johnc

F350 and a Featherlite 18' open car trailer.

There have been a number of threads over the years discussing this exact topic. Use the Search function on this site to check those threads out.

As Douglas implied and I will expand on... Aerodynamic modifications need to looked at as a whole car system if you are not just making changes for cosmetic reasons (nothing wrong with that.) You can achieve a lot with multiple aerodynamic modifications but be aware there's not "one thing" that gives you hundreds of pounds of balanced downforce. Its more an accumulation of many 20, 50, 75 pound changes that lets you realize significant downforce and the realted increase in grip. Using the vehicle's underbody for aero imposes a lot of ride height and suspension design limitations. Specific modifications to side sills and rocker panels will allow a car with 5" of ride height to see significant downforce with a diffuser, front splitter, turning vanes, etc. The volume, velocity, and control of the air under the car is what's important. Actually, the most important thing to control is not the actual ride height, but fore/aft pitch - witness Mercedes problems at Le Mans a couple years ago. Given extensive enough modifications aero can work well at low speeds. A Mod autocross cars are perfect examples of vehicles that can generate over 2gs of lateral grip at speeds under 60 mph. Most of that comes from gigantic wings though.

What you folks are talking about is a rear diffuser. They are an effective means of creating rear downforce (typically from 50 to 200 lbs) but the design is critical. The surface needs to be flat and the upslope angle needs to be as close to 7 degrees as possible without going over (measured at the dynamic ride height of the vehicle at your projected design speed). Over 7 degrees and the laminar flow separates and you just create turbulance and drag. Under 7 degrees and you're not getting the full effect. The diffuser also needs to be as long as possible (the 7 degree upslope section) and extend behind the rear bumper to get a clean flow break. A small rear spoiler on the rear hatch will help flow as long as you don't get turbulence affecting the flow exit. The diffuser also needs to be as wide as possible and have a clean transition from the flat section under the car (sealing the rear diff area) to the upslope section. You will need to add a diff cooler to keep the temps within reason if the car will be raced. Flattening the bottoms of the control arms with sheetmetal, aluminum, or CF will help at the transition area. Coincidentally, the custom ATL fuel cell in my 240 has a 7 degree upslope on the bottom of the can...

Most cars you see with roll cages are built for sanctioned racing. In many cases the sanctioning body specifies the number and type of attachments the cage can have to the chassis. In the SCCA ITS class where most racing 240Zs compete the rules allow 8 attachment points and none can be forward of the front firewall.

The issue with Tokico Illuminas (and other off-the-shelf shocks for that matter) regarding spring control has to do with rebound. The series of Illuminas that fit a 240Z rear (the standard rears or the fronts moved to the rear) can only control a spring with a rate of 300 lb. in. or less. "Stiffness" is compression damping which has little to do with spring control. Single adjustable shocks have a built in compromise in the relationship between compression and rebound damping. Unfortunately, the relationship is mostly linear. Stiffen up rebound damping to control higher spring rates and you get a corresponding linear increase in compression damping - whether you want it or not. A car with well tuned shocks does not feel stiff (assuming no aero ride height requirements). The suspension is compliant in bump and firm in rebound. You want bump compliance to keep the tires in contact with the road and to let the springs do their job. You want firm rebound damping to eliminate pitch and increase responsiveness. Unless you are running rear springs with a rate over 300 lb. in. I would think the Tokico Illuminas would be OK. Try different settings front AND back. When I ran 275 front and 300 rear springs I would have the tokicos set at 3 or 4 front and 4 or 5 rear. Also, check to see if you have a bad shock. The Tokicos do fail.

Dan and Bob, Stop! Don't even think about it! I might actually have to moderate something! WE ARE NOT GOING TO START A DISCUSSION ABOUT WHICH IS A BETTER TRACK CAR - CAR "A" OR CAR "B". That's a guaranteed message board death spiral. Now back to our original non-Z content discussion about tire wear...

My suggestion: You've got too many variables floating around and you're probably getting confused. 1. Put the car back to a known baseline. 2. Get a log book and write everything down. 3. Buy yourself (or borrow) a tire pyrometer. 4. Find a test day at a local track that you know well and are comfortable driving at the limit. 5. Find a couple mechanically inclinded friends who can go with you on that test day. 6. Load up your car and support vehicles with different springs, anti-roll bars, friends, food, drink, tools, etc. 7. Go out and test all day (starting at 7:00am), making only 1 change at a time. 8. You're the crew chief so you decide which things to test first. Focus first on getting the tire temps right. Once you've got that then start looking at lap times to see how you can bring them down while giving you a nice, easy car to drive. Testing tips: 1. Run no more than 3 laps for each change (1 warm up, 2 fast, NO cool down.) If its obvious things went wrong with the last change, come in early. 2. Write EVERYTHING down for each run including weather conditions, changes made, tire temps, tire air pressures, shock settings, lap times, gut feelings, color of pit crew's shirts, etc. 3. Stop and think for 10 minutes by yourself after each test before anyone picks up a tool. 4. Stop for lunch and talk with your crew about the testing progress. See if they have any suggestions. Thank them profusely all during the day. 5. When you get home, write everything down in a nice summary and post it here.

I'll be the skeptic. I think you need to check your ignition system (particularly the coil and the trigger) and your tachometer. Secondly, install a good external shop tachometer and then see what rpms your motor is turning. If all the above checks out, then I'll be a believer. Until then, I seriously doubt and stock SU carb'd L6 will hit 9,000 rpm - at least not more than once in its short life.

