How rigid is this chassis?

[ILLSMOQ]

Originally Posted by venturaII

I think a better question would be: why do you feel like rigidity needs to be added, and how can you be sure a cage is adding it in areas of any use? I understand you're making more power, etc, but the bottom line is that if the power hasn't cause the chassis to flex any more than it was before, why go to the bother?

You're right, which was my original question in the first place...seemed like the answer, from those who have been down this road, was that it doesn’t need any rigidity to be added.

I will say this though...I have noticed when lifting the car on my lift, I use blocks of wood under the jack points so the car is lifted by the jack points and not some other part on the car where the lift pad happens to be. Sometimes this makes one corner of the car higher than the other corners depending on which part of the lift arm the block of wood is placed. As the car is lifted eventually all four corners are resting on the blocks of wood on the lift.

Other cars I’ve lifted in this manner(uneven lift points) resulted in one corner of the car not actually resting on one of the lift arms.

Not a scientific test at all but it ssems to me that this chassis does flex or twist...wether or not it matters or is being stressed as intended I don’t know.

I’ll report back with my own findings once my build is complete and I’ve put it through its paces.

[Skeneypoo]

Originally Posted by ILLSMOQ

With or without a helmet???

Based on the intelligence I've seen in this thread, we should all be wearing helmets inside and outside of our cars.

[gtengr]

Originally Posted by venturaII

More to my point though, is that randomly increasing the rigidity of one section of the chassis does not equate to better performance.

Ever seen the movement of a dial indicator rigged up against the chassis floor in an E46 M3? That excessive movement is fixable by adding rigidity to just one section of the chassis.

[venturaII]

Originally Posted by gtengr

Ever seen the movement of a dial indicator rigged up against the chassis floor in an E46 M3? That excessive movement is fixable by adding rigidity to just one section of the chassis.

So, cage not needed. Curious what quantifiable improvement that extra rigidity nets, besides NVH...

[ILLSMOQ]

Originally Posted by Skeneypoo

Based on the intelligence I've seen in this thread, we should all be wearing helmets inside and outside of our cars.

[gtengr]

Originally Posted by venturaII

Curious what quantifiable improvement that extra rigidity nets, besides NVH...

The subframe rotates and displaces less, so a few suspension joints experience less drivetrain torque related displacement, the diff stays more aligned with the driveshaft, and the chassis floor connected to the subframe will have more resistance to tearing away from the rest of the chassis. Also, E46 sedans with a fixed back seat are about 50% stiffer than a E46 sedan with fold down seats, so it's clear some rigidity is lost with fold down seats. A rear strut/subframe brace, while not quite a fixed back seat panel, is a structural modification in an area that is known to be a weak spot on another car. I don't know how much power is needed for chassis tears to become a problem on the 86, but the E46 was very weak. It is expensive to quantify those things with testing, but the fundamentals on how and why it works are sound. NVH can increase but it's probably not a big consideration for the people who are looking at reinforcement as a need (+500 lb-ft or w/e, not sure what the number is) and not a luxury.

[venturaII]

For reasons of durability/strength (which also translate to safety..), I don't really dispute the gains. But unless someone is running aluminum or delrin bushings EVERYWHERE, any additional stiffness in the chassis would be negligible compared to the amount of deflection added up elsewhere in the suspension, so there's little to gain, performance wise in any vehicle except a max-effort track car where chassis deflection really becomes the LAST area that needs to be changed; the nth degree. It's only coincidental that cages are added earlier in the build process in response to safety requirements.

I was close to an E36 M3 purchase before finding my FRS, so having done the research on them as well as having a few friends who track and autocross theirs, I'm familiar with the E46 and E36's shortcomings in the rear suspension area. I'm not aware of ANY areas on the 86 where chassis strength is even remotely as frail as that. Driveline components can be brittle, but a cage won't resolve that...

[venturaII]

Originally Posted by ILLSMOQ

Bubbles is brilliant. lol

[ILLSMOQ]

Originally Posted by venturaII

Bubbles is brilliant. lol

He’d fit right in over here.

[gtengr]

Originally Posted by venturaII

But unless someone is running aluminum or delrin bushings EVERYWHERE, any additional stiffness in the chassis would be negligible compared to the amount of deflection added up elsewhere in the suspension, so there's little to gain, performance wise in any vehicle except a max-effort track car where chassis deflection really becomes the LAST area that needs to be changed; the nth degree. It's only coincidental that cages are added earlier in the build process in response to safety requirements.

I don't disagree except the premise of this thread is that ~650 hp will be involved, and OP already has solid subframe bushings and poly diff bushings. I don't think chassis tearing is a far-out concept at that power level either, but it's debatable.

[venturaII]

Originally Posted by gtengr

I don't disagree except the premise of this thread is that ~650 hp will be involved, and OP already has solid subframe bushings and poly diff bushings. I don't think chassis tearing is a far-out concept at that power level either, but it's debatable.

True. However, that is going to be one heavy and intrusive rollcage if it's going to be used to reinforce every suspension and subframe pick up point on the body. It'll definitely look racecar..

[cf6mech]

Originally Posted by TorontoNat

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.

Seems someone bought into the "CG" advertisement hyperbole. A car doesnt have to have a boxer/low CG engine to handle well or have a certain "feel". Tell that to all the MX5 owners.As far as extra weight its less than a passenger , and most swaps as far as LS swaps the weight distribution is unchanged from OEM specs.

As far as a roll cage, a half cage is fine on the street and no you dont need to wear a helmet....just make sure you use your 5 point harness.

[ermax]

I’m not sure people realize the LS is a very light engine. Around 450 lbs compared to about 480 lbs on the FA20. Yeah the FA20 sits lower but the bottom end of an LS would be where the bulk of the weight would be. I’m sure the CG would take a hit but I seriously doubt it would turn it into a tank.

[ILLSMOQ]

Originally Posted by cf6mech

Seems someone bought into the "CG" advertisement hyperbole. A car doesnt have to have a boxer/low CG engine to handle well or have a certain "feel". Tell that to all the MX5 owners.As far as extra weight its less than a passenger , and most swaps as far as LS swaps the weight distribution is unchanged from OEM specs.

As far as a roll cage, a half cage is fine on the street and no you dont need to wear a helmet....just make sure you use your 5 point harness.

If you wanted an LS, then why didn’t you buy a Corvette?