Do the front cross members offer rigidity?

[Ludachris]

I'm looking at the front cross members and wondering if they are helping stiffen up the chassis - especially the two running from front to back. It almost seems as if their main purpose is to support the engine in case the motor mounts break.

I'm planning on learning welding this winter and figured it would be a fun project to create some tubular versions of these cross members to save weight and free up some room. I'm just wondering how much material I should use if they were indeed responsible for stiffening up the chassis. I've seen a couple versions that use very little material but I think those were done with drag racing in mind. Road racing will obviously put more load on these pieces.

Any thoughts?

 

[Backinajiffy12]

The cross members are there for rigidity aka support so when making or modifying the chassi I would say as long as you have enough support all around that would be a breat way to shead so un wanted weight!

 

[Eagle 5]

Are you talking about the two "flat" bars that run from front to back? One kind of in center of motor, the other off to the drivers side? And the triangular piece on the passenger side?

If so I am sure you could make these tubular but how much weight would you really save and that would make ground clearance a little less. Though I know those are not necessarily the lowest points, maybe it is not a problem in those locations.

One of my friends front side-side crossmember on his FWD (one the front engine mount is on) broke once and they made a replacement one out of tubular steel. Looks nice and works great. Maybe the whole front could be made out of tubular members, baring the actual frame rails.

 

[tsiboosted]

If you did make them out of some sort of tubular version you may want to make them from chromoly steel (roll cage material). Very rigid obviously and likely lighter weight than what is already used there now. Just an idea on the material is all. I am not at the shop so it is hard to even venture a guess on how you could do it. Interesting thought though Chris.

 

[Ludachris]

Are you talking about the two "flat" bars that run from front to back? One kind of in center of motor, the other off to the drivers side? And the triangular piece on the passenger side?

If so I am sure you could make these tubular but how much weight would you really save and that would make ground clearance a little less. Though I know those are not necessarily the lowest points, maybe it is not a problem in those locations.

One of my friends front side-side crossmember on his FWD (one the front engine mount is on) broke once and they made a replacement one out of tubular steel. Looks nice and works great. Maybe the whole front could be made out of tubular members, baring the actual frame rails.

Yeah, those two beams plus the front cross member which attaches to the front motor mount. I'd venture to guess the weight savings would be somewhat significant, though not necessarily dramatic. But the combination of the weight savings plus the additional space savings due to less material would be a plus. Not to mention any weight you can remove from the front end is a major plus, regardless of how much it is. These cars are so nose-heavy that any little bit helps, especially in the front.

And I doubt there were be any change in ground clearance since the tubular pieces wouldn't be any thicker than the factory cross members.

 

[99gst_racer]

Funny you mention this, Chris; I'll be fabricating these same pieces for my 1G within the next month or two. I actually just planned it out yesterday.

For now, the plan is to use 1.250" x .095" chrome moly. I'm also going to make a small solid roll stop to weld onto the cross member to replace the bulky factory one. And the radiator's lower mount will be welded onto it as well, so that I'll be able to completely remove any sheet metal in front of the cross member.

As I make progress on it, I'll share pics.

 

[Ludachris]

Nice! Can't wait to see some pics.

 

[Eagle 5]

Also, you could run wiring through the tubing rather than having it attached to the outside of them or just "hanging" by them. Such as the large wire loom that runs under/ just behind the radiator. That would be more for "looks" though it would get the wiring out of the way and protect it from heat, debris etc. Maybe more room in engine bay as well. I do not think it would be hard either to run the wires through it. Just have a hole where the wires enter and leave and maybe a couple tiny drain holes on the bottom to keep water from settling inside. Or just use grommets for the wires. Just a thought.

 

[1fastlaser]

My buddy made one for me, it loses the 2 cross bars, but ive had it on the car for almost 10 months now and no issues. Front end is stiff as hell. Was going to go into making them for everyone, but little interest sparked.

Ill tell you one thing, taking the trans in and out is one of the easiest jobs with this sucker. I love it

 

[Ludachris]

Is that subframe used in a road racing application? It would have to withstand extreme stress.

 

[need2boostpsi]

My buddy made one for me, it loses the 2 cross bars, but ive had it on the car for almost 10 months now and no issues. Front end is stiff as hell. Was going to go into making them for everyone, but little interest sparked.

Ill tell you one thing, taking the trans in and out is one of the easiest jobs with this sucker. I love it

that looks pretty nice, i think i would also want a X-type or H-type member for the front to back to stiffen the car up some, do you have any front end squeaks?

 

[1992awdlaser]

I have one of my front to back ones removed. I forget which one. I have had no problems like this but I don't autocross it. I do have some fun around turns sometimes but that is about it.

I am going to be making tubular versions at the beginning of next year in college as a project.

 

[1fastlaser]

Is that subframe used in a road racing application? It would have to withstand extreme stress.

The intent of it was for drag racing. Altough i have taking some pretty hard turns at 90+ mph. I wouldnt doubt it holding up in auto cross/road race applications, but alot of guys would want maybe one extra brace from the front of the control arm to the center of the k member.

No front end squeeks, its pretty ridged, and the front end feels tight.

I wanted to incorporate a driveshaft loop into it which would be sweet.

 

[drivemusicnow]

You really need to add two bars that go from the load point on the front of the control arms back to the center of the cross tube. That construct screams of fatigue failure and flex, at least in a road course car. I can't tell exactly, but I think you just have the cross bar bottom welded to your control arm mount bar? thats not safe either.

Not tryiing to insult you personally, but that is dangerous if you actually do anything other than straightline with that, and even then it's questionable.

