tube80z

Of course you're always invited to drive a little farther and play with us. And we don't worry much about rules. FWIW, I had similar experiences in Portland and gave up trying to run there. Cary

On a similar car I've seen it pick up rear tires at times. If you're not running stiff springs (over 400/500) I think you may find that you have a hard time putting down the power with that little rebound. Cary

If I read Mike's post correct he's saying his struts are too short and he's rebound limited. Reminds me of when I got carried away shortening my rear struts, put them on, and whoops, they won't even let the wheel touch the ground. Cary

These people should have told you it depends on how much lateral force you generate. Above ground roll roll centers will generate jacking and this raises the car. If you have data logging and suspension sensors this can be seen. There's a relationship to the slope of the IC lines that's supposed to mathematically describe how this works. And I agree it's not necessarily a bad thing. Above ground roll centers will generally heat the tires more. So of you're needing to get more heat into the tires it can be a good trick to use. But what I think is far more important and what I really learned from Claude Roulle is that above and below ground RCs have different timings for lateral weight transfer and this is really the key thing we play with. To make the care respond quicker you can raise the RC. To make it respond slower you can lower the RC. In real terms this lets you use small ride height changes to balance the car and is a key tuning tool in my arsenal (albeit a very small one -- more like a gun closet). In the case of a stock Z front end there's a limited range of what you can use to stay in the suspension's sweet spot. So this discussion can get academic real quick. And back to Richard's point I use a slightly underground front roll center and stiffer springs than most people run. I had tried softer springs and a higher RC as well as stiffer springs and a smaller roll bar. For autox I found that the car was easier to drive when with an underground front RC. That may be related to the type of use but I can't say for sure. My use of droop limiters was to constrain the stock geometry to a certain extent. And in my case the front droop limiter raises the RC a little after initial turn-in. Anyone who doubts any of this really works should try it. You can feel quite a lot of difference. Cary

Raising the pivot points an inch is going to be about as useful as drinking a big gulp to keep your personal fire extinguisher primed in case you're car catches fire. 600 ft-lbs is going to make the back squat because of the design. If you don't want to use seriously stiff springs I could see a couple alternatives. Using packers on the rear shocks to engage the bump stops early, possibly a third-spring setup using the sway bar, and droop limiting the front. All these could be done at the track without ruining the street ride. Of course the best plan would be to put a live axle in it at that level of HP/torque. Having driven Gary's old car and another car with equally wild mods and a live axle, the latter worked much better. Cary

If you use an aluminum seat you could always mount the sliders to the sides to the seat rather than under for additional clearance. Cary

I wouldn't buy easy outs. You may well end up with the stuck in the end of the crank as well. Get left hand twist drills and drill it out. First center punch then remove. When you start drilling you'll probably find that backs it out at some stage. Then figure out why the bolt broke in the first place. Cary

Think about it. A vette has wide tires and a relatively stiff suspension. A celebrity has skinny tires and normally handles like a ♥♥♥♥ barge. In the wet where your maximum lateral acceleration potential goes from 1g to something maybe no higher than 6 tenths so this isn't that great a factor. For wet weather I don't need a rear bar and use a front bar about the size of stock. If you want to be able to play with the same car in both wet and dry you'll want two front bars and a way to quickly turn the rear bar off (pip pin on one rear down link for instance). Cary

Tires make a big difference. And I've found the biggest single factor for my car is the roll bar. When it's wet you need a lot less roll stiffness because you can't generate the same level of lateral accelleration. For me spring rate made little difference. Cary

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.

Sounds like a reasonable plan. It would be helpful to have an idea what the stock CG was on the doner cars compared to the Z. There are a number of spreadsheets floating around on the internet that you can use to get things in the ballpark for the new car. If you need suggestions we're always full of opinions Back before I decided to take the EMOD plunge I was going to build a street legal autox car. After thinking about a cage for a long time and not really wanting to deal with that on the street I really looked hard at creating a backbone frame that could be put in the Z and connect front and rear subframes. I think if you went down this path you could get close to the same torsional strength as a vette and keep the weight very similar to the Z. A cage is great in a race car but I don't think I'd want to live with it on the street and there's the issue of your head and how close the cage tubes are. I don't really want to turn this into a a-arm/mutli-link versus strut debate but I've been surprised at how well I've made struts work. I've driven a 510 that was converted from struts to a-arms using a plan very similar to yours by people who know what they are doing. And the difference wasn't as much as you'd expect. It was mostly easier to steer but didn't have any more grip than when it was strut based. I do think you're right about getting good components from a donor to save a lot of potential dollars. Just make damned sure you can use everything before you end up buying all the pieces over. Spend the time up front to do all the research. I've played this game far too many times myself. Good luck and hope to see some pics, Cary

The following is from Richard Pare and I think addresses droop limiting and zero droop suspension better than what Ortiz wrote. And as many know I've played with this a lot on my Z and found it to work for me, YMMV Cary

