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I have done this a few times. It stiffens the car up and is necessary for racing or autocross. You MUST be careful and jump around when doing this , don't weld very much in one place at a time. I will close up a gap then go to the other side or the back or front and don't come back till it cools. If you try to run a straight bead the whole way up a side you can possibly tweak the frame.
I did it on my 76 while the body was off mostly because I couldn't believe how bad the factory "welding" was! I wouldn't have been able to live with myself if I had put the body back on knowing how crappy the factory chassis assembly was.
I'm in the final stages of it now. Take a look at the factory skip welds on my replacement frame.... I have to believe that fully welding the seams is going to stiffen it up some.
From: Las Vegas - Just stop perpetuating myths please.
Welding is fun but be careful of distortion with long weld passes. You need to weld in steps something like 1 inch apart. Alternating from side to side or end to end in short passes is best. Weld on hot days is best for the cooling rate. Holding the frame in a jig would help but usually not an option for the hobbyist. Yes the factory welding is terrible.
So recently I bought a inverter stick welder form Home Depot for less than 100 bucks and it's great compared to the old heavy transformer buzz boxes. Over 100 amps capacity direct cuurent and only weighs 8lbs - I love it. Stick welding is fun and now it's very cheap. Just look on U-tube for filler rod selection and technique. What I'm saying is if you don't do it yourself your missing some fun.
I'm in the final stages of it now. Take a look at the factory skip welds on my replacement frame.... I have to believe that fully welding the seams is going to stiffen it up some.
haha...i can’t remember if these are sloppy robots or manual back then...i do know they set them very high amperage to penetrate some lazy welders...im still getting cut by errant wire slag
As an iron worker I plan on stiffing up my chassis while the body is off the frame as well. No way I could not correct some of the poor weld fitments and quality. I’ll be adding gussets in a few places that won’t cause any future interference for sure.
My main goal is to get some support at the area I have circled in red. This is where I feel the frame is subject to most of its flex loading. There’s a cheap stamped steel horizontal brace but no vertical support at the kick up area. Vertical torsion here has to be high under acceleration and cornering. Anyone ever add something here or do the aftermarket frames have better bracing in this area?
The more i think of this thread..maybe just for thought...
add more skip welds...hybrid idea? Add strength, clean up factory welds? But not continuous?
be aware that although im sure for cost reasons and production time as to why they did it this way.....you may want to keep areas open for drainage?
i would probably only mig weld with really good penetation...
A lot of good input here.
But my original question remains unanswered:
Q: Does anyone have any analytical measurements or subjective feedback of a welded frame vs stock?
Found two graphs in Duntov's engineering paper "the 63 Stingray". Both the front "S' bends and the "rear "kickup" areas are weak points.
First one is deflection with 1500lbs at each point. Rear kickup area is a weak point since curve is not exactly centered.
Second one is torsional rigidity. Front "S" bends are a weak point. Factory mentions "an internal bulkhead was added" to S curve.
Interestingly note the labels on the graph are reversed (typo). The lower one is the stronger 63 frame.
In theory a stronger frame should help the car handle better. But there is a very interesting comment by the engineers on page 17: Does this make any sense to anyone?
This comment is at the root of my question. What has been your experience?
Complete article below. Frame info on pages 16-17.
Last edited by leigh1322; Aug 9, 2020 at 12:20 PM.
I found some notes that said a convertible body cut the torsional strength by half. So the above 2374 ftlbs/degree for the frame only may be all there is for a C3 vert. The Birdcage should stiffen the coupe some, lets guess and say double at 4600ft lbs. +50% would also be a good guess at 3561.
If so that would be on a par or slightly better than a contemporary 65 Mustang at 3688. But no where near newer cars, a 2015 Stang was mentioned at 15,000.
The Porsche video above put his 70 vintage car in the same ball park as our C3. Around 3000 ftlbs/deg. And when he welded up the stitch welds in the uni-body the stiffness went up by 18% to 3600. So for him it was worth it. So welding up our frame stitch welds should help some. Would it be the same amount? Who knows. So maybe we could get it up to 4200 or 5500. It would take some serious triangulation with a good roll cage to move it up to 2015 or race car levels.
Our car transfers about 700 lbs onto the front wheels on 1G braking, and about the same in a turn or accelerating. So that could be as much as 0.2 degrees of twist, flex or alignment change when loaded. More in a bump.
I am half tempted to measure mine before & after welding, if anyone has any interest?
PS: Duntov says the whole birdcage only weighs 82 lbs. The whole bare body/birdcage is 397. (For a 63 vert.) I read the bare frame weighs 240.
Last edited by leigh1322; Aug 9, 2020 at 09:38 PM.
I have no data but I was concerned and added some elongated, diamond shaped 1/8” plates over the front kick up seams. Roughly 5” x 3”. The backside of the kickup’s have 4-link bars welded up the arches so it’s very well reinforced on the backside. Just a straight line car though. I did stitch weld to try to keep the heat down.
my 5 point roll bar bolts in to the kick up rails so it doesn’t triangulate down to the main frame rails which would be ideal. Full interior car though.
probsvly not the info you want but my .02 for what it’s worth.
Last edited by Corvettedave02; Aug 9, 2020 at 09:40 PM.
I found some notes that said a convertible body cut the torsional strength by half. So the above 2374 ftlbs/degree for the frame only may be all there is for a C3 vert. The Birdcage should stiffen the coupe some, lets guess and say double at 4600ft lbs. +50% would also be a good guess at 3561.
If so that would be on a par or slightly better than a contemporary 65 Mustang at 3688. But no where near newer cars, a 2015 Stang was mentioned at 15,000.
The Porsche video above put his 70 vintage car in the same ball park as our C3. Around 3000 ftlbs/deg. And when he welded up the stitch welds in the uni-body the stiffness went up by 18% to 3600. So for him it was worth it. So welding up our frame stitch welds should help some. Would it be the same amount? Who knows. So maybe we could get it up to 4200 or 5500. It would take some serious triangulation with a good roll cage to move it up to 2015 or race car levels.
Our car transfers about 700 lbs onto the front wheels on 1G braking, and about the same in a turn or accelerating. So that could be as much as 0.2 degrees of twist, flex or alignment change when loaded. More in a bump.
I am half tempted to measure mine before & after welding, if anyone has any interest?
PS: Duntov says the whole birdcage only weighs 82 lbs. The whole bare body/birdcage is 397. (For a 63 vert.) I read the bare frame weighs 240.
id be interested in the before and after data... I saw a notable difference after installing a spreader bar, and even more after installing solid motor mounts. My current chassis is seam welded, but changed too much to compare to a stock c3 chassis. If you have a mock-up block, it would be interesting to see the benefit of using the engine/trans as a stressed member in your data.
i see no reason to not fully weld the chassis, and do the bracing noted in the power book. Even for just a street car, the stiffer the chassis, the better.
I like to weld a plate over the kickup area circled in red. You can't add too much cause the body is very close there. 1/8 in plates are good.
FWIW a stiffer frame w softer springs and heavy bars is a good way to go for street use and is faster on track than a heavy spring soft frame car.
Last edited by Pop Chevy; Aug 10, 2020 at 10:16 AM.
I was intrigued by this frame bracing idea I lifted from the forum 8 years ago. If I did it, I think I would weld a plate to the frame where the braces attach.
Apologies to the member who did this for not giving credit; I don't remember who it was.
Frame Welding - Input Needed
