I read an article a while back about the HEI and it stated it didn't like much more than 6000rpm, so I asked the question here. Several members said they are running it and have no problems pushing past that.
I suspect some modules were made for 4 cylinder engines, some for 6 cyl, and some for 8. (Or maybe just 6&8, not positive) but thier part numbers are different.
Using a 4 cylinder module on a 8 cyl engine could push the module to 2X the RPM's it was designed to run at.
This is why I use 8 cylinder parts in my ignition kits. (not going to risk it)
Also, I'm not positive how to find out for sure besides running them to speed on a dizzy machine with a scope to see at what RPM's the spark starts to fail.
The reluctor gap could even cause the OP's issue if it hasn't been checked yet.