I've often heard this preload argument and think for the most part I have a hard to believing it. Are you putting 500 to 1000 pounds of load onto the part? That would be the only way I would think this would work. You'd need to make sure the parts were always under tension or compression to keep all the tolerances tight. Cary

I would say it depends on what you intend to do with the car. If this is just a street car adjustable lowers will get you in the ballpark. If this is a more serious endeaver then I'd recommend adjustable uppers. If you use a two piece camber plate design you can use this to help square the car. I've seen a lot of Zs that aren't that square, which isn't to surprising given their age. Squaring my car was a pain in the ass but really helped make it drive better and stopped the turns great left not so great right syndrome. And two of the most adjusted things for a track car are going to be air pressure and camber. It's much easier to adjust camber at the top with a lot less interaction with toe than if you adjust at the bottom. I'd also through in some adjustable swaybars and coilovers and now you have 90 percent of adjustability covered. Cary

I hope your happy, but you made me download the 2007 rules to take a look, and I should really be doing my day job I noticed composite doors are now legal. For the above I read 17.8 number 2 to say I can move the tower where I need it. As for the wheelbase it says "The wheelbase of the vehicle shall not be changed or relocated in a fore/aft direction by more than + or - 1". To me this says I can move the front wheels forward and the rear wheels forward by an inch. I guess it could also be the wheel base could get longer or shorter by an inch too. If I had a prepared car I'd try more caster to see if it worked. If it does then I'd move the top pickup point to where I needed it to make this work and use an adjustable bottom as you mention. If more caster than I could easily get didn't really do much for my combo then I'd call it a day. Cary

I think the answer to that is probably no. The safe route is to try and keep things in the sweet spot and not to get carried away with running anti-geometry. So that means keeping things near level side to side and front to rear when in a dynamic condition. A word of caution. The geometric RC most programs calculate is only a rough approximation. Most programs don't take into account tire or component deflection at all. And most programs roll the car around the centerline, which isn't correct. Depending on how the RC migrates you could have different results if you corner first and brake, versus braking and then cornering when you look at the car as a whole. I never really thought about this until I listened to a long explanation from Claude Rouelle. It seemed to be a sore point for him and he went as far to create a software package called optimum K that does take this into account. The price is about $5K for this program, which is well out of my league. In the end Claude explained the geometric RC is really a way to visualize how the elastic and inelastic forces are distributed. That's a fancy way of saying what proportion do the springs and shocks deal with and what proportion goes through the linkages. Why this is important is that control the speed of the transfer seen at the tire contact patch. Generally underground RCs are slower to transfer weight compared to above ground RCs. So to speed up reaction you can raise the RC. For an autoxer you may actually want to slow things down a bit and I've found the underground front RC works for me. Your current setup is very similar to where my car was. I ended up at this point through experimentation and it seems to work well. General consensus (not necessarily here) is that you should start with the spring rate equal to the corner rate for slicks and test harder/softer from there to see what works best. So you're setup is a little on the soft side, which is probably okay if your running where it's really hot and worried about tire temps. If you're running where it is cold you should think about going stiffer to work the tire harder and build more heat. As mentioned above staying in the sweet spot would be the easy thing to do - basically close to level in a dynamic condition. Does your program show you side-view geometries? These are also called anti-dive/anti-squat/anti-lift. Changing the vertical height of the rear TC mount should change these as well as your caster gain. The problem I've found is that a lot anti-dive can cause major understeer in slow corners. I removed most of mine and opted to use droop limiters to get some anti-lift in the rear. As it stands you can't change squat/lift in the back very easily because we don't have a true macstrut. Yes and no. Generally longer arms will slow the RC movement down and you should get a much more stable feel from that end of the car. So it's a big win for that. Where you run into problems is that side-to-side scrub you have as the suspension moves is lessened. In the case of short autox runs it may not get as much heat into the tires. I'll say more a little further below. For me I'd go longer as this has helped in previous cars. You need a lot more caster. I'd do big jumps to see what your tires think as they are the limiting factor. I'd try 4, 8, 12 degress. You'll get to a point where the turn-in is good but the front falls away (turns good them major push). Back off a couple of degrees from this and try again. Keep in mind that steering effort goes up big time as you increase caster. What you're looking for is whether or not it works and not so much steering effort. Once you find what works you can change what's called pin lead (the position of the spindle on the strut). If you move it forward (looking sideways at the car) you'll decrease the trail seen at the ground. This reduces the steering effort with lots of caster. BTW, simple rule of thumb is caster should be 1/2 of the SIA, which in the case of the Z is the about 12 degrees stock. So when you add in camber you can see how this is easily 7 to 8 degrees. Yes and no. The key is a concept called a magic number. There are a bunch of them but in this case we're interested in the percent of lateral load transfer handled by the front of the car. If we keep this number the same for a known setup we'll be able to change RC hieght, roll bars, springs, track width, etc. and still keep a setup that works very much the same. What I've found is that I can run really stiff springs in the cold the car works fine. What it won't tolerate is much roll bar. So one idea would be to go with stiffer springs, raise the RC, and finish it off with a small roll bar. The idea being the above ground RC will help to generate more heat into the tires along with the stiffer springs. This might be your Kansas setup. Or you could use your program to see if you can get your RC's up by raising the car. You may be surprised at how you can balance the car with a couple of turns of the spring perch in the front or the back. You lower the end that isn't sticking or raise the end you want to unstick. You can use your program to set limits on what is acceptable, which is a good use for these programs. I think this is a little unfounded. What I found is as I worked more and more on this that car didn't get massively faster but it got a lot easier to drive. I could get those demon runs more consistently without feeling like it was always going to bite me. I also noticed the car got a lot easier on the tires and they lasted longer. If you're looking to pickup real performance you need to look at reducing friction. Once you're at the level that your car is prepared to that can make a large difference. And if you have access to a data logger you can start to see a lot more of this if you log suspension displacement, i.e. are the shocks working correctly, how well does the car corner, does it get better or worse over a run, etc. I hope this doesn't come of like I'm some kind of know it all. I really started getting into this about 5 years ago. I've taken a number of classes and put those principles into work. At first I simply measure tire temps and air pressures. I kept good records and learned how to make the tires work better. What I can tell you from personal experience is that this is a never ending game. The more you learn the less you know … Cary

