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Old 06-05-2012, 11:25 PM   #13
VIR Specialist

JusticePete's Avatar
Drives: Camaro Justice
Join Date: Jun 2007
Location: Virginia
Posts: 20,245
Welding creates HAZ (heat affected zone). The metal changes and becomes more brittl and brittle leads to cracking when exposed to vibration. Add increased load to the increase in vibration and the probability of cracking is increased.

"The rear housing is chrome moly fabricated steel. I split a weld seam, from tire shake, at the bottom of the 3rd member mount."

Most production monocoque race cars are seam welded to increase stiffness. The benefit of the increase in stiffness is improvement in handling at the direct expense of durability. A direct result of the increase in stiffness is the assembly becomes brittle. If it can't flex it breaks. Next time you are in commercial airplane watch the wings. They have a tremendous amount of flex designed in to keep them from from being breaking off.

Stock Car Stress - All Stressed Out
Develop A Checklist To Make Sure The Parts And Pieces On Your Car Aren't Under Too Much Stress
From the February, 2009 issue of Stock Car Racing
By John Gibson
Photography by John Gibson

Off-Season Stock Car Maintenance

Maintenance Tips For Between Seasons To Keep You On Track
From the February, 2009 issue of Circle Track
By Bob Bolles
Photography by Bob Bolles

The stiffer you make it, the more cracks you will see. Street cars take the opposite approach. The OEM engineers are expected to deliver a chassis that will last hundreds of thousands of miles at the lowest possible production cost. That is a brutal engineering assignment. The life of a weld, the life of a component is validated with OEM wheels and tires, OEM bushes, OEM shocks, OEM sway bars, etc. The ZL1 under went a grueling battery of hard launch test. We all expect the ZL1 rear to be exceptionally durable, until we start modding. There is a point where increased RWHP and increased traction will create a load so high something will break. We all understand this or we should. So why would we assume that we can replace a compliant set of four rubber bushes with solid aluminum and expect the sub-frame to live to an OEM standard?

I only control the products that Pedders puts into the market place. I know we lose sales when we say that solid high durometer differential bushes transit more gear noise into the cabin. We could omit that information, but why would we when we know it is accurate? We know that at some point in time the steering rack or pump will fail under the increased loads generated by suspension upgrades. Increased loads equate to increased heat. Heat kills. Our radius bush snubber (EP6578) request came from a GM engineer and I took it to the next level with the EP6579. We know it won't be in 50k, we doubt it will be at 100K, but we also know there will be a price to pay and we have a cautionary note on the product (EP6579).

Every time this comes up we do the same dance that equates to mine is better than yours. People will believe what they want to believe. Believe this. There is no such thing as a free lunch.
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