What rev limit for 2.7 rebuild

[Brent Lineker]

I have about 2000 miles on a fresh rebuilt 2.7.I have new RS Mahle P&C's stock compression with e cams.I did all the usual upgrades to the case. I have 40 ida webers and ssi's installed.I have a 7100 rpm rev limiting rotor in now,is this a safe rev limit for this motor or should I stick with the stock 6500 rev limit.The motor has been taken to the 7100 rev limiter a couple of times and seems okay and does seem to make quite a bit a power above 6500.Long term would this be a safe limit,I am not tracking it or anything just using it as a weekend toy.

[Steve@Rennsport]

7100 RPM is fine and appropriate for E cams.

[Brent Lineker]

Thanks Steve I appreciate the advice.

[Henry Schmidt]

Turning the 2.4/2.7 crank at high RPM has always been a problem. The numbers you are concerned with are not an issue but since we're on the subject, why not expound on it.
The issue with the 2.7 crank seems to be an inherent imbalance that creates a rocking couple [To the extent crankpin motion is horizontal the imbalance is a rocking couple not to be confused with the 7th position in the Kama Sutra] during rotation under extreme loads (I.E.: horse power at 7600+). The vibrations created by these forces are different from a harmonic vibration caused by an unbalanced condition in that it can not be easily dampened.
The problem seems to be that the crank webs (flyweights) are too thin. As this imbalance becomes more pronounced the crank flexes and creates a vibration. This vibration causes two things, cracks in the flyweights and tendency for the flywheel to fall off. To remedy this the factory built the 2.8 RSR crank. It was made more stable by making the crank webs thicker facilitating the need for a narrower connecting rod. This development resulted in the SC rod configuration and was used on every race engine and most street engines ever since. I have eluted to this change many times. The 993 took the concept one step further by making the big end even narrower. The 993 development did not translate to a race development so there must be a law of diminishing returns in play here. The narrower rod allows for a wider flyweight but the bearing itself may become insufficient the handle the higher tresses not to mention the weight increase by using a thicker web.
The problem with the flywheel was handled by increasing the crank flange from 6 bolts to 9 bolts. This seems to have handled the problem because no other design change was ever adopted.