tube80z

Years ago I weighed a VG30DE (complete) with custom lightweight headers and a really light clutch and flywheel. It was 424 pounds. This was done using a bathroom scale and lever system. I've told Paul I'll weight this engine again as I still have it but with real scales this time (race car scales). I'm going to weigh a shell with a cage because I've never seen a weight posted for one that seemed realistic. What about something that looks like scissors. You put a spring on one side and the crane mounts to the other end. When you lift something it compresses the spring and you measure the compression. You pick a few known weights, measure deflection, and put that in excel and create a normalized curve. Seems a lot cheaper and close enough. I'd guess it would be 5 pounds accurate. Cary

I don't have a picture of it but I saw a sentra with a cow in the backseat. I about crashed from laughing so hard. It's head was sticking out one window and the backside out the other. Some old lady was driving. Cary

I had a airbox like that on my car. It also helps with cooling by slowing the air going into the radiator. Another option if the rules don't allow hood vents is to open the inner fenders and vent there. Ideally you should not have the tires sticking out in the aristream and a proper flare covering this. This is how most GT cars are done. Cary

You do realize the main hoop diagonal isn't straight in your model don't you? Are you trying to create a half cage for a street car? Cary

Staniforth's competition car suspension is a really good book to start with. There are a number of calculations given on the back of the book you can put into a spreadsheet and use to help make decisions. Bare in mind it's a little data but highly recommended. Adam's book has some useful info more on the chassis building side and is in general a disappointment. You might take a look at the following website, http://www.racing-car-technology.com.au/index.htm. They have some good information but don't bother with paying for their weight transfer worksheet. They give you all the info you need on the site and you can finish the rest with what you get in staniforth's book. Another idea is to see if you have any local shock or data experts. Many of these people put on weekend seminars to help out beginning racers. Being able to ask questions is a huge help. And once you have a good basic understanding you can go to the mother of all seminars by optimumG (http://www.optimug.com). Hope this helps, Cary

In that size I'm not sure if they even make 0.065. It may depend on your steel supplier but I think the thinnest I could get was 0.095. That may dictate what size tube you end up with. My personal feeling is 0.065 would be about the same as the stock rails. I'd start by measuring how thick they are and keeping close to that thickness. Cary

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