johnc

You have two things to think about when venting the engine compartment: Car stopped, car moving. Car Stopped Hot air rises. You need openings in the hood to let the hot air rise out of the engine compartment. If you can build chimneys from the exhaust header to a hood opening (a la Aston Martin Vanquish) that will really reduce compartment heat. Car Moving Generally you have a low pressure area under the vehicle so directing air in and then down behind the crossmember is effective. Move the air past the hottest parts of the engine (the exhaust header).

The wheels are custom Monocoque 16 x 9s. Flare installation takes a lot of time (I took a couple days) because you want to be very careful measuring, lining things up, marking, standing back and looking, etc. The actual metal cutting and hole drilling took a couple hours at most using an air nibbler.

> With a sway bar removed from the rear, you > would also use a higher rate to "compensate" as > well, yes? Anti-roll bars are a tuning tool. Ideally you use springs to achieve the overall balance and basic response you want and then add anti-roll bars to adjust response for driver style and track. In the real work, anti-roll bars tend to be relied on for balance more then they should.

I'll be running against Terry Chen's Motorsport Elise at the next Open track Challenge. Luckily last year the car ran in U4, but it was still buttloads faster then our ITS 240Z - until the Lotus broke. Hopefully next April we'll have them covered or we can hope for renowned British reliability.

You need internal balancing and external damping.

For SCCA you have to purchase their General Competition Rule (GCR) book because their rules require that you have it in your possession at the track whenever you race.

A 1/4" spacer on the front can help reduce understeer with 7" wide wheels IF everything else on the car has been setup correctly for autocross. Otherwise, it just adds weight.

Jeez! Cutting the main hoop basically makes the roll cage illegal for SCCA, NASA, NHRA, IHRA and pretty much any race sanctioning body. Hopefully you were not intending to do any formal racing with the car.

Worst packaging ever... Hewlett Packard's packaging for one ink-jet catridge: 8 1/2 x 11 heavy plastic welded edge panel. 8 1/2 x 11 cardboard display panel 5 x 5 x 2 cardboard box slightly smaller cardboard box instruction pamplet Mylar bag 1 CD full of advertising 1 CD sleeve two separate multi-page advertising pamphlets 5 single page advertising inserts

> Can someone please explain why the Z cars use > such a high rate in the rear so favorably? Now that I've posted the basics, I can answer this question: Stop comparing spring rates from different cars! A 600 lb.in. front spring on a Pony car probably works out to a 300 lb.in. wheel rate which is probably only slightly higher then the rear wheel rate. Vehicles with 50/50 weight distributions tend to run fairly equal wheel rates at each end of the car. Vehicles with 60/40 or 40/60 weight distributions tend to run more disparate wheel rates. Often, spring rates are "adjusted" from the best calculated rate to achieve some kind of handling trait that the driver or track prefers. Some people prefer a Z car that leans more towards oversteer so you "might" see a higher rear spring in those cars. Other drivers or tracks might prefer a more understeering Z so in those cases you "might" see a slightly higher front spring rate.

OK, back to basics... Spring Rate Force per unit dispalcement for a suspension spring alone. For coil springs (which we are discussing) this is measure axially along the centerline of the spring. Wheel Center Rate (Wheel Rate) Vertical force per unit vertical displacement at the location along the spindle corresponding to the wheel centerline, measured relative to the chassis. This rate is generally lower then the corresponding spring rate due to Installation Ratio (or the lever arm length from the spindle to the spring and control arm pivot). The wheel spindle vertical travel is almost always greater then the corresponding displacement (vertical travel) of the spring. Installation Ratio A geometric concept that relates to the change in length (or angle) of a force producing device (e.g., spring, shock, anti-roll bar ) to a change in vertical wheel center movement. Its the inverse mechanical advantage of the wheel center to the force producing device. More simply, its the rate of change of spring compression with wheel movement. ----- On a McPhereson strut equipped vehicle the coil spring center axis is essentially in line with and moves almost the same vertically as the wheel center. For purposes of our discussion there is no installation ratio to be calculated to determine the actual force AT THE TIRE (which is what we are really concenred with here folks). On a control arm suspension the spring is mounted inboard of the wheel center so there is an installation ratio that MUST be factored into determining the force at the tire. Assuming a linear change in installation ratio (no rising rate in the suspesnion) installation ratio is a standard calculation of the mechanical advantage of a lever expressed as a ratio. Here's the math: Kw = Ks(IR)squared where: Kw = wheel rate (lb.in.) Ks = spring rate (lb.in.) IR = installation ratio

