Some very good observations. I appreciate your input here.

 

honestly, what im seeing is neat, but a complete waste of time. unless your planning on a running 1000hp engine, you dont need to stiffen the frame. ive built many a dirt car chassis and been known to weld in a cage or two, so i feel like i can help you out with my .02. also a cage is where your gonna get most of your strength. a lot of what youve done will help but mostly youve just added a ton of weight, ruining any need to have a stiffer frame, ( like racing )
also maybe you should check your frame for damage, i havent noticed that my frame is weak. i can jack it up and both wheels will come off the ground and my door gaps dont change. thats a pretty stiff frame where i come from

 

You have obviously never thoroughly checked a C3 frame, it's as stiff as a wet noodle

 

maybe so but for a street car its good enough. and being stiffer isnt always a good thing. it just depends on what your trying to do. this reminds me of other threads ive seen where a lot of folks think that c3 brakes suck. they couldnt be more wrong if they tried

 

You're the first guy I've encountered who's used the phrase "stiff frame" when discussing C2/C3 frames.

 

while ive never had the gumption to pull my body off and check out the frame, it is obvious to me that it cant be that bad. like i stated the door gaps dont move on mine when i jack it up and when i jack it up for any reason to remove a tire, i can pick up both wheels from the ground on that same side. now im not saying that c3 frames are super rigid, im saying that unless your trying to race a season of pro mod or 24 hours of lemans with a c3 you dont need to stiffen the frame. will a few gussets here and there help? sure! but what the OP is doing, while really cool, is unessasary

 

You are correct. Probably 90% of what gets discussed in the Performance/Technical Section is unnecessary. A 100% stock NCRS rated Corvette will certainly get you down the road. It will be a slow, crappy riding and ill handling drive, but you'll get to your destination nonetheless. However I, like many other Corvette owners, want something that is faster and better handling than what the factory sent out the door.

 

thats cool. and like i said a few gussets will help, and a cage would definetly help, but anything outside of that is just overkill. all the weight he's adding is not helping, its hurting performance. welding up the seams and adding gussets are all thats needed. if anything beyond that is needed, then build a new frame.

 

hi, this is my first question to the forum, after reading about the extensive work you've done on your frame. I don't have the time to go as in depth as you have, but I've heard the one thing I want to make sure to do on my '63 chassis is to join up all the stitch welding on the frame tubes, making one solid weld, and to add gussets at all points where the frame tubes join at an inside 90 degree angle. am I on the right track, or wasting my argon?

 

69427 are you completely against any mods to the fiberglass floor of the car? building a backbone would be by far the best thing you could add to your frame without using a roll cage.

C3 frames are known to be bad about twisting at the rear frame kickup.

 

I completely agree with your backbone statement. I have spent a lot of time trying to figure out a way to add this structure to the frame without cutting the bodywork (floor included). The five speed transmission is so darn tight in the tunnel (compared to the Muncie) that there's no room to make a structure in there.
I did a few modifications (internal and external) to the rear kickup areas to increase the beam strength, but since then I've had a couple ideas that I wish I would have implemented that would probably have helped out the torsional strength, too.

 

my cage is welded right at the kick up and the rear crossmember just forward of the differential. it is also welded at the frame parallel to the drivers foot on the pedals. I am running over a 1000 hp and the frame does not show much flex, but then again I am not auto X'ing only drag.

 

any pics would be great thanks

 

Hi 69427, I first want to recognize that you are willing to challenge the status quo and make a better product, good on ya!

There is limited room in the cockpit of any year of Corvette. I had spent 20 years in the collision, frame and paint business and understand the aspects of metal. I commend you in wanting to apply torsional dynamics to eliminate frame flex. I have had many years experience of drag cars and understand the concept of flex.

We run a 1963 Acadian Beaumont Sport Deluxe, equivelant to a Nova SS. We had the same issues of frame flex within the uni-body design and went out of our way to reduce torsional problems. What I am saying is nothing new but with a 10 point roll cage we were able to stop the flex and enjoyed consistant 60' time within 1000 of a second round after round. I am able to jack the front corner of the car and with very and I mean with very little difference the same back corner comes up. The strength is in the 'cage'

Your home work had spelled out the problems and you are getting near solutions by positive discussion on this board. I am not an engineer but have done my fair amount of welds and cuts. I look at a frame as a 'bridge'. The basic frame in a ladder configuration resists side ways flex and in the most part 'diamond' flex from one corner to the opposite on the other end. What it is not limited on is torsional flex from corner to corner. If it was 12 inches thick that would reduce it somehat but that is not fesable. When a super structure such as a upper support is added the sum of all the parts make the unit stronger.

I think what you have done is sufficient with in the frame rail but will bring limited benefit to the outside. As a suggestion only; taking in consideration of strenthening a drag car which would include a halo and forward bars past the front suspension points, I recommend a short back support that runs up the left side, across real low just below the window frame and then down on the right side. This may be the highest point you wish to go taking in consideration of other board members appreciated comments. Once established, run connecting bars to the rear frame rails as far as you can go and weld to the frame rail to reinforce. As you need to build the cage around the body possibly flanges can be considered for assembly. Pipe - plate - plate - pipe connected with bolts.

The forward side bars would have to come from the newly added 'roll bar' parallel to the rocker/sill plate to a similar mini roll bar that starts again up the left side, under/below the dash and behind the console and then down the left side. Assembly considered.

Once this has been established a continuation of the forward bars through the firewall and onto the most feasible mounting area will give the 'bridge effect'. After considering chrome moly or HSS one could bring in the structual stability that you are very near achieving.

Just my 2 cents worth, Dano.

 

Hi bcusnavy,
Here is a link to a post I added quite some time ago. It might give you a decent overview of all the regular frame mods that you can do quite easily (even though this was on a 77).

http://forums.corvetteforum.com/c3-t...arge-pics.html

I ultimately also filled the frame with structural foam, which was a bit of a mess, but has proven to be quite effective with some of my friends that run rally cars (according to lab tests they pointed me to it adds about 40% stiffness at very little added weight).
I need to expand my post with some more details about this foam as I keep getting questions about it. Do NOT run out to Home Depot and buy some of those cheap cans - this stuff is closed cell structural foam and used to be sold by ITW Foamseal.

Good luck!
Michael

 

Don't mean to hijack the thread, but just found the URLs that might be of use if you are wondering about this whole foam thing. The following article is a bit older, but provides feedback from an actual application - my aplogies for making you look at a Nissan.

http://www.modified.com/projectcars/...t_5/index.html

I actually talked to the staff at ITW and that same foam is now being sold at Grainger. Quite a mess, though, and if I'd do it again, I would find an outfit that does this commercially and then just have the whole frame filled by them. Another forum member from Australia did this with very good success. There are actually different densities available with commercial outfits. I have tested about 3-4 brands and only one of them really makes sense for home use - the rest are so water-like runny initially that they quickly flow out of your frame again.

While this was quite a unique thing years ago, be aware that many new factory cars actually have their frames filled with this stuff nowadays (e.g. Lexus, etc).

I am just about to drop a very torquey LS376/480 in my 77 and was actually wondering what additional frame mods I can get away with prior to bolting the body back down to the frame. Great info in this thread !!

Michael.

 

I read the part of the article about the foam in the foam and it was pretty interesting to me. I remember when you posted about it the first time a few years ago. I was wondering how it turned out for you. Have you had a chance to try the car out since all of the mods you did to the frame and the foam?

 

V-twin, isn't it you that has diagonal crossmembers welded in?