Rocker extensions

[Jeremy]

I have been studying the C6 corvette and other performance cars and noticed that on all of them the edge of the frame rails comes out underneath the rockers or forms the rockers.

I looked under my 1980 TA and found that the edge of the frame is far inboard. I wanted to duplicate the perimeter frame on my car as I was still not happy with the chassis stiffness. I have braced between the frame rails and it helped, but as I got looking at my engineering books again, the farther from center and the taller the beam, the stiffer in torsion it would be.

I found that I could weld as big as a 2 x 2 steel beam under the rocker. I figured this would make a difference, but there was only one way to tell. I bought some 1 3/4 box steel, four foot long and some 1 1/2 flat stock to box the ends. All told for materials was $35. It took me 1 hour to box the ends and 1 1/2 hours to weld them underneath the rocker. I placed them outside of the 3/4 inch tall flange under the rocker (where the floor and rocker get spot welded together).

I still have to have the body shop weld along the outside edge (I don't want to take the chance of blowing through). I figure it will take them about 2 hours so it shouldn't cost a ton. My wife and I can't agree on color. I think white to match the body will look good and she thinks black to blend it in with the frame.

I still have to do some metal work to blend them back into the frame. I plan to weld some braces to the frame / subframe connectors to tie everything together. I figure I will go with a couple on the ends perpendicular and then two angled ones making a total of four triangles between the rocker and subframe. I figure this should allow me to remove the bracing inside the frame rails.

Each brace weighed about 10 pounds, but the weight is pretty low so I am not too concerned about that. Once it is all done, I should have added 30 pounds to the lower, outside edges of the car. The side impact crash protection should be much better (god forbid I ever need it).

I drove a 10 mile curcuit before the rocker extensions and the same section after. The afternoon temp was warmer by 10 degrees. The car was so much stiffer. I had no more rattles in the doors or dash. The car was much more predictable in the turns and very confidence inspiring. The throttle response was much better. It felt like I had added a significant amount of horsepower. I could not believe how much quicker it felt. The ride was much smoother and softer feeling as well.

I've played with a lot of different ideas on chassis stiffness and have all of the commercially available ones and this was by far the best. I doubt it would have worked well without the subframe connectors and solid bushings, but it further tied it all together.

Here's a poor pic, but you can see the added rail.



Here are some better pics from different angles.





On the front pic, it shows the area under the fender that I want to extend forward and then back to the frame. I have to do this area on the back side of the rocker flange due to the fender mounts. Once I get it welded in, I'll weld a gusset on a 45 degree angle to blend it all in.

Please chime in on your color choice.

[71dusterdan]

LOSE THEM, MAKE THEM BLACK, YOU DONT WANT TO HIGHLIGHT wife and her damn capslock. anyways i can see wanting to get people to see your work, but painting them black they will get lost and not detract from the nice lines of your car. how many times do you hear that the coolest mods are the ones the trained eye has to work to see. just my .02 nice lookin wheels on your t/a. Dan

[Jeremy]

We drove it to Wal-Mart today and they are definitely going black. Looking at the car across the lot, they pretty much disappear in the shadows anyway. I'll paint them the same black as the rest of the undercarriage and they should all but disappear.

I can't get over the ride and feel difference. It feels like a new car, super solid and tight.

[David Pozzi]

I have a friend with an old convertable. it has something similar but the whole bottom is enclosed, like running from the tube you added outboard, to the frame rail. The rocker panel is pretty stiff.
David

[Jeremy]

The body shop was able to fit me in today and seam welded the outside to the factory rocker. The whole car is very solid and any roof creaks are gone.

I have to seam seal it and undercoat the area, but the outside edge is done.

I thought they did me right charging me $50 to run 8 foot of weld.

[JMarsa]

Sounds like you read this thread cover to cover and applied your own technique.

https://www.pro-touring.com/forum/sh...ad.php?t=23278

--JMarsa

[Jeremy]

I got some bars welded from the rocker extensions to the subframe/subframe connectors today. I used 1 3/4 square tube again for the connections. I welded one at the front and one in the middle. I made them to fit real tight and had to persuade them into place with a 5 lb sledge. I then welded them all the way around.

I plan to weld a piece between the back edge and the subframe connector, just in front of the spring pocket as well. I should be done by then.

I went for a drive with just the front and middle connections and I am finally getting where I want. I can't get over just how flabby a 2nd gen with 2 tops really is. I pulled back into my drive today and it used to really get the dash and windshield header groaning. Now all I can hear are the poly bushings squeaking. I love it.