The tranny mount on my car used the stock ears but hooked to where the case split rather than under the back where the normal mount is. Not sure this helps as it was solid mounted. On the front it had kind of a tripod arrangement that came from the stock engine mount towers. I'm not sure I would have done it this way myself but it was seemed to work. Let me know if you want some pics. Cary

See number 4 on page 393. Sometimes I think you need a owners manual for this book. The only thing I can add is that I don't think it's possible to build a Z car that has so little PMOI it is undrivable. That will be tested when my car runs as the engine sits completely behind the firewall. Cary

You really shouldn't put holes in the top and bottom, those are the parts of the tube that are seeing the greatest loads when this is treated like a beam. The sides would be a better candidate. Cary

Actually all that was changed was the nozzles and needles to match a 2 litre roadster. I wouldn't have guessed it would have worked as well as it did if I hadn't seen the results. I think part of the key is decent linkage and good carbs. I know that a lot of SUs are in prety bad shape. I get to see what people send into ZTherapy and some you wonder how they even managed to run at all. Cary

I don't think you'd need to bore the 2 inchers at all. That was in relation to boring a 46 and comparing it to a stock 2 incher. Figuring out needles and nozzles will be the next order of business when running the 2 inchers. Cary

Actually, depending on weather conditions and surface they may be faster. Last year a number of MOD competitors found out that the setup and tires that worked for them on concrete weren't good for the new paved surface they were running on. A number of them are going to try and test to see what actually works better since they were beat by stock cars on R-compound tires. The hoosier street rubber seems to grip better at about 10 to 15 degrees lower temp than their slicks. Until these tires are out it's hard to say what will need to happen to spring rates. The tires will need to be measured for vertical stiffness, air pressure, and camber to understand how this changes the tire's rate. This assumes you want to run a setup that has a similar distributions of roll stiffness. The only other news I've heard is that hoosier is coming out with radial slicks to try and match goodyear. We found the difference between the hoosier bias ply atlantic tire was 8 tenths slower than the goodyear FA radial tire on a 48 second test course. Cary

I think you're right about the balancetube helping a lot. I added a balance system to our tripple weber setup years ago and it definitely helped the mid-range. I used some parker fitting for air brakes. They have a special small diameter pushlock hose that's easy to work with. One idea to speed along your project until you have time to fab a balance tube. Cary

Sorry I'm late to this party and I don't really intend to start a pissing match but this isn't really correct. My old 2.8 autox motor is now running a set of tripple SUs and I can tell you from driving the car it runs much better than it did when I had 2 high-flow SUs on the car (original Huffaker racing carbs). All these carbs were properly setup and in good condition, which is thanks to my friend Steve Epperly who owns ZTherapy. I've also ran 2 46 SUs on a L20B and an L18 in a 510 and can tell you they provide better top end than the smaller 38s. You do lose a little low end. But back to the tripple 46 Z setup. This works much better than you might imagine. It provides more top end like a tripple weber or mikuni setup and a lot better low to mid-range. The only problem with all this is you need a manifold and a lot of custom linkage. I think the trick in making all this work is using the 2 litre roadster nozzles and needles. With regards to the bored our rebello carbs I'd make sure to mount them so they are supported. When you bore a stock 46 MM body that large you'll find that only the outer ribs are holding it together. A few of these carbs have broken in wrecks. You'll also find that the larger 2 inch SUs have a much larger piston, which become the bottleneck when you start boring these carbs out. Hope this helps, Cary