weld or bolt in SFCs

[JoeliusZ28]

I agree the total deflection per unit load of a generalized welded component will be less than a bolt. However, there is a few factors you did not account for.. what is "the load" on that bolt. Nobody has measured what force that bolt is actually seeing. this is critical to determine if bolts are adequate.

if no one is breaking bolts (i havent heard any) id say the bolts are adequate. I am sure? no, but i dont care enough to find out for sure either.

And to bring it one step further, there is Tension that is preloaded into the bolt via 'torque' therefore the load required to move or lift that bolt increased significantly. A weld does not have this "preload" or clamping force. Depending on the geometry and loading conditions, i can argue that either one may be more or equally as rigid. There are calculations that can show how "rigid" a properly torqued fastener can be in tension and how much clamp load it can provide.

For example if you have a 100 lb/inch spring, under a free state condition it would deflect 1 inch for every 100lbs placed on it. However, if you then 'preloaded' that spring to 800lbs and then placed 100lb weight on it.. it wouldnt deflect.. Untill you reached the 800 lb preload.. then you would need 900 lbs for it to deflect one inch from the preloaded state and it would continue to deflect one inch for every 100lbs thereafter.. Bolts are esentially just very stiff springs with lots of preload.

Also, as the chassis gets stiffer, the natural frequency rates (ride rate) would increase as well. You can calculate it like two springs in series and determine where the point of diminishing returns lies. You only want to make the chassis stiff enough to not add significant impact to the suspension stiffness (no point in adding extra weight). Likewise, As you increase the suspension stiffness, you also would want to increase the chassis stiffness (rigidity, natural frequency, etc). in a VERY BASIC sense, there are two "springs" you need to worry about... suspension springs and chassis rigidity. (there is also, tires, swaybars, compliance, aero loads, etc.. but we wont go into that)

So my statement there, is that the vehicle is a system, you mess with one thing, there are others that are affected. The degrees to which are affected still need to be determined, however.

all true, but the change in how the entire system works is the entire idea of adding SFCs isnt it?

[JoeliusZ28]

my only concern with the 3 point is that it would need to be removed whenever you are working on the underneath of the car

why? mine are three point they havent gotten in the way of anything yet. ive done headers and a clutch swap even.

also for the record i recommend my kenny brown double diamonds. they tuck up extremely well.

either way, i'd get a 3 point mount, dont even waste your time with 2 point if you are doing SFC's.

Just to prove my point, the 3rd point mount is on a spot welded piece of sheetmetal.. i highly doubt there is much force going through the SFC's if this area has not been comprimised.

not claiming to be an expert, but i think the third point is just to prevent torsional effect between the other two points.

[Formula Z]

Thanks guys didnt think it was going to be a big debate. both are making great points. thanks for the info about your 3 points joel, i may do that now. ill let you know if i decide weld or bolt in.

[JoeliusZ28]

I completely agree with DanO that getting bolt-ins and welding them later is a good way to go if you arent sure. As long as the weight of the car is ON ITS WHEELS on a LEVEL surface, youre chasis will be OK.

[willasc]

I personally chose the bolt on ones when I had it SFCs installed. I am not sure what brand you will buy (I had UMIs), but mine did get in the way of the fuel line toward the front on the vehicle on the LH side. It is unlikely that those plastic fuel line will be a concern, but the SFCs will have to be removed to service those fuel line if it ever does happen.

I don't know what the your main goal of install SFCs are. But for me, the bolt ons were adquate. I even took them to autocrossing with no deflection, loosening of the bolts, nor was there any any plastic deformation in the part, bracket, or the body.

Also, keep in mind that when the engineers are tuning the ride and handling of the car, some body deflection is accounted for and expected when tweaking and adjusting various components of the body and suspension. So over-stiffening the vehicle might not always give a positive overall result. The could include squeak and rattle and other NVH issues.

[JoeliusZ28]

I personally chose the bolt on ones when I had it SFCs installed. I am not sure what brand you will buy (I had UMIs), but mine did get in the way of the fuel line toward the front on the vehicle on the LH side. It is unlikely that those plastic fuel line will be a concern, but the SFCs will have to be removed to service those fuel line if it ever does happen.

this is a good point. whoever installed my SFCs slightly tweaked the line and put it over the SFC (between the SFC and the ground). I wouldnt have done it that way, but its been perfectly OK that way.

[WMCCjames]

Well, I noramally agree with DanO on topics we discuss around here, but this one.......Bolting vs. welding.....lol. A bolted interface can be as strong as a welded one in the right conditions....however, this is not one of them. Weld them in and forget about it.....you will never have to touch them again, period....they will not loosen, they will not squeek, they will not rattle, the holes will never elongate and they will never fall off the car going down the road. Do the job right the first time so you don't have to screw with it again later.

