Chassis rigidity

Gary,

The car has some seious flex points that are revealed when pushing it hard. Goran Malmberg has done an article identifying these areas of flex. You can also find old pics of the group 4 race cars and see how Michael Parkes (designer of the Gp4 cars) addressed the same issues in 1972 that Goran identified 30 years later.

Unfortunately toes get crunched when I point out that none of the rigidity kits address the same areas. They appear to be more show than go.

The areas on the body where Panteras most commonly "crack" are a result of this flexing, yet the rigidity kits do not prevent flexing in these areas.

The roof is a stressed member, yet it is thin sheet metal with no reinforcment to prevent twisting or buckling. It is attached to the body with a very weak A pillar, and the attachment point is small and unreinforced. It is common for windshields to crack, and common for the A pillar to crack or even break where it attaches to the cowl/front fender area.

The rear sub frame that supports the engine, trans and rear suspension also flexes & twists. It is common for the body to crack in the areas where the rear fenders join the roofline for this reason.

Gary Hall built a Pantera that he calls purple passion, it is a targa top car, and is supposed to be very rigid even though it has no roof at all. What ever he did to stiffen the car from underneath, is what is needed for racing. I understand the bracing was extensive and addded 75 pounds to the car. The other option is to use a roll cage as a stressed member, which is what was done with the Gp4 cars.

your friend on the DTBB

I have Gorans article. I figured there is more then one way to add rigidity and each way will have benefits and consequences. I am thinking of a roll bar with possible a removable front portion. I am really just starting to evaluate where I want to go with it and how much I really want to do with it. I am thinking of doing more to the car then I initially wanted to. I wanted just to swap engines but I keep seeing things I need to or want to take care of.

Gary, I posted a pic or 2 of my inside mounted bar 3 point. I can see there is room behind the rear glass but still in front of the motor for a fabricated bar. That looks like a good area to me, I can picture a couple of smaler dia. bars coming back to the upper wheel houses. Maybe cut through the outsides of the firewalll anr run two more into the cokpit to the threashold. Your going to be making a lot of twisting torque. I can't tell you enough how well the hood pins in the rear deck help with flexing also. I have shown that setup in a previous post. I don't think you need big thick tubing either. just good triagulation.

LPB I had thought abut the bar about the bar on the back side of the glass above the front of the engine but the thought that I want 1 or 2 forward bars in the cockpit keeps coming back to me. I would like to make the forward bars removable.

IMHO, unless you weld up all the seams on the body, instead of just the resistance tack weld they came with, all other stiffening methods will be comprimised. Solid full welds will go a long way in making the chassis stiffer. I know it isn'
t glamorous or showy or expensive, but it is effective.

Actually one of the reasons I am asking is I may do somehting altogether different. I don't really like anything I have seen but I may do something along those lines anyway.

Actually, I am pretty suprised how stiff mine is. If I jack up on corner 3 wheels automatically come off the ground. I cannot get 4 jack stands to all touch at the same time.

George do you have a link to Goran's article on chassi flex?

George,

I don't think the article is available on line anywhere, although you may want to check Goran's personal web site.

The article appeared in the winter 2003 issue of PI magazine (117).

Great name by the way!

your friend on the DTBB

quote:

Actually, I am pretty suprised how stiff mine is.

Yeah mine used to be that way too. But I got older I guess.

Solid triagulation. Removable on driver only. I think another memeber asked about required bars. The more cage and strengh .....the faster they let you go. Comp2, is this the FE block? Post pics.

Seems i remember discusssion on the POCA email forum and that Hall designed his system by putting the body on a machine to flex the body. I think the Byar's Bros use the same braces.

You may want to search the POCA email archives. Also check Chuck Melton's site. He has some pics of bracing.

Gary,

Below is a pic of an early group 4 Pantera. Do you see the 2 bars pointed out by the arrows in the picture? They pass through 2 holes in the rear window (made of plexi) and attach to the roll bar inside the passenger compartment. The roll bar was attached to the unibody at 4 corners inside the passenger compartment. This is to control the flexing in the rear subframe by taking the job of reinforcement of the subframe away from the rear fenders/roof/A pillars and instead reinforcing it with the roll bar assembly.

Your friend on the DTBB

George, I like that alot. I just don't know if I want to do that to the back window.

LPB, the engine is sitting here ready to go. Look like only one real issue which is headers. First glance I thing the engine mounts are the same. The left header is already too close to the gas tank. The guy who had the car before me removed the gas tank shield so he could have room for the header. That makes me a little uncomfortable. I'll just fab up a new set of headers.

