Aluminum parts replacement

[908ssp]

Actually the crash bars do add some rigidity to the frame. By tying the ends of the frame together it distributes some forces from one side to the other. I think you crash bar is plenty strong certainly stronger than the one I built for my 2010. Mine was made from magnesium. Adding additional braces in strategic places will more than make up for the lighter crash bar.

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[Trackaholic]

I Radiator support might be interesting. Not sure if you can get the one from the GT350 in there.

Also, I think K-member is the one under the car, while K-brace is the one from the strut towers to the firewall.

I think the front K-member and rear sub frames are good candidates for weight reduction. Both look to be designed to be low cost first, so maybe doing some custom work there would provide good dividends. At the same time, those are some pretty critical components, so some decent engineering behind any updated ones would be important IMO.

-T

 

[Trent W]

Thanks for the tips everyone, I'm going to get to work on the following parts:

K-brace (I dont have one so this will only add to overall strength)
K-member
Strut tower brace
Radiator support

There should be about 10-20lbs there.

While I have the bumper off again I'm going to move the washer fluid to the trunk with some hard brake line instead of rubber hose. I'm hoping to get close to a 50/50

Probably wont be posting any results until after Christmas as The wife would not be happy if i was under the hood instead of spending time with the in-laws...

Just a side note I was helping a buddy with a header install last night and found out that the base model 15 GT doesn't even have ANY supports. No K-brace (the k brace is just a piece of plastic) or strut tower brace so if the car can handle being without it I'm sure anything i make would only help even if it isn't as strong as OEM.

 

[plc268]

You'll get the K brace if you have the 20in wheels option. Strut brace comes only with PP (and convertibles, I think).

 

[kz]

No calculations yet. I drove over the steel one with my truck and it bent i drove over the aluminum one and it didn't even bend just flexed slightly then went back to normal when i drove off. Not very scientific I know but it was faster than doing actual testing. Plus its a crash bar its not really a structural component. If I do braces and components I would be doing calculations though. I would test the strength of the parts i took out and try to get the aluminum to at +/- 5% of its steel counterpart by adding or modifying the design.

I'll be using 6061 T6 aluminum (structural applications). Yield strength is roughly 40,000 psi. the only problem with that is bending it creates cracks so I will have to cut/weld or only bend a radius close to its thickness which doesn't give me very much lea-way. I will be heat treating it once I get a finish product.

I know very well what 6061 yield strength is, did you check what the steel you replaced yield strength was ? It's not about YS, it's about stifness. You can make stiffer and at the same lighter components out of 6061 but you need to put some thinking into it. Right now you're setting yourself up for a disaster (for clarity, I designed steel, aluminum, nickel and Ti alloy components for living )

 

[Trent W]

I know very well what 6061 yield strength is, did you check what the steel you replaced yield strength was ? It's not about YS, it's about stifness. You can make stiffer and at the same lighter components out of 6061 but you need to put some thinking into it. Right now you're setting yourself up for a disaster (for clarity, I designed steel, aluminum, nickel and Ti alloy components for living )

Then your the perfect person to talk to! I'll post up some of my prototypes I build before I install. I would love some constructive criticism. Looking forward for some input.

 

[Schu]

Frankly I dont see any need to make the bars as strong as required by dot or as strong as oem... we're trying to drop pounds here. The main reason for these elements isn't chassis rigidity but sub 5mph crash is it not?

The frontend has a bulkhead at the rad support and the rear is not even an issue in as fas as chassis rigidity.

Just make me something that will support my bumper cover at 160+mph, weight significantly less than the original and I would be extremely happy.

 

[DivineStrike]

If you sacrifice rigidity somewhere you would want to increase it in another place. It's better to just lose weight and try to keep the same rigidity.

 

[Trent W]

Sunday was productive. I need to grind down the welds and polish it a bit more but I got lazy and sick of sanding. Its it's actually Just about the same strength as the OEM bar. I can jump on it and it would only flex slightly, same with the OEM bar. Its only 4lbs lighter though. I had to use more aluminum than I thought to get it as strong as the OEM. It does flex a tiny bit more.

Ive decided for the radiator support i'm going to use structural rivets and glue where I would need to weld. That way heat wont weaken it and it would actually be stronger than any weld. The K member i'm going to use a solid peice of Aluminum 1/4" thick and bend it. Basically make an exact copy of the OEM

 

[Schu]

Nice^...

 

[kz]

Sunday was productive. I need to grind down the welds and polish it a bit more but I got lazy and sick of sanding. Its it's actually Just about the same strength as the OEM bar. I can jump on it and it would only flex slightly, same with the OEM bar. Its only 4lbs lighter though. I had to use more aluminum than I thought to get it as strong as the OEM. It does flex a tiny bit more.

Did you weld it ? Did you heat treated it after weld ? If not, expect it to crack at the welds very very soon. Also, you just confirmed what I was trying to tell you - making an exact copy just is not going to work. 6061 is way less stiff than any decent steel, to make the component as stiff and lighter you typically need larger cross section to handle appropriate loads (hint - geometric moments of inertia are the key depending on the loads). Think about what are the loads transmitted by your brace and whether this is a point load applied at the middle of it or whether it is compression along its length and torsion between mounting points - this is how you should test your brace...

Basically make an exact copy of the OEM

See above why this is a terrible idea. Hopefully you do not plan on redesigning any structurally important components...

 

[kz]

Also, bending aluminum obviously exceeds it's yield strength. You may want to think about it what happens (also fatigue-wise) with it's structure when that happens and how far away you're going to be from UTS...

 

[Trent W]

Did you weld it ? Did you heat treated it after weld ? If not, expect it to crack at the welds very very soon. Also, you just confirmed what I was trying to tell you - making an exact copy just is not going to work. 6061 is way less stiff than any decent steel, to make the component as stiff and lighter you typically need larger cross section to handle appropriate loads (hint - geometric moments of inertia are the key depending on the loads). Think about what are the loads transmitted by your brace and whether this is a point load applied at the middle of it or whether it is compression along its length and torsion between mounting points - this is how you should test your brace...



See above why this is a terrible idea. Hopefully you do not plan on redesigning any structurally important components...

The strut tower brace is twice as thick and has a channel unlike the OEM I'll take a profile pic later just imagine it a 1x4 square tube. Its pretty stout.

The K-member will about 30% thicker.

Not doing structural components the stuff I'm doing really isn't going to hurt anything so I'm really not worried about it doing that sort of testing cuz it's just a waste of time for a strut tower brace and a support that holds the radiator and bumper.

 

[Trent W]

Ok So Version 2 of the Strut tower brace... IT was not strong enough and didn't help during my testing over OEM. Kz you were 100% right I had to add riveted 1/4" plate across it to stiffen it up.

Test method was used a jack under one tires and raised it until the other tire came off the ground and measured the difference. And tried again with the different braces. The K-Brace is 1 inch wider than the OEM and slightly thicker. I dropped the weight in half over OEM Braces and maintained the same rigidity and body flex.... SO these are fully functional!

 

[Freedom]

the W design looks nice

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