A tight converter. The low rpm launch flashes the converter allowing rpm to climb at a much faster rate, allowing quick rpm rise through the bog rpm range.
I had the same issue with a mild 283 in my El Camino until a 5k converter was installed.
My .02..

My bbc is actually doing something similar. I put a tighter converter in it and it stumbles about 0.1 after I get to wot on the TB. It’s efi so I’m able to add fuel at that point, but I’m totally baffled why it does it. Only thing i can figure is the converter is too tight for the cam and it goes into reversion. Had no problems before tightening the converter.

Years ago I had a carb bbc that did something kinda similar. I ended up putting some epoxy in the intake runners and it fixed it.

quote:

Originally posted by Mike Allred:
A tight converter. The low rpm launch flashes the converter allowing rpm to climb at a much faster rate, allowing quick rpm rise through the bog rpm range.
I had the same issue with a mild 283 in my El Camino until a 5k converter was installed.
My .02..

It's a 3200-ish 10" TCI currently. Seemed like plenty of converter for what I'm trying to do with the car.

quote:

Years ago I had a carb bbc that did something kinda similar. I ended up putting some epoxy in the intake runners and it fixed it.

I was thinking maybe it was a velocity thing through the carb so maybe a smaller carb or to your point, choking down the intake a little bit. The fact that it seems to work perfectly fine (on the street only so far) at a lower RPM sort of killed that thinking.

Like somebody else mentioned, when you start lower you’re accelerating through the problem area quicker. I’d try some different spacers. A 4 hole with an anti reversion lip might be the ticket