TimZ

Two inches? Holy Crap! Sorry - I'm just jealous - it must be nice to live where they have smooth roads - you could never get away with that in Detroit. Anyway, check these threads, where we have beaten the bumpsteer issue to death... http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=6&t=000344 http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=6&t=000566 http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=6&t=000549 As far as strut length goes, it doesn't have that much effect on the bump steer curve itself, but it will change what part of the curve you normally use. Trouble is, the stock curve is less than desireable (generally alot less) when you lower the car. So, these discussions are still valid for you. As far as changing the shock settings, there is a good chance that the ride might become more bouncy if you go to the lower settings. Maybe not, though. Is there a reason you haven't just tried it? You'll be the best judge of whether or not it's acceptable to you. For starters, I'd recommend changing all the settings the same way, though - this should keep your base handling characteristics the most similar. [ May 13, 2001: Message edited by: TimZ ]

Sounds like you are on to something there. From your description, I doubt that your problem is a leak, though. I'm more inclined to think that you have a restriction somewhere between the compressor and the TB. Maybe a restriction, followed by a leak. The most obvious culprit is the intercooler. I'm not sure how to flow test one of those, but it would be interesting to see what pressure drop it generates for a given amount of airflow (specifically, the amont of airflow you generate at 20lb of boost). As I recall, your I/C was from a turbo diesel application. I'm guessing that you are flowing quite a bit more through it than it's designers intended. Another possibility, depending on how you have your crankcase vented, is that the intercooler is filling up with blowby oil, which is actually pretty common in turbocharged engines. This would cut off the bottom tubes of the I/C, and effectively make the intercooler smaller and smaller as it fills. Also, any oil spray lining the walls of the remaining tubes will greatly reduce their efficiency, and if any of it gets to the intake, it will reduce the effective octane of your fuel. Anyway, that's where I'd start looking. Good job in using instrumentation to identify your problem areas, BTW.

I had one of the Cartech Triple Mikuni setups on my car, and have since upgraded to EFI, and a bigger turbo and wastegate. The Cartech setup was a single turbo with a 2 core intercooler, and Cartech claimed 315hp at 12psi of boost, as I recall. The horsepower numbers listed sound reasonable, assuming the boost had been cranked up a bit, and alot of tuning had been done on the Mikunis. Cartech offered this kit in the mid to late 80's, and it has not been available for over 10 years, to my knowledge. I don't know why Jim Cook still shows it in their catalog. In it's day (remember that this was before any aftermarket EFI systems were available) this was the most exotic setup that was available for the Z, and it worked reasonably well, at least at full throttle. The Mikunis did not deal with transients very well - the engine would bog severely, say, if you downshifted from 5th to 3rd and nailed it. So overall, the system made pretty good power, but the driveability was not so great. When I converted over to EFI (TEC-II), the driveability difference was night and day, even before I had the thing dialed in.

Doh! It just keeps getting worse. Anyway, I pulled the trans last night, and am taking it in today. I think I'm getting a little too good at this - 2.5 hours from car intact on jackstands to trans in the trunk of the Taurus...

quote: Originally posted by jpd280z: Q1 - AIR, there is a VW strut insert that is the preferred choice when shortening struts. What year/model VW? Tokico part #? Any other choices? Is that car similar in front-end weight to a 280Z? Any caveats with this strut? We had a pretty good discussion on this a while back: http://www.hybridz.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=6&t=000319 quote Extension tube? Not sure what this is. On a 280Z, you can lower the car by an inch, while keeping the same travel, just by using the rubber isolator assembly from the front - they are about an inch shorter. If you are using camber plates, you might also be able to get away without sectioning - depending on the plate, this can lower the car by 1.5" or more, as I recall. quote Compression travel will be increased by the amount the strut is shortened, all else equal. You also need to look at the difference in mounting height between the stock isolators and the camber plate, if you are using one. quote A butt weld should work fine, as long as the joint is prepared well, and the weld has good penetration. I sectioned mine in the middle - it seemed easier to put braces on them to keep them straight while welding this way. In retrospect, it probably would have been just as easy if I'd made my cuts near the top. This would minimize problems that would occur if sections weren't welded back together perfectly straight. Just make sure that you leave the threaded part, so you can attach the gland nut. I clamped the tube sections together between two long pieces of angle iron to keep them straight. Also, I'd recommend buying or renting a tubing cutter that's large enough to fit on the strut tube (~2-1/16"). It might not be able to cut all of the way through, but it will get most of the way, and leave a nice straight cut for you to work with. I would think that for a piece of tubing to be strong enough to act as a splice, it would end up being thick enough that it would interfere with the spring. It would definitely interfere with the spring collar - you need to slide it over the strut to install it. Hope this helps - good luck.

