SLP IROC-Z

iTrader: (1)

im not an engineer nor fabricator BUT, i have a set of Alston SFCs and tonight i sat them in the subframes to get ready to weld them in. i had a long thought before i put the car on jackstands. ive heard two sides of the installation 1) put jack stands under the front control arms and the rear end so the car sits like it would on the ground and 2) put the jack stands on the chassis.

both ways seemed kind of a crude way of installing these things, either way u cant be sure if the cars sitting perfectly level. so my idea was why not jack up the car, put the jack stands under the rear subframe and front subframes, let the car sit on the jackstands, get out the old tape measure and take some meaurements and see if the distances from certain parts of the car (fender lip, subframes, etc) had the same distance to the ground all the way around.

i quickly found out how well of shape my unibody is when i put it on the stands (hardtop car) my car is lowerd so getting a jack under it is one hell of an ordeal so i have to kinda go up on each end a little at a time. well while getting it in the air i didnt put one jack stand as equally high as the other in the rear, suprisingly when i let the car down, it was elevated on three stands and didnt even flex enough that my eye could catch. i was pretty impressed by that.

anyway, when i got the car up as high as i want i proceeded to place the jack stands underneath, let the car down on them, took my meaurements all around and they all came out to be the same distances, great.

isnt this be a better way to make sure the frame is sitting 100% level?

MrDude_1

short answer?

it will work. this is how chassis fabbers and race shops build and modify frames.. they set it on a whats basicly a big bench, and measure everything....




the reason they say to leave it sitting on the suspension though, is that there is tenson and compression on parts of the body when its sitting on the chassis, and thoes parts move around and flex....

by having the weight on them like it is on the street, you are positive that the SFCs arnt holding it away from its "natural" position.... and theres less stress on the SFC at rest... meaning its stronger when a force is applied.....



or atleast thats the concept.

SLP IROC-Z

iTrader: (1)

so the way im going about doing this is a good way to do it? the way i see it, is if i know my frame is straight, then i set it down and i got one side sittin higher then the other, i know its cause i got a spring in wrong or somethin. in a sense what the way im doing it is putting the chassis in its natural position.

MrDude_1

weelllllll the only diff i see is this...


a chassis fabber is making a tube frame chassis... it doesnt flex when you set it on the flat level ground..



our unibody cars do... its basicly a flat floor pan and thats it.. the roof really doesnt do a whole lot....

i would set it on the suspension and measure it then.... that way you know if you tweaked it while jacking it up.... i wouldnt take a unneeded chance with a welded in thing like SFCs....

SLP IROC-Z

iTrader: (1)

this is my problem with having my chassis "loaded" i know when my car is sitting on the ground two of my fender lips are higher off the ground then the other.

Left Front=25.75
Left Rear=26.0
Right Front=26.25
Right Rear=26.25

this is with eibach sport line springs. as u can see the levels arent perfect all around. now i dont want to be welding subframe connectors in and holding my car in that position because maybe these aftermarket springs arent 100% perfect or maybe i have one in wrong. i just think welding the SFCs with it loaded with my current meaurements on its wheels is a lot worse then having the chassis it self perfectly level then welding the SFCs in and fine tuning my suspension components when its on the ground so it sits even all around.

i feel that having the car on its wheels then welding the SFCs in is basically letting the chassis "flex" and make up for a spring not sitting right or somethin.

MrDude_1

measure from the suspension mount points, not the fender lips.

SLP IROC-Z

iTrader: (1)

well for the front thatd be where the lower control arms bolt to the K member correct, for the rear where would i measure? from the torque box to the ground?

MrDude_1

i would go from where the LCAs bolt on.. and id go off the actual location they bolt into, not the bottom of what they bolt into...

SLP IROC-Z

iTrader: (1)

alright i measured in on the stands, in a second im going to let it down on the floor so its on its tires.

Right Front=16 3/8ths
Right Rear =15 1/16th
Left Front= 16 1/4
Left Reat=15 1/8th

i took the right front jack stand out to see whatd happen, well the measure meants all stayed the same.

SLP IROC-Z

iTrader: (1)

alright now with it on the ground...

