Looks like the bottom end is pretty strong. Looking back at the european car shootout all of the cars had stock bottom ends. Anyone have a major failure?

 

Halle Berry?



Looks like I'm gonna milk this joke for all it's worth. :-)

 

Hmm...there's a pun in there somewhere...

 

two of my rods were S shaped Not sure if I should be proud of that....

 

Yes, I have, Carrillo's solved that problem.....

 

K24,

A better question might be has anyone else bent all six?

 

Yes Chad yours were classic. Rob and I were joking that your rods had arthritis.

Chad IYHO what do you think safe torque levels are for stock rods?

 

My ex girlfriend at one time bent my rod...

 

K24madness,

That's almost a trick question. Alot has to do with how much power is being delivered to the pavement and I'm not refering to spinning your tires. The real question is how much real power is being delivered to the ground.

Another parameter would be how often do yo use it?

 

Yes Chad it is a tricky question. Rob and I have beaten it to death. I was there the day they pulled the heads and barrels. We were both quite shocked. At that point we knew that the new turbos were working quite good.

Thanks to you and your car I have some guidance. Since we both use the same dyno, I say as long as I keep it under Chads numbers I should be ok.

 

The problem is not always the rods. It is the rob bolts. I am pulling these motors apart and can confirm the bolts are letting go. You also can not compare the 996 to the 993. The temps are hotter and the efficienty s far less creating failure at different levels than the 996. I have had 993 cut loose at 600HP at the crank. More than once.

 

Stephen not sure I understand something. I am sure the rods and bolts are treated at over 1000 degrees.

I find it unlikely that those temps are exceeded below the piston. In the 993 failures you speek of it sounds more like a case of overreving.

Were the 993 motors you speek of race motors? What RPM's were they pushing?

Most rod bolt failures are from overreving.

Thanks for your 2cents. I respect your opnion. Just trying to understand how the extra force of "pushing" causes rod bolt failure and how it can be different from one car to the next if working below the heat treated levels of the bolts and rods.

 

This is not an issue of heat melting a part. This is an issue of added heat in the case at the rods killing the efficiency of the system. Heat creates a list of problems. To keep things simple for those that are reading heat will cause fatigue and added movement. 993 are hotter everywhere from the cylinder temp to the oil temp.

While the rods can and will bend the greater issue is the bolts stretching. They are not able to deal with the torque created by the added power. For the record they can not deal with a raised rev limiter at all. The tensile strength of the bolts and nuts are not up to the task. They are a stretch bolt and will continue to stretch under big power. The result is the bearing ovals, when the bearing ovals the bearing will eventually pinch. When it pinches it will stop moving and come apart. When that occurs you now have natural ventilation, a thrown rod through the case.

The motors I have seen this on, not race motors. They were street motors. Most rod failures are not from over revving on the street. On these motors that are supposed to be ok the rods as soon as 6K miles are showing shadowing on the outer edges. this represents a out of round rod and uneven wear on the bearing. Some of these motors have raised limiters, some do not. The result and evidence remains the same.

 

I know the Rods don't melt. I understand that if temps are kept below the heat treated temps that they would not have the hardening worked out of them.

I do not doubt what you have seen. I am sure what you say is true. I am not sure I agree as to how this may have occured. I do not see how it is possible to streach rod bolts from forces above the cap. I can see additional torque distorting the shape of the bearing surface above the cap.


Stephen thank you for sharing your experances. Your knowledge is well documented. I will heed your warnings and keep power levels in check until I can get deeper into the motor for safety reasons. The only problem is when I get inside and address rods and head sealing then I will want to run 1.5 bar.

 

K24,

When I mention hp, I am refering to rwhp. I don't have any personal experience with 993tt's, however in my conversations with Rob, the 993tt's he built seemed to start having problems around 700 hp. Corrrect me if I'm wrong. Isn't that where rod failure started to occur?