1971 240Z BSP Build: Suspension Advice needed

[GabeD1]

I just bought a 71 240 to build into a BSP car for autocross.

I am completely new to Zs but I have been autocrossing and working on cars for about 5 years.

I am on a tight budget and I would like to keep this car streetable but still competitive locally.

 

Here is what i have planned for the suspension:

225/45/15 tires (Hoosier A6 or Toyo RA1)

15x7" or 8" wheels 4" Backspace

AZC springs with 1"f, 3/4"r sways OR ST springs with 1.125"f, 7/8"r

Koni shocks OR maybe illumnas

Strut tower braces

Poly Bushings everywhere except TC rod

 

Is there anything else I should do to the suspension. Any advice is appreciated. TIA.

 

Here are some pics of the car:

 

 

Here is my current DSP car:

[JMortensen]

You can get a lot more crazy than that with the suspension in B/SP. It sounds like it would be a fun car to drive, but probably not terribly competitive. I guess the question is how competitive do you want to be and how streetable do you want the car to be? I'd stick with the stiffer springs and the lighter swaybars, and I would also definitely go with the Konis (yellow, not red). I've run Illuminas for years and I'm not happy with them, unfortunately cost has kept me from going to something better. When I do it will be Konis or Bilsteins.

 

There is a video of the B/SP champ from 2001 here if you want to see what they can be capable of:

http://www.siastuning.com/Video's.htm

[katman]

In the mid/late 1990's I set up Atlanta Region BSP champ Chet Wittel's 280Z (later 4 time ARRC Champ Chet Wittel). I'm sure the rules have evolved, but from what I recall to be competitive you almost have to trailer it. Here's what we did. Everything revolves around Hoosier Autocross tires. Get it low. You can do that by dropping the suspension, which causes all sorts of geometry and shock travel problems, or by running shorter diameter tires. We had all solid or spherical bushings everywhere. Springs were not that stiff really, in the 200 in/lb range for two reasons- one, parking lots are bumpy, and two, soft rear for early hard throttle application has always been one of our mainstays. Car at minimum weight. Maximum allowable engine mods. Limited slip 4.11 diff. Adjustable Koni shocks, because autocrossing is 60 seconds of transitional handling. Shocks are key, which is why you see a lot of remote reservior double adjustables in that sport now. But the most important cog in the machine is the driver. Jon is correct in his assessment; sounds like a fun car to drive, but competitive BSP will require something a little more extreme.

[tube80z]

Here's an old post from a different list about this same topic. Keep in mind that a lot of this was aimed at trying to make a top running car and as Katman pointed out would make a horrible street car. You might want to take a look at the SCCA rules before you get too far along. You may find street modified is a better match for a lot of the common mods that are done to Zs.

 

For let's start from the beginning:

4) car set-up as per John Coffey:

Camber - 3 degrees neg front and 2.5 neg rear

Caster - 6-8 in front (you can decrease camber if you have more caster)

General rule of thumb is one half KPI (steering axis inclination). When running this much caster you also need to check to make sure you don't have too much caster trail (mechanical trail). You'd like to have around half an inch. Also try to have no more than 20 percent of tread width as scrub.

Toe - 1/4 to 3/8 out in front and 1/16 to 1/8 in in the rear

For tight track try rear toe out.

 

Ride Height - 4.5 to 5 inches at the rocker

 

Springs - 400 all the way around. You'll need proper shocks to make this work. Helps to quicken transition times and keep suspension geometry for going all over the place. This is a key difference from what you would have seen a long time ago where the shock was used to keep the car from moving.

 

Sway bars 15/16 front max -- both need to be adjustable and connect to the strut, not the control arm. Sway bar should be in a low friction mount, which is not poly or other form of pinch block. Ideally at least one is driver adjustable for when you need to make the last minute tweak between runs.

 

Offset bushing - Will be needed for street prepared but should be avoided in other classes. Never. Poly has too much friction. These need to be low friction pieces to help with mechanical grip.

