Black,i'm still unable to find the old thread about the tower upgrade but i remember the thickness was about 5-6 mm.The tower was made with 2 lateral bars and a top bar welded together( the material was too tick to make a clean bend since it was welded).The result was a very strong tower,probably more than needed ,but safe...for sure.Not a big deal if you are handy with a welder.i remember the QA1 set up used a very large coil.

edit:
i found the reference pictures and the member was LD85 from Digital Corvettes here a link to a Grumpy thread very informative for all of you guys.
http://garage.grumpysperformance.com...-on-a-c-4.483/

here the towers pics

 

I made the left side with 5 mm, and the right side with 4 mm, I think 4 mm is enough.

Here is a pic of the right side mocked up, just a quick pic in the dark to show you where Im at. Still gotta get the swaybar sorted too.

 

Black, do you plan to get rid of the old towers grinding them out and replacing with the new one ?,or, do you want just weld them over the stock one to reinforce them?

 

Black you need backing part/plate for your U-bracket like tunedport85 has towards the top, it will make it a lot stiffer.

 

One of the companies makes the brackets you see for my swaybar and it fit without issue.

I mocked up LD85's setup with a few changes.

 

No, the original shock tower stays in place. this tower has an angle (it leans rearward slightly) that matches the top arm, it also has an angle on the top that matches the angle that the shock goes into it.

The stock tower is also welded to a bottom section (at the chassis) for strength, and has side and rear supports welded into the chassis. So its actually a pretty well engineered set up. The only 'what if' is the fact it was only designed to carry a shocker.

The brace I have made is bolted around the stock tower. It has bolts on the bottom arms that go thru the point where the top and bottom of the shock tower meet, so it ties 3 points together.
the top is also bolted thru where the original shock hole is.
It is also bolted where the shock now goes thru.
its a bit like a stud girdle in that it locks everything together, while retaining the good features of the original tower.

 

as above I will use the original shock tower as the backing.

 

Here a lot of guys are running with absolutely no issues coil overs on the stock towers,and all they say that it is strong enough.I'm not an engineer ,but i would make you think about some basics concept.As you highlighted above
1) the entire weight of the car ,at least the front end portion, is supported by the towers previously designed just to hold a shock absorber. Plus, you have to consider the kind of dampening this stuff produce,we are talking about a stiffer ride that turn into hard stress to the welding points,it's like you hit with an hammers instead of tapping lightly....
2) if you look at the welding in the lower tower bracket it seems to be pretty weak.
3) your approach seem to be not strong enough in my opinion.The enforcement you'r doing require a massive welding job were the braces connect to the frame walls.Again, the two parts remain separate parts where they meet the frame.If you are worried about cutting off the factory towers, i would consider working with the welder around the edges and making solid contact in the frame wall area.sorry Black i don't want be tedious.

 

The thing about stock shock towers is that the dampers impart an order of magnitude higher forces on the towers than the springs ever will. And they are over-designed for those high loads. That means that adding the load of the springs just isn't much of an increase over the loads they were already seeing. If you add stiff aftermarket shocks to the car (without coilovers), you are increasing the loads much more than if you just add the spring loads. Yet nobody ever expresses any concerns about that. Likewise, there should be no worries about spring loads on the shock towers.

That said, the issue in this case is the need to mount the top of the coilovers further out toward the edge of the towers. But blackozvet is adding the braces to bolster the strength at that new location. I think it is a sound plan.

 

Some other cars have issues when converted to stock location coilover using the shock tower, just saying.

 

Sorry Matthew,let me learn,if i've miss something:
1) In the stock setup the weight of the car is supported by the transverse leaf spring,it is positioned in the middle of the cradle frame.The fulcrum is in the middle of the leaf spring where it meets the cradle frame . The "arms" of the lever are the same length and are pivoted on the lower A Arm .In this setup if you take out the shock absorber the car is supported by the leaf spring,TOTALLY.In the same system, if you take out the leaf spring, the weight of the car will collapse the shock absorber.
This means that the engineering dept wanted the leaf spring support the weight of the car and this force is acting in its fulcrum positioned under the cradle frame in the middle of engine bay and in the lower A Arms connecting point, pivoted to the frame .
2) The shock absorber is just dampening the forces produced by the system leaf spring-A Arm.I deduce that the support frame for the shock absorber is obviously designed just for dampening NOT support purpose,even if over-designed .

