johnc

>> On a 280Z you might be able to run the >> 300 rear springs without a roll bar, but >> I doubt it. > ** (Me, with asterisks) This seems counter- > intuitive - stiffer springs with the > existing roll bars ought to eliminate some > of the body roll, hopefully without > upsetting the balance I have worked so > hard to achieve. When I used the term "roll bar" above I meant the kind that goes inside the car to protect yer noggin. > ** I have a bolted-in cage - not much help > but it ought to keep the car from twisting > more than 10 degrees. Bolted in cages can work well to help stiffent the chassis, but you have to fabricate some good mounting and backing plates for each spot the cage is bolted to the chassis. The ones I've seen "out of the box" from Autopower are good from a safety standpoint but need some more fabrication to help the Z chassis. > Maybe 250/300 is too much - 225/250 sound > better? With your cage I would go to 250F/275R. The Tokico Illumina applications used in a 240Z have trouble controlling rebound with spring rates over 300. When I ran them on the back of my 240Z (with the 300 springs) I had to keep them at 4 or 5 to get close on the rebound, but that made compression WAY too stiff and the back of the car would hop over bumps. With 275s you can turn them down to 3 and with 250s you can, maybe, turn them down to 2. > Speaking of suspension setups, the hot > ticket for racing these days (on a 240, > anyway) seems to be stiffer springs in > front than in back, and NO rear anti-roll > bar! Seems odd to me, Seems odd to me too. I'm haven't had any lengthy discussion with any of those guys to figure out why they run that setup. Its run mostly by East coast ITS racers and there's no arguing how fast they go.

On a 280Z you might be able to run the 300 rear springs without a roll bar, but I doubt it. On a 240Z the rear of the car will start flexing with spring rates over 275 unless you have a welded in roll bar or cage. On the front you need a strut tower brace (and more if the rules allow it) to run spring rates over 225. Also, if you go with the higher spring rates you might need to drop the anti-roll bar diameters a bit. There are generally two schools of thought on suspension tuning: 1. Big springs, little anti-roll bars. 2. Little springs, big anti-roll bars. With the advances in shock technology today, #1 is where most everyone is going. With the triple adjust Penskes on my 240Z, I currently run a 25mm front and a 23mm rear anti-roll bar with 275F and 300R spring rates. I'm actually thinking about dropping the anti-roll bar diameters a bit more, but I'll have to have them custom made. fyi: My car weights 2200 lbs and has almost perfect cross weights. Your car is probably different, so adjust accordingly...

Now its time to up the spring rates. What size anti-roll bars are you running?

Racecar Egineering's editorial office is at: Focus Network Racecar Engineering Dingwall Ave. Croydon CR9 2YA England +44 020.8774.0600 I buy the magazine off the newsrack at Barnes and Noble ($7.95). I used to have a subscription, but when RE moved to their new offices I stopped getting it. Another good resource is Race Tech. They publish 6 times a year. Again, I get it off the newsstand but both magazines are distributed by: Eric Waiter Associates (EWA) 205 US Hwy 22 Green Brook, NJ 08812 732.424.7811 You can probably contact EWA and get a subscription going. Race Tech is happy to publish well written and photographed car engineering/design stories from regular racers like us. Their editorial office is at: Race Tech 841 High Road Finchley London N12 8PT England +44 020.8446.2100 FYI... Both recent magazines have a great discussion about Ackerman steering. [ June 20, 2001: Message edited by: johnc ]

And the recent discussion about the Advantage CFD software in the June issue of Racecar Engineering confirms that, without a rolling ground plane, wind tunnels are inaccurate by some significant numbers when testing underbody aero. More Advantage CFD testing trivia: Running your race car close to "the wall" generates drag and creates a yaw force turning the front of the car away from the wall and pulling the rear of the car towards it.

What Mike said is correct. For years I ran stock calipers and rotors ('cuz the rules wouldn't allow any changes) and they work surprisingly well. You do have to do two things: 1. Take meticulous care of the calipers, rotors, pads, drums, and shoes and bleed the brakes after EVERY track session. In general, I would inspect and completely rebuild the brake system on my car every year. 2. Get LOTS of air to the front rotors. You have to build special cool cans to route the air to both sides of the rotors.

Funny that this topic has come up... I've been half-heartedly designing one for my 240Z but its not for top speed, more for downforce. The floor pans of a 240Z are actually OK from an aerodynamic standpooint, you would just have to seal off the drivshaft tunnel. The diffcult parts are from the spoiler to the firewall and from the rear of the floor pan to the rear bumper. So far I've determined: 1. The front crossmember has to be replaced. 2. The rear fuel tank has to be moved up or forward. In addition, you ahve to some work to help with engine, transmission, and diff cooling. No timeframe on when I'll get this figured out (if ever) but its fun to think about.

I don't think they really check noise at smog inspections. The exhaust system from the cat back is pretty much open in CA.

