tube80z

You could always switch to SUs if you wanted to go fast, worked for me I don't think you need to add the gussets in addition to the tube you have. I used a number of these to add weld area on my old car since the PO wasn't a very good welder and had a tendency to due some scary stuff with body filler. I do think a good location for them is the halo to main roll hoop if you decide not to do a small tube there. Cary

He used bathroom scales

Build a simple model using balsa and glue. If you put an X into the ladder design it will be a lot better. If you integrate a cage and keep building triangles that hook the front and rear suspension together it will get better. Don't overlook bolt-in structures that cover the engine. I'd recommend you try and find a copy of Costin and Phipps masterpiece on racing and sports car chassis design. It may be old and out of print but has all the relevant info you need. My personal feelings are the 2x3 connectors in 0.120 wall or heavier tubing or a waste in the Z. It sounds like someone is trying to build a half ton truck. I think the bad dog rails or similar or more than enough. Closing the bottom of the tranny tunnel to the rails would help to increase the strength. Then this starts to look more like a backbone design. There's lots to learn and building models, virtual or real, is a good way to see what works and what doesn't. GRAPE is a shareware FEA program you may find useful. Racetech had some articles on how to use it. Cary

My personal feeling from having been a long ways down this road is you'd be better off cutting the front and back off the shell and using a cage to tie a couple of suspension cradles together. Getting a tube car sealed up to deal with weather is a major pain and you already have all that done. Sure it might be lighter but you'll fight leaks forever. I spent far more time dealing with the passenger compartment on my build than I did on the front or rear suspensions. And if you're like me you may end up building two. Because you'll see better ways everything could be done and your skills will get much better. I really like 74 5.0's car. It is a good example of a street car with tubed front. He's got a lot of great pics in his gallery to look at. Cary

Are you trying to put the entire drivetrain into the 240 or did you really want to put a Z body on the corvette chassis? The examples you have listed are really more putting the drivetrain into something else. Both frames are poorly designed and will have much lower torsional stiffness compared to the corvette chassis, which will lead to poor handling compared to the original corvette. So this ends up being a lot of work that has no more payoff than just putting the drivetrain into the Z. I'm not trying to dash your plan but you need to be aware that there's a lot more to how the vette handles and getting that same level of handling in a Z. Cary

Well I got hosed on the bag I bought then I really only make the large ones I need, like where the A-pillar bar bends near the door, another idea for your gusset party. I've also seen them done where the halo meets the b-pillar. Cary

You can buy them but they only come in a couple of sizes and aren't that cheap. To make them you cut out flat pieces then use a press the pushes these between two bars that have enough space for the thickness of the metal. It's not hard, just a little time consuming. I have a pattern for my plasma cutter that makes this easy. Cary

You don't need camber plates to slot the towers. That would be a cheap option. My guess is the car is losing camber at front and this leads to understeer. Softening the front will not solve this issue and only lead to chasing your tail. Cary

I'm sure it's safe but it sounds like you're trying to build a 3/4 ton truck rather than a sports car. Cary

On the front these hook where the bumper mounts and come out. Similar on the rear. My car didn't have a front or rear bumper so I made simple hooks for these locations I could hook into with tiedowns. Cary

JohnC's trailer above is very similar to mine. I bought a used steel trailer and rewired it with much better wiring and LED lights because I got tired of dealing with the normal lights being out before I'm about to leave for the weekend. In addition to a well laid out tool box I added a nitrogen bottle to mine and will plumb the trailer with airlines this year. I also spent a lot of time figuring out how to get the car on and off quickly. It's nice at the end of the day to be able to load the car and be gone in 15 minutes or less (when it's really hot out). External tie downs on the chassis are a lot easier to deal with than climbing under a really hot car. I also found that having the rear ramps stay hooked the trailer and fold down was easier for me to deal with and a lot quicker on the load/unload sequence. There definitely seems to be two schools of thought on how to tie a car down. One says by the tires the other says to tie the chassis. I fall in the latter. Cary

The only thing that is currently regulated is rim width and diameter. Tire construction is free (DOT are fine). Cary

Exactly how experienced are you? That's not mean to be an offensive remark but it sounds like you're pretty new to this game and autox has a steep learning curve depending on what you drive. You either have too much front brake bias or you are simply asking too much of your front tires. Street tires (even R compounders) can only give you a finite amount of grip. The total grip is distrubuted between cornering and braking. Too much of one and the tire will start sliding because you're asking more than the total grip allowed. How do you downshift? It doesn't sound like you double clutch at all. If you did this wouldn't be an issue. I typically don't use the clutch at all when downshifting. Worn out synchros are more of an issue when you try and upshift fast, at least for me. You are in the rock and a hard place that happens when you build a car you like and then decide to go play with it. This is why we tell people if they intend to race their cars they need to look at the rule book and be careful what they do. SM2, EM, or local run what you brung class are your only real options. As others have pointed out your engine wouldn't be legal in FP. Cary

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