 

This is correct: the springs support the sprung weight of the car (the whole car except for the wheels, tires, brakes, and half the suspension/axles). So in a typical C4, both spring perches (one front and one rear) support roughly half the weight of the car, perhaps 1600lbs each. In switching to coilovers, each of the four springs supports half that weight because there are now four separate spring perches instead of the leaf springs' two. So in a coilover setup, each spring may have to support maybe 800lbs at rest. Perhaps as the suspension is compressed the perches might have to support three times that at full compression for a moment or two (if the spring is compressed 2 inches).

This is not quite accurate. The shocks (dampers) are damping the motion of the suspension which is created by the speed of the car, the mass of the car, the undulations in the road, and the acceleration forces acting on the car in all four directions (dive, squat, heave, roll). That is, the dampers create a force resulting from velocity of the damper shaft. The force the damper imparts to its mount is determined by the velocity of that motion, the damping rates, and either the sprung mass of the car (in compression) or the unsprung mass of the car (in rebound). That's a really important point to understand: dampers react velocity, not force or displacement like springs. They don't support any of the weight car. But unlike weight, which doesn't change as we drive down the road, the suspension velocity can change a lot, depending on how fast the car is moving and the shape and size of the bumps in the road. On a heavy car going quickly over a sharp, tall bump, the shocks can impart forces many times higher than the springs: many thousands of pounds.

That is why I would never worry about a shock mount having the capacity to also carry a quarter of the weight of the car for a coilover setup. I am unaware of any production ever having a problem with the structural integrity of the shock mount in a coilover conversion.

 

Thanks Matthew, very accurate explanation

 

Thanks for that explanation Matthew, one point that is probably overlooked is that the coilovers introduce 2 separate mounting points at the front instead of 1.

I really appreciate the input and questions by everyone and its good to have an understanding of chassis dynamics if you are going to modify things.
I'm fairly pragmatic so I do what i have to do to make things fit, and I dont want to spend my whole life in the garage working on it, it would be nice to put the wheels back on and drive it down the road at some stage, but having said that it needs to be strong enough that the wheels dont fall off at some stage while Im driving it down the road !

 

this^^^^^^^^

 

I have now bolted the brace onto the right side, using 3/8" stainless bolts and washers at each side and one at the top in the original shock hole.

I have also cut out the bent pieces on the original shock tower, you can see the freshly cut pieces. It makes it look a bit cleaner and gives a fraction more room for the spring.



with the spring in place and jacked up to approx ride height I have now started getting the swaybar ready. I have ground the back radius of the swaybar to give clearance to the spring. You can also adjust the shock back a bit, it has slots on the T bar so you can slide it backwards a bit (before doing it up) to gain some clearance.
I have bought 7/16" male and female rod ends, both in right hand thread.
Im going to use angle to make the bracket in the original position, this will keep the rodends as straight as possible.

 

has anyone else who uses Photobucket noticed that its become a pain to use ??

anyway here is the photo that it dropped off the above post,

with the spring in place and jacked up to approx ride height I have now started getting the swaybar ready. I have ground the back radius of the swaybar to give clearance to the spring. You can also adjust the shock back a bit, it has slots on the T bar so you can slide it backwards a bit (before doing it up) to gain some clearance.
I have bought 7/16" male and female rod ends, both in right hand thread.
Im going to use angle to make the bracket in the original position, this will keep the rodends as straight as possible.

you may notice that i have cut a chamfer on the right side of the brace to clear the sway bar bolt. keep in mind that the end of the swaybar moves thru an arc as the suspension moves, but there is a motion ratio, the swaybar moving at a lesser rate, usually around .6 or .7

 

Everything is assembled (excluding the swaybar links) wheels on and dropped it on the ground.
next problem, the 10" spring is too long. with the coilover adjusters all the way down the chassis heights are 6" in the front (or 27" eye-brow height)
it was 5 & 5/8" with the z51 spring in.
Probably should have gone with a 9" x 550 lb spring.
The installed height of the 10" 600lb spring is 8"
spoke to guru jim, he says bring the springs in and he will try and 'scragg' them down an inch.
thats cool I dont mind jacking it up and taking everything apart again !

 

Another method on an '85 from the Racing forum.

 

I most certainly have not. Long story but I will not buy from Viking.