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SN95 chassis stiffening for coups and verts
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<blockquote data-quote="SlowSVT" data-source="post: 15133586" data-attributes="member: 20202"><p>My apologies for the delay in posting this installment. It would have been posted much earlier but this is the second time I wrote it. I lost the 1st one when I hit the “submit” button Molliza timed out the cache and I lost the whole thing….. arrgh!</p><p></p><p>On this post I will cover the front frame rail and the lower cross member to the rocker panels reinforcement.</p><p></p><p>Again, this can get addicting where you will be tempted to reinforce other areas especially the upper fender apron and fire wall. DO NOT GO THERE! I have used my experience and knowledge of mechanical engineering and came up with bracing that will not concentrate stress on areas you are not likely to reinforce which will cause work hardening and cracking elsewhere. I take no responsibility for what you do to your car and am providing this information as “reference” only.</p><p></p><p>What is going to be covered here is what can be done to reinforce the front clip to the chassis. Mainly the frame rails to the sub-frames. This applies to both coups and verts and will go a long way in actually “nailing” the front suspension down to the chassis. Again, our biggest villain here is “torsion” and we want to get as much twisting flex out of the chassis as possible. Most people are fat & happy knowing their engines makes 700 ft lbs at the flywheel but are not considering the chassis is seeing 2500 ft lbs. in 1st gear. This constant twisting is what eventually loosens-up the chassis where it starts to creek, rattle and drive like a marshmallow on wheels. </p><p></p><p></p><p> If you drop the K-member and slide under the chassis on a creeper and actually start looking at the front frame in detail you will become angry <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite3" alt=":(" title="Frown :(" loading="lazy" data-shortname=":(" /> Note where the frame rail miters downward then levels out again. The front frame rails are folded sheet metal and are not connected at these mend points and are merely spot welded to the inner fender wells. The good thing is it's an easy fix but the bad thing is the engine and tranny needs to come out unlike the shock tower reinforcement. Peeling the carpet back from the firewall wouldn't hurt either.</p><p></p><p>MIG weld with #35 wire all the seams around the frame rails, anywhere you see a gap, join those features and don't forget to cool the bead with a wet towel as you weld to limit how much heat saturates into the chassis. Alternate from LH rail to RH rail and back to even the heat distribution to the chassis which will allow it to expand and contract at an even rate minimizing any distortion to the structure. KEEP IN MIND THE POTENTIAL FOR FIRE AS YOU WELD CLOSE TO THE FIREWALL/FLOOR BOARDS and keep that extinguisher handy just in case. Always have someone keeping an eye on the interior when welding near those areas. There is some real flammable stuff on the inside of the car and you will be in a world of hurt should you burn-up something or perhaps the whole car.</p><p></p><p>The metal thickness of the frame rails is not overly impressive. I made cardboard patterns following the inside, bottom and outside contours of the frame rail from the beginning of the shock towers back to where they blends-in with the firewall/floor boards then used those to cut .050” thick chromolly sheet metal plates with a few plug weld holes drilled in the middle along the length. Take your time doing this and study the area you intend to reinforce. I find it best to tape the patterns to the chassis and just look at it and think about how this feature is carrying the load. Some of my best ideas have come to me with a Budweiser in my hand reflecting on how best to stiffen the chassis. </p><p></p><p>After your satisfied with your patters paint the inside surfaces with weld-thru primer and weld the cut plates in place then smooth the rough welds with a grinder. Now you have frame rails that are 5-10 x stiffer then before HOORAH! :rockon:</p><p></p><p>[ATTACH=full]668397[/ATTACH]</p><p></p><p>[ATTACH=full]668398[/ATTACH]</p><p></p><p>The next area we want to turn our attention to is the lower frame rail-to-rocker panel attachment bracket. This is the formed stamping at the bottom the rear of the wheel wells and is made from fairly thick metal. Weld-up all the seams on this part with is what ties the frame to the outer chassis structure. AGAIN be mindful of fire!</p><p></p><p>As stated earlier in this thread one of the goals is to distribute the load more evenly throughout the chassis and to remove stress risers. One area of opportunity is where the fender well sheet metal meets the firewall. This joint is just a bent flange spot welded to the firewall at a right angle which is pretty nasty since this is a load carrying member. Here I cut out a cardboard pattern and formed a “fillet” for this seam. It may not look like it but this modification is pretty substantial by redirecting and smoothing the transition from the frame rails/inner fender well to the rockers and sub-frame connectors. In a front-end collision this will prevent the frame rails from breaching the firewall and redirect that load outward. Here is a pic of the corner fillet after it was painted.