340 and octane

With 237 duration at .050 intake you should be somewhere around 10.75:1 to 11.0:1 SC, (static compression), to make good use of that cam. So your just about a point low. Something around 216-220 at .050 would wake up your combo with that compression ratio. Over duration is actually lowering your compression ratio, DCR (Dynamic compression ratio) so what your seeing and the other members have stated is correct, 87 at the most 89 octane would be a better fit. 91-93 your loosing a lot of efficiency. Efficiency equals power and in your case torque. Your going to have to have to tune your timing to get the most out of 87 if you have set up for 91. You won’t be off much, if any, but test and tune anyway.