Stiffening the framework Options

[Rand]

I'm looking into ideas to strengthen my car. Not a full cage, just a few tubes. I've read the classic threads and I'm in awe of the caliber of guys (like Brad, Jeroen, etc) we have offering help around here... hoping for your comments on this...

My goal is an aggressive street car that is strong enough for a V8 conversion. I'm looking for the simplest way to add some strength (with the least amount of added pieces). It's all about function and I don't need to be concerned with racing classifications and rules.

I'm thinking the first stage is bracing from the rear shock tower to firewall, then inside firewall to frame rail, something like the red bars in this image:

(IMG:http://www.4nets.com/baldwinpowersports/images/stronger1.gif)

Is the firewall a strong enough part of the structure to use this way (if the tubes are just welded to their respective side of the firewall)? Or should the tubes go through the firewall, welded directly to each other at the top, and another down tube tied in (like the green)?

[SirAndy]

QUOTE (RandyLok @ Mar 11 2005, 05:54 PM)

Is the firewall a strong enough part of the structure to use this way (if the tubes are just welded to their respective side of the firewall)? Or should the tubes go through the firewall, welded directly to each other at the top, and another down tube tied in (like the green)?

the firewall needs to be "sandwiched" ...

seam AND spot weld two fairly large and thick plates onto the firewall on both sides (same location obviously),
then weld the tubing to those plates.

(IMG:http://www.914world.com/bbs2/html/emoticons/welder.gif) Andy

[bondo]

Be careful about doing this sort of thing. You can concentrate loads on places that weren't intened to handle them. From your drawing it looks like you're greatly stiffening the front and rear of the longs, but not the middle. Now that section between the tubes has to take all the bending load, which it may not be able to handle. If you reinforce that area, then I think it'd be alot safer. The best would be to bring your triangulating tubes together in the middle of the long, but I'm guessing you didn't for people access.

[r_towle]

you would be transfering a dynamic load to the middle of the long in the door frame...this area has been known to fail...

You need to either extend it forward or put in an inner long re-inforcing kit (sold in the resource area)

A cross brace behind the firewall , in the engine bay, tying the two new tubes together would also be a good idea.

The green tubes should be angled down more and attached at the bottom to the suspension console.

Good luck.

Rich

[xsboost90]

with an interior long reinforcement kit, that could work fairly well, but it still wont keep the car from twisting- well the reinforcement kit would help, but your bars wont.

[r_towle]

thus the cross bracing..

[Brad Roberts]

Hi Randy (IMG:http://www.914world.com/bbs2/html/emoticons/wavey.gif)

You are on the right track... everyone above me is correct about the longs being weak. The first place I see them split is just north of the ebrake handle recess. The V8 cars *really* twist the chassis' with their torque. I like your tube placement.. the only thing I would add would be one of the "Engman" cabin/interior stiff kits. This will box the frame and give you a sturdy place to mount scab plates for your tubes.

Another area that I rarely speak about: Just below the rear window all the way across the car. I use square tubing here and it is basically hidden below the engine lid. It helps tie the car together.

B

[riverman]

You might want to look at Brad Mayeur's stiffening kit. It is basically some preformed panels that fit over the outside longitudinals and up to the rear suspension mounts. It was primarily designed as a way to strengthen a 914 after it developed rust problems in the longs but it also does a great job of strengthening the frame for v8 conversions. There is some information about this kit in the PP technical forum.

However, that being said I would listen to comments about strengthening a car and the redistribution of forces. You could end up doing more harm than good.

[Brad Roberts]

QUOTE

that fit over the outside longitudinals and up to the rear suspension mounts

Correct... but... the issue in our cars.. when you increase the weight (V8 or 6cyl) and you increase rear spring pressure to make up for it... the chassis starts to split just in front of the shock towers... Brads kit doesnt address this and neither does the GT stiff kits. His tube placement will help distribute this load IF he picks up the front of the shock tower.

Brads kit is super thick and super strong (no question).. but it attaches to the frame rail COVER not the frame rail. Our frame rails are strong/have strength on the inside of the car... not the outside.

B

[Rand]

Cool - I was planning on Engman's kit first anyway. Any more thoughts about the down tube (green bar in drawing)? It seems to me like the firewall would provide enough strength in that area to make it unnecessary?

[xsboost90]

i think w/o that green bar going somewhere, the other bar is just going to flex in the middle, making it useless.

[Trekkor]

Engman's kit is very special.

KT

[Rand]

QUOTE

i think w/o that green bar going somewhere, the other bar is just going to flex in the middle, making it useless.

I'm not following you here. If the two red bars are welded to the firewall at the top joint, where is it going to flex? It can't lift the firewall...
(IMG:http://www.914world.com/bbs2/html/emoticons/confused24.gif)

[SirAndy]

what brad was trying to tell you is that our cars have a weak spot right where the big blue line is.
you need to address this even more if you stiffen up the rest of the chassis.

the forces you put on the chassis will be exactly the same, with or without stiffening.
stiffening one area only means the forces will be shifted to other areas.
from your drawing, the weak spot in a 914 (lost of twist) will see *amplified* twist forces now that you have stiffened up other parts of the car.
especially with a V8, if you don't do anything to that area, it *WILL* crack right there. i have seen it before ...

(IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) Andy

[riverman]

QUOTE (Brad Roberts @ Mar 11 2005, 09:48 PM)

QUOTE that fit over the outside longitudinals and up to the rear suspension mounts Correct... but... the issue in our cars.. when you increase the weight (V8 or 6cyl) and you increase rear spring pressure to make up for it... the chassis starts to split just in front of the shock towers... Brads kit doesnt address this and neither does the GT stiff kits. His tube placement will help distribute this load IF he picks up the front of the shock tower. Brads kit is super thick and super strong (no question).. but it attaches to the frame rail COVER not the frame rail. Our frame rails are strong/have strength on the inside of the car... not the outside. B

When you say the car will split in front of the shock towers, are you refering to the suspension riser breaking? Is this because the Mayeur kit doesn't extend beyond the suspension mounts and a weak area is left between the suspension mounts and the shock towers?

If this is the case, should I reinforce the area between the suspension mount and shock tower? Also, would it be advisable to stiffen the lower firewall (much like the Engman kit) and tie it in to the Mayeur kit to counteract twisting?

Also, when you talk about a car splitting, are you refering to race cars or street cars?

[Rand]

Andy... I understand what Brad was saying. What I don't get is what xsboost90 was saying, specifically about the green bar and the firewall.