I am thinking of deleting the A/C. I think with the compressor, condensor, hoses, etc, I can save at least 75lbs. I may do away with the wing too. I can see doing a couple of things and getting around 150lbs or more so chasis stiffners would just bring me back to where I am I gues.

What about under car frame stiffiners? Do they help much?

I am heading out on another trip. Won't be online much till tomorrow; maybe late this afternoon.

Gary

quote:

Originally posted by comp2:
...What about under car frame stiffiners? Do they help much?...

You know yourself from jacking the car up, the front end is very stiff, its boxed very well. I seriously doubt the "under car" or "in trunk" braces sold by the vendors produce any measurable results in the front end.

Listen, can you hear it, the sound of toes crunching from being stepped on? Ha, ha, ha .....

The brace sold for the rear of the car, that mounts between the sub-frame rails, probably does add a bit of stiffness to the lower control arm mounts, for more stable toe and camber settings. But it does nothing to resolve the major problem with the chassis. So installing that brace without first doing something about the chassis' major flexing problem, is like sticking your finger in a crack while the dam crumbles around you.

There it goes again, that sound of toes being stepped on. Sorry guys, I have to call them as I see them.

Your friend on the DTBB

George,

I was talking to Larry Stock a while ago re bracing and he is of the same opinion as you that the OEM front tub construction provides adequate rigidity in that area.

Larry's (PPC, Reno) lower rigidity braces are in quite different than the other vendors, although not so popular (functionality, rather than aesthetics?). He runs them on his ORR car and swears by them.

The GP4 roll cage sounds like a good stiffening idea. I was taken with a 4 ponit one I saw that rather than go through the window was located behind it in the engine bay with tubes out to the rear inner fenders. The internal one seriously impact an already cramped space.

Here's a photo of PPC's braces and I'm gonna post another one of a slightly different novel thought on bracing. (I'm too stupid to be able to attach two photos in the same post)

Julian

Here's that other photo, but I cannot for the life of me remember where I got it or who's car it is.

The bracing ran from the inner rear fender to the decklid mounts!

Jouls, I like that! The PPC braces in your previous post I was wondering about as well.

How about tubing thicknesses and material?

I am aware of Larry's long brace that attaches beneath the passenger compartment. It is certainly trying to address the real problem, I'm just wondering how successful it is, due to the relatively small size of the tubing and the fact that it attaches with bolts, rather than welding. I would love to do some before & after measurements. Even if it cuts flex down by 1/3 it would be worth using it. Until I have data to confirm the usefulness of the brace, I don't feel comfortable recommending it. Again, let me state, it is at least adressing flex in the proper area of the car. I tend to like Larry's ideas. They show an understanding of the problem.

As to the engine compartment "struts" in the second picture, they may help stabilize the rear subframe a bit, as the tubing will be stronger than the fender panels, BUT they are attached to the roofline, which is a weak spot. The whole roof flexes, to the point that it cracks the windshield and breaks the A pillars off where they attach to the cowl area. Since the new struts flex less than the fender panels, they may actually increase the forces transmitted into the roof and A pillars, and make the buckling & cracking worse! I would not advise duplicating this design.

your friend on the DTBB

I like pauls for basic roll bar. I think the rear bars would help keep the bar from colapsing and add some stiffness:

http://www.panteracars.com/higgs.html

But it lacks the triangulation Goran has done here:

http://hem.passagen.se/hemipanter/Hemi%20motor%202jpg.jpg

My thought here is there is more then one goal with all this stuff. I obviously can't do everything unless I wanted a tubed chasis car.

These are going to help keep the wheel wells from moving:

http://www.geocities.com/pantera_project/2004UpperRearTruss002M.jpg

quote:

Originally posted by george pence:
So installing that brace without first doing something about the chassis' major flexing problem, is like sticking your finger in a crack while the dam crumbles around you.

What kind of flex(torsional or bending) are we talking about here? and where does it occur?

Thanks.

quote:

Originally posted by Joules5:Larry's (PPC, Reno) lower rigidity braces are in quite different than the other vendors, although not so popular (functionality, rather than aesthetics?). He runs them on his ORR car and swears by them.Julian

I'm having trouble visualizing how the Larry Stock Braces in the photo are installed. How and where do they attach to the body?

Thanks.

quote:

Originally posted by jeff6559:
...What kind of flex(torsional or bending) are we talking about here? and where does it occur?...