</p><p></p><p>[ATTACH=full]668399[/ATTACH]</p><p></p><p>There are areas on the fender apron and the upper corners of the dash/lower A-pillar that could be reinforced but that will blow this process-up to a big project you would need to gut the interior which would change the whole scope of this effort. What we have done here is reinforced the lower portion of the structure taking stress off the upper portion. This is especially important for convertibles that lack a roof structure where you want the load to stay as low in the chassis as possible since the A-pillar is doing “zero” to stiffen the chassis. If we reinforced the A-pillar column for a coup would require extending the stiffening along the roof line all the way to the C-pillar and beyond! There are to be no gaps in any of the stress paths we reinforce :nono:</p><p></p><p>If I have not overlooked anything this should cover the front frame rail reinforcement. I would give it a weekend to make all the patterns and to cut and grind the plates to fit. Followed by another weekend to weld them in place and to clean-up the welds. Remember do not grind the welds flush. It is not necessary and may weaken the joint in some places. Always be mindful of corrosion and use the weld-thru primer where you can. The inside of the frame rails has had the factory finished burned off where it was welded, I used a long handled brushes on the inside of the rails to loosen the welding scale and compressed air and blew the debris out the bottom of the frame rail drain hole. Afterwords I sprayed and fogged the inside of the rails with cold zinc galvanizing compound. You will need to repaint the engine bay where you burned the paint off by welding. You don't have to go to crazy here because very little of it will actually be visible after everything is reinstalled.</p><p></p><p>You may be tempted to extend some of the reinforcement forward of the shock towers. Do not do this! The factory incorporated “crumple points” all along the front end of the car. You can see V-grooves and voids punched into the chassis so in the event the car is in a collision the front end folds and absorbs the impact which you want to maintain. What you can do on the front clip is stiffen the rad support to stiffen the front end to eliminate or reduce cowl shake. I will address this on another post.</p><p></p><p>My next post will cover the mid-section of the car and how you can make your sub-frames more effective now that it's connected to something more worthy. Just keep in mind as stated, this stuff gets addictive and you can find yourself on a slippery slope and before you know it your in a full blown chassis upgrade which takes 100's of hours so make a plan and stick with it don't bite off more than you can chew. Just the shock tower and lower frame rail reinforcement will take a month worth of weekends and that does not take into account removing stuff and then reinstalling it on the car.</p></blockquote><p></p>
[QUOTE="SlowSVT, post: 15133586, member: 20202"] My apologies for the delay in posting this installment. It would have been posted much earlier but this is the second time I wrote it. I lost the 1st one when I hit the “submit” button Molliza timed out the cache and I lost the whole thing….. arrgh! On this post I will cover the front frame rail and the lower cross member to the rocker panels reinforcement. Again, this can get addicting where you will be tempted to reinforce other areas especially the upper fender apron and fire wall. DO NOT GO THERE! I have used my experience and knowledge of mechanical engineering and came up with bracing that will not concentrate stress on areas you are not likely to reinforce which will cause work hardening and cracking elsewhere. I take no responsibility for what you do to your car and am providing this information as “reference” only. What is going to be covered here is what can be done to reinforce the front clip to the chassis. Mainly the frame rails to the sub-frames. This applies to both coups and verts and will go a long way in actually “nailing” the front suspension down to the chassis. Again, our biggest villain here is “torsion” and we want to get as much twisting flex out of the chassis as possible. Most people are fat & happy knowing their engines makes 700 ft lbs at the flywheel but are not considering the chassis is seeing 2500 ft lbs. in 1st gear. This constant twisting is what eventually loosens-up the chassis where it starts to creek, rattle and drive like a marshmallow on wheels. If you drop the K-member and slide under the chassis on a creeper and actually start looking at the front frame in detail you will become angry :( Note where the frame rail miters downward then levels out again. The front frame rails are folded sheet metal and are not connected at these mend points and are merely spot welded to the inner fender wells. The good thing is it's an easy fix but the bad thing is the engine and tranny needs to come out unlike the shock tower reinforcement. Peeling the carpet back from the firewall wouldn't hurt either. MIG weld with #35 wire all the seams around the frame rails, anywhere you see a gap, join those features and don't forget to cool the bead with a wet towel as you weld to limit how much heat saturates into the chassis. Alternate from LH rail to RH rail and back to even the heat distribution to the chassis which will allow it to expand and contract at an even rate minimizing