Interesting watch.

https://www.youtube.com/watch?v=RfDPUD-RhMM...s7x-uda9r9hMtTQ



https://www.youtube.com/watch?v=RfDPUD-RhMM

Interesting, thanks for posting.

I wonder what it would’ve been if he put a chassis bracing bar (as is commonly done) between the shock towers?

Interesting, thanks for posting.

I wonder what it would’ve been if he put a chassis bracing bar (as is commonly done) between the shock towers?

Probably not much difference. The whole front end moves around. That brace between the shock towers would only negate pulling in our pulling out of the shock tops from each other.

I liked the part where he showed how much bend there was with so little force.

That caught my eye as well-yikes!

Hey 914 world!

That's my video.

I agree that the strut tower brace probably won't change the torsional rigidity much. At least the way I measured it. I'm not saying they aren't useful, but as someone else mentioned the cross brace prevents the towers from flexing in and out.

I plan to make one of these diagonal things and I think this will improve the test results some.


Click to view attachment

Stay tuned as I will repeat this test after each improvement made. I would expect similar results with a 914 chassis. Maybe someone here will do something similar which would be cool.

Thanks for watching the vid guys.
Tom

that's pretty cool. just for a bit more precision - use an exact weight placed at exactly the same spot on the lever each time, say 150lb at exactly 48" from the fulcrum.
at any rate - cool idea and cool findings, thanks for posting!

Welcome!

Very interested to see how this turns out on a 914.

BTW - we have a very active Southern California group here, come on out and meet some of the local Mafia.

Cool, I wish I would have seen the tech session notice earlier. Maybe I'll hang out at the next one

Oops - wanted to ask what voltage and wire speed and welder you were using.

So cool to see others doing this kind of stuff. I did basically the same thing and measured the stiffness of the 914 before I made my tube frame for it. I tested a 996 cab as well. See here for my post http://www.914world.com/bbs2/index.php?sho...6845&st=120 Check Post 138 through 152. Final numbers were: the 996 C4 Cabriolet has a stiffness of 4,568 '#/Degree. The 914 has a stiffness of 3,326 '#/Degree.

Murrieta is not that far from Huntington beach and I have a frame rack that we can place your car on and test it.

I placed the car on the frame rack, leveled everything up, supported the rears on jack stands, then strapped the rear of the car so that it would not lift off (it lifted if I did not place the straps on) of the stands, then place the third stand in the front middle and then added a 100 lb weight at a distance of 10' to get a 1000 ft-lb torque and measured with dial indicators at two suspension bolt holes. I did that since one of the bolts will rotate up and the other will rotate down. In this way, I was able to get a really accurate measurement on the 996 and the 914 in order to compare the numbers after I build the tube frame for it. I'm really close to being able to measure the torque results with the tube frame installed.

Super cool, thanks for posting this.

Woah, what a small world. Who knew two guys are testing a 40 year old chassis at the same time within 50 miles of each other.

Your project is super cool, and ambitious! Best of luck on it. I'll be watching for your new torsional rigidity numbers. Very cool.

I'm not super interested in what the actual stiffness numbers are. For me its about making good build decisions that actually help. The stitch welding wasn't that hard so I gave it a try. Now that I know it works, I will most likely be doing more in the door opening area and pillars.

I will be using some strain guages soon to determine what weak points remain. I'm not doing a full cage like you are.

Hope to meet you someday. I'm sure we could talk for hours about this stuff, or better yet help each other out.

The 914 crowd seems to be more interested in my low dollar methods which is great!

Cheers,
Tom

Most of us here are all DIY and inexpensive things are great projects. With a 914 the rear of the car is the flexy part. We have an advantage of the 2nd firewall in the front to further box things in between the strut towers. When you can see the whole car flex as you have depicted, it changes how you view what stiffness is.

It would be good to see this on a 914, but twisting at the rear through the trailing arm mounts and stabilizing the front.

Yes, that would be cool. The setup is fairly easy and doesn't take a lot time or tools which is why I did it in the first place. That whole video was shot in a day most of which was welding and waiting for the smoke to clear! Time is the main reason I didn't use cement bags or weights to load the bar, because I didn't have time to go to home depot, ha ha.

I guess the responsibility lies with the next person who is strengthening a 914. Step on up, I for one would honored if someone repeated or improved what I did in the video.

@TravisNeff - where would you brace the rear OR just use one of the kits like from Maddog?

I was just stating that doing this experiment on a 914, but test the flex at the rear pickup point instead of the front would be interesting.

