leverage you mentioned.  My mind boggles with the idea of 800 pound springs in the rear of the ZX. The 240 Z (no X) racers out here use half that. But as you pointed out the ZX rear is not at all the same. And probably for that reason so few race it, that I cannot get any first hand advise on rear rate. If you know anyone who servioulsy raced ZX back in the day, and if they still have memory...  

Alas.

Art

Answer
The ZX rear suspenison is a semi-trailing-arm arrangenemt called the "Weissach Axle". Developped in 1955 for the racing Porsche RS series- - -it didn't work the cars were unpredictable and handled like fat street sedans. Eventually they sold the incredibly stupid idea to BMW who used it on the 2002 series-- - - it still didn't work.  Nissan (Datsun) came along and copied to for the PL 510 which I race- - -it STILL didn't work but BMW sued Nissan so they had to quit making that model of 510.  The first Z cars had a symmetrical lower A arm with Chapman strut arrangement which worked very well and the cars were raced successfully for at least 3 decades. But in 1979 Datsun in their wisdom , decided that the semi-trailing-arm arrange ment still had potential so they started using it on the 280 ZX and the 300 ZX- - -it still didn' twork- - -and it NEVER WILL !  Make it stiff as hell and live with it - - -all you can do.

Note that the springs on the older Z cars are very close to the wheel, while those on the ZX's and the 510 are halfway to the middle of the car's A arm- - - it's the Germans fault for the stupid design, the the Japs fault for stealing it and thinking they got away with something !

All the Trans AM ZX race cars were converted to a solid rear axle with a Frankland or Halibrand quick change center section. They were tube frame cars with  four link rear, and coil overs. They handled like race cars and won several championships with Paul Newman, Bob Sharp, John Morton and others.  

There's a history lesson for you, and my best answer !

Dan Liddy