JMortensen Posted February 25, 2009 Share Posted February 25, 2009 Here's my front strut tower bars. One connects to the cage as close as I could get it to the rocker, the other V's to the dash bar and then goes straight back to the rear strut towers via a bar right down the middle of the car a la Herb Adams in Chassis Engineering. This necessitates a right side net. I could have done an X from the strut towers to the A pillar bar at the dash bar nodes on either side. That probably would be a better solution, but I think that would make it a lot harder to get the engine in and out of the car. My other nit pick with what I did is that the tube to attach the strut tower to the sway bar mount is straight, but it has to hit a bracket off of the strut tower instead of hitting the tower itself. The bracket is pretty beefy, and this is not so much to brace the strut tower as it is to brace the frame rail, but still I think I like bjhines' solution a bit better: Quote Link to comment Share on other sites More sharing options...
S15 200sx owner Posted February 25, 2009 Share Posted February 25, 2009 The owner of this car has previously had a BIG side impact crash in a Z car, and was lucky enough to be still here. So he has put alot of effort into the cage's ability to sprend the load of an impact throughtout the rest of the car, as you will see in these pics. Quote Link to comment Share on other sites More sharing options...
S15 200sx owner Posted February 25, 2009 Share Posted February 25, 2009 Jon, Could you post a better pic of what you have done here? Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 25, 2009 Share Posted February 25, 2009 http://forums.hybridz.org/showthread.php?t=106974 I'm off to bed. If you want to see more of mine, search "2 year roll cage" and read the link above. I think I had a thread on stitch welding too. You might look at my project post. It's on the last page, as I think I was the second one to post one and then I've never updated it... Quote Link to comment Share on other sites More sharing options...
S15 200sx owner Posted February 25, 2009 Share Posted February 25, 2009 http://forums.hybridz.org/showthread.php?t=106974 I'm off to bed. If you want to see more of mine, search "2 year roll cage" and read the link above. I think I had a thread on stitch welding too. You might look at my project post. It's on the last page, as I think I was the second one to post one and then I've never updated it... Thanks for that, but all the pic's are dead..... Quote Link to comment Share on other sites More sharing options...
johnc Posted February 25, 2009 Share Posted February 25, 2009 10,000 pounds per corner when you hit a good sized bump??? We're talking about normal suspension loads from road racing, not large, chassis bending impacts. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 25, 2009 Share Posted February 25, 2009 Thanks for that, but all the pic's are dead..... Around the end of the thread I reposted a lot of the pics. Quote Link to comment Share on other sites More sharing options...
MoNkEyT88 Posted February 25, 2009 Share Posted February 25, 2009 Realistically you need to be able to install the engine in the chassis, or you just end up with a chassis where the tops of the suspension mounts do not go up. Sure would be easy to use substantial bars to tie the towers together across the body, and weld them in place, not just counting on heim joints to locate them. Back to the topic. Essentially there are a bunch of Z's driven on the track without a full cage. The uni-body is sufficient enough that the Z doesn't twist so much that the suspension geometry is lost. When you add a full cage, the body will still twist around the cage. Tying in the strut towers to the cage should stop a lot of the twist. Adding gussets from the body to the cage is a good idea for how much more rigid the chassis will be. Then the uni-body can be lightened to reduce weight. (Doors weigh a lot, and can be gutted) Here's the battle S30Z shown with tons of cage to body gussets. It says that it's a 23 point cage. I also don't see the need for such large body to cage gussets, I think smaller ones in key places will do the same thing. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted February 25, 2009 Share Posted February 25, 2009 Back to the topic. Essentially there are a bunch of Z's driven on the track without a full cage. The uni-body is sufficient enough that the Z doesn't twist so much that the suspension geometry is lost. Try relying on the unibody and then improving the stiffness and see if you can tell a difference. When I added some strut tower bars I damn near drove off the road on the inside of a corner because the car reacted so much differently. Why did it react differently, because geometry was being lost previously. In particular, the strut tower bars help to keep your camber settings steady. The Z chassis is not very rigid out of the box. In fact, I'd say it's really flexy out of the box, a wet noodle compared to any modern sports car. This is also why you hear people like John saying "don't use more than a 300 lb spring without increasing chassis rigidity" because after a while things like sway bar changes and spring changes don't have the effect they should, because the chassis can't take the strain and it flexes too, lessening the impact of a change that should affect the handling. Quote Link to comment Share on other sites More sharing options...
