How do you convert a 76 shovel head to 81 CI?

If you have a 74 inch engine to start with, you can install 80" barrels on it but this would bring down the compression so low you wouldn't be able to ride it. This would be basically the same as boring out the 74" barrels .060 (IF the 80" barrels are standard bore!) But your 74ci engine would only be about 76ci. To convert your 74" to a true 80" you would need to change the flywheels to gain the additional stroke length. (4.25 for 80" as compared to 3 31/32 for the 74").

emperor norton