Body stiffness of w body

[mycarsucks]

Anybody know what the hz rating for 1st gen w bodies is stiffness wise? I know the H body cars (bonneville and lesabre) was around 25hz which was very good for the time. I always thought the 1st gens seemed more flexy than the 2nd gen w bodies but can anybody confirm this? Also does anybody know how much inner rockers contribute to body stiffness or is that mostly through the roof/abc pillars

[Schurkey]

I didn't know that car-body stiffness was measured in Hz.  I'd have guessed force-degrees.  Pounds per degree of twist, or somesuch.

[Bake82]

Interesting topic as I was thinking alot about body stiffness for my 3800SC Cutlass.  

 

2 thoughts on stiffness

1. I believe the inner rockers, at least on a 1st gen are major structural component in body stiffness, as it was a large area of focus when GM build the convertibles.  

2. I had some thoughts this summer to add "frame rail connectors" basically connecting the front "frame" (the portion where the front subframe connects to the body) and run a 2x3 piece of steel to the rear foot panel/front of the fuel tank area and tie into the trailing arm mount areas.    I think it would add a TON of structure to the chassis.    But I decided for now to forgo the project as it would be a large endeavour to do this. 

 

Interesting to know your thoughts as to why and if you had a plan for stiffness?  

 

 

[Vegeta]

The only time I have seen a car flex is when its a convertible.  The 4 door is stiffer than the 2 door, if body stiffness means something for your application.  the G6 convertible flexes much much more than any w body I have owned.  

Please tell me what hz means.

[mycarsucks]

On 11/17/2024 at 1:57 PM, Vegeta said:

 

Please tell me what hz means.

Body stiffness is rated in Hertz or Hz because that is the best way to measure its natural frequency of vibration. Higher "Hz" rating = stiffer chassis. 

Edited November 20 by mycarsucks

[mycarsucks]

On 11/13/2024 at 12:11 PM, Bake82 said:

Interesting topic as I was thinking alot about body stiffness for my 3800SC Cutlass.  

 

2 thoughts on stiffness

1. I believe the inner rockers, at least on a 1st gen are major structural component in body stiffness, as it was a large area of focus when GM build the convertibles.  

2. I had some thoughts this summer to add "frame rail connectors" basically connecting the front "frame" (the portion where the front subframe connects to the body) and run a 2x3 piece of steel to the rear foot panel/front of the fuel tank area and tie into the trailing arm mount areas.    I think it would add a TON of structure to the chassis.    But I decided for now to forgo the project as it would be a large endeavour to do this. 

 

Interesting to know your thoughts as to why and if you had a plan for stiffness?  

 

 

My personal 1st gen (a grand prix sedan) seems to be extremely flexy. When the car is on the ground I have to almost pry the rear doors open, but when I jack up on the front of the front subframe, the body equalizes and suddenly the rear doors open and close like normal. The car DID have rusted rockers, but they since have been replaced and I can't seem to understand why my car is doing this. I had a park avenue which had the inner rockers completely gone and never had any issues with the doors opening or closing. I have also seen many 97-03 GPs with no rockers or strut towers left and the doors dont have troubles opening or closing. This leads me to believe that the 2nd gen w bodies might have a much stronger roof structure which allows the unibody to function like normal even when the inner rockers are not present. The A/B/C pillars ARE thicker on the 2nd gens so that may lead to increased body stiffness but I don't know if there are any GM documents which state what the body stiffness is on each gen of the w bodies. Another point to the design of the 2nd gen is that the front frame rails under the car which end abruptly in front of the b pillar on 1st gens, go almost all the way to the rear of the car on the 2nd gens. I wonder if one extended the "box" structure from where it ended on the 1st gens further rearward if it would increase body stiffness or not. I agree with you that a subframe connector of any kind would add a lot of structure. It seems the 1st gens are extremely underbuilt underneath compared to other unibody cars from GM which puts lots of unnecessary stress on the inner rockers. Replacing the original inner rocker panels with 1/8" thick steel would also greatly benefit these cars.

Edited November 20 by mycarsucks

[jiggity76]

Been reading some of the comments here and one thing I will say...the front structure of our cars, and I'm referring more to the 1st gens, they have an extremely strong front end.  I believe this is why the derby guys love them so much.  The rad support being welded in and with the way it's designed along with the added bars that connect the rad support to the strut towers, they can take a lot of impact.  I think those bars are more for directional or controlled collapse in an accident, but maybe the do add to the stiffness of the front end.

[Amanita]

1st gens definitely love more rigidity, my Grand Prix noticeably benefited from the front and rear strut tower bars.

