In the 914 EV conversion world a number of people have reported vibration problems with their conversions. Here's the latest example: Peter's Blog (see the April 6 post). While the author is thinking the flywheel needs balancing, I suspect it's more likely to be an issue with the transmission. Scrolling through his old blog posts I see the transmission was rebuilt during the conversion process, so maybe the flywheel is the problem (especially if it had been balanced with the crank at one time). What were 901 & 915 transmissions designed for as far as input rpm? Is it possible that even with the rebuild it just can't tolerate input rpms in the 5k range on a regular basis? What sort of time does a racing engine spend about 5k?

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we know why Peter's EV 914 vibrates:
1. the EV conversion motor is solid mounted to the engine bar
2. engine bar is solid mounted to chassis
3. clutch and flywheel was not balanced
4. EV motor hub was not balanced
5. solid mounts of any kind are the handywork of Satan himself
6. harmonics are a bitch
7. 10 year old tires dont help much either
8. clutch package designed for WAY different operating parameters (inertia, mass...)

the 10jereen's 901 lives mostly over 5000rpm
many of my six customers have hot track-rat motors that rarely dip below 5000 rpm
I have run 901 in teh 8000 range and they live just fine
...it aint the box.

Race 901s are in the 5-8k RPM range all the time. It is likely other rotating components that are out of balance.