 

Good advice on notes deleted. A tire pyrometer is good to indicate wear but not a lot more. But tire pressures are more accurate on how the tires are used. You should work on a setup that gives you an even rise in pressures. This is where good notes and understanding what you need for a hot tire pressure is important. You can switch to nitrogen to help eliminate the effects of water vapor in the tires.

 

To adjust chassis balance you can change the rake. Rule of thumb is two turns of the spring collar to start. If the effect is too much try one turn. You lower the end that isn't sticking. Make sure you keep the arms near level and don't end up too low. The car should be corner weighted. Make the front level and the front weights as close as you can and live with what you get in the rear. Move as much weight down and towards the back as you can but not behind the rear wheels.

 

Remember you need to make ride height changes to compensate for weather conditions to keep a balanced chassis.

 

Also consider using shims for camber/caster plate alignment. These allow rapid known changes and/or allow you to get the car put back together without having to do a major alignment. Before an event always know all your settings. Keep notes of any changes that you make at an event. And at the end of an event do a setdown. This last step is important and few people do it.

 

If you're using the same size tires all around keep notes on how hard they were used and rotate to keep the use as close to the same as you can. Do all chassis setup work on old tires (but not junk). New tires will mask a lot of the changes until you have killed them. By doing all this you'll end up having a car that is kinder to its tires.

 

Test, test, test, and have lots of fun.

[GabeD1]

Thanks for the quick responses, that settles the springs and the shocks dispute. I was leaning that way anyway as I currently use konis on the maxima and they are way better than the tokicos I had before.

 

I dont think solid bushings are allowed anymore, the rules state:

"Suspension bushings may be replaced with bushings of any materials

(except metal) as long as they fit in the original location."

 

Im really not expecting to be that competitive with a street driven car, because this is a pretty competitive area (Washington, DC and Philly region) We generally have between 150-280 participants at each event and there are some serious cars in BSP around here.

 

I should run the 275/35/15 hoosiers to be more competitve but those are a little bit outside my pricerange for now

[katman]

"I dont think solid bushings are allowed anymore, the rules state:

"Suspension bushings may be replaced with bushings of any materials

(except metal) as long as they fit in the original location.""

 

I remember that stupid rule!. Instead of the typical Kontrolle style delrin/aluminum rear inner camber/toe bushings I had to make some completely out of Carsan or something like that. Ditto the T/C rods and outer rear. We might have used poly for the front control arms. What a PITA. @%#$ SCCA...

[johnc]

I dont think solid bushings are allowed anymore, the rules state: "Suspension bushings may be replaced with bushings of any materials (except metal) as long as they fit in the original location."

 

Hydlar Z has a harder durometer then aluminum and is legal for BSP. Its just stupid expensive at around $67 per foot for a 2" OD rod. Black Delrin is even a little bit harder but not as abrasion resistant as Hydlar and is only $16 per foot for a 2" OD rod.

[GabeD1]

One question, although I know this is the wrong way to do things:

I have found that tokicos generally have a lot of compression damping and not enough rebound damping, so would it be beneficial to pair the tokico illuminas with the softer ST springs but set the shocks to full stiff. This would theoretically increase the springrate on compression and hopefully keep the suspension from bottoming. Also by using the softer springs, the illuminas would be able to control the rebound better. The reason I would even consider this over a stiff spring/koni setup is so I could soften the shocks for street driving and it would cost much less.

 

Is my theory completely off or is this a plausible compromise for price and streetability?

[johnc]

This would theoretically increase the springrate on compression and hopefully keep the suspension from bottoming.

 

Nope. Shock valving is not spring rate. Repeat. Shock valving is not spring rate.

 

You would be better off running softer springs and bigger anti-roll bars. Spring rates at or below 200 lb. in. work fine with the big 1 1/8F and 7/8R anti-roll bars.

[GabeD1]

Yeah, I know, I know

 

I was just putting it out there because some of the stock class drivers run way overdamped since they can't change springrates.