I have been chasing an annoying issue on my 92 LT1 6 speed. I call it my turbo vette issue, but my vette isn't turbo. She is stock. She idles smooth, runs great, has plenty of power and has no codes. When I accelerate at wot or even heavy throttle she gets a boost over 3000-3500 RPM. Right at that range it feels like a turbo kicks in and she gets a boost. She does this hot or cold with or without the ASR deactivated. I just did the timing chain and while I was there replaced all the lifters with USA made Mellings (had to return China made ones they tried subbing at the autoparts store), the intake manifold gaskets, the oil pan gaskets and valve cover gaskets. I also just put in Bosch III injectors. She still runs exactly the same, but now I don't have oil leaks. I also have put in new plugs, wires, o2 sensors and knock sensors. No change. Ran just the same before and after I have done all these things.
The previous owner did the opti, intake manifold gaskets and water pump. He used some chaulky grey sealer on everything that caused a pretty bad oil leak from the china wall. I didn't take pictures of the opti when I had it out, but it was new. I don't think it was a quality one though. It had a Made in Taiwan stamp on it. I'm wondering if this cheap opti could be my issue.
I don't think it is coil related as it would suffer at higher RPM rather than low. Same with all the other things I can think of, plus they'd throw codes. Also, she will occasionally pop out of the exhaust when I get on it and then back off really quick. I'm tempted to do a leak down test, but it is such a pia to get the driver's side plugs out. She doesn't use oil, doesn't back fire on normal acceleration, doesn't smoke out of the exhaust or any of the other tell tale signs of bad valves. In fact she passed CA smog with good numbers in November 2021 when I first had to register her.

 

Obvious symptoms for a bad opti is backfiring and misfiring, after reading your post I think this not your issue

 

That's why I'm thinking it might be a cheap opti causing this. It's good enough to run ok, but cheap enough where it pops out the exhaust (light backfire) and doesn't have full timing down low. It's almost like the timing is steady until 3k rpm and then it gets it's full advance at once. Maybe I need to get the cord and laptop to data log and tune it.

 

Did you ever scan it and see what your timing is doing? Is it laying back on timing and suddenly going into advance ? That can give you the symptoms you are experiencing.

 

That's what I'm thinking it is doing. I'm now buying the parts to scan, datalog and even burn a chip to tune it.