Chrome moly crossmember

[Barnes]

I might have to draft something up in AutoCAD tomorrow because I think a lot of folks aren't understanding the purpose of the members that are eliminated by the piece that Alpha Male linked. A strut tower bar will not replace the lost ridgity.

 

[IncorpoRatedX]

and im the dick for calling them morons? i say g'damn! /ubbthreads/images/graemlins/banghead.gif

 

[curtis]

Ok been sick and haven't posted but try now.

My subframe connectors are to add to take away from the chassis flex not to substitute what a cage can do. For example if you jack up a car on the corner , any corner it will start to lift that one corner before it lifts any other after the connectors are in that goes away and the body tries to stay flat. Mainly because from the factory you have a front frame and rear rear with a flat piece of metal in between more or less.

This front crossmember is actually a good idea that was only 50% built in my opinion. Its probably heavier than stock but does gain rigidity and also gain in space only problem I see is its not connected to the subframe. They're there to keep everything straight and square under the engine going down the road. Like was said take them off and drive 2 weeks and try and put them back on. The bushings will deform and you've had an engine twisting up between the two, besides just the static weight of everything pushing straight down.

We've all seen pictures of subframe cracked because that little 5 bolt plate wasn't reinstalled. Same as that pita brace on a 3000gt VR4 transfer case. People leave them off then 3 months later the transfer case twists off. Cars in general are piles of sh*t from a design stand point. Tube cars like an ariel atom or cars designed with a CF tub like a F40 are different but most cars built in the last 30 years are stamped steel turds that have as little welds as they can get by with and sealed with seem sealer to save on welding. Its mass production plan and simple. The brace not being on the car is a bad idea. Think about it this way would an auto maker build a part like these two braces if they really wasn't needed. I'm sure they don't pay alot for them but even at 20 for both thats 20 times 500K over the history of the car if not more.

Now as for fabricating these proper I thought of it years ago also front and rear subframes and other geewhiz braces and things but with anything like this you need a jig and a supply of materials. My buddy just dropped 5K on two bundles of chromemoly for a 25.2 chassis he built and got certified a few weeks ago. I think he said it was 6 or 7 dollars a foot and took 6 months to get it because of defense contractors buying it up for the war effort.

A proper jig for a well designed subframe would start on a 1/2 sheet of steel ( minimum ) on a special built steel table then mounts for the mounting points built etc. You could easily have 1500 in a jig table before you ever build the first one. All the bushing would have to be duplicated out of steel and welded into place so the new blanks dropped right on top. Then you start cutting chopping and welding them set the price and watch them not sell. This is the main reason you don't see front and rear subframes built and sold, built correctly and the amount of design time, work time and effort cutting notching etc plus materials $800 would be a cheap price each. You have to remember all the mounting points are machined to fit replacement poly bushings or you would have to redesign to use a standard size like 2 inch etc. But then the pin bushing are to be considered etc. Not 2 many people would drop 1600 for a set of tubular K members. Another problem is shipping big items like that...heavy and bulky is a pain to ship. Even with a label stuck on it and shipped no packaging a pair would probably be 200 bucks if Fed ex or UPS would even take them.


Now this substitution of a strut tower brace ....wrong answer not the same. forces on a strut tower are coming up from the ground trying to push them up and in not keep it from twisting underneath. the strut towers have sh*t for welds to the front frame rails so thats all it helps. Even strut tower braces need to be a triangle and connect to the firewall.

for example click me.

 

[NateCrisman]

This is a part that I would use on a car like my 1g...it's a racecar. I believe we had a thread about this specific part last winter and I determined that it would save around 13 to 14lb compared to stock parts. Some of that weight was figured by taking the two long subframe connectors and cutting them down so that they only use the rear sets of bolts. (you absolutely would need to do this as running the car without these bars causes the steering rack subframe to crack). I can't say that the rigidity is adversly affected or front traction due to alignment change, all I can say is it's going to save about 14lb of dead weight. Granted, I wouldn't pay $165 to save 14lb of sprung weight, but if you could make this yourself for cheap...I'd do it. Plus I don't give a crap if the car gets a little bent up, it's just a racecar toy to beat on.


for a street car that is going to see mileage, bumps, potholes and cornering/twisting forces: I think this is a pretty poor modification and will eventually lead to the hood/fenders/radiator support becoming tweaked and not lining up. And for what: to save 14lb. /ubbthreads/images/graemlins/dunno.gif

Note: this is coming from one of GalantVR4's most weight concious people who spent days and nights cutting up the wiring harness in his GVR4 to save weight from unused wire. I'v gone to some pretty extreme efforts to ditch weight and even I wouldn't use this on my streetcar.