Another reason to do the remote oil filter with an oil cooler would be so that you could run filtered oil through the cooler. The sandwich adapters pretty much force you to put the cooler before the filter.

I don't think it should hurt anything, but c'mon, Tom... TWO hoses are going to take until winter to hook up? I hate to think how long it takes you to change the oil...

I'd been meaning to say something about that - If you are running oil lines to the front, I wouldn't use anything smaller than -10 (5/8") hose. A lot of the racing coolers come with -12 (3/4") fittings. Otherwise, I think you'll see an unacceptable amount of pressure drop.

Well, it's always something. I finally got my car back on the road a couple of weeks ago, with a freshened trans and diff, new clutch, new CV's, etc., and it had been running exceptionally well. I drove it around for several hours yesterday, and it didn't skip a beat. This morning, I pulled it out of the garage, polished up the wheels, and then pulled out of the driveway to go for a ride. Oddly, in first gear, there is a definite periodic clunk sound coming from the drivetrain. I put the car up on jackstands, checked underneath and didn't see anything obvious, so I started it up and tried just releasing the clutch in different gears. The noise is definitely there, and it only does it in first gear. I can hear it quite clearly if I put my ear to the gearshift knob. Next, I drained the gear oil out of the trans, and checked the magnet in the drain plug. There were a fair amount of fine shavings, but no big pieces of gear tooth or anything. I'm guessing that I'm going to have to pull the trans back out and have it looked at. The weird thing is that I drove it all over creation yesterday, and everything was fine, and now this morning it sounds like it lost a tooth. I guess maybe something was almost ready to let go, and it decided to do it today? Anybody have any ideas/suggestions, before I pull this thing? I'm going to wait a day or so, just in case I'm not thinking of something obvious.

Another couple of tidbits that should help... For any triangle, the sum of the three angles is 180 degrees... a+b+c = 180deg I'm guessing that the problem that you are having has to do with the fact that the triangle that you have described is not a right triangle, so you aren't sure how to apply the trig functions. Another trick that you can use is to split the unruly triangle into two right triangles. Since you know one of the angles, and all of the lengths of the original triangle, you will have one of the angles and the length of the hypotenuse for one of the smaller triangles, which means that you can use the trig functions to get the lengths of its other two sides. Once you have done that, the lengths of the sides of the other triangle are a couple of easy subtractions away, and then you are home free.

Mike... This is precisely what I was advocating in the previous bumpsteer posts. If you replace the stock tie rod end with a Heim joint rod end, you can do the bumpsteer adjustment independently of the other suspension settings, by using spacers between the Heim joint and the steering knuckle. The adjustable steering rack height idea would work in the same manner, but I'm guessing that it would be harder to implement, especially since you need to have seperate adjustment on the right and left sides. To my knowlege, ALL of the other methods of changing bumpsteer are coupled to other suspension geometry aspects (roll center, camber gain, etc), and require tradeoffs to be made. (you just knew I'd respond to this, huh?)

The blowoff valve as boost boost regulator is also not a very good approach. It is best used as an emergency backup to a wastegate, as was done with the stock zx turbos. You are going to have to fabricate something anyway, you might as well fab the wastegate plumbing. This will give much better results.

My gut feel is that you should have a wastegate. However, some of these early turbo kits had the turbos sized such that they were naturally boost limited. While this will be effective in limiting your boost pressure, you should know that this is about the worst method out there for controlling boost pressure. Basically, the turbine is sized such that it chokes itself off above a certain flow rate. The turbo is forced to run out of it's efficient range, and will heat the charge air significantly. Also, this causes a ton of exhaust backpressure (this is bad). If this turbo originally came with the kit, and you are sure that it never used a wastegate, and that it didn't overboost, then you can probably use it as is. Don't expect much power out of it, though. In this case, I'd recommend getting a more modern turbo, and using a wastegate. If the turbo didn't originally come with the kit, then you should definitely use a wastegate. Also, you do realize that you need to modify your fuel injection system to supply the proper amount of fuel for all of that air that you are now forcing though it, right? This is not a trivial task, and the stock FI system will definitely not be able to cope, as is.

