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waxhead

Alloy mustache bar

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Mr camo man

I need to get it right with the holes in there as its a water jet job and as such they cant do depth

I suppose i could do it with out holes at all but it wouldn't look as trick

 

Yep, maybe make it not as wide with no holes, if that's stronger.

 

Not sure about how much load the front diff mount takes. I do know if the mount is worn out the diff wants to tilt up into the underside of the car, which is why there's an strap over the top of it. I'm no engineer but, I'd think most of the loads are on the mustache bar.  I think the front mount is just there to stop the upwards motion.

 

 

Stevo: Some torque figures I found on Hybrid Z

Modified L24:

231.5 HP at the wheels

195.9  lbft torque

 

Turbo L28:

341.44whp

390.31  lbft torque

at 23.7lbs max boost

 

Another turbo L28:

 

403.16 whp

365.92  lbft torque

at 17lbs max boost

 

Not sure where that torque is though.. engine, or wheels?

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Mine is going to be running an rb30det so there is going to be some torque through it

There is a certain amount of force from the sheer weight

But i believe as long as the front mount is ok your going to be transferring load to the chassis through there more

The front of the diff is further away from the twisting cntre so its going to hit that mount hardest first

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Yes I have to say I think the original design is flawed in that any holes straight through the bar would weaken it too much. As we all know there will be movement especially if there is not a solid mount on the front of the diff. This movement will fatigue the metal and eventually break or crack it where the holes are. Personally I think you might be re inventing the wheel. The earlier link to the alloy Bar in the States is good value given the state of the dollar at present. For me I still question that one because it has 8 screws that might make there way lose with the vibration.

So as silly as it sounds my old moustache bar is going back into my car. Whilst I did break one of these years ago I think it might have been due to the movement and not having the front diff locked down. With this done (Brace) I think the original should be up to the task.

Personal opinion only guys. Good luck with it as I will keep an eye on this thread and see where you end up.  ;)

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I am reinventing the wheel

Its just part of my playing with my car

I'm trying to make things look different / better

Thanks for your input I'm not sure myself yet if its going to be strong enough but I will keep working on it

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Hey Wax, could you resend me the design with the extra bolt hole in it as an .igs? Adding the bolt hole myself is giving me geometry errors when I use my professional software. I'm just going to confirm that simulxpress was giving us accurate results for stress concentrations, and I'll also test those torque figures.

 

Also, perhaps send us an .igs file with the cutouts removed, and we'll see how much different stronger it is compared to your current design

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Yes I have to say I think the original design is flawed in that any holes straight through the bar would weaken it too much.

 

As we all know there will be movement especially if there is not a solid mount on the front of the diff. This movement will fatigue the metal and eventually break or crack it where the holes are.

 

I think there is potential for this design to perform well. The way I see it, the holes are removing 'lazy material' in the design, which is material that does not have much stress acting on it during a stress cycle.

 

You are right that a design with holes may have higher stresses than a design without, but what if the material removed from the holes was added to areas where the stress concentrations are high?

 

I'm just working on the latest stress analysis using Straus7 atm will post results soon. I'm going to use some of the torque figures that were supplied as estimates and see what stresses you get if the front diff mount goes and the entirety of the torque is transmitted through the mustache bar when you drop the clutch. In other words I'm going to apply the entire torque of the motor through the two bolt holes.

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I think there is potential for this design to perform well. The way I see it, the holes are removing 'lazy material' in the design, which is material that does not have much stress acting on it during a stress cycle.

 

You are right that a design with holes may have higher stresses than a design without, but what if the material removed from the holes was added to areas where the stress concentrations are high?

 

I'm just working on the latest stress analysis using Straus7 atm will post results soon. I'm going to use some of the torque figures that were supplied as estimates and see what stresses you get if the front diff mount goes and the entirety of the torque is transmitted through the mustache bar when you drop the clutch. In other words I'm going to apply the entire torque of the motor through the two bolt holes.

 

There is one thing you may be overlooking here.  Most torque figures picked off a dyno are done in 3rd or 4th gear.  If you use 1st gear, surely the amount of torque produced is far greater, due to the gearing change?  Likewise the diff ratio would probably have a similar effect?

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You're right! And judging by what I've calculated, I would need to be using 4.5 kN at each hole to reproduce 400 lbft of torque, which is way higher than I previously estimated. Obviously this is not the loading condition supported by this bracket.

 

I think I might stick with the 1kN per hole figure so that it is easy to compare results.

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You're right! And judging by what I've calculated, I would need to be using 4.5 kN at each hole to reproduce 400 lbft of torque, which is way higher than I previously estimated. Obviously this is not the loading condition supported by this bracket.

 

I think I might stick with the 1kN per hole figure so that it is easy to compare results.

 

Out of curiousity, how did you get to that figure?  Without knowing the gearing used by the car that put the dyno figures down, you'd have to assume worst case scenario, which would likely be 1:1 gearing (4th gear) with a 3.5 final drive, and then assume that the car now is in a very short first gear (say perhaps around 3.8 or 3.9) with a 4.3 or 4.5 final drive.

 

Obviously the bracket shouldn't ever see the full extent of this loading anyway, unless it was solid mounted to the body - which from memory they aren't, they have a large rubber mount at either end which should absorb a portion of the torque transmitted....

 

So many variables when you start to actually work this stuff out on paper!

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I've attached the basic working. I am assuming 1:1 gearing which you have pointed out is incorrect, since the maximum stress will occur in first gear.

 

However, even with the rubber mounts on either end, if the other mounts for the diff are stuffed, then once the rubber has given as much as it can this full torque would indeed be transmitted through the bracket. I don't think it would cause immediate failure though, unless it was already fatigued. I'll post results soon.

post-931-144023545288_thumb.jpg

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I'm not 100% on which 6061 aluminium alloy to choose, because as you can see here: http://en.wikipedia.org/wiki/6061_aluminium_alloy the yield strength can vary significantly.

 

Anyway here are the results for the repositioned bolt holes. The first example is showing the 1kN forces and the second example is showing what would happen if the entire motor torque of 400lbft in 4th gear was transmitted to the bracket in first gear instead.

 

187 MPa = bang since yield (failure) is around 55 MPa for standard 6061.

 

edit: This does not mean the design will fail, since as Wax has stated, there are other mounts which will absorb some of the forces involved. It's just interesting to see that if 100% of the motor torque was applied to this bracket alone in first gear it would break,

post-931-144023545297_thumb.jpg

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Thats also assuming you have traction at that point to huh

I think trying to put 400ftlb down in first gear with out breaking traction would be a hard thing as well

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This one performs much better.

 

Mass of V2: 2.006 kg

Mass of V3: 2.007 kg

Mass of V4: 2.135 kg

 

By increasing the mass by 6% the maximum stress under this particular loading condition has been reduced by 56%.

post-931-144023545325_thumb.jpg

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Thats awesome, that will be the design i get cut out then

Thanks heaps for that , i wouldn't mind a copy of that software you have

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sorry guys i just want to add something ... ive seen the models on the twisting of the bar ..... ive got 260kw atw... it doesnt want to twist it gets pulled down pretty evenly ......the front diff bracket wants to go up thats why its straped down.... ive got wear on the mustache bar from the down right brackets holding the A arms... the diff wants to spin nose over tail if there is same amount of force to each wheel ... so in my oppinion what you guys are doing will work very well but you guys know more about the structure than me clearly

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