OEM exhaust design...

[mPlasticDesign]

Originally Posted by Nate@IND

When our friends at Fall Line ran an OEM exhaust system, the CV boots did not melt, but after installing their competition exhaust system with no heat shields, they experienced quite a bit of trouble with melted CV boots. Since then, Fall Line has added heat shields to their competition exhaust, and it is this experience that leads me to believe that heat shields are necessary to protect the rubber CV boots.

I have been to Fall Line, they are a very reputable shop and I trust what they say.

[PLAY_HRD]

About the bends, crimps, and flat spots, I have my own theory. They are purposely engineered into the exhaust to continually disrupt the air flow, this greatly reduces drone and standing wave vibrations.

[lucid]

Originally Posted by Nate@IND

When our friends at Fall Line ran an OEM exhaust system, the CV boots did not melt, but after installing their competition exhaust system with no heat shields, they experienced quite a bit of trouble with melted CV boots. Since then, Fall Line has added heat shields to their competition exhaust, and it is this experience that leads me to believe that heat shields are necessary to protect the rubber CV boots.

Thanks for the info. So, it sounds like this happened on an E92 M3 racecar pushed hard without a shield in that area of the exhaust. There are sevaral things going on at the same time: heat is being transferred to the joint via conduction from the diff; heat is being transferred to the joint via convection from the exhaust pipe (can be significant when the car really slows down and/or comes to a stop after running hard and there is no forced convection but a really hot pipe briefly, or in any other situation when flow is interrupted); heat is being transferred to the joint via radiation (although the magnititude of this effect appears small, when combined with the other heat transfer modes in extreme driving conditions, it seems that it indeed does make a difference in overheating a rubber part). Placing a shield obviously does not do anything to reduce conduction from the diff, but blocks radiation and reduces convection from that section of the pipe.

[IND-Distribution]

100% correct. Although the differential may generate enough heat to damage or wear the CV boots on it's own, my intention with placing heat shields on our connecting pipes was just to make sure that the pipes were not contributing to any damage caused.

This makes me sleep a bit easier at night.

Originally Posted by lucid

Thanks for the info. So, it sounds like this happened on an E92 M3 racecar pushed hard without a shield in that area of the exhaust. There are sevaral things going on at the same time: heat is being transferred to the joint via conduction from the diff; heat is being transferred to the joint via convection from the exhaust pipe (can be significant when the car really slows down and/or comes to a stop after running hard and there is no forced convection but a really hot pipe briefly, or in any other situation when flow is interrupted); heat is being transferred to the joint via radiation (although the magnititude of this effect appears small, when combined with the other heat transfer modes in extreme driving conditions, it seems that it indeed does make a difference in overheating a rubber part). Placing a shield obviously does not do anything to reduce conduction from the diff, but blocks radiation and reduces convection from that section of the pipe.

[Definitive]

Does anyone know the diameter of the exhaust pipes? The bent area you are talking about. I plan to install cutouts. Just doing my research now and looking at pricing of the race ready kits.

D

[SOCAL]

Originally Posted by Definitive

Does anyone know the diameter of the exhaust pipes? The bent area you are talking about. I plan to install cutouts. Just doing my research now and looking at pricing of the race ready kits.

D

The OEM system is roughly 2.5" OD throughout but it changes shapes a few times.

See here... http://www.m3post.com/forums/showthread.php?t=352503

I replaced the kinked sections with mandrel bent tubing and addressed the heatshield issue with high tec header wrap, now you can literally put your hand on the exhaust tube after the car was driven for an hour, no joke!!! Waaaaaaay better than stock.