quote: Originally posted by jpd280z: OK, spacers are OUT! So much for the quick fix. (ME) For this reason, I do believe that the CA pivot mod is a good thing to do, just don't expect it to zero out your bump steer curve. (jpd280Z) Not expecting zero BS, but an improvement is an improvement. I might try your BS measurement trick - could this be done by measuring the front and rear track width of the tires at different heights? You know, groove to groove? Well, here's the thing... the pivot point mod does essentially the same thing to your suspension geometry as the spacers, so there is the distinct possibility that it won't be an improvement at all. As far as just measuring the toe from groove to groove, yes you can do it this way, if you want to get a feel for whether you have a problem, or whether things have gotten better or worse. I would highly recommend doing at least this, if you do the pivot point mod. If you decide that you want to dial out the bumpsteer, you will need to do each side individually. That said, as JohnC pointed out, I probably did get a bit carried away with the bumpsteer discussion - I just think that this area could use some pointed discussion. I completely agree with John that you should try to find out what's going on with the understeer in your current setup before making such major changes. Try the changes that John already listed out - those are all excellent advice.

Ohhhh man... now you dun gone and did it... You got me talking abut bumpsteer again... quote: Originally posted by jpd280z: 1) I might be bottoming out the front suspension. The CO's helped a lot, but didn't solve the problem. I have my doubts though - my decidedly low-lateral-G street tires exhibit the same tendency, even though the suspension is not loaded as much. However, if (have not jumped to conclusion - all opinions are still valid) I move the inner CA pivot up, which lowers the CM, and thereby the car, then I could crank up on the adjusters to gain some suspension travel. Maybe, if it is a good idea for geometry. Did you section the struts when you added the coilovers? Better question - when the car is sitting at it's nominal ride height, is the shock near the center of it's travel? How much travel do you have left in the compression direction? If you are near the middle, your suspension should not be bottoming. Also, raising the CA pivot point will have almost no effect on ride height whatsoever. Your ride weight is determined by the distance between the bottom of the tire and the upper spring perch. I said almost, because changing the pivot point will have a small effect on the angle bewteen these two points - actually this will probably raise the ride height imperceptibly. I agree that your setup does not sound like it should have a high degree of understeer. One thing that comes to mind - when you say "trail brake like there's no tomorrow", are you describing braking as hard as you want when entering the turn? Forgive me if you already know all this, but inducing oversteer by trail braking is a very subtle technique. There is a relatively narrow range of braking force where this is effective. The trick is to shift the weight forward just enough that you unload the rears. If you go too far, the postive effect of the weight transfer is negated by the fact that the longitudinal braking force uses up too much of the tire's available force, leaving little or no reserve for generating lateral force(i.e. you end up with understeer). Remember - any given tire has a maximum total force that it can exert in any direction - if you are using all of that force for braking, then there is nothing left for cornering. Sorry if you already knew this, but I've seen people make this mistake many times. quote If your roads are relatively smooth, then this will work pretty well. On bumpy roads, the car will quickly turn into a handfull, though. quote: 3) Spacers might help by getting the OEM bumpsteer back and raising RC. Someone said that the MSA BS spacers (appropriate name?) are not the right size or shape - what IS the right size and shape, and who sells 'em? Anyone have pics and a write-up on heim jointing the TRE's? Those spacers are where my experience started with all of this. When I installed them, the actually made my bumpsteer WORSE. I measured the bumpsteer curves before and after, and was pretty much shocked at the results. BTW, I'm talking about single-side toe change on the order of 1 INCH through the suspension's range of travel. Probably not something you'd want to live with. I'm not saying yours will definitely turn out that bad, but I'm not saying it won't either... As far as what is the right size and shape - your guess is as good as mine - sorry. I don't have any pictures of my tie rods, but the basic fabrication is pretty simple: Get a length of steel rod, and drill and tap it on either end to accept the rack end and the heim joint. You would probably want to use one of the high misalignment types of heim joint, to help ensure that the joint doesn't bind through the full travel. I had to put a bend in mine, so that the joint was centered in its travel at the nominal ride height. Next, drill the taper out of the steering knuckle, and use a long grade 5 or 8 bolt to connect the knuckle to the heim joint. As I recall, I used a 5/8" heim joint and bolt. You can then adjust the bumpsteer by adding different sized spacers between the heim joint and the knuckle. I used 5/8" id steel tubing cut to different lengths for the spacers. Now, I mentioned this in my post before, but I will reiterrate - changing the CA inner pivot point does have some positive effects -namely correcting the camber gain curve on a lowered vehicle (camber gain is the amount that the camber changes with suspension travel). Mike was spot on above when he mentioned needing a small amount of droop in the control arm at your nominal ride height. If you think of the control arm describing an arc as it pivots, you will see that if it is flat at the nominal height, any suspension travel will decrease the camber. The reason for adding some droop is to cause the camber to increase for the few degrees of roll instead, which generally helps the tire's grip. For this reason, I do believe that the CA pivot mod is a good thing to do, just don't expect it to zero out your bump steer curve. As I said before - it might improve it. It might make it worse. The only way to know for sure is to measure it. One more thing - I made my bumpsteer guage out of a couple of pieces of scrap plywood, a hinge, a couple of machine screws, and a cheap plastic caliper with a depth gauge. It's not like you have to spend a fortune to do this. My procedure was basically this: 1) Remove the springs, and reassemble the suspension 2) Place a couple of 4x4's under each tire, in order to allow a jack to fit under the crossmember at full compression. 3) Start off with the suspension at full compression (on the bump stops). 4) Setup my plywood gauge, so that the two screws (spaced the diameter of my wheel apart) are an equal distance from the leading and trailing edges of the wheel rim, respectively. The wheel will move around a bit with suspension travel, so you don't want the screws to be touching the wheel. 5) Use the jack to raise the car 0.5" at a time. Each time, use the depth gauge on the caliper to measure the amount that the distance from each screw to the rim has changed. The difference will be roughly the amount of toe change. 6) Plot the results for the full travel of the suspension, and you now have a plot of your bumpsteer curve. Yes, it's a pain in the ass and time consuming, but it's not particularly expensive, and not rocket science. Okay - I'll shut up, now... ...For a while [ April 30, 2001: Message edited by: TimZ ]

