Chassis stiffness

[thstone]

Originally Posted by itsnotanova

The more I think about it the more I think my original idea might work. There really isn't a great place to attach a brace to on the front of the cabin. The screw holes where the sunvisor attaches look to be the easiest place to fabricate an attachment point to. I'm starting to think the window frame might be able to handle that added stress. The A pillar is very strong. I'm bringing a boxster to scrap this week and to make it smaller I tried pushing down on the windshield with my tractor. The A pillar didn't budge with the front weight of my tractor on it. The front wheels of the tractor came a good foot or two off the ground. I had to push in the very middle of the windshield to get it to collapse and even then the A pillars were standing tall. That's maybe 1500-2500lbs pushing down on it. It's not like the brace would be forcing that much pressure on the frame? At least under normal track usage. I have a few boxster shells I could test on.

The windshield frame is quite strong! It is reported that the windshield frame can withstand 1.5 times the weight of the car.

If you look at the chassis image, there are boron steel reinforcements (green) that start down in the bottom of the door sill, goes up thru the chassis and then from the chassis into the A-pillar of the windshield frame. Its job is to keep the floor pan from collapsing upward and and the A-pillar from collapsing downward in a rollover.

The windshield frame header has no such reinforcement so it will deform much easier and further than the A-pillars.

With that being said, I'll have to think about connecting the windshield frame to the roll bar...

[rfuerst911sc]

For those of you that have owned 914's in the past and are familiar with the website 914world there was a gentleman with a last name of Engman ( now deceased ) that manufactured what was called " the Engman kit " to help strengthen the tub on 914's . Many called it a clam shell but basically it was a very heavy duty L shaped piece of metal . It was aprox. 1.5 " wide at the top and sat on the horizontal portion of the interior rocker structure . It was aprox. 3 - 4 " deep and that portion went against the vertical portion of the rocker . The L pieces had many holes drilled into them and that's where you welded them to the rockers . The pieces were long enough to go from the door posts at the front to the firewall . It also included a piece that went on the bottom of the firewall .

When all 3 pieces were welded in they provided a big increase in chassis stiffness , I installed one on my GT clone with a 3.0 911 engine and the difference was VERY easy to feel . Now to be fair we also are talking a chassis that was designed and built 40 + years ago . But the principle may apply to the Boxster chassis also .

[The Radium King]

i think a bar attached to the winshield frame would only work if it was triangulated in some way; otherwise it would help the (for want of better terms) the 'foldin' of the car, but not the 'twisting' of the car. in my experience, most of the frmae movement seems to be of the twisting type (ie, backing out of a driveway crooked - as jaykay says, when you stiffen suspension, etc., you start to introduce flex elsewhere).

that engman bracket sounds interesting. go go gadget search engine skills ...

edit, here we go:

http://forums.pelicanparts.com/porsche-914-914-6-technical-forum/414638-pics-my-engman-kit-installed.html

[jaykay]

Originally Posted by rfuerst911sc

For those of you that have owned 914's in the past and are familiar with the website 914world there was a gentleman with a last name of Engman ( now deceased ) that manufactured what was called " the Engman kit " to help strengthen the tub on 914's . Many called it a clam shell but basically it was a very heavy duty L shaped piece of metal . It was aprox. 1.5 " wide at the top and sat on the horizontal portion of the interior rocker structure . It was aprox. 3 - 4 " deep and that portion went against the vertical portion of the rocker . The L pieces had many holes drilled into them and that's where you welded them to the rockers . The pieces were long enough to go from the door posts at the front to the firewall . It also included a piece that went on the bottom of the firewall .

When all 3 pieces were welded in they provided a big increase in chassis stiffness , I installed one on my GT clone with a 3.0 911 engine and the difference was VERY easy to feel . Now to be fair we also are talking a chassis that was designed and built 40 + years ago . But the principle may apply to the Boxster chassis also .

It would be good to see a conceptual sketch of this if you are so inclined. Might be Boxster viable for those with no cage; performing a comprehensive canyon carver build. I will try and search up the kit.

I must say I am very drawn to 914-6 GTs and would consider building a clone someday. I believe the actual cars had a full cage and fixed roof so stiffness should have not been an issue?

Most feel they are ugly cars but I think they are fantastic looking. If you able to find a car that won't corrode and carry out this mod, one could have a very nice GT clone sans cage and a removable top...

[rfuerst911sc]

Originally Posted by The Radium King

i think a bar attached to the winshield frame would only work if it was triangulated in some way; otherwise it would help the (for want of better terms) the 'foldin' of the car, but not the 'twisting' of the car. in my experience, most of the frmae movement seems to be of the twisting type (ie, backing out of a driveway crooked - as jaykay says, when you stiffen suspension, etc., you start to introduce flex elsewhere).

that engman bracket sounds interesting. go go gadget search engine skills ...

edit, here we go:

pics of my Engman kit installed - Pelican Parts Forums

Great detective work there you found my post on 914 world . The pics sure help with the explanation of how it works . Maybe some engineer with a Boxster can look the kit over , visualize a Boxster solution then work with a metal fabrication shop to come up with a prototype .