The thing to think about on a street car is that you start eliminating the crumple zones by stitching and adding metal to everything. If you get his that energy has to go somewhere. I do have a inner long kit in mine and I like it a lot. I got it too hot when I put it in and bent the tub. It was a puckering experience to get it back straight.

Yes... it makes the car stiffer. But it was designed with the spot welds so the front and rear of the car crumple in a predictable fashion, absorbing energy from the crash. If you weld up all the seams, then YOU become the item that absorbs that energy.


Watch an Indy car or F1 race and notice how much stuff flies off the car during a wreck. Each part it sheds is energy that is not going into the safety cell or into the driver. Today, drivers regularly walk away from wrecks that would have killed them 30 years ago.

So think very carefully on how much energy you are willing to absorb when you get hit before breaking out the welder and welding up the seams.

I've been considering building a "bolt in" X brace that ties the shock towers to the rear of the transmission carrier for autocross. I already have Tangerine's scab plates on the inner ear and Mad Dog's long kit. The car is stiff, but can always be stiffer.

As a narrow body car running Hoosier A7's I just don't have room for the GT style stiffening kit on the inner, rear fenders. I need the "bolt in" as I need the space to carry all my crap to the events.

I added a link to your YouTube video of a discussion I started some time ago on that other Porsche forum:
http://forums.pelicanparts.com/porsche-911...nforcement.html

While not directly applicable to a 914, anything helps since 914 sheet metal is not as robust as on a 911.

Sherwood

Sherwood! Didn't know you where here too, you've been a big help on my 911 over on Pelican.

Very worthwhile thread.

Interesting that I just read a Motortrend article on the new Honda Civic Type R. It gets more seam adhesive and where welds are used they are spaced .8” apart vice the 1.6” apart for the normal Civic. That equates to two additional hours in the weld shop.

The article does not mention the resultant increase in stiffness, but This technique obviously works and their concern for altered crush zones does not trump their desire for performance

I realize that the crash protection in these modern cars utilize many measures not incorporated in our 60’s designed structures, but it is an interesting point to consider

Click to view attachment
New homemade strut bar brackets and strut tower plates welded in! Who thinks the front strut bar will improve the torsional stiffness? I have my doubts, so I've instrumented a temporary strut bar with an inline load cell and a data acquisition system to monitor forces in the bar. My hunch is that the strut bar won't improve torsional stiffness much, but it may help with cornering and suspension loads.

Unfortunately, my car isn't driveable but I have a few tests in mind to play around with.

Stay tuned for more results.
Tom

Very tidy work. Keen to learn what you discover.

I don.t think it will do much for torsional rigidty of the chasisis.

Good Luck.

This week I did some experimentation with the forces in the front strut bar. I thought the results were quite surprising! Maybe not very relevant to the 914 because it already has better front strut support than the 911.

1) Increased torsional rigidity is about 10%
2) Max load in the horizontal bar was measured at 70 lbs
3) The loads alternate between tension and compression
4) Changes in camber are very small with or without the strut bar


This video is a bit long, but I did everything I could to make the strut brace look good. At the end of the day it didn't impress me much.

https://youtu.be/QjGYaeYew8s

Click to view attachment

Thanks for putting that video together, we all love the data!

This is very cool stuff-super impressed!! Please note, I haven't watched watched the video yet, so please ignore if you covered the questions below. Just curious on your thoughts.

To me, 10% stiffness gain is a lot. I would have killed to have gained that with minimal weight in the tube chassis cars I've designed. Why aren't you happy with that number?

Out of your scope, but it'd be interesting to see if there would be a difference if the strut bar was more of a strut panel with two wide spaced vertical attachment points and a larger vertical dimension (more box that bar) to make it more like a shear panel. I feel like something that could resist twisting loads might more effective than what's effectively a pure tension/compression member.

Thank you!
The ten percent increase is measureable and I'm happy. If I compare the 10% to seam welding, I think was 19%, I prefer seam welding with even less weight added. So overall I'm happy with that improvement but the 10% comes from the diagonal bar and not the strut bar. I measured a torsional stiffness with a two point strut bar and a three-point strut bar configuration.
The two point strut bar did nothing to improve torsional rigidity.


Your idea of a strut panel is very good. That's exactly what I learned from this test. Rather than a solid panel I think two bars with a shape of an X in the same plane as the strut towers would do the the most to improve structural chassis rigidity. It's easy for me at this point to add two more tabs to the lower corner where it attaches to the bottom of the strut tower. These bars pictured were temporary so the actual bars that I will use will be in the shape of an X. A X shape is almost the same as a solid sheer panel.
Cheers,
Tom