I have Alston tubular SFC's on my car...can be bolted or welded. I first put them on the car by bolting them in because I did not own a welder at the time. Let me tell you, what a waste of time and effort....I pulled them back off the car becuase they would not stay tight and the holes started to elongate. I was ready to chuck them in the garbage until cooler heads prevailed....so I saved them, put them away on a self for years. Once I could re-install them by welding they have been great! My car is a t-top car and used to flex ALOT. One test I did was the finger laying across the t-top seam while drivng into a steep driveway at an angle. Before the SFC's (and after the bolted in SFC's worked loose) the seam would open up enough it would actually pinch the skin on my finger after proceeded into the driveway.....we are talking about almost a 6mm gap8-O Now when I do it I barely feel any movement on that seam. And it's been that way for 4 years.

[DanO]

Well, I noramally agree with DanO on topics we discuss around here, but this one.......Bolting vs. welding.....lol. A bolted interface can be as strong as a welded one in the right conditions....however, this is not one of them. Weld them in and forget about it.....you will never have to touch them again, period....they will not loosen, they will not squeek, they will not rattle, the holes will never elongate and they will never fall off the car going down the road. Do the job right the first time so you don't have to screw with it again later.

I have Alston tubular SFC's on my car...can be bolted or welded. I first put them on the car by bolting them in because I did not own a welder at the time. Let me tell you, what a waste of time and effort....I pulled them back off the car becuase they would not stay tight and the holes started to elongate. I was ready to chuck them in the garbage until cooler heads prevailed....so I saved them, put them away on a self for years. Once I could re-install them by welding they have been great! My car is a t-top car and used to flex ALOT. One test I did was the finger laying across the t-top seam while drivng into a steep driveway at an angle. Before the SFC's (and after the bolted in SFC's worked loose) the seam would open up enough it would actually pinch the skin on my finger after proceeded into the driveway.....we are talking about almost a 6mm gap8-O Now when I do it I barely feel any movement on that seam. And it's been that way for 4 years.

well thats an easy fix... just buy a 4th gen

Seriously though, that totally depends on the design and mounting location for the SFC's 3rd gens may be mounting and deflecting differnetly than the 4th gen chassis. Sounds like you were loading the bolts in "shear" not "tension" thus elongating the holes

either way.. you found what works for what you have. I bet if you changed the load paths through the bolt interface you would have achieved the same result however.

Thats the thing i kinda hate about 'generalization' of bolt vs weld SFC debates. The thing you should be arguing is how poor of a "bolt in" design the system has.. which is compensated for by welding..

I dont argue that your weld in system fixed your problem.. i just say that the bolt in system you had sucked and was probably designed by someone who could barely do algerbra..

[JoeliusZ28]

i thought the undercarriage of 3rd and 4th gens were "nearly" identical??

[81DaytonaPaceCar]

i thought the undercarriage of 3rd and 4th gens were "nearly" identical??

x2...structurally, I thought they were very similar...

[WMCCjames]

They are just about identicle from the front seat pan to the rear bumper support. The 4thgen has a completely different front suspension so the changes are from the front seat pan forward.

But what do I know, I'm just working from actual experience not from the bible internet here-say.

[PACE]

Everything that i have done, I will not use Bolt Ons, Had way to many problems with them, evan with Locktight. Tryed different brands also, always came loose, or squeeked bad, and from bolt ons to weld ons from what i have done, ( and thats lots) is that the weld on ones make the chassie much tighter... You can alway tell when i get done with some weld on SFC... Its deffenently hugs alot better than bolt ons ........

This is my experance with this hole process....

I LOVE WELD ONS.... They just got to now what the hell there doing !!!!!!!

[tenpin842]

Everything that i have done, I will not use Bolt Ons, Had way to many problems with them, evan with Locktight. Tryed different brands also, always came loose, or squeeked bad, and from bolt ons to weld ons from what i have done, ( and thats lots) is that the weld on ones make the chassie much tighter... You can alway tell when i get done with some weld on SFC... Its deffenently hugs alot better than bolt ons ........

This is my experance with this hole process....

I LOVE WELD ONS.... They just got to now what the hell there doing !!!!!!!

LOL...thats why when I get ready...I'm taking a road trip to have you weld mine in!

[BP_Z28]

I love reading these lil debates go back and forth.. You guys should be lawyers!!!

[JoeliusZ28]

good in theory, but theres no money in automotive cases