Jeff please see my first post on page 1 of this topic.

your friend on the DTBB

with a couple years of fabrication of roll cages ... most of what I see on Pantera's helps but doesnt always 100% address the problem. I have a Hall Bolt IN cage and its nice but not complete either. The cage going back to the rear should extend as far to rear as possible like to the frame rails beyond the rear axle and the X brace should trangulate and be wleded together where they cross. Its a little tough to explain in words ...

One of the RULE books for RACING will give you exact specs on pipe sizes and where they can be used. MY memory tells me 11/4" Mild steel for the cage and 1" for the bar that crosses behind the seats that seat belts and the seat back fastens to .. it been a while.

I would also love to see this article on chassis stiffening for the PANTERA that this Gentlemen Goran wrote. This comes at a perfect time.

My 2 cents.

Ron

quote:

Originally posted by accobra:
with a couple years of fabrication of roll cages ... most of what I see on Pantera's helps but doesnt always 100% address the problem. I have a Hall Bolt IN cage and its nice but not complete either. The cage going back to the rear should extend as far to rear as possible like to the frame rails beyond the rear axle and the X brace should trangulate and be wleded together where they cross. Its a little tough to explain in words ...

One of the RULE books for RACING will give you exact specs on pipe sizes and where they can be used. MY memory tells me 11/4" Mild steel for the cage and 1" for the bar that crosses behind the seats that seat belts and the seat back fastens to .. it been a while.

I would also love to see this article on chassis stiffening for the PANTERA that this Gentlemen Goran wrote. This comes at a perfect time.

My 2 cents.

Ron

I second that. I could use a "text" on the Pantera chassis stiffening.
I think the "roll bar" could go in the engine compartment. It can bolt to the roof and be braced towards the rear.
Does anyone have some pics of the factory GT4 roll bars and cages? I'm sure they will help.

I had a friend with a 72 Pantera with a full cage.
the bars across the doors were hinged and could be opened after the doors were.
For my use I wouldn't go that far but I wanna brace the back at least.

quote:

Larry's (PPC, Reno) lower rigidity braces are in quite different than the other vendors, although not so popular (functionality, rather than aesthetics?). He runs them on his ORR car and swears by them. Julian

quote:

I'm having trouble visualizing how the Larry Stock Braces in the photo are installed. How and where do they attach to the body?

Jeff,

The rear attaches each side to the three motor mount bolts on the chassis and then to the rear body. It requires drilling & bolting (removable for oil pan access) or welding in place. I believe the front requires all new holes drilled & bolting or preferably welding in place. The photo wasn't that good; if you have a real interest I could run down to Larry's with the camera, he's only two buildings down from where I work. If there's a potential sale in it, I'm sure he won't object.

Julian

Goran Malmberg is very tech savvy, his EXCELLENT site can be found here. You may want to read the chassis stiffening, suspension, and cornering articles since they are relevent to each other.

Ron

quote:

Originally posted by ParaPantera:
Goran Malmberg is very tech savvy, his EXCELLENT site can be found here. You may want to read the chassis stiffening, suspension, and cornering articles since they are relevent to each other.

Ron

Yikes! I guess that I'm not serious enough to turn my car into a plastic swisscheese junglegym.
I'm going to look for GR4 factory stuff I think.
That makes more sense for me.

Thanks for the information.

Gorans findings are elementary. His "X bracing at the back and floor bracing are obvious solutions to some problems but is exactly what people are trying to get around. The Pantera body from is really like a card board box with the ends cut off. Without the center firewall and some curves it would fold pretty quickly. The "X" brace he has is an obvious solution but man it just ruins the aesthetics of the car. His floor re-enforcement's mess up seating arrangements. Second is it does not fix all the problems.

I think before I would come up with enhancements that help some things that are that messy I would rather create a tubed frame car all together. The real problem is what do I want out of the car. I want something to drive around town, and an occasional trip to the track. With track use I am going to want some rigidity enhancements but there is more then one area so let's break down the issues:

1. Chasis twist front, back, center and combined

2. Wheel wells migrating (collapsing)

3. Rollover protection

The solutions are personal for everyone.

Which upgrades?
How many upgrades?
Upgrades not tried yet.

I am kind of leaning toward Pauls roll bar with arms that come back to the wheel well although it does not have a triangulation brace. I could ad a removable one though.:



Then perhaps the wheel well supports both front and back.

quote:

As to the engine compartment "struts" in the second picture, they may help stabilize the rear subframe a bit, as the tubing will be stronger than the fender panels, BUT they are attached to the roofline, which is a weak spot. The whole roof flexes, to the point that it cracks the windshield and breaks the A pillars off where they attach to the cowl area. Since the new struts flex less than the fender panels, they may actually increase the forces transmitted into the roof and A pillars, and make the buckling & cracking worse! I would not advise duplicating this design.

your friend on the DTBB

George I was thinking in the photo Joules had if it could be a combination of roll bar with a roof attatchemt to help stop the cardboard box effect. With a roll bar like pauls ahead of the engine, tubes that run back to the wheel well (further back then Pauls) and a vertical riser to tie in the roof at the hinge points. With a removable cross on the back tubes.