 

[NateCrisman]

Cut/Paste from previous thread the last time around:


Quoting NateCrisman:
The three crossmember bars and the front roll stop were exactly 20.5lb on my scale. So if this replacement bar is 5.5lb, we are talking about 15lb of weight savings. And at the very least, you need to use the rear chunks of the factory n/s bars to box in the subframe, which will add a pound or two.

Is this worth doing on a 3200lb street GVR4..hell no for both cost/gain and stucture reasons.

Is this worth doing for a flat out racecar (dragstrip) that is already down to 2300lb, already has CF body parts, 9lb wheels, and all the typical weight loss? HELL YES.

15lb is .015 of ET and a smidge less stress on your drivetrain. Granted this should be on the lower end of the list of "To-Do" when it comes to weight and power production, but to just say "forget it" on 15lb is foolish. This is the way you drop race weight...little bit at a time and generally every little bit is a sacrifice in money, effort, safetly, convienence, durability, or other negative factor.

This is something you do when there is no more "turn up the boost" available, there is no lighter car to buy, and ultimate performance is theonly goal. When you want to go 9.99 on a 16G turbo, then this is the kind of stuff one needs to look into. It's a RACECAR modification in my opinion.

 

[mountaineerjeff]

as far as the replacing with a strut brace, I didnt mean the practically useless one that are available, I meant (and previously stated) a 3 or 4 point bar that would at least tie in the firewall or maybe even the front cross member as well. Like I said I would def like to have a tubular bolt on sub frame, but I dont think I would pay $800 for the whole thing let alone half. I like how civics get k braces for like $150. If it really is only 14 lbs then it really isnt worth it, I think his ad listed close to double that. Ill probably just do solid mounts and leave well enough alone

 

[NateCrisman]

He says his bar weighs 5.1lb. I'd guess he has measured this on a real scale since he lists it to the tenth of a pound.

He then says "it saves an estimated 20-25lb". I take that as implying that he doesn't really know what the stock parts weigh. If he had put the stock parts on a scale, he should quote an exact weight difference. (afterall, that's why you would buy this right?) That is unless he figures he will sell more by being vague and guessing, hoping that his customers don't bother to weight the stock stuff and just take his word for it.

I DID measue the stock parts on a digital shipping scale: see post above: 20.5lb. And that's giving some "benifit of the doubt" too as the stock parts I measured included five 17mm headed bolts and a few ounces of oil/grime/dirt mix! /ubbthreads/images/graemlins/rofl.gif directly off a parts car, still assembled.

 

[OMFGeofffff]

New design opinions?


click

 

I like the front bar. there is absolutely nothing wrong with the way the ends are made and mount up. i would rather use a poly front motor mount though. If the other three mounts are poly, the motor will still move everywhere, its just going to flex that brace more and cause premature failure.
I would have used 1.5x065 moly tube though. A tube gets more of its strength from the OD than the wall thickness.
the fore-aft supports with the rod ends is craptastic though. its asking for movement and flex and adds a ton of unnecessary weight.
I will probably end up making one of these one day, and more than likely i will make the lateral bar just like he did(except with a poly motor mount), but the longitudinal bars will be solidly mounted to the lateral bar. i will either make it all one piece, or make them removable with something like this:
click

 

[Barnes]

I don't see how the rod ends are craptastic. They take care of the load that most people complained about. /ubbthreads/images/graemlins/dunno.gif

 

They add too much weight, complexity and price for me. One advantage is you can preload the chassis though.

 

[bustedsm]

I run one and have had ZERO chassis problems. Add to the fact that they're light as hell too made me have to get one. He's also upgraded his setup to offer a three piece design that combines this, and the two front-back braces.

 

[Galantvr41062]

Quoting OMFGeofffff:
New design opinions?


click



The only issue with that is the stock cross member in the back is not that strong, thus why the factory lower pieces attach in a few places on the back side. The swagger tube idea is good, but I would add mounting points to the rear mount. Anything is better then nothing, the original piece is stupid for eliminating vital chassis strength. I have offered for a few local people to weld on mounting spots for the stock lower braces.

Or you can cut the front end off and make it all from tubes, only recommend for the series racer with a full roll cage:

 

The way those longitudinal braces are mounted is a lot more how i like than the rod ends.
i like the way that car was done, its similar to what i did with my chevelle but a lot further into the chassis and bigger tube.