Scottie - I certainly don't want to be held responsible for blowing your motor up (i.e., try this at your own risk ), but you could try just disconnecting the knock sensor for a run and see if your problem goes away. As long as you have confidence in your base calibration, and are certain that the timing didn't _need_ to be pulled for some reason, and you are running enough octane, this shouldn't be a problem. I'm pretty sure that the sensor failure detection for the knock sensor is almost non-existant, so the controller should think everything is fine. (Oops - just noticed that Blkmgk already suggested this - I still think it's a good idea, though...) [ April 27, 2001: Message edited by: TimZ ]

...sorry - I accidentally posted this twice - the refresh button doesn't appear to work like it used to, and I doesn't look like it's going to let me delete it, either... [ April 26, 2001: Message edited by: TimZ ]

quote: Originally posted by Mikelly: On my crossmember I plan to do a stepped approach with the unit Jamie has in Richmond.. Drill several holes. Mike and Pete - you are on the right track, but I would recommend slotting, as opposed to drilling several holes. If you are worried about slippage after finding the right spot, you can use a thick washer under the bolt head and nut for the pivot, and weld the washers down when you find the right spot. A series of holes will not have anywhere the resolution that you will need to get this right, and it's worth the extra effort on a 200mph speed record car. When you actually make the measurement and do the fine tuning, you will not believe how sensitive this adjustment is. Another (IMHO superior) approach would be to put the pivot point wherever you need it in order to get your camber gain right, and tune the bump steer at the steering knuckle, by drilling it out and using a heim joint for the tie rod end. You can then adjust the bumpsteer with spacers between the knuckle and the heim joint. In this manner, you can make your camber gain mods, and have them decoupled from the bump steer. Does that make sense? The only drawback might be if this is an illegal mod for a specific racing class, which I don't think you guys are too concerned with - heck, the JTR mod might be illegal by itself, for that matter...

You need to be sure that you have the proper sized spacers underneath the struts - I'm assuming that you are using the front cartridges in the sectioned rear housing. If the spacer is too short, the cartridge will be free to move up and down inside the housing, exactly as you described. This will be the case, no matter how tight the gland nut is, since in this case, the gland nut is only tightening down to the strut housing, and is not actually making contact with the cartridge at all. The only way that I know of to check for this is to remove the spring, and then pull up and down on the strut shaft. If there is any free travel before the strut starts offering resistance, the spacer is probably too short. And ,yes, I do know what a pain in the ass this is to do on the rear suspension with camber plates, but I this is the 'easiest' way I can think of to check for a short spacer - sorry... The spacer should be sized so that the top of the cartridge sits high enough that you can be absolutely sure that the gland nut will cinch it down tight. As I recall, mine are sized so that the top of the cartridge protrudes about 1/16" above the top of the housing.