[rfuerst911sc]

Originally Posted by jaykay

It would be good to see a conceptual sketch of this if you are so inclined. Might be Boxster viable for those with no cage; performing a comprehensive canyon carver build. I will try and search up the kit.

I must say I am very drawn to 914-6 GTs and would consider building a clone someday. I believe the actual cars had a full cage and fixed roof so stiffness should have not been an issue?

Most feel they are ugly cars but I think they are fantastic looking. If you able to find a car that won't corrode and carry out this mod, one could have a very nice GT clone sans cage and a removable top...

I may be wrong but the only 914-6 GT's that came from Porsche with a cage were race cars the street cars had no cage . When folks started sticking hyped up sixes in that chassis they started to increase the torsional flex . Even guys with high HP fours were looking for solutions for the chassis flex . Mr. Engman saw an opportunity to come up with a solution and here we are . No it does not replace a full roll bar/cage but for a hot street car/AX machine his kit worked well .

[The Radium King]

yeah, i think the market for this is small - race guys have cages, and street guys have suspension that is compliant enough to absorb the flex and not transfer it to the chassis; the hot street/ax/track rat is the target.

so, to the engineers (of which i am one, but not my area of expertise) which would provide more rigidity (speaking specifically to the passenger compartment, and more specifically to the four 'wells' in that compartment):

- the engman approach to reinforce the rockers, tunnel, and bulkhead? lots of welding; would be an intrusive job;
- the cross-bracing approach of running diagonal members? could be accomplished with bolt-in brackets and threaded rods or somesuch;
- a combo of one of the above with the addition of welded/bolted gussets in the corners?
- or screw it, just seam weld the car!

[mikefocke]

A 914 that won't rust is an impossible find. They rusted. Just google 914 and hell hole. A rust free 4 cylinder can be $25k and you don't want to even think of the 914-6's prices.

Owned a '70 4 cylinder. Sold it maybe a week before the warranty ran out. The joke at work was the dealer had installed a name plate with my name on it as it was there so often. Audi had just come out with a $3500 can and the dealers went from selling $6+k 911/912s to two cheaper cars and their service and parts departments were overwhelmed. Mine was showing signs of rust after 2 years as a daily/only (I took it to go skiing a lot) and a doctor-to-be from Philadelphia bought my $3600 car for $2100 and I was glad to be done with it. Even though it was surely the most fun car I ever owned. Bought a BMW and curiously enough stopped getting tickets.

[Stroked & Blown]

What about making a bolt-in door bar like this:
Miata Bolt-in Door Bar
Seems like it would stiffen the fore/aft flex in the tub.

[The Radium King]

holy cow. quick bit of seaching shows that it is super effective (on miatas) as well. could bolt one end in to the same studs that mount the roll bar, and the other end into the strong green steel in the front footwell ...



miatas also have a cool thing called a butterfly brace for the transmission tunnel.

[The Radium King]

ok - first pic is of the rear of the pssgr compartment. you can see the door jamb on the left and the front mounting point for the roll bar. it is at about the same level as the jam, sits a bit inboard, and there is enough thread on the studs to accommodate a mounting plate.



second pic shows the front footwell of the pssgr compartment. you can see where the strong green steel member runs - it is the darker section just below the insulation with the three holes in it. again, you can see the door jamb on the right and it is about the same level as the jamb. would be very easy to fabricate a plate to bolt here.



otherwise, the bar would be low - just a bit higher than the jab. run close to the jamb at the front and move in a touch as it gets closer to the rear. looks like no interference with the door panel unless aftermarket door speakers that stuck out too much, and would fit with my seats. would require trimming front and rear carpet panels; no wiring appears to be in the way.

[Robert986]

Originally Posted by The Radium King

ok - first pic is of the rear of the pssgr compartment. you can see the door jamb on the left and the front mounting point for the roll bar. it is at about the same level as the jam, sits a bit inboard, and there is enough thread on the studs to accommodate a mounting plate.



second pic shows the front footwell of the pssgr compartment. you can see where the strong green steel member runs - it is the darker section just below the insulation with the three holes in it. again, you can see the door jamb on the right and it is about the same level as the jamb. would be very easy to fabricate a plate to bolt here.



otherwise, the bar would be low - just a bit higher than the jab. run close to the jamb at the front and move in a touch as it gets closer to the rear. looks like no interference with the door panel unless aftermarket door speakers that stuck out too much, and would fit with my seats. would require trimming front and rear carpet panels; no wiring appears to be in the way.

Interesting idea there!!! But wouldn´t it interfere with the fuse box on the drivers side?

[Robert986]

Found this old thread.. Did I actually kill the thread with my negativity? (I'm sure my wife would think so..)

Any new thoughts on this topic?
One thing I thought about, would it be possible and effective to glue on a couple of layer of carbon fiber to the side/floorpan/tunnel, thus adding extra stiffnes? Why not?