Right Front=6 3/8ths~7/16s
Right Rear=5 1/2
Left Front=6 3/8ths
Left Rear=5 11/16s

guess i know how to do it now

25THRSS

If you put them in without loading the chassi on the wheels you will regret it.

AGood2.8

does alot more than you think- this is why I don't have a t-top f-body, they don't handle as well. Look at most hardtops and you will see stress cracks on the upper rear top portions above the side windows. They develop from frame twist in hard corners. The ultimate setup is a full cage for reinforcement, but outside rail SFCs help dramatically to help prevent this.

MrDude_1

umm. the only diff between a Ttop car and a hardtop is that the hardtop has a thin sheetmetal skin over the exact same bracing as the Ttop...

thats why it cracks.. because its not any stronger..... if the roof was that much stronger, thoes cracks wouldnt happen



3rdgen ASC verts come with additional bracing undernieth

im willing to bet money that a stock 3rdgen TTop or hard top is not as stiff as a ASC vert.

stock for stock.

AGood2.8

Hardtops have historically performed better and are more desirable in racing than convertables and t-rops- check any historical racing log.

How much did you say you want to bet?

You also missed the whole point of my post- the tops crack from stress- If the roof didn't matter when pertaining to unibody chassis flex, then why do they crack over time?

MrDude_1

well duh... unless you count early road racing... most of thoes were open cars..... and all of thoes mostly evolved into open wheel racers...


in anycase, a STOCK 3rdgen vert vs a STOCK 3rdgen coupe, the vert is stiffer.

once you mod the coupe, im sure it can be stiffer because of its tiny advantage.

AGood2.8

A convertable (even with extra bracing underneath) still flexes more than a hardtop.

MrDude_1

prove it.




granted, a hardtop with SFCs will be stiffer then a vert with SFCs, but stock for stock, the vert is stiffer.




ive driven and ridden in several verts and coupes.... im pretty sure that im right as far as 3rdgens go.





and why do people race with hardtops instead of verts? cheaper, and the rules are set in favor of hardtop cars....

AGood2.8

There's an old saying that is ringing in my head right now- and I am ignoring it...("never get into a battle of wits with an unarmed person")

Prove it? Why do road race cars add cages to there cars?-

1) is for roll over safety

and 2) the cage boxes the frame from engaging in plain twist.

The frame is flat. No matter how much lateral bracing (thats side to side on a horizonal plain for those that don't understand lateral) it will twist. It has to be boxed from above and cross braced to eliminate all flex. Hardtops are boxed, but not x braced until a proper cage is added. Convertables have only lateral bracing- no boxing at all.

Thank you for your time- Send me $20 and well call it even.

AGood2.8

Hardtops are lighter weight-

That'll be another $20 you owe me.

25THRSS

I agree with just about everything AGood2.8 said, but my t top car has those stress cracks as well.

MrDude_1

heh, im not saying that verts are better in any way shape or form for racing..


just giving you a piece of random 3rdgen trivia.


the STOCK (note i keep saying stock, with ZERO MODS including ZERO rollcages, SFCs or 2x4"s duct taped to the floorpan) vert is stiffer then the STOCK coupe because of the bracing.... once you add SFCs to the coupe it is much stiffer then a vert with SFCs because of the shape and design.... but thats not what i was talking about...

i was just giveing a piece of random 3rdgen trivia.

AGood2.8

I am well aware that you are talking stock hardtop vs stock convertable . You are wrong- I will repeat my quote- I too was talking stock vs. stock
-----------------------------------
AGOOD2.8 Quoted:
The frame is flat. No matter how much lateral bracing (thats side to side on a horizonal plain for those that don't understand lateral) it will twist. It has to be boxed from above and cross braced to eliminate all flex. Hardtops are boxed, but not x braced until a proper cage is added. Convertables have only lateral bracing- no boxing at all.
-----------------------------------

This pertained to the"extra" lateral STOCK bracing that the convertable has vs. the stock upper body "boxed" desin of a STOCK unibody hardtop.

Don't try to weasel out of this- you were incorrect on your statement. Accept it like a man, move on. I make mistakes also- we are all human. Problem here is- this is a tech board, so info has to be accurate.
Edit: I just noticed you have "vert" and realise you feel a need to be best- now I understand you passion.

ede

this thread is done, but it sure was fun while it lasted