Anyone used the longitudinal outer clamshells on a street car?, Time for hard choices Options

[Superhawk996]

Curious if anyone has use the outer longitudinal clamshell reinforcement on a street car?

Did you have any unforseen down stream effects to other panels like the door jamb, or the rocker panel? Also thickens the upper flange and I'm wondering if this will cause fit issues later with the door stripping, or maybe even the cosmetic sill plates.

Starting to seem like this might be a good idea for race car prep but probably not ideal for just trying to fit up replacement sheetmetal and still have OEM fits. (IMG:style_emoticons/default/idea.gif)

I'm not in love with the additional weight either.

I can keep mocking up additional pieces but thought I'd see what the collective wisdom of the forum knows.

[dr914@autoatlanta.com]

I originally designed the clamshells to support a rusty car that was way too rusted to consider restoring properly, Also, as a backup, someone could reinforce a racing car. The go over the original assembly so best installed by first removing the sill plate.
These days, with the value of 914s going higher and higher, very few choose to "patch" the cars, so the clamshells are frankly out of favor. All of the original panels are available and with a bit of welding and cutting skills, the cars are so simple that they can actually easily be repaired.

Curious if anyone has use the outer longitudinal clamshell reinforcement on a street car?

Did you have any unforseen down stream effects to other panels like the door jamb, or the rocker panel? Also thickens the upper flange and I'm wondering if this will cause fit issues later with the door stripping, or maybe even the cosmetic sill plates.

Starting to seem like this might be a good idea for race car prep but probably not ideal for just trying to fit up replacement sheetmetal and still have OEM fits. (IMG:style_emoticons/default/idea.gif)

I'm not in love with the additional weight either.

I can keep mocking up additional pieces but thought I'd see what the collective wisdom of the forum knows.

[Superhawk996]

I originally designed the clamshells to support a rusty car that was way too rusted to consider restoring properly, Also, as a backup, someone could reinforce a racing car. The go over the original assembly so best installed by first removing the sill plate.
These days, with the value of 914s going higher and higher, very few choose to "patch" the cars, so the clamshells are frankly out of favor. All of the original panels are available and with a bit of welding and cutting skills, the cars are so simple that they can actually easily be repaired.

Nice. Thanks Doc. I had no idea who desinged them you or RD. I guess that is answered.

Really appreciate the insight that they were designed to add strenght to an already weak chassis. That most certainly isn't my case after completely replacing the innner wheelhouse, the C-section of engine compartment, as well as both the inner and outter longitudinals.

I did use the short J-section of it that reinforces the transtion up to the rear suspension mount.

I hate the idea of adding any more weight to the car. The whole point of a 914 is light weight and mid engine handling. Weight just begets weight.

I'm a beliver in Colin Chapmans philosophy: “Adding power makes you faster on the straights; subtracting weight makes you faster everywhere”

I think based on your advice, I'm inclined to leave the rest of it off and see how stiff this puppy is 1st. I can always add the rest of it back on later when I completely return the car to OEM paint color but that is a few years away!

I did a little quick math this morning on the bending stiffness of a hollow rectangular tube and at best the stiffness gain is 30% maximum. However, that assumed I added 0.060" of section thickness to the whole section (top, sides, and bottom). In reality the clamshell only add thickness to 1 side + a small piece of the transition radius under the long. I'd need to do more CAD work and FEA to get the exact number but I'm thinking with only 1 side the improvement is more like 15% max. Not enough to justify the weight.

[jd74914]

I did a little quick math this morning on the bending stiffness of a hollow rectangular tube and at best the stiffness gain is 30% maximum. However, that assumed I added 0.060" of section thickness to the whole section (top, sides, and bottom). In reality the clamshell only add thickness to 1 side + a small piece of the transition radius under the long. I'd need to do more CAD work and FEA to get the exact number but I'm thinking with only 1 side the improvement is more like 15% max. Not enough to justify the weight.

I went down by 0.5" with my custom longs and increased stiffness by a calculated ~200% based MOI calculated in CAD for the new structure vs. original or changes with Engman reinforcements, etc. Note that I did not include weld stiffness though as I'm not that kind of engineer (IMG:style_emoticons/default/laugh.gif) A little more involved than the manufactured parts though.

27lbs added in calculation...Forgot to weigh the actual metal (IMG:style_emoticons/default/bootyshake.gif)

http://www.914world.com/bbs2/index.php?sho...p;#entry2127676

[Superhawk996]

@JD74914

Damn James, you're going to force me to up my game! (IMG:style_emoticons/default/idea.gif)

Trying to the AutoCAD Invertor loaded back on my home computer after I lost it in a crash about a year ago. Then I can get a more accurate estimate on stiffness improvment from the clamshell.

[jd74914]

Damn James, you're going to force me to up my game! (IMG:style_emoticons/default/idea.gif)

Trying to the AutoCAD Invertor loaded back on my home computer after I lost it in a crash about a year ago. Then I can get a more accurate estimate on stiffness improvment from the clamshell.

(IMG:style_emoticons/default/happy11.gif) As I tell the guys who work for me...my goal is to motivate people to be their best selves. (IMG:style_emoticons/default/laugh.gif)

I work slow though...so you're waaaaayyyyyy ahead of me.

I've been debating changing it on the inner long side to something like rob mentions above, except with a two piece design which sandwiches the floor. That way I keep the extra 12 mm depth, floor at the same height, and increase torsional stiffness with the horizontal flange. That's a lot more work though, but since I've only got one side 'done' maybe not so bad. (IMG:style_emoticons/default/idea.gif)

Very interested to see what you come up with!