How rigid is this chassis?
 

Got to thinking about that tonight. I’ve been drilling holes and moving metal to fit all this power and hardware into this car. I’m noticing that everything bends, drills, stretches and tears pretty easily...started wondering at what point do you need to add a cage to strengthen the chassis?

When you are required by a race track.
Or when you have 5 point harness and need a roll bar as per scca rules. Or at least that was the new rule with having 5 point harness.

Thanks but I’m not talking about race track rules...I’m talking about stresses on the unibody and chassis flex. The seems on this car are spot welded and glued together, they come apart pretty easily. It was designed for 200hp right? Doing an engine swap, we are throwing double or triple or more hp at it. Even the subframes are not super beefy...the sheet metal in between the subframes is pretty weak.

Some others that have done swaps may be able to answer, how well does the car seem to handle the extra power and torque?

Not very. It twists like a wet noodle.

The car is designed to crumple on impact and absorb the forces instead of the driver. If you "beef" it up too much you negate all of that engineering and risk being pulped in a crash.
Conversely if you start drilling holes, tearing and stretching things then it may crumple more than it should and crush you.
When you swap engines you pretty much change the whole engineered safety aspects of the car and there is not much you can do about it. It is the compromise and risk that you have to accept.

Starting to think a cage of some sort is probably a good idea.

With the HP you're going to install,,, it certainly couldn't hurt. What do you think one would run,,,, $3k or so??

Is this going to be a street car? Cages are designed to be used with a helmet and can be very hazardous when used on the street without one.

ITT: a bunch of people who haven't played with actually floppy chassis from early 90s japanese cars.

Definitely a smart thing to think about...and I hadn’t thought about that. It’s a street/track toy.

I really don’t want a cage in it but I think this thing is going to need some rigidity added to it.

I’m thinking something along the lines of this...

http://cdn.speednik.com/wp-content/b...e-complete.jpg

Are there any sort of sub frame connectors available for these cars?

They are all over the place...few hundred to a few thousand.

For safety, you typically need a fixed back seat and helmet once you get a roll bar in. And a helmet on the street is usually not legal.

The chassis is reasonably stiff for what it is, but that's because of how it's engineered. It doesn't have to be thick materials or insanely strong glues, etc; it's all in using the materials so they're strong in the direction they will be stressed.

Hmm, it did feel pretty tight the few times I drove it before I started the swap.

Maybe it is strong enough when stressed as intended...but yeah it definitely seems pretty flimsy when I’m banging on it with a hammer lol :bonk:

I think having a sheet of aluminum bead rolled for strength behind the rear seat isn't a bad idea, or a copy of Spencer Fabrication brace

People have been saying that about unibodies for 50 years now, yet here we are. From F1 cars to spaceships to cheap sports cars, 'stressed as intended' is responsible for most of the mechanical engineering gains seen in the last 40 years as computational analysis has become more and more available.

It's like sitting on the hood of a car and saying "they don't make 'em like they used to" when you get sad about the dent. The damn hood weighs 5 lbs, you can't have your cake and eat it too.

Dang truer words. Go ahead and swap all the body panels on modern cars to some nice thick steel panels. +800lbs later...

Used to get into a debate every single time I went to a meet in one of my 50s cars and some guy would say "They don't make 'em like they used to" or "that thing would be a tank in a crash". The concept of dissipation of force is lost on many and what seems to be flimsy will actually save your ass.
I wish I had the video below available back then just to show people how bad rigid can be. They were right they don't make 'em like they used too and that is a good thing.


Pay special attention to what happens at :49 and 1:10. Which car would you rather be in?


[ame="https://www.youtube.com/watch?v=joMK1WZjP7g"]Crash Test 1959 Chevrolet Bel Air VS. 2009 Chevrolet Malibu (Frontal Offset) IIHS 50th Anniversary - YouTube[/ame]

I notice it most when leaving the driveway on a slant, and all the ice on the roof cracks and slides off.

I love that video. I have a friend who purchased a '60 Chevy Fleetmaster (same color, 4 door, lower spec trim than the Bel Air) not long before that video came out. He was not happy when we showed it to him...

our LS car had no cage for 3 years, now it has the LSA blower and TH400 trans. no weird stress issues or anything

I have had the same argument with friends many times that would think it would be a good idea to get an old "tank" for their teenager because "it's safer".


Also, the "roll bar in a street car" argument. Yea buddy, good idea to have a solid bar inches from your head!

Well forget about how it used to drive... The balance/weight distribution will be off completely unless you are doing some serious engineering before cutting things and slapping what I'm guessing (Don't know what engine you are putting in) is a not flat, heavier/bigger engine in there.