Do you still have the old 14" wheels/tires? If so, try putting them back on temporarily, and see if the twitchiness gets any better. The lower aspect ratio 17" tires can definitely be more prone to following grooves in the highway. I agree with everybody else, as far as checking your toe-in, and other alignment settings. Also, from your description, I doubt that this is causing your current problems, but (I'm risking being accused of heresy here )contrary to popular belief, moving the front control arm pivot point up and out by some pre-determined amount (15/16" ands 1/4", in this case) will most likely NOT cure your car's bump steer characteristics. Change it? Definitely. Make it better? Maybe. Make it worse? Maybe. You car's bump steer characteristics are highly dependent on it's individual suspension geometry, and in all three dimensions. The ONLY way that I know of to acheive a known good bump steer curve is to directly measure it, and keep readjusting the geometry until it's what you want. This is a huge pain in the ass, and the curve is amazingly dependent on the geometry. Two brand new factory vehicles can have markedly different bump steer curves. If you've ever tried tuning this, then you know that you haven't got a prayer of getting it right by moving it a set amount once, and quitting. That said, there are still two very good reasons to relocate the pivot point - (1) You can get more negative camber (2) You can acheive a much better camber gain curve on a lowered car (this is the amount that the camber changes with suspension travel - bump steer is the amount that the toe changes with suspension travel - they are not the same thing). Sorry to rant, but I keep hearing this mod referred to as fixing the bump steer curve (probably because that's what JTR said it does ). It's greatest value is in acheiving a more desireable camber gain. It will change your bump steer, but not necessarily make it better. Don't let anybody tell you otherwise... Exact same story for the 'bump steer spacers', BTW. Oh - one more thing - you really need to change the front and rear sway bars as a matched pair, unless you have an awful lot of experience as a suspension tuner. Increasing the stiffness of the rear bar will increase your car's tendency to oversteer - you are already complaining about the rear steeping out, this will only make it worse. Also, all else equal, the shorter the arm on the bar the stiffer it is.

Someone posted a very similar problem on the izcc mailing list recently - it turned out that their problem was that the calipers were reversed right to left, making it impossible to bleed it completely. The bleeder valves have to be at the highest point in the caliper.

quote: Originally posted by Scottie-GNZ: TimZ, when you say one good CV adaptor, are you sayin the shop did one correct and screwed up the other? Yes, that's right. My shop screwed one of the adaptors up when they welded them together. When I received them from you, they were fine. Sorry- I had just posted about the screwup in the "Driveline" forum the night before- hope I didn't make anybody think that I was talking about the adaptors as I received them from you - this was not the case. [This message has been edited by TimZ (edited April 11, 2001).] [This message has been edited by TimZ (edited April 11, 2001).]

Shortening the links shouldn't change the stiffness of the bar, unless they are so short that the travel is limited, due to something binding somewhere. (This is what I'm worried about with that solution, BTW) I think that you are thinking of shortening the length of the sway bar arms - that will increase the stiffness of the bar. Also, stiffening the bar isn't necessarily good or bad - it just changes your understeer/oversteer balance. Stiffer rear bar increases oversteer. Stiffer front bar increases understeer. [This message has been edited by TimZ (edited April 10, 2001).]

Evan - I just posted a response to this over on zcar.com (so sue me... I was having connectivity problems here again, so I went there first... ). One other thing - if you don't intend to spring for custom rods, you might want to consider going with 240 rods (only the ones with the 9mm rod bolts, though). Those rods are longer than the 280 rods, and you'll have to get a non-standard piston pin height, but this is simple when they are making them for you, anyway. The longer rods basically reduce the maximum angle that the rod needs to have with the piston, and also increases the dwell time at TDC and BDC. This will make you less sensitive to cam timing errors. I believe that it's also supposed to be better for high RPM operation, due to the reduced side loading on the piston pin/rod bearing. Actually, I've heard of people using the L20 rods, which are even longer, but I'm not sure if you need to do anything funky with the pin location to get this to work, though. Anyway - one more thing to think about... [This message has been edited by TimZ (edited April 10, 2001).]