any distortion to the structure. KEEP IN MIND THE POTENTIAL FOR FIRE AS YOU WELD CLOSE TO THE FIREWALL/FLOOR BOARDS and keep that extinguisher handy just in case. Always have someone keeping an eye on the interior when welding near those areas. There is some real flammable stuff on the inside of the car and you will be in a world of hurt should you burn-up something or perhaps the whole car. The metal thickness of the frame rails is not overly impressive. I made cardboard patterns following the inside, bottom and outside contours of the frame rail from the beginning of the shock towers back to where they blends-in with the firewall/floor boards then used those to cut .050” thick chromolly sheet metal plates with a few plug weld holes drilled in the middle along the length. Take your time doing this and study the area you intend to reinforce. I find it best to tape the patterns to the chassis and just look at it and think about how this feature is carrying the load. Some of my best ideas have come to me with a Budweiser in my hand reflecting on how best to stiffen the chassis. After your satisfied with your patters paint the inside surfaces with weld-thru primer and weld the cut plates in place then smooth the rough welds with a grinder. Now you have frame rails that are 5-10 x stiffer then before HOORAH! :rockon: [ATTACH=full]668397[/ATTACH] [ATTACH=full]668398[/ATTACH] The next area we want to turn our attention to is the lower frame rail-to-rocker panel attachment bracket. This is the formed stamping at the bottom the rear of the wheel wells and is made from fairly thick metal. Weld-up all the seams on this part with is what ties the frame to the outer chassis structure. AGAIN be mindful of fire! As stated earlier in this thread one of the goals is to distribute the load more evenly throughout the chassis and to remove stress risers. One area of opportunity is where the fender well sheet metal meets the firewall. This joint is just a bent flange spot welded to the firewall at a right angle which is pretty nasty since this is a load carrying member. Here I cut out a cardboard pattern and formed a “fillet” for this seam. It may not look like it but this modification is pretty substantial by redirecting and smoothing the transition from the frame rails/inner fender well to the rockers and sub-frame connectors. In a front-end collision this will prevent the frame rails from breaching the firewall and redirect that load outward. Here is a pic of the corner fillet after it was painted. [ATTACH=full]668399[/ATTACH] There are areas on the fender apron and the upper corners of the dash/lower A-pillar that could be reinforced but that will blow this process-up to a big project you would need to gut the interior which would change the whole scope of this effort. What we have done here is reinforced the lower portion of the structure taking stress off the upper portion. This is especially important for convertibles that lack a roof structure where you want the load to stay as low in the chassis as possible since the A-pillar is doing “zero” to stiffen the chassis. If we reinforced the A-pillar column for a coup would require extending the stiffening along the roof line all the way to the C-pillar and beyond! There are to be no gaps in any of the stress paths we reinforce :nono: If I have not overlooked anything this should cover the front frame rail reinforcement. I would give it a weekend to make all the patterns and to cut and grind the plates to fit. Followed by another weekend to weld them in place and to clean-up the welds. Remember do not grind the welds flush. It is not necessary and may weaken the joint in some places. Always be mindful of corrosion and use the weld-thru primer where you can. The inside of the frame rails has had the factory finished burned off where it was welded, I used a long handled brushes on the inside of the rails to loosen the welding scale and compressed air and blew the debris out the bottom of the frame rail drain hole. Afterwords I sprayed and fogged the inside of the rails with cold zinc galvanizing compound. You will need to repaint the engine bay where you burned the paint off by welding. You don't have to go to crazy here because very little of it will actually be visible after everything is reinstalled. You may be tempted to extend some of the reinforcement forward of the shock towers. Do not do this! The factory incorporated “crumple points” all along the front end of the car. You can see V-grooves and voids punched into the chassis so in the event the car is in a collision the front end folds and absorbs the impact which you want to maintain. What you can do on the front clip is stiffen the rad support to stiffen the front end to eliminate or reduce cowl shake. I will address this on another post. My next post will cover the mid-section of the car and how you can make your sub-frames more effective now that it's connected to something more worthy. Just keep in mind as stated, this stuff gets addictive and you can find yourself on a slippery slope and before you know it your in a full blown chassis upgrade which takes 100's of hours so make a plan and stick with it don't bite off more than you can chew. Just the shock tower and lower frame rail reinforcement will take a month worth of weekends and that does not take into account removing stuff and then reinstalling it on the car. [/QUOTE]
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