Honda Fury 'Regular' Fuel Requirement
Advertised compression ratio is NOT the issue here because it is only theoretical (the ratio of swept cylinder + combustion chamber volume to combustion chamber volume). It does not reflect actual "dynamic" compression pressures which are controlled by a number of factors including valve timing (intake valve is open when piston is at the bottom or beginning of the "compression stroke"), intake air-fuel charge velocity and ignition timing (spark occurs before piston reaches top of "compression stroke"). Crankshaft rotation with valves closed before ignition can be as little as half the 180° rotation of the crank pin from BDC to TDC on a high performance four stroke engine. Although this sounds very inefficient consider that at the bottom of the stroke the connecting rod and crank pin have similar arcs resulting in limited piston movement while at the top of the stroke the arcs are opposing resulting in more rapid piston movement. This is why typical cam/valve timing (degrees of rotation) shows more than twice the valve overlap (int & ex valves open at the same time) at the bottom of the stroke than at the top.
Although not relevant to the Fury and larger V-twin engines, high revving motorcycle engines often list very high compression ratios but also have more radical cam/valve timing and faster moving pistons (less time for detonation pressure spikes) so that dynamic compression is balanced to regular fuel requirements. The Fury/VTX 1300 engine develops its power at lower rotational speed similar to large displacement car engines and yields similar power and torque curves.
High octane fuel has lower volatility and therefore burns slower (SirGCal) reducing combustion pressure spikes (detonation). Regular fuel required by the Fury is more volatile and burns faster, so, because our engines have low dynamic compression they can take the faster push (burn) without detonation (absence of pinging). Theoretically you will get more power and better gas mileage, although not both at the same time
.
As SirGCal points out there is a lot of incomplete info regarding premium fuel. Detonation occurs after spark ignition when fuel burns too quickly spiking the combustion pressure instead of building a steady increase. This excessively rapid pressure rise while the crank pin is still at a high angle (harder to turn) and before the piston is far enough down it's stroke to absorb the energy is often referred to and heard as "pinging".
Advertised compression ratio is NOT the issue here because it is only theoretical (the ratio of swept cylinder + combustion chamber volume to combustion chamber volume). It does not reflect actual "dynamic" compression pressures which are controlled by a number of factors including valve timing (intake valve is open when piston is at the bottom or beginning of the "compression stroke"), intake air-fuel charge velocity and ignition timing (spark occurs before piston reaches top of "compression stroke"). Crankshaft rotation with valves closed before ignition can be as little as half the 180° rotation of the crank pin from BDC to TDC on a high performance four stroke engine. Although this sounds very inefficient consider that at the bottom of the stroke the connecting rod and crank pin have similar arcs resulting in limited piston movement while at the top of the stroke the arcs are opposing resulting in more rapid piston movement. This is why typical cam/valve timing (degrees of rotation) shows more than twice the valve overlap (int & ex valves open at the same time) at the bottom of the stroke than at the top.
Although not relevant to the Fury and larger V-twin engines, high revving motorcycle engines often list very high compression ratios but also have more radical cam/valve timing and faster moving pistons (less time for detonation pressure spikes) so that dynamic compression is balanced to regular fuel requirements. The Fury/VTX 1300 engine develops its power at lower rotational speed similar to large displacement car engines and yields similar power and torque curves.
High octane fuel has lower volatility and therefore burns slower (SirGCal) reducing combustion pressure spikes (detonation). Regular fuel required by the Fury is more volatile and burns faster, so, because our engines have low dynamic compression they can take the faster push (burn) without detonation (absence of pinging). Theoretically you will get more power and better gas mileage, although not both at the same time
.