Use a tire pyrometer to determine the appropriate camber settings - not tire wear. If you are getting even (or very close) tire temps across the face of the tread and the temps are between 170 and 200 then you are making full use of the tires. A lot of unnecssary caster could be contributing to your inside tire wear problem. Once you get the tire temps right with your camber settings, try backing off the front caster a degree at a time. Still keep a close eye on the tire temps because you will probably have to adjust camber as the the temps change from the reduced camber gain from steering angle. You should also back off your camber settings when driving on the street. So little time is spent driving hard in corners ont he street the extra camber only increases tire wear. In the end, you should also look at your driving style. If the front tires are hotter then the rears you might be entering the corners too hard and using the front tires to slow the car while you're turning because some necessary braking isn't getting done. You might also be getting on the gas too soon or too hard in a corner causing corner exit understeer.

All the cities mentioned are tame compared to.... Athens Greece! 1. Car to car contact is common and expected when merging. 2. Two lanes of travel in one direction will easily accomodate 4 cars side-to-side at speed and 6 if there are no broken down vehicles on the shoulders. 3. Bump drafting starts when the light turns green. 4. Red lights are ingored until enough cross traffic has filled the intersection to physically stop any further running of the light. 5. At intersections, sidewalks are used as the right turn lane. 6. Driving the wrong way is OK as long as you're only going a block or two.

> Personally, I would rather be able to say my > car is fast and I built the motor instead of > saying, Hey I paid Sunbelt 10 grand to build me > a 300 hp NA engine. No personal attack assumed, but I've had a few people privately tell me the same thing some I guess its time to defend myself a little. I'm a chassis/suspension guy. I would much rather disassemble a shock and try different valving then take an engine apart. I've rebuilt and modified about a dozen engines over the years but I just get more excited about what's involved in suspension and chassis setup. To me an engine is just big heavy a lump that gets the way of good suspension design. They never make engough power and what little power they make is always at the wrong rpm. Plus, they are tempermental and require a lot of attention. If I have the money I would much rather pay someone to build me an engine to my horsepower specs and provide a warranty on their work. Luckily, for the first time in my life, I had (notice the past tense here) the money!

Ya skip a topic for a couple days and look what happens! Given enough time, money, and talent any L6 head can be made to make good power. The only valid comparisons that we (as non engine builders) can make are between stock, unmodified heads. I had a discussion about this exact topic with Jim Thompson before he started on my 3L and a couple years earlier with Don Potter. Both agreed that the early E88 (for 2.4L) and the N42 (for 2.8L) were the best heads to use assuming you couldn't do any modifications. This is coming from engine builders who have build (combined) hundreds of ITS L6 engines over the years. One caveat - I think the P79 is not ITS legal on the 280Z and no one runs a 280ZX in IT that I know of, so Jim and Don probably never really looked seriously at that head. The E31 got a good reputation because its closed chamber increased compression and horsepower enough to overcome its smaller valve and reduced port flow. Since then, the above two guys figured out how to reach the ITS 9.5 to 1 compression limit other ways, they prefer the E88 and the N42 because you get the best of both worlds. Going back to DATTOZG's original question about using (I assume) an unmodified head on his 2.8L I would go with what Jim and Don go with when they build racing motors for paying customers. As a side note, when it comes time for me to refresh the N42 on my 3L Jim wants to build up a P90 head. He thinks there might be ways to get a little more out of that head (for reasons he wouldn't tell me) then what I'm getting out the N42. FYI... my N42 is heavily modified.

Dan you're right. With the wheel striaght ahead the stock Z suspension does gain camber in bump. With the wheel turned you get that normal camber gain plus any additional camber gain inhernet with positive caster. In my mind I guess I never separate the two because I'm always thinking about what the suspension is doing in a corner. But, the built in bump camber gain and the steering angle camber gain from caster are two separate items.

Aluminum/Delrin bushings work geat on a race car but they must be properly installed, checked many times during the racing season, and replaced regularly. They are not designed to last like OEM parts and they will wear out quickly.

Most of the VIN checking web sites only work with the type of VIN number the US government standardized around 1980. Before then an auto manufacturer could issue whatever they wanted as a VIN number. The HLSxxx is correct for your Z.

> You may laugh, but with 30 years of oil left in > this world it might be a good contingency > hybrid to explore. Heard that back in the early 1970s and again in the late 1970s. I guess it must be a rolling 30 year supply...

Ask to do some welding with it at the seller's shop. If it works, then its probably wortht he money.

Something is probably bent or worn out. If the car's hit a curb sometimes the spindle pins get bent and cause odd toe settings. Of course, if you have offset inner control arm bushings and they are not tight or pinned they sometimes rotate and you end up with the problem you describe.

Sounds like your clutch might be slipping a bit. I've always been able to tighten that nut with the trans in 4th and someone sitting in the car with their foot on the brake. You might try removing the starter and wedging a pry bar against the ring gear.

Yes the rack has inner joints but, if the rack is in good shape the inner joints are probably in good shape too. They are also pretty expensive. Try replacing the outers first and see if that cures your problem.

Mike... I might be mistaken, but I think your guys are running bias ply slicks. If that's so, they work best with 1 to 1.5 degrees of static negative camber. Radial slicks and DOT-R tires prefer more static negative camber regardless of the camber gain in the suspension. On the early Z suspension caster controls the amount of camber gain in bump. More positive caster, more camber gain. I think the stock suspension will pickup about 3/4 of a degree negative camber in bump. With a lowered car and modified caster/camber you can increase that to about 1 degree. But, getting the driver comfortable is important too. If Richard is happy with the way the car handles and the tire temps look good, there's no reason to change it.

That's fast. Watch out for dragon flies.

You'll find out when you try to remove the insert. You can also place a good straight-edge vertically against the tube and check 4 places around the circumference.

Maybe because the Z32 TT is a really nice car? Don't worry about their attitudes, just beat 'em on the track.