My previous post was typed very quickly (as you can tell by the spelling) 'cuz I was late for a meeting. Here's some more information that I've been able to figure out (remember, my thinking was along the lines of downforce for road racing): Front Pan --------- You need to run more of an air dam than a spoiler. Attached to the bottom of that you need a splitter poking forward a minimum of 4". This splitter continues, completely flat, rearward and then curves up behind the radiator, then back down and flat again right at the front wheel center line (the steering rack and the crossmember get in the way here). The intent of the upward curve is to create a low pressure area right in front of the the front wheel center line, creating some front downforce (the splitter does this too). The belly pan continues rearward and mates with the stock floorpan at the firewall. The sides of this front pan need to be sealed from the front wheel wells and the wheels wells need to be vented at the tops of the front fenders just in front of the front wheel cetner line. You also need to figure out where the air exiting the radiator can go (normally it exits down). You'll probably have to cut a big hole in the hood to vent the radiator air up. This can also be tailored to generate downforce. Floor Pan --------- Take a big hammer and pound a concave profile (looking from front to rear) the length of each floor pan making some simple, shallow tunnels. Rear Pan -------- This one will be tough. It will be basically flat from the end of the floor pans but you will have to tuck it above the lower control arms. It will probably have a fairly complex shape. Right after the rear control arms you angle it upwards from 5 to 7 degrees constant (this is is where the fuel tank gets in the way). This rear diffuser would continue past the rear valance and extend about 2" past the rear of the car. Some strakes would need to be added in the diffuser to control flow. Exhaust System -------------- The exhuast should exit into the lower center of the rear diffuser to add some flow velocity. The pipes should be contained within the sealed center tunnel. Heat Management --------------- Haven't figured that out. Ride Height ----------- 1.5" to 2.5" maximum. Spring Rates ------------ You are changing the platform itself from one based on mechanical grip to one based on aero grip. Starting rates would be 500 lb in????? - ultimately determined through aero testing. What you are building here is an aerodynamic platform that must be strictly controlled. Fore-aft pitching and lateral roll upsets the platform and severely reduces downforce (grip). Conclusion ---------- It would turn the 240Z into something that it couldn't be good at. You would save money by buying a GT3R Porsche and end up with a much nicer car. [ June 14, 2001: Message edited by: johnc ]

FWIW... I feel that the Kumho V700s are closest in feel to my sorely missed Yokohama A008RS2s. The best part is that the Kumhos stick better that the old A8s.

Loosen those links! You've most likely preloaded the front anti-roll bar. With the car sitting on the ground and level (side to side and front to back) you should just snug down the link bolts. The bushings on each side of the bar end should be just snugged to the bar end - ditto with the bushings on each side of the lower control arm. And don't be upset if more thread is exposed on one link bolt - that won't affect the anti-roll bar or how the car responds. FYI... I replace the nut on top of the link bolt with a self-locking Nyloc nut. [ June 06, 2001: Message edited by: johnc ]

I think you're better off fixing the problem instead applying a band-aid. FYI... Hypercoil spings are made by Hypercoil in Indiana. I've been to the plant and seen the springs being made.

For track events you want to hit and maintain a hot tire pressure. For autocross you start with a cold tire pressure and (hopefully) see a 4 psi increase (for Kumhos) to about the same hot track psi. What you REALLY want to accomplish with tire pressures is to control rollover and tire temps. Kumho V700s need to roll over to the tops of the tiangle shaped wear indicators. Adjust your tire pressures to get to that point. You can use shoe polish to check the rollover during each track session. If you have a tire pyrometer, you already know enough (assuming you knew why you just spent $150...) to get the pressures where you want them. FYI... on my 2200 lb 240Z I start with cold pressures of 26 to 28 psi and run hot pressures of 32 to 34 psi.

I've driven on the street, autocrossed, and done some track time with a welded up R180. For the street its a real pain and not worth the trouble. For autocross the car's suspension has to be setup for it and your driving style has to be changed to work with (not against) the understeer created by welding up the spiders. For track, its not that big a deal, although some suspension and driving style changes are necessary. So, if you need the traction for competition purposes and your willing to adjust the car and your driving, then its a good and cheap route to take. For street use, its a waste of time, tires, and your patience.

Wow! I'm cited as an expert on something! That's scary... Sorry for the late reply, but I've been traveling a lot for work. I've run a welded diff, a Nissan Comp LSD, and I'm now currently running a Quaife. My car is a BSP prepared 240Z (L6 with ~175 rwhp and full racing suspension) and it gets autocrossed and tracked at least once per month. The Quaife is by far the best diff I've run and I'll never run anything else (in any car I race). Its so effective I had to adjust the suspension to take advantage of it. So far, no manintenance and no troubles. In the past I had to rebuild my Nissan Comp LSD every year. Autocross is particularly hard on diffs.

I had a set of A032s on my 240Z and sold them as quickly as I could. Incredibly noisy and nowhere near as good as the old A008RS2s. Dan, you might want to look at a set of full tread depth Kumho V700s. Cheaper and they work really well.

