Too much gear?

The exhaust is not a major contributing factor IMO. My stock everything but cam and headers 340 with a smaller 268° advertised hydraulic would pull to 7K. Not just rev, but pull. Stock Thermoquad intake, Thermoqaud carb, '68 long block, stock electronic distributor and Jacobs Energy Team running it. In an E body it went 13.0s with me rowing it. That was in the 80s before really good mufflers or pipe larger than 2.25" was the norm. Yes, gains are to be had - but there's something sick with it if it can't go into the 12s even without the pipes and the smaller cam. I think it's a porting or valve job issue.