[mycarsucks]

1 hour ago, jiggity76 said:

Been reading some of the comments here and one thing I will say...the front structure of our cars, and I'm referring more to the 1st gens, they have an extremely strong front end.  I believe this is why the derby guys love them so much.  The rad support being welded in and with the way it's designed along with the added bars that connect the rad support to the strut towers, they can take a lot of impact.  I think those bars are more for directional or controlled collapse in an accident, but maybe the do add to the stiffness of the front end.

the 1st gen front ends are extremely strong. I just wish that they continued that same rigidity for the rest of the car. Primarily around the B pillar area and the rear end.

[Vegeta]

Ah ok so its still frequency but I didn't know a weakness in the chassis would lower the resonance.  Tune a stereo to the frequency of your vehicle for fun.  Tune it to whatever frequencies counteract the stress the chassis is under.   Anyway, where do you see any of these tests or results?  I didn't have much luck with the googles.

[jiggity76]

10 hours ago, mycarsucks said:

the 1st gen front ends are extremely strong. I just wish that they continued that same rigidity for the rest of the car. Primarily around the B pillar area and the rear end.

I own a 91 Cutlass International Series coupe and a 96 Cutlass Supreme sedan.  I guess I haven't noticed anything hinky going on with them when driving.  The sedan does great in the snow though, great traction, but that's another topic.

Just for fun...a bit scary though.  But, it's also a 50 MPH crash so most cars from this era perform about the same.  I need to watch my rearview mirror more often, LOL.

 

 

This poor vert took a pretty good hit too.  Looks like it performed pretty well for not having a metal roof.

 

 

 

 

Concerning the B pillar area.  This very rare 90 International coupe met it's end unfortunately.  It still breaks my heart seeing it.  Accidents are so odd.  Can't believe that quarter glass is still intact.

 

 

Edited November 20 by jiggity76

[SuperBuick]

Does the convertible strut brace make any difference?

 

What is the part number for those, are they still available?

[jiggity76]

1 hour ago, SuperBuick said:

Does the convertible strut brace make any difference?

 

What is the part number for those, are they still available?

Not available anymore.  You'll need a bar from a 93-95 year range vert.  The previous 90-92 style bar won't work on your LQ1.

[Schurkey]

Interesting read concerning a 1960s British car, and how it was engineered to be admirably stiff.

https://www.autospeed.com/cms/a_112137/article.html@populararticle

 

I'll say it again--I've never heard of vehicle body stiffness being rated in Hz.

[Black92GS]

On 11/19/2024 at 9:27 PM, jiggity76 said:

Been reading some of the comments here and one thing I will say...the front structure of our cars, and I'm referring more to the 1st gens, they have an extremely strong front end.  I believe this is why the derby guys love them so much.  The rad support being welded in and with the way it's designed along with the added bars that connect the rad support to the strut towers, they can take a lot of impact.  I think those bars are more for directional or controlled collapse in an accident, but maybe the do add to the stiffness of the front end.

Not all 1st gen Ws have the rad support bars. My 88 and 89 Regals had them, as did my 92 Cutlass. Those cars had the 2.8, 3.1 and 3.4 respectively.  My current 92 GS never had them.  The holes are there...but they were never tapped for threads on the rad support end. 

It seems to have something to do with it being equipped with the 3800 series 1, as those are the only ones that never have them. 2.8, 3.1, 3100, 3.4 and 3800 series 2 equipped 1st gens coupe or sedan all seem to have them. 

[jiggity76]

13 hours ago, Black92GS said:

Not all 1st gen Ws have the rad support bars. My 88 and 89 Regals had them, as did my 92 Cutlass. Those cars had the 2.8, 3.1 and 3.4 respectively.  My current 92 GS never had them.  The holes are there...but they were never tapped for threads on the rad support end. 

It seems to have something to do with it being equipped with the 3800 series 1, as those are the only ones that never have them. 2.8, 3.1, 3100, 3.4 and 3800 series 2 equipped 1st gens coupe or sedan all seem to have them. 

Wow, this is news to me!  Interesting and thank you for explaining.  I just assumed no matter what engine option, all 88-96/97 W's had them as standard.

[Black92GS]

53 minutes ago, jiggity76 said:

Wow, this is news to me!  Interesting and thank you for explaining.  I just assumed no matter what engine option, all 88-96/97 W's had them as standard.

So i kind of take all of that back. 92-95 regals with the 3800 don’t seem to have them. I just found a bunch of pictures of 91s with the 3800 that have them! 

If they are designed to help promote crumpling in a collision, the only thing I can think of is that there is more clearance somewhere in the engine bay with the 3800 series 1 that they aren’t required.