Got the idea from converting my daycruiser hull to sandwich with a distance material (divinycell) and fiberglass/epoxy. The boat became very stiff without adding much.

[Van914]

Has anyone seen this?

Hey guys, I've found some good low cost mods for a 987 Boxster that's really worthwhile if you're sensitive to chassis flex. This doesn't really improve performance, even though a lot of aftermarket companies that sell bracing might claim so. However, for someone like myself who hates the little bit of "reverb" vibration emanating through the car's structure over rough roads or even normal bumps, this is great couple of mods. It does increase steering precision at very high g loads as well, but it's a minor difference.

So onto the mods. For the 987 chassis, Porsche decided not to include the diagonal braces in the front compartment that the 997s have.



The mounting holes for these braces are already in place in the 987, you only need to buy the braces and the 6 bolts for this to bolt right on.

Parts:
99650423301 (DRIVER SIDE)
99650423401 (PASSENGER SIDE)
90037810001 Hexagon-Head Bolt M10 X 45 2
90007501003 Hexagon-Head Bolt M6 X 12 4

If you're on a budget, go ahead and buy the braces used on Ebay or something, otherwise they're still only $130 USD or so. The bolts can be bought anywhere or ordered through a dealer as well. These braces will slightly improve steering precision when the suspension is loaded up in corners. The difference isn't huge, but it does work. Why Porsche left them off the 987, I have no idea.

[Escy]

After your post i've just checked out my 987 and those bars aren't there. They are on the 986. Seems odd to leave them off the 987.

[ksjohn]

Other options? I have a Z-top that I am planning to use on a project car this year. My previous Boxster had a hardtop that I basically never took off. One thing I disliked about the removable hardtop was that it squeaked on rough roads or on a steep angled driveway. I interpreted this as the top moving when the chassis flexed.

My idea for the Z-top is to permanently bond it to the chassis front and rear with the hatch still operable. Most likely I would do this with epoxy glue.

This would eliminate the squeaking and would probably stiffen the chassis as well. My only concern is that the Z-top is light and I wonder how it would hold up over time. I suppose I could add some fiberglass or carbon fiber reinforcement to the top before installing.

Any thoughts?

[ike84]

I have never noticed any flex in the center of the vehicle, even under quite "spirited" driving conditions (i.e. finding the limits of what michelin ps2 sports are capable of lol). I did have quite a bit of softness with vertical accelerations (going through big dips or over humps) but that went away completely when I got rid of the stock struts and put in GodSpeed MAXX coilovers. The only other play that I have noticed was in the rear while pushing G limits of high speed turns and this resolved with a homemade version of the rear strut brace that I made out of a 1" aluminum square bar (I can take my favorite turn 3-5mph faster without the feeling of the rear giving out).

If you can really feel the tub flex then I think the only answer would be roll-cage anti intrusion bar setup (like those miata bars) but that would be less than ideal for a DD. If the bigger issue is a rattle/squeak from the hard top I would counter by saying that it is the top thats the problem - its not easy to hang on to that car while doing high G maneuvers and it wouldn't surprise me if that would create some hard-top chatter if the part is an aftermarket cosmetic piece and not a racing hardtop.

Just my 2c.

[Robert986]

Originally Posted by ike84

I have never noticed any flex in the center of the vehicle, even under quite "spirited" driving conditions (i.e. finding the limits of what michelin ps2 sports are capable of lol). I did have quite a bit of softness with vertical accelerations (going through big dips or over humps) but that went away completely when I got rid of the stock struts and put in GodSpeed MAXX coilovers. The only other play that I have noticed was in the rear while pushing G limits of high speed turns and this resolved with a homemade version of the rear strut brace that I made out of a 1" aluminum square bar (I can take my favorite turn 3-5mph faster without the feeling of the rear giving out).

If you can really feel the tub flex then I think the only answer would be roll-cage anti intrusion bar setup (like those miata bars) but that would be less than ideal for a DD. If the bigger issue is a rattle/squeak from the hard top I would counter by saying that it is the top thats the problem - its not easy to hang on to that car while doing high G maneuvers and it wouldn't surprise me if that would create some hard-top chatter if the part is an aftermarket cosmetic piece and not a racing hardtop.

Just my 2c.

Any pictures of that diy rear strut bar?

[Robert986]

Sorry for bumping this one again :-)

If time permits I´ll be putting on some side skirts before summer, this I can admit is for the visual appearance. I'm considering adding a few layer of carbon fiber over the rocker panels before adding the side skirts, to add a bit of extra strength.. Would this be totally meaningless?

Another thing that I might try later would be to fill in the open parts of the floor with panels of carbon/divinycell and epoxy-glue it in. If they fit it should add some torsional stability, at least that's my experience from working with speed boats.

Well well, as long as I'm having fun..

[The Radium King]

given the mechanism of the flex - twist - i'd suggest you would be testing the strength of your epoxy more than the stiffness of the CF?