 

[JFatch1890]

for the two front to rear supports a friend of mine made them out of U channel aluminum, and they seem to be working great. there are no stress cracks in them, there is no welds also

 

[1fastlaser]

You really need to add two bars that go from the load point on the front of the control arms back to the center of the cross tube. That construct screams of fatigue failure and flex, at least in a road course car. I can't tell exactly, but I think you just have the cross bar bottom welded to your control arm mount bar? thats not safe either.

Not tryiing to insult you personally, but that is dangerous if you actually do anything other than straightline with that, and even then it's questionable.

None taking. I understang as this was a first off piece. Its all tig welded by my buddy at Haggard Fabrication He does some wild stuff over there. I trust him pretty good, and i beleave another link from the control are mount bar to the cross k member part would be nice. I have the specs on the material used in the k-member thread i made when it first was done. Its pretty thick stock, plus i have hit some pretty insane bumps, one of which.... ADMIN EDIT... my front suspension bottomed out completly, and it felt and sounded like hell.. It kinda gave me the "well i guess if it didnt break on that, its not really gonna break at all" thought.

 

[Lonnie gandee]

I drag race my cars..ALOT.. I've run both cars without both bars...


Its been 2000miles on my dd...

 

[drivemusicnow]

I do like the idea, but if you could add the two diagonals that make it a true K member and come up with a better way to connect the ones I circled in green... You'd have a solid, and still light, piece.

The issue with the green areas is that the side load path is not at all supported. the gusset is on not as stressed side and you need to add a slight corner brace. (you see this joint better in the other pictures)


Think about all the different loads that can occur starting from the wheel.

 

[1fastlaser]

I do like the idea, but if you could add the two diagonals that make it a true K member and come up with a better way to connect the ones I circled in green... You'd have a solid, and still light, piece.

The issue with the green areas is that the side load path is not at all supported. the gusset is on not as stressed side and you need to add a slight corner brace. (you see this joint better in the other pictures)


Think about all the different loads that can occur starting from the wheel.

oh yeah very understandable. That was exactly where i want to add more structural integrity. Like i said we thought about incorporating a driveshaft loop also. Might have to pull it out for the winter since i got a new turbo/exhaust/suspension setup going on the car. Im also fixing some other little things that typically are not worried about.

Ill keep an update, maybe if my friend Matt at haggard dosent want to get into them, i can work something out with someone else.

 

[JFZERO ECLIPSE]

My buddy made one for me, it loses the 2 cross bars, but ive had it on the car for almost 10 months now and no issues. Front end is stiff as hell. Was going to go into making them for everyone, but little interest sparked.

Ill tell you one thing, taking the trans in and out is one of the easiest jobs with this sucker. I love it

If I recall there were quite a few of us that still wouldn't mind having 1 but apparantly not....

 

[1fastlaser]

If I recall there were quite a few of us that still wouldn't mind having 1 but apparantly not....

Yeah like i said it sucks. If you go into the original post i made when it was first done http://www.dsmtuners.com/forums/bolt-tech/272492-custom-tubular-k-member.html

Theres was mixed thoughts, and just like anything didnt catch on right away, which i know you cant expect. I will like i said pull it out over this winter, and see if i can work out a deal with someone to have them made if my buddy dosent want to mess with them. I know hes swamped right now, because i gave him a call to see if he could make my v-band exhaust for my gt4294 going on this winter. Ill see what i can do.

IHatedsms and I are trying to rent a garage to do some side work and kinda get something going, We are long time friends, and hopefully we get something together. Then we can really move on some stuff like the k-member. He's going nuts with his build. And im trying to make one nasty street car. Here is his build for which ever you guys havent seen yet http://www.dsmtuners.com/forums/drag-strip/290305-my-1992-awd-drag-talon-build.html

 

[JFZERO ECLIPSE]

Thanks, I understand fully trust me....A little extra bracing wouldn't be a bad thing though...

Just like Sturt tower bars....yay strut to strut....

Get a REAL bar 1 that bolts to the firewall....triangular...much stronger/less flex

 

[eclipsh]

Chris, I can tell you from experience that those bars do make a difference with chassis flex. I missed putting the center bolts in the driver's side the first time I took it out. These bolts attach it to the front side of the K-member. When I took it off again (probably a couple years later) I saw a large wear patch from it rubbing back and forth over the k-member. I also can't get the bolts back into the center holes if the car is being supported by the front end, I have to lift it from the jack points behind the front wheels or it flexes the car enough that they won't line up.

I know Rick (pagosa dsm) has talked about building these same pieces, including the front cross member with the motor mount. He's got some plans together for control arms too. I'll be sure to take pictures of any and all of these and get them up in his gallery once they're done.

1fastlaser, is there any chance of getting you to take your car into a frame shop to see if it is flexing more or less with your k-member versus the stock one? You said it feels stiffer but I'd like to see some data besides the butt dyno Maybe when you pull everything this winter you could drag the car to a friend's shop and see what happens.

 

[TunaTalon]

Here's a chance to add to the community knowledge base.

Chassis stiffness can be measured by the resonate frequency of the chassis. If a tire is out of balance the car will vibrate most at the speed where the tire rotation is at the resonate frequency of the chassis and decrease at higher or lower speeds.

Before installing any device that is supposed to increase chassis stiffness add a wheel weight to one front wheel and drive straight and level to find the speed where the vibration is greatest. Using tire circumference and speed calculate the chassis resonate frequency. Add the stiffener and repeat the test. If the chassis is stiffer the resonate frequency will go up.
Caution, caution my Talon with front and rear strut tower braces has a resonate frequency of about 21 Hz which comes on at 90 MPH.

 

[99gst_racer]

I drag race my cars..ALOT.. I've run both cars without both bars...


Its been 2000miles on my dd...

So, you don't run a front roll stop at all?