The attatchment point of the rear tubes could also contain an additional bar for wheel well suport.

Sorry Mark, I am using one of your photos here.

This is what I am thinking. A 2-bar roll bar ahead of the engine. Two bars come back to the wheel well. The light blue line shows a n attachment point at the hinge to stabilize the roof to help with the cardboard box effect. The green cross bar is removable for track use. An additional attachment across the wheel well to keep the wheel well from migrating. The blue line is the original wheel well suport.

The car is monoquoc. You are going to convert it to tube if you continue this line of thinking.
I think that the existing monoquoc just needs to be reinforced at the attachment points like one would put chassis connectors in a Mustang, etc.
Mustangs have similat issues. The rear tubs are part of the chassis. They are semi-monoquoc chassis.

Well PD, the roll bar is probably going in. There will probably be an aditional cross suport for the wheel wells as they migrate. The only thing extra is the tubes from the roll bar to the whell well.

quote:

As to the engine compartment "struts" in the second picture, they may help stabilize the rear subframe a bit, as the tubing will be stronger than the fender panels, BUT they are attached to the roofline, which is a weak spot. The whole roof flexes, to the point that it cracks the windshield and breaks the A pillars off where they attach to the cowl area. Since the new struts flex less than the fender panels, they may actually increase the forces transmitted into the roof and A pillars, and make the buckling & cracking worse! I would not advise duplicating this design.

Actually if you look a littler better at the photo Joules posted, he has more structure then what is seen in the photo. It is hard to tell what heas really done there. He obviously is attatched tot he roof but I can see more tubing and cross braces tired into probably something similar to what I drew.

I went through the same scenario with my car.PanteraDoug is correct in making comparisons with the Mustangs.I sat down with a chassis geru who builds GTP and Trans Am cars in my local area.In his opinion the most cost effective and constructive way was to install a six point cage. 4 points in the passenger compartment,2 points out the rear window.Lastly and really important was to tie the 2 forward bars in the passenger compartment to the front passenger compartment fire wall.He also suggested ultimately running rectangular tubing through the floor boards connecting the rear chassis rails to the front chassis rails.BUT that meant cutting up the floor pans.He only suggested the latter if the car was to be purely dedicated track car with extreme horsepower and slicks.

Dan

There are some Unique issues with the Pantera such as wheel well colapsing issues.

Comp2, what do you mean by wheel well collapse issues? Do you mean structual integrity issues due to rust?I'm certainly no expert on this but the chassis guy thought having the 2 bars out the rear window to the rear tubs with a 4 point cross brace to tie it in was enough.I suppose if you speak with 2 different chassis guys you'll get 2 different methodologies.

Dan

quote:

I suppose if you speak with 2 different chassis guys you'll get 2 different methodologies.

Dan

Absolutley. I think it's going to be a personal thing for everyone right or wrong but that's what makes hobby cars fun.

My understanding is with rust (and hard driving) the wheel wells and a-frame attachent points migrate. This is one of the braces to stop that as the original brace moves too much:




What exactly does this do for the front?:

http://www.pim.net/3222006BLKGT5S73.jpg

quote:

Originally posted by Danno:
...I sat down with a chassis geru who builds GTP and Trans Am cars in my local area.In his opinion the most cost effective and constructive way was to install a six point cage. 4 points in the passenger compartment,2 points out the rear window.Lastly and really important was to tie the 2 forward bars in the passenger compartment to the front passenger compartment fire wall.He also suggested ultimately running rectangular tubing through the floor boards connecting the rear chassis rails to the front chassis rails.BUT that meant cutting up the floor pans.He only suggested the latter if the car was to be purely dedicated track car with extreme horsepower and slicks...

I would say you received good advice Dan. As a side note: the large cross brace sold by Larry Stock is designed to tie the front frame rails to the rears, just as suggested by the chassis builder you had consulted.

quote:

Originally posted by Danno:
...the chassis guy thought having the 2 bars out the rear window to the rear tubs with a 4 point cross brace to tie it in was enough.I suppose if you speak with 2 different chassis guys you'll get 2 different methodologies...

The only other way to stiffen the chassis will be to work solely under the car, such as Gary Hall's modifications to purple passion.

your friend on the DTBB