11-04-2023, 12:30 PM
In a past life, I was an engine dyno tuner and regraphed many distributors to better suit the modifications and fuel being used. With programmable timing and cyl timing offset available these days, regraphing distributor advance curves by changing springs and advance weights as well as changing the length of the advance curve are a thing of the past.
These days, a timing signal using a magnet embedded in the flywheel and hall effect sensor (that was already part of the bay dealership tuning set up) can be used to determine timing for each cyl and fire a coil pack for each cyl ..... the dist drive could be used for a high pressure mechanical pump if needed for additional injection of a higher octane fuel to avoid the detonation issues, particularly with turbo engines or high compression engines.
The rule of thumb was to start off with very little advance, it saves starter motors, but bring the advance in as low as 1,000rpm to assist that poor performance pulling out of a corner negating the change down a few gears.
LPG isn't really a fuel of choice these days, but the advance curve for LPG is very different to that required by unleaded fuel. LPG wants all the advance by 1500rpm, between 20* and 30* depending on how you drive and what the max cruise rpm will be, the advance needs to be reduced above roughly 3500rpm if the engine breathes well, not so critical if it doesn't, being a bit asthmatic reduces the combustion load at higher revs.
There is a science to it, but theory rarely matches reality, dyno tuning at all throttle settings and rpm is the only true method of setting the correct fuel curve and spark curve .... just to throw a swing ball in to the equation, rotaries require substantial spark retard as the turbo boost increases, well after top dead centre or the spot where peak compression would normally be calculated .... so this means valve overlap or lack of it plays a big part .....
Atkinson cycle forced induction throws even more spanners in the works, but a fascinating theoretical venture into future hybrid technology ..... an electric driven intake air compressor driven at the speed required for that particular engine rpm and load to achieve peak torque but minimum fuel ....... combined with electrically operated valves using oil as the valve solenoid driving force ...... No more cam operated valves or distributors, all powered by the hybrid battery .... tuning flexibility to run any fuel
T1 Terry
These days, a timing signal using a magnet embedded in the flywheel and hall effect sensor (that was already part of the bay dealership tuning set up) can be used to determine timing for each cyl and fire a coil pack for each cyl ..... the dist drive could be used for a high pressure mechanical pump if needed for additional injection of a higher octane fuel to avoid the detonation issues, particularly with turbo engines or high compression engines.
The rule of thumb was to start off with very little advance, it saves starter motors, but bring the advance in as low as 1,000rpm to assist that poor performance pulling out of a corner negating the change down a few gears.
LPG isn't really a fuel of choice these days, but the advance curve for LPG is very different to that required by unleaded fuel. LPG wants all the advance by 1500rpm, between 20* and 30* depending on how you drive and what the max cruise rpm will be, the advance needs to be reduced above roughly 3500rpm if the engine breathes well, not so critical if it doesn't, being a bit asthmatic reduces the combustion load at higher revs.
There is a science to it, but theory rarely matches reality, dyno tuning at all throttle settings and rpm is the only true method of setting the correct fuel curve and spark curve .... just to throw a swing ball in to the equation, rotaries require substantial spark retard as the turbo boost increases, well after top dead centre or the spot where peak compression would normally be calculated .... so this means valve overlap or lack of it plays a big part .....
Atkinson cycle forced induction throws even more spanners in the works, but a fascinating theoretical venture into future hybrid technology ..... an electric driven intake air compressor driven at the speed required for that particular engine rpm and load to achieve peak torque but minimum fuel ....... combined with electrically operated valves using oil as the valve solenoid driving force ...... No more cam operated valves or distributors, all powered by the hybrid battery .... tuning flexibility to run any fuel
T1 Terry