MoNkEyT88 Posted February 25, 2009 Share Posted February 25, 2009 Wow, that's amazing. My 6 litre Z only has a roll bar in it. I can't wait to see what it's like driving one with a full cage. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 25, 2009 Share Posted February 25, 2009 All of this is about two things: 1. Mass acceleration. The sooner you can get the sprung mass of the car moving in the right direction the faster you can be around a race track. If parts of the car flex (chassis) or absorb the acceleration (rubber engine/trans mounts) it delays when everything takes a set and starts moving. 2. Repeatability. The car does the same thing, the same way, in each corner. If things are flexing or moving then the wheel/tire alignment changes in an unpredictable manner. Quote Link to comment Share on other sites More sharing options...
drmiller100 Posted February 26, 2009 Share Posted February 26, 2009 on the jmortensen car, there is a down bar which goes from the top of the front strut tower to the passenger's feet. This provides a downward force in tension into the cage. This is exactly what I am talking about. It is relatively hard to do on the front of the z. When he tied the tops of the strut towers back to the dash, that was really cool, as it again ties loads from the top of the towers moving back and forth into the cage, which is hopefully pretty rigid. When building the brace across between the strut towers, heim joints sure improve stiffness. However, there is no need for a heim joint, and it might be more rigid to make it solid bars. i made mine removable by welding it to a plate sandwiched between the 3 bolts that hold the strut in. Remove 3 bolts on each strut tower, remove the cross brace, then reinstall the bolts to pull the engine. On the rear, the monkey car has a bar going from the top of the rear strut up into the roll bar. most of the rest of that cage is just extra weight. I shot from the hip on the loads to the tops of the suspensions. Fred Puhn suggests 5 G's is a design load, so with an 800 pound corner weight, we are only talking 4000 pounds. Per corner. But hey, cages are only put into cars for safety, never competitive advantage, right???? Quote Link to comment Share on other sites More sharing options...
johnc Posted February 26, 2009 Share Posted February 26, 2009 Fred Puhn suggests 5 G's is a design load, so with an 800 pound corner weight, we are only talking 4000 pounds. Per corner. So, you're building a 3,200 lb. 240Z? 550 to 650 is the typical range for corner weights for a road race 240Z and you would never see the 5Gs on all four corners at the same time. I'm not sure what your argument is regarding strut tower bracing, cage design, and gusseting in a 240Z? All of the designs shown here are based on decades of racing experience with the car here in the US, Europe, and Japan with many different race sanctioning bodies. These designs are effective and efficient and have helped the cars win multiple national championships in the countries listed above. Adding bracing to solve a non-existent problem just adds weight to the car. In most cases, the 240Zs real advantage in racing is its light weight and more cage means you're reducing the car's advantage. Quote Link to comment Share on other sites More sharing options...
drmiller100 Posted February 26, 2009 Share Posted February 26, 2009 Adding bracing to solve a non-existent problem just adds weight to the car. In most cases, the 240Zs real advantage in racing is its light weight and more cage means you're reducing the car's advantage. so why are you guys throwing in all those bars going everywhere except where the suspension ties in???? Sorry, you are the expert, I'm new. I will quit asking questions and causing problems. Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 26, 2009 Author Share Posted February 26, 2009 When building the brace across between the strut towers, heim joints sure improve stiffness. However, there is no need for a heim joint, and it might be more rigid to make it solid bars. i made mine removable by welding it to a plate sandwiched between the 3 bolts that hold the strut in. Remove 3 bolts on each strut tower, remove the cross brace, then reinstall the bolts to pull the engine. If you have EVER worked on a car built like you describe then you know how hard it is to get the holes lined up and the bar bolted back in place. Especially when you change corner weighting or god forbid have hit something even lightly. The heim joints I am using will hold in the ways forces are applied. Keep in mind that the joints remove any bending or twisting forces acting on the bars. Forces can only be applied in a straight line through the bars using heim-joints. The only improvement that could be made would be to use a material or shape that held stiffer under compression. You also have to consider clearance for the engine and the fact that the hood is very close to the tops of the strut towers. My main focus was to use STRAIGHT BARS, not the bent designs I have seen on nearly every other car out there. Quote Link to comment Share on other sites More sharing options...
bjhines Posted February 26, 2009 Author Share Posted February 26, 2009 so why are you guys throwing in all those bars going everywhere except where the suspension ties in???? Sorry, you are the expert, I'm new. I will quit asking questions and causing problems. The primary focus of the cage is safety as required by SCCA and other organizations. I have tried to add stiffness as well. This is the art of race car chassis design. So far you have not supplied anything but hollow arguments. Please provide something more than hot air to this discussion. There are plenty of chassis pictures available to scribble on. Scribble away matey, I think you will come to some of the same conclusions we have once you get pen to paper(or mouse to pad). I fully respect your arguments and believe me I have made quite a few compromises. For instance, my main hoop is not technically SCCA compliant because I wanted to tie into what I consider a stiffer area of the chassis than the typical SCCA approved designs. Quote Link to comment Share on other sites More sharing options...
johnc Posted February 26, 2009 Share Posted February 26, 2009 Sorry, you are the expert, I'm new. I will quit asking questions and causing problems. You're not causing problems, I just don't understand what your concerns are. Is your background off road racing, rally racing, or something that really sees large suspension loads? And I'm not an expert. I'm just a monkey-see-monkey-do engineer. Quote Link to comment Share on other sites More sharing options...
MoNkEyT88 Posted April 7, 2009 Share Posted April 7, 2009 Here are some pics of gusseting I found interesting.. It's not exactly chassis to cage, but wow. Quote Link to comment Share on other sites More sharing options...
bjhines Posted April 7, 2009 Author Share Posted April 7, 2009 More More!!!! That is some cool stuff you found. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.