A blueprinted and tuned L78 might make 400 hp. From the factory, the actual compression ratio was probably down around 10-1. Timing was retarded with a slow advance curve for emissions. The jetting was way lean for the same reason. Mid 14s was about all you could expect from one of these engines in this condition. 280 hp might be a generous number in this scenario. With tuning and headers 13.3s would be reasonable, at least from my experience. 320-340 hp might then be possible. We'll see what the dyno says. I'm usually wrong.
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Chevelleless after 46 years......but we did find a low mileage, six speed, silver 2005 Corvette. It will just have to do for now.