> part of the reason that race cars use a > straight weight oil. Let's see... 2001 SCCA CSCC ITS champ uses Mobil 1 15W-50 2000 ALMS GTS runner up uses Mobil 1 15W-50 2001 ALMS Paul Revere 250 winer uses Redline 15W-50 1999/2000/2001 Chili Bowl SuperSprint winner uses Mobil 1 15W-50 In racing, your biggest concern regarding oil is keeping the temperature down. Worrying about additive packages, etc. is a waste of time. Keep the oil as cool as you can. If you can keep the temps consistently under 220 then regular oil is fine. If your temps creep up and run at 240 consistently then a synthetic is a better choice. A spike now and then in temp doesn't instantly "kill" the oil. I've seen 260 on regular oil and 310 on synthetic and later chemical analysis showed no probblems. BTW... for a street car you biggest concern should be the detergent package. I have yet to see a street car consistently run its oil temps up around 220 (except maybe a poorly tuned Bug on a hot day).

No. There are a bunch out there and they are not reliable. Every 24 hour endurance racing car I've had the chance to look under or work on uses a belt driven mechanical pump from Peterson, Barnes, etc.

OK, I forgot the shock shaft is structural too.

> The Z car is a strut suspension. Correct, McPhereson struts in front and Chapman struts in the rear. > This means the "shock" not only damps but is a > structural member of the suspension, a locator > if you will Nope. The strut tube is the structural component. The shock itself runs inside that tube as either a piston running directly against the internal wall of the strut tube (as originally delivered by Nissan) or as a completely sealed insert inside the strut tube. > and the spring is around the strut cartridge. Nope, its around the strut tube. When a shock body in a custom installation also works as the strut tube its mostly referred to as a "strut" by SCCA and NASA but, occaisionally, its called a "shock" (in particualr when referring to threaded shock bodies). Go figure.

For a street car you're fine and a lot of this doesn't really apply until you're pushing the edge on a race track.

What TimZ said...

I just wanna see the frickin' torque wrench they use to tighten the mains down.

In my case, with a custom 20 gal. ATL fuel cell, the angles from the stock location and the rear plate are too shallow to work with racing dump cans.

Here in the US there are easy coast and west coast schools of thought regarding ITS Z spring rates and anti-roll bars. Easy Coast used higher spring rates in front, a big front anti-roll bar, and no rear anti-roll bar. West Coast reverses the spring rates and uses a small front anti-roll bar and a medium or big rear anti-roll bar. One day I would like to arrange a test at a neutral track somewhere in the midwest, invite Chet Whittle and Erik Messley, bring a well powered ITS 240Z, and a bunch of springs and anti-roll bars to do hours of back-to-back testing.

Welding temps are about 2,800F regardless of process. Any coating on the opposite side of an 18ga steel weld will probably see 2,799F. Not much will survive that.

Dan, On a 240Z you do not want equal spring rates at all 4 corners. You will get some opposite phase oscillations depending on the bumps on course which feels as I described above. I just spent some time tuning a friend's WRX and his car exhibits the same tendency. Until we can increase the front spring rates we have to run so much rear rebound that the inside rear tire picks up occaisionally.

Inlet size reduction. I don't know about the quality of the muffler. BTW... the two best performance mufflers are: Coast Fabrication Borla XR-1 The first is too loud for the street and the second is tolerable - for a little while.

Sometimes when bleeding an old brake system you overextend the seals in the master cylinder by pushing the pedal to the floor. That pedal probably hasn't been near the floor for years so the master cylinder piston seals now get forced through varnish and dirt built up in the bore. Any leak is bad. Replace parts to fix the leak. Also, expect to go through a couple quarts of brake fluid bleding a purged system.

If you're starting from scratch, calcualting the correct spring rate for a particular end of a car is pretty complicated. It involves much more then just static corner weights and wheel rates. Other things like: Transient Stability and Control Ride and Roll Rate Suspension Geometry Wheel Load and the big nasty one: Aerodynamic Load Luckily, the OEM engineers figure a lot of this stuff out for us, so a quick and dirty way is to double the spring rates at each end, maintaining the same percentage relationship as the stock spring rates. This will get you into the ballpark (or maybe the parking lot of the ballpark). To do it right, you need to do a lot of math. Buy "Race Car Vehicle Dynamics" by the Millikens and use the formulas they provide (I stole the list above from some of the chapter headings). There are also a number of suspension design programs that will show you the numbers but generally won't tell you which ones are right. For the Datsun 240Z a lot has been figured out so looking at what people have been using for years is a good practice. I doubt someone will come up with a new winning spring package that hasn't already been run by at least 20 other people. One thing though, no one to my knowledge has applied any of the cutting edge downforce generators to a 240Z. When that happens you will see significant changes in spring, shocks, and anti-roll bars. Be careful about copying those setups (and be wary of someone trying to sell you that setup) unless your car generates similar downfoce numbers. This is an example of where "Monkey-see, Monkey-do" can get you in a wreck.