Here's the idea. We want to build a full "tube" chassis car, built around a 240sx coupe. We want it to be look like a 240 coupe, but be slightly shorter and not quite so tall. Set the motor a bit further back. shorten up the noise shorten up the tail end and chop the roof shorter like old school hot rods. We figured making a chassis then putting the body panels on it would be the best way to go about doing all of that modification. The original idea was the keep the stock suspension points and just modify around them, so we could keep it easy and use off the shelf 240sx parts. Then we got to thinkin, if we're makin a full chassis the way we want it, why not upgrade to a better suspension set up instead of just keeping the McPherson style, like a double wishbone.
We don't have anything drawn up electronically that I can post. So I guess that is a question there, anyone know of any good programs that you can use to design a chassis/suspension?

tips, tricks, general discussion
thoughts, concerns, pointers?

 

Do some Googling on "Locost", particularly Miata-based. Miata parts are plentiful and cheap and will give you a MUCH better suspension than a 240.

You could, if you wanted to, use the entire Miata front and rear sub-frames and just tie them together with a tube-frame.

 

I have been doing what you want to for years now, and I am not sure you know what you are getting into...

To start off, if you are going to design your own suspension, then start your homework. Why are you wanting to get away from a Mac Pherson setup? There are a number of reasons why you might, but you will want to understand the pros and cons to each. If you go to a dual a arm, then you have options of parallel, non parallel, equal length, unequal length, and have to understand the pros and cons of those alone, etc. Getting your caster, camber, KPI pneumatic trail, and scrub radius correct is a pain in the ass. Steering rack placement is also of utmost importance. Some programs that you can use are Susprog for your suspension kinematics. Its inexpensive and relatively easy to use. Its what we have been using for 9 years now. Susprog will provide you will the tools that you need to design these systems, but its up to you to understand the values that it provides. If you use all stock components, then much of this is unnecessary.

As far as the tube chassis goes, you will want/need to do finite element analysis if you want to make that chassis light and strong. Choose your material whether its 4130 or mild. Intelligent tube placement makes a world of difference, as does tubing diameter (remember that diameter is where the strength in a tube is, not nearly as much as wall thickness).

The program that you can use to do all this is Solidworks. The program is amazingly powerful and again relatively easy to use once you get the hang of it.

The next issue that you run into is tooling. Getting a tube bender, optical table and a decent MIG/TIG is expensive enough. And I couldn't build anything that I design without my lathe and milling machine either.


Good luck with your project. I am unsure as to your knowledge and skill level, so please don't take anything that I have said the wrong way. Many people do not go to this extent, but IMO if you want to do it and do it right this is the only way. I have seen many hack jobs before that just made me cringe. Shit, just today I looked at the suspension design on an old British Jensen and just laughed, and it was a production car nonetheless!

 

Thanks for that. That's actually what I was looking for..

k, so to respond to what you asked and pointed out...

I've been doing homework and what not in regard to suspension. I know I've got a lot to learn about all of it. I find it all fascinating to say the least. To answer the question of why I would want to change from the mcpherson set up, its about control. I want to be able to control the camber and all that jazz. The mcperson set up is great for a daily driven car with concerns of comfort. But with this build, Its more about traction and handling. Why go through of the trouble of a custom chassis if you aren't gonna get the most out of it, know what I mean? The best way to think of this build is that it would be a trackcar, that would still be street legal in order to be driven, perhaps even daily. From the bit that I know, I know that the double A frame is going to provide the balance and control that I'm looking to obtain. As far as parallel, non parallel, equal length, unequal length goes, I'm still doing homework about. I don't really know anything about any of those other than what their name implies. With the caster, camber, KPI pneumatic trail, and scrub radius, that is part of what we are looking into about as far as overall design goes. That's kinda why the original thought was to just stick with all of the stock suspension and build around it, but we're going all out, might as well go all the way out, know what I mean...

the chassis design, I'm kinda looking as something along the lines of a stock car kind of design. I don't want the body paneling to be part of the actual structure. I want the chassis to be completely independent and everything just bolt up to that. See what I'm sayin? I want the car to look like a 240 coupe on the road, but be able to un bolt all of the body panels and have a chassis that is still driveable. I don't know that I need it to survive a 200+mph crash into the wall unscathed, but some safety level above a standard car would be nice. I've got some ideas in my head and stuff that we have jotted down on napkins at applebees when an idea strikes, but nothing "good" yet. I havn't been able to acuire the dimensions of the 240 coupe, so I've not been able to really start working on anything to scale and all kinds of things don't become appearent until you really find out what kinds of angles you are dealing with.

I didn't know that about diameter, I just assumed it had just as much to do with thickness...
that'll prove a useful tid bit when designing the chassis, especially the passenger area. I don't want, nor expect a stock interior or anything like that, but I do want it to maintain some level of functionality, as it would be driven pretty much everyday. I know, a lot to expect, but right now it is still in the dream phase, just starting to get into the planning phase.
Right now, I'm taking the approach of, if I could build whatever I wanted, however I wanted, how would it be... Then from there, it'll get boiled down to what is and isn't realistic...

As far as tooling goes, I would love to be able to do it all myself, but I'm thinking part of the plan is finding a shop that can and will do it the way I want. This isn't something that is going to happen in a matter of months, the budget just isn't there for it. So over time, I have no doubt that I'll eventually get everything I need and get a little shop set up of my own going, but that is all down the road. I think right now, the goal is to get it all laid out, all planned out and put on paper in a way that every detail is covered from the chassis to the suspension to the powerplant to the electonics to the odds and ends so that anyone, or almost anyone could pick up the plans and build that car.

I really appreciate the help. I'm hoping to make this an on going discussion. I am more than open to everyone and anyone's point of views. I'll post up ideas and plans and what not. No offense at all to critic or suggestion or anything. I welcome it. I know there are plenty of people out there that have much more working knowledge and understanding than I do. I'm still gaining enough knowledge just to begin to understand a lot of things.

 

The engineer speaks, and believe me, he knows his stuff!-Bob

 

oh yeah, I totally agree.
I remember reading about this stuff with my oldscreenname- NoRacheHere... I knew both you and him was one of the few that really know what they are talking about

 

Thanks for the kind words.

You might check out this thread and the pictures.
Need ref. for rep. cage builder
https://www.tamparacing.com/forums/c...e-builder.html

Ted has a big chassis surface plate and jigs to hold things in place.

It's not widely known that he built a Panoz chassis
back when he was down the street from me in Tampa.

As well as some stunt cars and race cars.......-Bob