The center of gravity (You know..That thing that actually makes this car amazing) will be completely off as well rendering the whole feel of the car stock completely irrelevant to you.

If you are cutting things your car's safety goes straight out the window. Rigidity doesn't equal safety anyway as we have explained.

Now if you have made this car have body roll while turning as a result of what you have done then you might want to consider a roll cage and some sway bars... but that's another story.

Good luck with the swap... It is an ambitious endeavor you have embarked on.

Thanks for the well wishes and valuable insight Toronto Nat...in taking your novel post to heart, perhaps I should have consulted you and the other geniuses before embarking on this perilous journey into creating a top heavy, wobbly, death trap of a machine :eyebulge: haha!

...starting to realize that even though this is the Swap forum perhaps this isn’t the best place to actually get swap information and advice...instead, aside from a few helpful posts, it’s mostly know it all answers from those that only know what they know:thumbsup:

From the responses of those that actually have experience with the original topic of the thread, it sounds like the car takes the extra power well enough.

I think it will hold up fine, but I'm getting a cage from Custom Cages out of the UK. It's a bit extreme. But I like the design of it.

That is serious...looks like it could be pretty heavy?

So you wanted only one answer and forget the other very relevant responses?

48.5kg or about 107 pounds.

Not at all, I posed my question about the rigidity of the chassis and its ability to handle the extra power. There were a few relevant responses , including some of yours which are appreciated.


...Also had some irrelevant responses, that have nothing to do with the question and one response in particular that had more of a condescending, "keep the 86 as it was designed, you've ruined it" tone to it, hence my response.


By your reaction to my response I wonder are you including yourself in the "Genius" group I mentioned and taking offence or actually just curious as to the nature of my response?

Just curious more than anything but your cryptic statement will have more than one person with a sincere response wondering if you included them.
This is a community and as such you will get both the info you want and some that you don't. Lashing out at the people with answers you don't like won't stop them and just makes you look as bad.

Listen guys, we all appreciate the hostility, but let's get back to the subject on hand. If you're driving your car in a manner that would be deemed "dangerous" on highway roads, it's a good idea to have a cage.

Let's all just agree with me and be done with it.

Thanks and you’re right.

With or without a helmet???

You can use dial indicators and cameras to aid in deciding on whether to reinforce the subframe-chassis hard points.

One option is to build a rear strut bar that ties into the subframe mounts. That would give you local rigidity while retaining some safety for street driving. You'd lose some of the rear crumple zone, but wouldn't have the safety risks of a full cage.

I mean our stock chassis has been in the 7s already ��

7's with no cage?

No it is not.
A cage is intended for a dedicated race car and is to be used in conjunction with other safety devices.

Not irrelevant...It was clearly said that the chassis felt tight when you drove it stock implying that it will retain this same "tightness" afterwards. I was merely explaining why that is not correct.

I was actually hoping you'd respond with.. "Putting a Porsche flat 6 in there so jokes on you!" But I guess not.

Just because you don't like the information doesn't make it false but don't mind me, I am just one ricer in a slow and uncomfortable car among thousands passing through here.:burnrubber:

He isn't just slapping some engine in there. He is using well thought out mounts which put the engine as low and far back as possible while still retaining enough clearance for everything to work as intended. The engine/transmission combo he is using is somewhere around 60-80lbs more than the factory engine/trans combo, and most of the weight is gained in the transmission, which is low and center. Factory Weight Bias is retained, while more than tripling the factory power output (without use of a turbo).

He is simply asking if the chassis could handle the power/torque increase without causing any negative effects. I don't blame him for asking.

Coming in and responding to a thread in which you have no direct experience and spreading speculations without even know what is going on doesn't help.

Welcome back Mat:cheers:, You were so focused on center of gravity and body roll, I completely missed where you actually addressed any part of my comments.

Also, I wouldn’t call your information “information”...it’s more of an opinion and you know what those are like. Everyone’s got one. You can flush what comes out of yours next time thanks:w00t:

Read through the swap thread and it doesn't look like you have compromised the integrity of the chassis to any great degree. Looks like it was pretty well thought out.
I would skip the idea of a cage for adding strength though. Any increase in rigidity it may give is poorly located and of little value anyway. A long piece of pipe with several bends in it and a very small contact footprint with the car is not going to gain you much.
If I was in your position I would go with one of the available brace kits. You may have to do some minor surgery to get some to work with your engine though.


https://www.frsmod.com/products/fr-s...it-for-frs-brz