The 280Z stub axle has 27 splines on the companion flange end, while the 240Z stub axle has 25 splines. The 280Z stub axle is still available from Nissan new and are a better design than original (better radius on the flange to axle weld). [ May 16, 2001: Message edited by: johnc ]

I drove a Nissan Patrol when I lived in Lake Tahoe. They are pushrod 6 cylinders and appreaed to based on the Chevy 235 6 as Ray said above (they use the same oil filter). [ May 16, 2001: Message edited by: johnc ]

Those are the EMI Racing camber plates and Erik has a patent on the design. He's had to hire a lawyer to enforce that patent a couple times with some very well known suspension design companies. In fact, it looks like those plates in the picture are the ones we just took off my 240Z. I have a new, slightly improved design on my car now which uses a Teflon monoball and stronger Torington bearings int he front. FYI... I can get 8 degrees of positive caster using those plates.

A question for you folks... Background SCCA Solo has just announced a regional only class (eventually a national class if enoguh competitors are interested) that allows our Zs to compete using the same Street Modofied rules (http://streetmodified.org) that allow open engine and driveline mods. Unfortunately they require and engine from the same manufacturer as the chassis... There are displacement, weight, and aspiration breakdowns of which two are relevant: A. 3.0L Forced Induction 2,100 lbs B. 3.0L N/A 1,900 lbs My current BSP 240Z weights 2,200 lbs wet and I can probably get it down to 2,000 lbs easily and still meet the rules. So, I was thinking about building a motor for this class. I talked with Jim Thompson at Sunbet and he gave me two basic options: 3.0L N/A L6 with ~275 hp. 3.0L N/A VG30 with ~350 hp. Going the VG30 route looks like about double the cost and triple the time because of the fabrication involved and lots of driveline changes. My question is: which one would you folks do? FYI.. the RB engine series is not allowed because it was never installed in a US spec Nissan.

Uuuhhhh... there are a bunch of software programs out there that figure this stuff out. Here's a link to a lot of stuff: http://roadsters.com/software/#software

Forget bumpsteer for now. It seems that the REAL problem is understeer. Let's come up with a list of things to work on to correct that problem, using the existing hardware on your car. 1. Driving Style. As TimZ inferred, this is absolutely the #1 cause of understeer in ANY car. Entering a corner with the brakes on fire and then throwing in an armful of steering will unstick the front tires instantly. I'm not saying that's how you're driving the car, but I suggest that you try a session at your next track event without any trail braking. Entering a corner, do all of your braking in a straight line and then smoothly turn in. Personally I don't trail brake my Z at all. 2. Ride Height. Most people don't realize how important this is on a Z given its limited suspension travel. With the spring rates and shocks that you have the car can bottom pretty easily. To start, shoot for 5" at the front of the rocker panel and 5 1/2" at the rear. This rake will place a little more weight over the front giving you better grip and turn in. 3. Camber. 3.5 degrees negative on the front is great. Don't go any more. Run 2.5 to 3 degrees negative on the rear. 4. Toe. Toe out in front will help turn in but increase understeer. Try 0 toe in front as a starting point. Make sure you have the stock toe measurements in the rear. Unless you are running rims over 8" wide in the back you can't run more than 1/4 to 3/16 toe in in the rear. 5. Caster. As close to 6 degrees positive in front as you can get with the camber plates, bushings, etc. that you have. 6. Tire pressures. 30 psi front cold and 30 psi rear cold on the Kumhos. If you have a tire pyrometer try for temps betweem 150 and 180 event across the face. If you don't have a pyrometer, bleed off air pressure to about 35 psi when they are hot. I suggest you forget about any hardware changes until you've established a good baseline using the stuff I mention above. Once you've got the car as balanced as possible using alignment and tire pressures then start looking at hardware. BTW... all of this assumes the hardware on the car is in perfect condition. Look for any asymetry to identify a bum shock, etc.

Check out this thread from last January: http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=6&t=000344 A few points: 1. Bumpsteer is not always a bad thing. 2. Total elimination of bumpsteer is probably not possible (or desirable). 3. Removing bumpsteer affects other suspension geometries (you don't get something for nothing).

A new stock diff mount and a new strap, cinched down tight against the front of the diff works as well as a solid mount. It just requires a bit more work to get the strap down tight.

Alignment specs for my 1970 Solo2 BSP car: L6, 15 x 8 rims, Kevlar offset bushings, non-adjustable anti-roll bars. Ride height: 4.5" Rake: .5" negative Cross weights: Diag 50.2% - 49.8%, Long 50.1% - 49.9% Front Camber: 3.5 degrees negative Camber gain: .5 degrees negative Caster: 6.5 degrees positive Toe: 3/8" out Bump: 1/8" out Rear Camber: 3 degrees negative Camber gain: .5 degrees negative Caster: forgot...? Toe: 3/16" in ------------------ John Coffey johnc@betamotorsports.com [This message has been edited by johnc (edited March 30, 2001).]